CONSTRUCTION OF MULTIDIMENSIONAL METAL-ORGANIC FRAMEWORK
VIA SELF-ASSEMBLY APPROACH: THE HARVEST OF INTERESTING
MOLECULAR TEXTURES
By
Bich Tram Nguyen Pham
A thesis submitted in conformity with the requirements
for the degree of Master of Science
Graduate Department of Chemistry
University of Toronto
Copyright by Bich Tram Nguyen Pham, 2008
ii
Construction of multidimensional metal-organic framework via self-assembly approach:
the harvest of interesting molecular textures
Bich Tram Nguyen Pham
Master of Science, 2008
Department of Chemistry
University of Toronto
Abstract
Metal organic framework (MOF) has emerged as a new class of porous, thermally stable
material which has attracted great attention due to their wide applications in gas storage,
separation, catalysis etc. Self-assembly is the operative mechanism of MOFs syntheses;
however, the control of MOF self-assembly is still a challenge in the construction of
predetermined, structurally well-defined MOFs. The goal of the research is to arrive at
multidimensional, highly porous and functional MOFs via hierarchical assembly of smaller
molecular building blocks and, at the same time, to examine the possibilities for different
interesting molecular textures. This goal is to be accomplished by the knowledge of ligand
coordination mode, and geometry as well as logical choices of ligands and metals from which
the MOFs are to be constructed from. Preparations of novel frameworks as well as other
interesting molecular architectures are highlighted with their structures characterized.
iii
Acknowledgements
First and foremost, I’d like to express my gratitude to my supervisor, Datong for giving
me the opportunity to learn more about inorganic chemistry from my project. His guidance,
understanding and many nights running diffraction for my crystals are deeply appreciated.
I want to thank the Department of Chemistry for the vibrant research niche and financial
supports. I’d like to express my many thanks to funding agencies including NSERC, CFI and
the Connaught Foundation for their generosity in funding this research.
I also want to let my groups members, Yang (for guiding me the very first steps on how
to do research), our good old Alen (for his helpful discussions), Ali (what’s up?), Hualing (for
being so cute), Ping Pong Peng (for being a great friend), Liisa “Linda” Lund (for making me
nervous with your countdown), Runyu (for those late dinners and great sport), and Fiona, know
that I am grateful to have worked with them for they are so fun, welcoming and for their great
teamwork. Also, I want to thank Yen, Thi, Marc, Andy and many more friends in the
department who has made my time here filled with laughters and very memorable. I am also in
debt to other colleagues, Geogetta Masson, Wendong Wang, Joanna Poloczek, Bettina Lotsch in
the department for their assistance with many different instruments in characterizing my
compounds. I also want to thank Christoph Deckert and Richard Huang, the undergraduate
students who has tremendously expedited the ligand synthesis.
Finally, I’d like to thank my family so much for their endless supports, encouragement
and love during my graduate study.
iv
For my parents, Duy, Bao, di Tuyen, di Tu, and Lacey
v
Would not trade this experience for any other
vi
Table of Content
Page
Abstract ii
Acknowledgements iii
Table of Contents vi
List of Tables viii
List of Figures ix
List of Schemes xi
List of Abbreviations xii
Chapter I: Introduction 1
1.1 Supramolecular self-assembly (SA) 1
1.2 MOF composition and synthesis influenced by self-assembly process 2
1.2.1 Secondary building unit 3
1.2.2 Metallic nodes 4
1.2.3 Linkers 4
1.2.4 MOF synthesis 5
1.3 The significance of metal-organic frameworks 5
1.3.1 MOFs as attractive H2 storage system 6
1.3.2 MOFs as catalysts 9
1.3.3 MOFs functioning in chromatography 10
1.4 Luminescence in MOFs 10
1.5 Scope of the Thesis 11
vii
Chapter II: Experimental 14
2.1 Synthesis of 3,3'-(biphenyl-4,4'-diyl)dipentane-2,4-dione (LigAH2) 14
2.2 Synthesis of 4,4'-(ethyne-1,2-diyl)dibenzoic acid LigBH2 15
2.3 Synthesis of Zn2(LigA)(phen)2(OAc)2,, 1 15
2.4 Synthesis of [Zn(LigA)(CH3OH).CHCl3]n , 2 15
2.5 Synthesis [Zn2(LigB)2(DMSO)2]·2MeOH, 3 15
2.6 Synthesis [Eu2(LigB)3(DMSO)2(MeOH)2]·(DMSO)2(H2O)3, 4 16
2.7 Synthesis [Tb2(LigB)3(DMSO)2(MeOH)2]·(DMSO)2(H2O)3, 5 16
Chapter III: Results and Discussion
3.1 Construction of dinuclear Zn(II) complexes of LigA2- 28
3.2 Construction of 1D Zn-containing coordination polymer 30
3.3 Construction of 3, a 2D interpenetrating Zn-containing framework 33
3.4 Construction of 4 and 5, 3D open frameworks 37
Chapter IV: Conclusion and Future Outlook 44
References 47
Appendix 50
viii
Lists of Tables
Page
Table 1 Crystallographic data for compounds 1-5 17
Table 2: Selected bond lengths (Å) and angles (deg) of numbering atoms in 1 19
Table 3: Selected bond lengths (Å) and angles (deg) of numbering atoms in 2 19
Table 4: Selected bond lengths (Å) and angles (deg) of numbering atoms in 3 20
Table 5: Selected bond lengths (Å) and angles (deg) for 4 21
Table 6: Selected bond lengths (Å) and angles (deg) for 5 23
ix
List of Figures
Page
Chapter I: Introduction
Figure 1: Illustration of secondary building unit 3
Figure 2: Type I gas absorption isotherm 7
Figure 3: Interpenetration and interweaving MOFs 9
Figure 4: Antenna effect in lanthanide luminescence 11
Figure 5: Schematic representation of research objective 12
Chapter III: Discussion
Figure 6: Crystal structure of LigAH2 with only the alpha hydrogen shown (in pink) being
chelated by the acac moiety. 26
Figure 7: UV-vis absorption profile of LigAH2 (dash line) and sodium salt of LigA2-
(solid line) 27
Figure 8: ORTEP drawing of Zn2(LigA)(phen)2(OAc)2 (1) crystallized from
DCM/hexanes 28
Figure 9: Crystal structure of 1, Zn2(LigA)(phen)2(OAc)2 grown from CHCl3/hexanes 29
Figure 11: 1D coordination polymer 2, [Zn(LigA)(CH3OH).2CHCl3]n 31
Figure 12: ORTEP drawing of the building block of 2 31
Figure 13: Schematic description of the self-assembly of pillar supported structure 32
Figure 14: UV-vis absorption of free LigBH2 (bold solid line) and its salt in different
water and DMSO (dash and thin solid line) 33
Figure 15: (a) Structure of the paddle-wheel dinuclear Zn carboxylate units of
framework 3; (b) Structure of the 2D grid of framework 3. 34
Figure 16: 2D interpenetrating, sheet-like structure of 3 35
x
Figure 17: Emission spectra of MOF 3 under different excitation wavelengths 36
Figure 18: Normalized solid state emission and excitation profile of MOF 3 36
Figure 19: The asymmetric unit of 4 (left), and 5 (right) 38
Figure 20: Bimetallic Eu unit showing the versatile coordination modes of the carboxylate
groups of LigB2- 39
Figure 21: Space-filling diagram of the extended structure of 4 showing triangular channel
looking down the a axis. 39
Figure 22: Powder X-ray diffraction calculated and found pattern
for framework 5 40
Figure 23: Magnified region of 2θ = 3 to 9o in both calculated and found PXRD patterns
of 5 40
Figure 24: TGA of 4 and 5 under N2 atmosphere and heating rate of
5oC/min 42
Figure 25: Weight loss of 5 over time (min) 43
Figure 26: Solid state excitation-emission spectrum of MOF 4 44
xi
List of schemes
Page
Scheme 1: Synthesis of LigAH2 via Ullmann coupling 26
Scheme 2: Synthesis of dinuclear Zn complex 1, Zn2(LigA)(phen)2(OAc)2 28
Scheme 3: Synthesis of 2, [Zn(LigA)(CH3OH).2CHCl3]n 30
xii
List of Abbreviations
1 Zn2(LigA)(phen)2(OAc)2
2 [Zn(LigA)(CH3OH).2CHCl3]n
3 [Zn2(LigB)2(DMSO)2]·2MeOH
4 [Eu2(LigB)3(DMSO)2(MeOH)2]·(DMSO)2(H2O)3
5 [Tb2(LigB)3(DMSO)2(MeOH)2]·(DMSO)2(H2O)3
LigAH2 unprotonated ligand A (3,3'-(biphenyl-4,4'-diyl)dipentane-2,4-
dione)
LigBH2 unprotonated ligand B (4,4-(ethyne-1,2-diyl)dibenzoic acid)
acac Acetylacetone)
δ chemical shift
CHCl3 chloroform
Cont. continued
d day
deg degree
ρ density
CH2Cl2 dichloromethane
DCM dichloromethane
DMSO dimethyl sulfoxide
N2 dinitrogen
N/A not applicable
dpdo 4,4’-dipyridyldioxide
Et3N triethylamine
FW formula weight
GC gas chromatography
xiii
g gram
h hour
lig ligand
M metal
min minute
mmol milimole
MOFs metal-organic frameworks
mol mole
NMR nuclear magnetic resonance
Phen 1,10-phenanthroline
ppm parts per million
% percent
PXRD powder x-ray diffraction
1D one-dimension
rt room temperature
SXRD single crystal x-ray diffraction
THF tetrahydrofuran
3D three-dimension
2D two-dimension
λ wavelength
wt weight
0D zero-dimension
1
CHAPTER I
INTRODUCTION
1.1 Supramolecular self-assembly (SA)
The foundation of supramolecular chemistry was laid down less than fifty years ago and has
since developed rapidly and become increasingly interdisciplinary. Supramolecular chemistry
has diversified into host-guest chemistry and crystal engineering. Upon association of the host
and guest, the properties of either or both constituents can change. A more stable aggregate
often results. We have enjoyed many applications of inclusion complexes such as drugs
(Nitropen), catalysts, sensors for clinical measurements.1
Pre-organization, recognition, and self-assembly are central concepts of supramolecular
chemistry.2
Preorganization is the spontaneous arrangement of reagents into appropriate spatial
orientation to facilitate chemical reactions or self-assembly processes.1a The structure adopted
by a molecule in the crystalline state is determined by a balance of attractive and repulsive
forces, each possessing varying degree of strength, distance dependence and directionality.3
Hydrogen bonding exhibits the strongest directional properties and is often used in the field.
Hydrogen bonding in some cases can help add a new dimension to a network even in the
absence of a covalent linker.
Molecular recognition requires shape and electronic complementarities between host and
guest molecules. “Key and lock” and “induced fit” concepts have been proposed to explain such
phenomena.
There are covalent and supramolecular self-assemblies; formation of the latter is driven by
weak, but numerous intermolecular forces including hydrogen bonding, and van der Waals
interactions (i.e. π-π stacking, dipole-dipole and ion-induced interactions),. The interactions that
bind molecules in crystals are also ones responsible for molecular assembly in solution. By the
2
virtue of having many weak, non-covalent forces, or for that matter metal-donor bonds, the final
products as a result of self-assembly is in thermodynamic equilibrium with its components. This
lead to unique and important properties of most supramolecular systems: they have an in-built
capacity for error correction that is normally unavailable in fully covalent system. In other
words, a system that self-assembles can do so reversibly. Irreversible aggregation without
adjustment of the positions of its components leads to glasses or amorphous materials.3
In summary, all the mentioned processes play a sequential role in complexation:
preorganization selects out appropriate spatial orientation of sub-components for their
subsequent recognition by one another followed by the spontaneous self-assembly of the
required supramolecular entity.2
1.2 MOF composition and synthesis influenced by self-assembly process
Coordination polymers and supramolecules are formed by self-assembly process — a facile
approach to materials of useful properties.4 Thus, the physical property of individual
constituents, such as luminescence, chemical functionality, and chirality, can be translated into
that of the assembled MOFs.11 In coordination polymers, metal-ligand modules are linked
infinitely into one, two or three dimensions via metal-ligand covalent bonds and the ligand must
contain bridging moieties. There are several ways to define MOFs. MOFs can also be thought as
coordination polymers.5 Some large, extended MOFs structures are indeed
metallosupramolecules.6 They are also assemblies of metal ions or clusters functioning as nodes
and organic ligands as the linkers.7 The cavities of as-synthesized MOFs are often filled with
solvent molecules or counter ions. MOFs are thus essentially host-guest systems.
The functions of materials are largely determined by their solid state structures.5 This
theorem is in turn the driving force for the desire to rationally design and control the assembly
of MOF building blocks. MOFs are highly crystalline, and their crystals can be regarded as a
manifestation of self-assembly and self-organization mentioned above.
3
1.2.1 Secondary building unit:
As pioneers in the field of MOF, Yaghi and coworkers have also coined the term secondary
building unit or SBU which refers to molecular complexes or clusters that can be extended into
porous networks using polytopic linkers.7 SBU is a useful tool for the overall topology
prediction for MOFs. As illustrated in Figure 1, the four carbon atoms of the paddle wheel form
square secondary building units (Figure 1a) which in turn can, by means of linkers, form
polyhedra, 2D sheets, and 3D networks.8 Factors such as solvent templating, metal ion
solvation, linkers’ geometries, temperature, pH, presence and nature of available anions may
play decisive roles in the formation of various structures.6,9
MM
O O
OO
O
O
O
O
MM
OO
OO
O
O
O
O
MM
OO
OO
O
O
O
O
MM
OO
OO
O
O
O
O
MM
OO
OO
O
O
O
O
Linker
paddle wheel unit
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
SBU
Figure 1: Illustration of secondary building unit.8
Researchers have been trying to find a way to control and predict the structural outcomes of
MOFs. However, there has not yet been a way to truly control a self-assembly process; rather,
what commonly so-called “rational” design can only help do so in a pseudo-controlled fashion.6
Utilizing SBUs and the linkers of well-known geometry and chemical properties can lead to
better predictions. For a given shape of the building blocks, only few simple, high symmetry
network of general importance are most likely to form from these subunits. 9
4
1.2.2 Metallic nodes:
The metal atoms in MOFs can be thought of as templating joints for bridging ligands.5 Late
transition metals are often used in MOF construction. Lanthanide metals are also used to impart
luminescence properties to the framework. Although frameworks made of light main group
metal cations such as Li+, Na+, and Al3+ would be lighter, they have not been observed to date.
Metal ions can be introduced to the nodal positions of MOFs as single metal centers or as metal
clusters. Group 2 MOF are rare, having few reports on Mg, Ca, Ba, Sr-containing structures.10, 11
Among metal clusters at nodes, Zn cluster are most often encountered.8, 12
Utilizing metal clusters as nodes of MOFs can be an effective approach to circumvent the
lack of coordination sites that is often experienced with transition metals (i.e. Cu, Zn, Cd etc.)
largely because metal clusters can accommodate sterically demanding organic ligands.12b This is
also one of the strategies to obtain rigid structure without a tendency to interpenetrate.13
1.2.3 Linkers:
The ability to derivatize and modify organic linkers gives chemists limitless access to
various linkers. Oxygen- and nitrogen-donor ligands are often used in MOF synthesis. Polytopic
ligands such as 4,4’-(ethyne-1,2-diyl)dibenzoic acid are widely used as ligands due to their
ability to bind to various metals with versatile binding modes.14
The use of molecular rather than monatomic bridges leads to the desirable outcome of
enlarging the void space of MOFs by means of further extending the distance between metal
nodes.11 Expansion of the network can be achieved by using long or polytopic ligands which
effectively enlarge the pore of the framework cavity.7 However, this strategy is not always
preferable, especially when MOFs are to be functioning in gas inclusion. This aspect will be
discussed later on.
5
1.2.4 MOF synthesis:
In MOF synthesis, what essentially happens is the assembly of discrete molecular units into
extended network.7 This synthetic approach allows reactions to take place at room temperature.
Generally, little is known about the M-L species preformed in solution before the assembling
process.5 MOFs are typically obtained by means of slow vapor diffusion and solvo-thermal
synthesis. In the former synthetic condition, the materials can be obtained in one-pot synthesis,
often under mild conditions. 9, 11 A solvo-thermal reaction follows a liquid nucleation model in
which a fast kinetics of nucleation and crystal growth or the reversible nature of the process can
lead to formation of good quality crystals.13,14 Heating helps lower barrier to rotation of the
linkers which can result in more stable MOF structures. Solvent switching in synthesis may
also produce novel structures.9,24
The often found solvent molecules or counter-anions in MOF cavities can act as templating
agents directing the formation of certain structural outcomes. Additionally, dimensionality of
MOFs can depend on the solvent or/and the strength of base employed to deprotonate the
organic ligands.15 For example, the use of triethylamine as the base is preferable over pyridine
in forming 3D MOF as the latter is a weaker base and a better ligand. Coordination of pyridine
to the metal centers will prevent the desired organic ligands from coordinating to the metal
centers, limiting the dimensionality of the framework.
In order for a pre-determined MOFs structure to be attained, MOFs constituents need to be
able to self-correct; that is, to assemble in a reversible manner. This is also an inherently
prominent feature of self-assembly process.
1.3 The significance of metal-organic frameworks:
As the unrenewable fossil fuel becomes increasingly depleted, hydrogen comes into play
as one of the best alternative fuels due to its highest energy density among all common fuels
(e.g. three times the energy density of gasoline).11 For hydrogen economy to be feasible, a light
6
material with high capacity is required for the safe storage of hydrogen. This remains
challenging in realizing a hydrogen economy.11
The US Department of Energy (DOE) has set a target for hydrogen storage system — 6
weight per cent and 45 kg H2 per m3 by 2010, and 9 weight per cent and 81 kg H2 per m3 by
2015. Thus far, compressed hydrogen gas and cryogenically stored liquid hydrogen are being
used by many automobile manufacturers. However, 90% of the system mass is contributed by
the containment vessels. Another significant drawback is the large amount of energy input for
condensation in the cryogenic storage. 11 Possibility of breakthrough in hydrogen storage
efficiency has therefore been pursued in chemical systems, examples of which include metal-
hydride complexes. Mg2NiH4, NaAlH4, and borohydrides of Group 1, 2, and 13 elements all
have large gravimetric capacities; however, they has all have their own drawbacks such as high
desorption temperature, requirements for catalyst for recycling, and unknown reversibility. 11
Hydrolysis of alkali metal-hydrides provides a convenient route to H2 release; however, the
decomposition products generated from the process need to be recycled off-board. Carbon
nanotubes while having low density, high surface area and good chemical stability can only
uptake a few weight per cent of H2 even under high pressure. Overall, research in H2 storage
still awaits a breakthrough material. To reduce mechanical requirements of pressurized vessels,
MOFs have been investigated for their ability to physically absorb H2 .11
Metal organic framework (MOF) is a class of microscale, crystalline inorganic- organic
hybrid that has first captured the research attention as a new candidate for hydrogen storage
materials. MOFs have many attributes, including high porosity and facile synthesis, making
them the focus of hydrogen storage research.11
1.3.1 MOFs as attractive H2 storage system:
The purpose of this section is to highlight MOFs’ applications as H2 storage systems and
through that many structural insights about MOFs will be better elucidated to readers. Many
7
MOFs have very high apparent surface area which makes them appealing H2 storage materials.
Among the reported structures, MOF-177 by Yaghi and coworker exhibits the highest uptake of
N2 among all materials to date. It has a surface area of 4500 m2/g and a pore volume of 0.69
cm3/cm3.16 This translates to an uptake of up to 7 weight per cent H2. However, measurements
for a large set of Zn4O-based MOFs revealed that only a small fraction of the surface is
occupied by the guests. This then necessitated a need for pore optimization.
Surface area and pore volume can be determined by gas absorption isotherms. All porous
MOFs so far are microporous by IUPAC definition, having pore size of less than 2 nm and
displaying type I absorption isotherm (Figure 2). The assumption taken in such measurements
is that a homogeneous monolayer of the absorbate is formed on the walls of the absorbent. The
apparent surface area is then the product of the number of molecules uptaken and an accepted
value for the area occupied by an adsorbate molecule.11
Figure 2: Type I gas absorption isotherm .17
H2 uptake mechanism has been theoretically studied by means of computation. H2 can
bind to both the metallic nodes and the organic linkers.18,19 In the Zn-based MOF being
examined by Goddard and coworkers, the former is thought to be the more favored adsorption
sites at low pressure. However, at higher pressure, H2 are preferentially adsorbed onto the
organic linkers.18 Larger aromatic linkers are therefore recommended for improved designs of
8
MOFs in H2 storage. 18 Other strategies towards improving hydrogen uptake of MOFs include
linker modification, incorporation of coordinatively unsaturated metal and lighter metals
catenation, impregnation.11
Maximal absorption of guest molecules comes with maximizing the total van der Waals
forces on the adsorbates. It is worth noting that having a large pore size does not necessarily
mean maximal storage capacity for H2. In fact, many reported MOFs to date have cavities that
are too large for effective H2 storage. For example, MOF-5 structure has a pore diameter of 15.2
Å which is much larger than the 2.89 Å kinetic diameter of H2.11 If a shorter linker isn’t used to
reduce the pore size, MOF-5 is simply too leaky to store H2. MOFs with constricted pores might
appear non-porous with absorption isotherm measurements as their small pores could not admit
N2 but allow the passage of H2. Another case where this can happen is that the as-synthesized
MOFs contain solvent molecules in the cavities that occlude entrance of other targeted guest
molecules (i.e. H2, N2, CO2 etc.).20 Decreased pore size might translate to a decrease in
gravimetric density of hydrogen uptake; however, their volumetric capacities might be
enhanced. There will always be a compromise to make along the line of MOFs structural design.
Other alternatives in optimizing pore size for H2 uptake include impregnation and
catenation. In impregnation, a non-volatile, well-anchored guest is inserted to provide additional
H2 absorptive sites. Impregnated MOF-177 with C60 molecules encapsulated within its 11.8 Å
diameter pore can provide additional surface absorption sites.
Framework catenation has long been recognized in the MOF research and is often
encountered when long linkers are used.7,11 Catenation has also been interpreted as a means of
further stabilizing the framework that relies on the support of cavity solvent molecules. In some
cases catenation can lead to undesirably nonporous networks.14 Nevertheless, some materials
have been reported to display porosity while possessing interpenetrating networks.12a
9
Catenation takes the form of interpenetration and interweaving. The former occurs when two
or more frameworks have the maximal offset from each other (Figure 3b) while the latter occurs
when the frameworks have the minimal offset and exhibit many close contacts (Figure 3c).
Interpenetration is desirable as it maximizes the exposed surface of catenated MOFs while
interweaving results in blockage of potential absorption sites.11 Depending upon the degree of
penetration, the resulting framework still can exhibit void space for selectively trapping of small
molecules as demonstrated in this thesis. Still, there is not yet a control over formation of non-
penetrating over penetrating framework.
Figure 3: Interpenetration and interweaving MOFs a) repeating unit of MOFs with SBU shown
as cubes and linkers as rods; b) interpenetrating frameworks; c) interweaving framework.11
1.3.2 MOFs as catalysts:
Application of MOFs in this domain has been met with limited success, mainly because the
metals in MOFs are coordinatively saturated. Nevertheless, useful catalytic systems have been
achieved with MOFs in the catalysis of cyanosilylation of aldehydes20a, hydrogenation of
nitroaromatics, and oxidation of alkylphenylsulfides etc.20b Hill and coworkers have recently
reported a redox active vanadium- and terbium-containing MOF that can catalyze the oxidation
of PrSH to PrSSRPr using only ambient air under mild conditions. 21
10
1.3.3 MOFs functioning in chromatography:
The petroleum industry relies on the important process of separating linear from
branched alkanes in order to boost octane ratings of gasoline. MOFs can be useful for such
purposes due to their selective sorption and high thermal stability.15,22 Good GC separation of
mixture of linear and branched alkanes has been reported when MOF-508 was used as the
stationary phase.22
Overall, MOF applications originate from their abilities to function as host-guest
systems.
1.4 Luminescence in MOFs:
Luminescence is a light emitting phenomenon from any emissive substance. It involves
electronic transitions from excited states to the ground state. Luminescence can be classified
into fluorescence and phosphorescence depending on the nature of the excited state (i.e. singlet
vs. triplet excited state.23 Supramolecular luminescent materials are mostly small organic and
coordination compounds. The most important application of the latter is their use as sensors and
light-emitting diodes (LEDs). Luminescent materials then can be classified based on the origin
of emission; i.e. whether it is ligand-based or metal-based emission. Luminescent MOFs can
also be devised that way by incorporate the emissive lanthanide metal ions. For the scope of
this research, it is most relevant to discuss the single metal center-based emission. Many
lanthanide ions with a partially filled 4f shell are emissive due to f-f transitions. Depending on
the lanthanide ions, blue, red (Eu) or green (Tb) emission can be seen. f-f transitions are Laporte
forbidden rendering lanthanide luminescence rather weak (ε <10 M-1 cm-1). In order to enhance
luminescence, a suitable ligand can be chelated to the lanthanide ion. The role of the ligand is to
harvest photon energy and effectively transfer that energy to the emissive metal centers. Such
phenomenon is often termed the antenna effect and is describe in Figure 4.
11
Ligand based luminescence often occurs in organic molecules and coordination
compound. It involves the electronic transitions of the ligands.23 Many luminescent organic
molecules contain aromatic moieties. Both of the organic ligands employed in current study are
luminescent and are examples of such molecules. Many coordination compounds luminesce
because of the electronic transition of the ligands only. Often, formation of complex involving
luminescent ligand enhances the emission of the resulting complex as compared to that of free
ligands. The main reason rests in the ability of the ligands to make more rigid structures upon
chelating. Quite a number of Zn (II) complexes, including the Zn framework generated from this
study, are luminescent.5,23,24
The combination of organic ligands and metal center in MOF is seen as a method for
creating new types of electroluminescent materials for potential LEDs applications.5
The combination of organic ligands and metal center in MOF is seen as a method for creating
new types of electroluminescent materials for potential LEDs applications.5
1.5 Scope of the Thesis:
The goal of the research is to arrive at multidimensional, highly porous and functional
MOFs via hierarchical assembly of smaller molecular building blocks (Figure 5) and, at the
same time, to examine the possibilities for different interesting molecular textures. More
Figure 4: Antenna effect in lanthanide luminescence
Antenna
hv Luminescence
Excitation
Energy transfer
Eu (III)
12
specifically, a dinuclear Zn complex was created by using oxygen-donor, linearly bridging
ligand (i.e. LigAH2). Capping ligand such as phenanthroline was also purposely introduced in
creating such complex as it provides a mean for subsequent control of extra dimensional
synthesis using such dinuclear Zn as the building blocks. The attained Zn-based motifs can then
be polymerize into 1D coordination polymer by replacing the capping ligand with another
equivalent of the bridging ligand. Altering the choice of ligand as well as metal in the syntheses
can lead to the formation of new structures. Utilizing similarly linear but more rigid carboxylate
bridging ligand in combination with Zn whose maximal coordination number is well-known, a
novel 2D MOF structure was attained. This resulting 2D framework can then be further
extended into 3D by coordinating the newly chosen rigid ligand to metals having high
coordination number such as lanthanides. Overall, the strategy taken is very much a stepwise,
hierarchical assembly of small building blocks into larger, multidimensional frameworks. Such
strategy has been proven to be successful as different molecular architectures have been
obtained including luminescent 2D and 3D MOFs in the current research.
M =
n
Lig =
0-D 1-D 2-D 3-D
Figure 5: Schematic representation of research objective.
13
Luminescent MOFs are of important applications. Despite a great numbers of MOFs in
the literature, reports on luminescent MOFs are still scarce and their applications are still
extremely modest.5,24 In this class, MOFs exhibiting metal-based luminescence are outnumbered
those displaying ligand-based emission.24 This study will demonstrate the synthesis and
emissive properties of luminescent MOFs belonging to both categories. Porous MOFs such as
those obtained from current study can potentially be used as host-guest systems for detection of
pollutants using their inherent luminescent property as the trigger.
14
CHAPTER II
EXPERIMENTAL SECTION
General Remarks. Unless otherwise stated, all the chemicals were purchased and used without
further purification. Acetylacetone, DMSO, DBU, water, trimethylsilylacetylene were degassed
prior to reaction.
Physical characterization. Thermogravimetric analysis (TGA) was performed on a SDT Q600
unit under N2 at a heating rate of 3oC or 5oC/min (vide infra). Fluorescence spectra were
recorded on a Fluorolog-3 Jobin Yvon Horiba luminescence spectrometer equipped with a
450W xenon lamp as the excitation source. UV-vis absorption measurement was performed on
an Agilent 8453 single-beam diode-array spectrophotometer. Elemental analyses were
performed on a Perkin Elmer 2400 Series II CHN/S Elemental Analyzer at the Department of
Chemistry, University of Toronto. All samples were dried in vacuum prior to analysis. 1H-NMR
spectra were recorded on a Varian 300, 400 MHz and 13C-NMR spectra on 100 MHz NMR
spectrometer. Chemical shifts are reported in ppm relative to an internal standard of TMS.
2.1 Synthesis of 3,3'-(biphenyl-4,4'-diyl)dipentane-2,4-dione (LigAH2): followed modified
procedure reported by Jiang, Y. et al. 25
A mixture of K2CO3 (8 equiv, 13,6g), CuI (20mol%, 0.47g), and L-proline (40mol%,
0.5671g) in 50 ml DMSO were added to an argon-purged two-neck-Schlenk flask followed by
slow addition of 4,4’-diiodobenzene in 120 ml THF (5g, 0.0123mol). With good stirring, the
resulting mixture was refluxed at 90oC under N2 atmosphere for 60 hrs. The cooled solution was
acidified and extracted with DCM. The combined organic layer was washed with water, brine
(3x200ml); dried over Na2SO4 and concentrated. The residue was chromatographed (8:1
Hexane: EtOAc) to afford 3,3'-(biphenyl-4,4'-diyl)dipentane-2,4-dione (or LigAH2) in 38 %
(1.6 g) yield. 1H-NMR (400MHz, CDCl3) δ 16.7 (s, 2H), 7.66 (d, 4H), 7.27 (d, 4H), 1.94 (s,
15
12H); 13C-NMR (100 MHz, CDCl3) δ 191.1, 139.7, 136.4, 131.8, 127.5, 114.9, 24.4 (Appendix
for spectra). Anal. Calcd. for C22H22O4 (350.41): C, 75.41; H, 6.33. Found: C, 75.57; H, 6.14.
2.2 Synthesis of 4,4'-(ethyne-1,2-diyl)dibenzoic acid (LigBH2): according to previously
reported procedure 4, 26
A 5-g reaction gave 76.6% LigBH2. The product is insoluble in common organic
solvents except DMSO. 1H NMR (300MHz, DMSO-d6) δ 13.19 (s, 2H), 7.99 (d, J = 8.4Hz,
4H), 7.71 (d, J = 8.4Hz, 4H); 13C-NMR (100MHz, CDCl3) δ 166.7, 131.8, 131.0, 129.6, 126.1,
91.1. Anal. Calcd. for C16H10O4·0.25H2O: C, 70.91; H, 3.89. Found: C, 71.11; H, 3.91.
2.3 Synthesis of Zn2(LigA)(phen)2(OAc)2, 1
A mixture of Zn(OAc)2.2H2O (0.0251g, 0.144 mmol), LigAH2 (0.0401g, 0.144mmol)
and phenanthroline (0.0206g, 0.144mmol) was dissolved in 6 mL of CH2Cl2/MeOH (1:1 by
volume) and stirred at ambient temperature for 2 hrs. After the solvents were removed in vacuo,
the residual solid was recrystallized by diffusing hexanes into a CH2Cl2 solution to afford the
title compound as colorless crystals.
2.4 Synthesis of [Zn(LigA)(DMSO)2(CH3OH)]n , 2
To a solution of Zn(OAc)2.2H2O (0.0210g, 0.0958mmol) in 1.6 mL of methanol was
added a solution of LigAH2 (0.0504g, 0.1438mmol) in 2.4 mL CHCl3. The resulting mixture
was filtered through Celite into a small vial which was then inserted into a bigger vial
containing a 0.28 M solution of Et3N in MeOH/CHCl3 (1:1 by volume). After several days, X-
ray quality crystals can be collected. The reaction is reproducible; however, every time an
unidentified insoluble solid formed together with the crystals.
2.5 Synthesis [Zn2(LigB)2(DMSO)2]·2MeOH, 3
A solution of Zn(NO3)2·6H2O (0.0168g, 0.0563mmol) in 3 mL of MeOH was mixed
with a solution of LigBH2 (0.0151g, 0.0564mmol) in 2 mL of DMSO. (Note: the DMSO
16
solution of LigBH2 was sonicated and heated slightly to improve the solubility of LigBH2.) The
resulting mixture was filtered through Celite into a small vial which was then inserted into a
bigger vial containing a 0.015 M solution of Et3N in MeOH/DMSO (1:1 by volume).The title
compound was collected as stable yellow, opaque crystals (16% yield) after several days.
Unidentified white needles were formed as a bi-product. Anal. Calcd. for
[Zn2C36H28O10S2]·2CH3OH: C, 51.88; H, 4.13. Found: C, 51.37; H, 3.46.
2.6 Synthesis of [Eu2(LigB)3(DMSO)2(MeOH)2]·(DMSO)2(H2O)3, 4
A solution of EuCl3.6H2O (0.055g, 0.150mmol) in 4 mL of MeOH was mixed with a
solution of LigBH2 (0.08g, 0.3mmol) in 12 mL of DMSO. The resulting mixture was filtered
through Celite. Vapor diffusion (similar to Section 2.5) using 0.015M Et3N in MeOH/DMSO
(1:1 by volume) was then performed. After 17d, single crystals of 4 were collected (0.055 g,
48%). The title compound is fully reproducible. However, an unidentified white, opaque solid
always formed as a bi-product. Anal. Calcd. for C58H60O20S4Eu2 (formulated as 4-H2O due to
partial solvent loss under vacuum): C, 46.16; H, 4.01. Found: C, 46.0; H, 3.70.
2.7 Synthesis of [Tb2(LigB)3(DMSO)2(MeOH)2].(DMSO)2(H2O)3, 5
Procedure for synthesis of 5 is similar to that of 4 except that EuCl3.6H2O was replaced
by TbCl3.6H2O. After 2 weeks, single crystals of 5 were be collected in a 42% yield (80 mg).
This synthesis showed good reproducibility. However, an unidentified white, opaque solid was
always formed as a bi-product. Anal. Calcd. [Tb2C58H60O20S4] (formulated as 5-H2O, due to
partial solvent loss under vacuum): C,45.74 ;H, 3.97. Found: C, 45.61; H, 3.51
17
X-ray crystallography.
Dif
frac
tion
da
ta
for
crys
tals
of
co
mpl
exes
1-5
wer
e co
llec
ted
at
150
K
on
a N
oniu
s K
appa
C
CD
diff
ract
omet
er w
ith
Mo
Kα
rad
iati
on (λ
= 0
.710
73 Å
), o
pera
ting
at
50kV
and
30
mA
.. T
he d
ata
wer
e in
tegr
ated
and
sca
led
usin
g th
e D
enso
-
SM
N p
acka
ge.
All
str
uctu
res
wer
e so
lved
usi
ng t
he d
irec
t m
etho
ds a
nd r
efin
ed b
y fu
ll-m
atri
x le
ast-
squa
res
proc
edur
es o
n F
2 usi
ng
SH
EL
XT
L 6
.10.
The
cry
stal
logr
aphi
c da
ta o
f 3-5
are
sum
mar
ized
in
Tab
le 1
. Sel
ecte
d bo
nd l
engt
hs a
nd a
ngle
s of
1-5
are
pre
sent
ed i
n T
able
2 to
Tab
le 6
, res
pect
ivel
y
Table 1: Crystallographic data for compounds 1-5
1
2 3
4 5
For
mul
a C
51H
43C
l 3N
4O8Z
n 2
C24
H25
Cl 3
O5Z
n C
19H
18O
6SZ
n C
58H
62O
21S
4Eu 2
C
58 H
62O
21S
4Tb 2
F
W
1076
.98
565.
16
439.
76
1525
.26
1541
.16
Tem
p (K
) 15
0(2)
K
150(
2)
150(
2) K
15
0(2)
15
0(2)
K
λ (Å
) 0.
7107
3 0.
7107
3 0.
7107
3 0.
7107
3
0.71
073
Cry
st. S
ys.
Mon
ocli
nic
Ort
horh
ombi
c O
rtho
rhom
bic
Mon
ocli
nic
Mon
ocli
nic
Spa
ce G
rp.
C2/
c P
na2 1
P
bca
P2 1
/c
P2 1
/c
a 27
.567
3(15
) 18
.010
(4)
15.8
816(
4) Å
10
.429
9(2)
10
.445
6(3)
b
12.5
710(
7)
16.7
93 (
3)
9.29
74(2
) Å
13
.521
9(3)
13
.531
2(4)
c
16.5
027(
10)
16.6
28 (
3)
25.2
870(
7) Å
31
.664
2(6)
31
.575
1(10
) α
(de
g.)
90
90
90
90
90
β (
deg.
) 10
4.38
3(3)
90
90
97
.620
8(13
) 97
.641
5(15
) γ
(deg
.)
90
90
90
90
90
Z
4 8
8 2
2
V(Å
) 55
39.7
(5)
5029
.0(1
7)
3733
.82(
16)
4426
.22(
15)
44
23.2
(2)
ρ(ca
lc.)
Mg/
m3
1.29
1 1.
493
1.56
5
1.14
4 1.
157
Abs
Coe
ff. (
mm
-1)
1.06
2 1.
328
1.46
1
1.55
1 1.
732
F(0
00)
2208
23
20
1808
15
32
1544
θ
ran
ge (
deg.
) 2.
96 t
o 25
.00
2.94
to
27.0
0 3.
03 t
o 27
.46
2.92
to
25.0
0 2.
99 t
o 25
.00
18
Table 1: Crystallographic data for compounds 1-5 (Cont.)
1
2 3
4 5
For
mul
a C
51H
43C
l 3N
4O8Z
n 2
C24
H25
Cl 3
O5Z
n C
19H
18O
6SZ
n C
58H
62O
21S
4Eu 2
C
58 H
62O
21S
4Tb 2
Ref
lns
coll
ecte
d 13
070
1997
2 28
751
3018
3 17
823
No.
of
uniq
ue r
efln
s 48
55
8392
42
53
7787
75
19
GO
F o
f F
2
1.01
9 1.
022
1.06
7 1.
044
1.06
9 R
1,w
R2 [I
>2σ
(I)]
0.
0928
, 0.2
560
0.09
40, 0
.228
2 0.
0545
, 0.1
373
0.07
76, 0
.229
9 0.
0767
, 0.
2245
R
1, w
R2
all
data
0.
1831
, 0.3
284
0.19
01, 0
.298
7 0.
0908
, 0.1
557
0.10
45, 0
.258
9 0.
1016
, 0.2
507
19
Table 2: Selected bond lengths (Å) and angles (deg) of numbering atoms in 1
Zn(1)-O(1) 1.981(5)
Zn(1)-O(2) 2.017(6)
Zn(1)-O(3) 2.058(8)
Zn(1)-N(2) 2.103(7)
Zn(1)-N(1) 2.162(6)
O(1)-C(16) 1.275(8)
O(2)-C(14) 1.262(10)
O(3)-C(24) 1.213(11)
O(4)-C(24) 1.191(11)
N(1)-C(1) 1.259(10)
N(1)-C(12) 1.355(9)
N(2)-C(10) 1.344(10)
N(2)-C(11) 1.363(10)
C(1)-C(2) 1.480(12)
O(1)-Zn(1)-O(2) 87.7(2)
O(1)-Zn(1)-O(3) 145.2(3)
O(2)-Zn(1)-O(3) 94.7(3)
O(1)-Zn(1)-N(2) 120.6(2)
O(2)-Zn(1)-N(2) 91.2(3)
O(3)-Zn(1)-N(2) 94.1(3)
O(3)-Zn(1)-N(2) 94.1(3)
O(1)-Zn(1)-N(1) 89.5(2)
O(2)-Zn(1)-N(1) 165.6(3)
O(3)-Zn(1)-N(1) 95.7(3)
N(2)-Zn(1)-N(1) 78.1(3)
C(16)-O(1)-Zn(1) 128.7(5)
C(14)-O(2)-Zn(1) 127.8(6)
C(24)-O(3)-Zn(1) 108.4(8)
C(1)-N(1)-C(12) 119.1(7)
C(1)-N(1)-Zn(1) 127.6(5)
C(12)-N(1)-Zn(1) 112.9(5)
C(10)-N(2)-C(11) 116.6(8)
C(10)-N(2)-Zn(1) 129.1(7)
C(11)-N(2)-Zn(1) 113.9(5)
N(1)-C(1)-C(2) 123.2(8)
C(3)-C(2)-C(1) 116.2(9)
Table 3: Selected bond lengths (Å) and angles (deg) of numbering atoms in 2
Zn(1)-O(4) 1.978(10)
Zn(1)-O(1) 2.014(10)
Zn(1)-O(3) 2.028(10)
Zn(1)-O(2) 2.029(9)
Zn(1)-O(5) 2.032(12)
Zn(2)-O(6) 1.949(10)
Zn(2)-O(7) 1.977(10)
Zn(2)-O(9) 1.991(10)
19
Zn(2)-O(8) 2.013(11)
Zn(2)-O(10) 2.045(13)
C(23)-O(5) 1.411(18)
O(7)-C(27) 1.249(16)
O(4)-C(15) 1.275(18)
O(1)-C(2) 1.280(17)
O(8)-C(36) 1.254(17)
O(6)-C(25) 1.304(17)
O(3)-C(13) 1.254(17)
C(46)-O(10) 1.36(3)
O(2)-C(4) 1.294(16)
C(26)-C(25) 1.409(18)
C(20)-C(9)#1 1.51(2)
O(9)-C(38) 1.282(17)
O(4)-Zn(1)-O(1) 152.4(5)
O(4)-Zn(1)-O(2) 86.5(4)
O(1)-Zn(1)-O(2) 88.3(4)
O(4)-Zn(1)-O(3) 88.5(4)
O(1)-Zn(1)-O(3) 88.6(4)
O(2)-Zn(1)-O(3) 162.9(5)
O(4)-Zn(1)-O(5) 108.9(5)
O(1)-Zn(1)-O(5) 98.7(5)
O(2)-Zn(1)-O(5) 101.1(5)
O(3)-Zn(1)-O(5) 95.9(4)
O(6)-Zn(2)-O(7) 86.6(4)
O(6)-Zn(2)-O(9) 150.4(5)
O(7)-Zn(2)-O(9) 86.0(5)
O(6)-Zn(2)-O(8) 90.5(5)
O(7)-Zn(2)-O(8) 159.6(5)
O(9)-Zn(2)-O(8) 86.6(4)
O(6)-Zn(2)-O(10) 104.9(5)
O(7)-Zn(2)-O(10) 105.2(5)
O(9)-Zn(2)-O(10) 104.7(5)
O(8)-Zn(2)-O(10) 95.1(5)
C(27)-O(7)-Zn(2) 130.3(10)
C(23)-O(5)-Zn(1) 129.9(9)
C(15)-O(4)-Zn(1) 126.0(8)
C(2)-O(1)-Zn(1) 125.7(10)
C(36)-O(8)-Zn(2) 127.0(9)
C(25)-O(6)-Zn(2) 131.9(9)
C(13)-O(3)-Zn(1) 128.7(10)
C(46)-O(10)-Zn(2) 123.8(13)
C(4)-O(2)-Zn(1) 129.2(9)
C(25)-C(26)-C(27) 121.9(14)
C(25)-C(26)-C(29) 114.3(12)
C(38)-O(9)-Zn(2) 128.6(9)
O(4)-C(15)-C(14) 127.0(12)
O(4)-C(15)-C(16) 111.4(13)
O(7)-C(27)-C(26) 125.7(13)
20
O(7)-C(27)-C(28) 118.7(13)
C(26)-C(27)-C(28) 115.4(14)
C(22)-C(21)-C(20) 121.4(18)
O(6)-C(25)-C(26) 122.0(11)
O(6)-C(25)-C(24) 117.3(13)
C(26)-C(25)-C(24) 120.7(14)
O(3)-C(13)-C(12) 117.5(14)
O(3)-C(13)-C(14) 121.3(15)
C(12)-C(13)-C(14) 121.2(14)
O(8)-C(36)-C(37) 126.0(13)
O(8)-C(36)-C(35) 115.1(13)
C(37)-C(36)-C(35) 118.9(14)
O(1)-C(2)-C(3) 127.7(15)
O(1)-C(2)-C(1) 110.7(14)
C(3)-C(2)-C(1) 121.6(14)
O(2)-C(4)-C(3) 123.0(14)
O(2)-C(4)-C(5) 115.4(12)
O(9)-C(38)-C(37) 123.3(13)
O(9)-C(38)-C(39) 115.7(13)
Table 4. Selected bond lengths (Å) and angles (deg) of numbering atoms in 3
Zn(1)-O(5) 1.984(3)
Zn(1)-O(3) 2.007(3)
Zn(1)-O(4)#1 2.046(3)
Zn(1)-O(2)#1 2.059(3)
Zn(1)-O(1) 2.073(3)
Zn(1)-Zn(1)#1 2.9786(9)
O(5)-Zn(1)-O(3) 103.57(13)
O(5)-Zn(1)-O(4)#1 97.98(12)
O(3)-Zn(1)-O(4)#1 158.35(13)
O(5)-Zn(1)-O(2)#1 99.23(13)
O(3)-Zn(1)-O(2)#1 90.70(13)
O(4)#1-Zn(1)-O(2)#1 87.92(12)
O(5)-Zn(1)-O(1) 100.95(13)
O(3)-Zn(1)-O(1) 89.86(13)
O(4)#1-Zn(1)-O(1) 83.93(13)
O(2)#1-Zn(1)-O(1) 159.09(13)
O(5)-Zn(1)-Zn(1)#1 170.28(9)
O(3)-Zn(1)-Zn(1)#1 86.15(9)
O(4)#1-Zn(1)-Zn(1)#1 72.31(9)
O(2)#1-Zn(1)-Zn(1)#1 80.30(9)
O(1)-Zn(1)-Zn(1)#1 78.88(9)
C(1)-O(1)-Zn(1) 127.9(3)
C(1)-O(2)-Zn(1)#1 127.2(3)
C(9)-O(3)-Zn(1) 119.4(3)
C(9)-O(4)-Zn(1)#1 136.3(3)
S(1)-O(5)-Zn(1) 121.99(17)
21
Table 5. Selected bond lengths (Å) and angles (deg) for 4
Eu(1)-O(5)#1 2.349(5)
Eu(1)-O(1) 2.391(4)
Eu(1)-O(8) 2.398(5)
Eu(1)-O(2)#1 2.403(4)
Eu(1)-O(6) 2.415(4)
Eu(1)-O(4) 2.422(4)
Eu(1)-O(7) 2.438(6)
Eu(1)-O(3) 2.582(4)
Eu(1)-O(5) 2.809(4)
Eu(1)-C(9) 2.843(6)
Eu(1)-C(17) 2.947(6)
Eu(1)-Eu(1)#1 4.1381(6)
S(1)-O(8) 1.513(6)
S(1)-C(26) 1.546(15)
S(1)-C(27A) 1.68(2)
S(1)-C(27B) 1.832(18)
O(1)-C(1) 1.260(8)
O(2)-C(1) 1.246(8)
O(2)-Eu(1)#1 2.403(4)
O(3)-C(9) 1.260(8)
O(4)-C(9) 1.257(8)
O(5)-C(17) 1.264(8)
O(5)-Eu(1)#1 2.349(5)
O(6)-C(17) 1.262(8)
O(7)-C(25) 1.369(9)
O(5)#1-Eu(1)-O(1) 73.37(15)
O(5)#1-Eu(1)-O(8) 148.09(16)
O(1)-Eu(1)-O(8) 138.46(16)
O(5)#1-Eu(1)-O(2)#1 77.95(16)
O(1)-Eu(1)-O(2)#1 130.56(16)
O(8)-Eu(1)-O(2)#1 78.88(16)
O(5)#1-Eu(1)-O(6) 123.21(15)
O(1)-Eu(1)-O(6) 81.86(15)
O(8)-Eu(1)-O(6) 74.01(17)
O(2)#1-Eu(1)-O(6) 81.35(15)
O(5)#1-Eu(1)-O(4) 89.34(16)
O(1)-Eu(1)-O(4) 75.47(16)
O(8)-Eu(1)-O(4) 96.58(18)
O(2)#1-Eu(1)-O(4) 143.66(16)
O(6)-Eu(1)-O(4) 132.53(15)
O(5)#1-Eu(1)-O(7) 78.13(18)
O(1)-Eu(1)-O(7) 134.79(18)
O(8)-Eu(1)-O(7) 74.7(2)
O(2)#1-Eu(1)-O(7) 74.29(18)
O(6)-Eu(1)-O(7) 143.33(18)
O(4)-Eu(1)-O(7) 69.79(16)
22
O(5)#1-Eu(1)-O(3) 131.35(15)
O(1)-Eu(1)-O(3) 69.46(15)
O(8)-Eu(1)-O(3) 73.76(15)
O(2)#1-Eu(1)-O(3) 150.69(17)
O(6)-Eu(1)-O(3) 81.24(15)
O(4)-Eu(1)-O(3) 51.90(15)
O(7)-Eu(1)-O(3) 107.64(19)
O(5)#1-Eu(1)-O(5) 73.65(14)
O(1)-Eu(1)-O(5) 66.78(14)
O(8)-Eu(1)-O(5) 116.17(15)
O(2)#1-Eu(1)-O(5) 66.93(14)
O(6)-Eu(1)-O(5) 49.59(15)
O(4)-Eu(1)-O(5) 141.59(16)
O(7)-Eu(1)-O(5) 135.68(17)
O(3)-Eu(1)-O(5) 116.67(14)
O(5)#1-Eu(1)-C(9) 109.00(18)
O(1)-Eu(1)-C(9) 66.90(17)
O(8)-Eu(1)-C(9) 87.99(18)
O(2)#1-Eu(1)-C(9) 162.35(18)
O(6)-Eu(1)-C(9) 106.48(18)
O(4)-Eu(1)-C(9) 26.07(17)
O(7)-Eu(1)-C(9) 91.0(2)
O(3)-Eu(1)-C(9) 26.29(17)
O(5)-Eu(1)-C(9) 130.23(16)
O(5)#1-Eu(1)-C(17) 98.77(19)
O(1)-Eu(1)-C(17) 76.03(17)
O(8)-Eu(1)-C(17) 93.3(2)
O(2)#1-Eu(1)-C(17) 69.56(17)
O(6)-Eu(1)-C(17) 24.77(18)
O(4)-Eu(1)-C(17) 146.65(16)
O(7)-Eu(1)-C(17) 143.51(18)
O(3)-Eu(1)-C(17) 101.48(18)
O(5)-Eu(1)-C(17) 25.23(17)
C(9)-Eu(1)-C(17) 123.50(19)
O(5)#1-Eu(1)-Eu(1)#1 40.65(10)
O(1)-Eu(1)-Eu(1)#1 64.53(11)
O(8)-Eu(1)-Eu(1)#1 141.38(11)
O(2)#1-Eu(1)-Eu(1)#1 67.39(12)
O(6)-Eu(1)-Eu(1)#1 82.58(12)
O(4)-Eu(1)-Eu(1)#1 121.69(14)
O(7)-Eu(1)-Eu(1)#1 111.65(16)
O(3)-Eu(1)-Eu(1)#1 132.82(11)
O(5)-Eu(1)-Eu(1)#1 33.00(9)
C(9)-Eu(1)-Eu(1)#1 128.55(14)
C(17)-Eu(1)-Eu(1)#1 58.16(16)
O(8)-S(1)-C(26) 103.3(7)
O(8)-S(1)-C(27A) 103.9(9)
C(26)-S(1)-C(27A) 97.5(11)
O(8)-S(1)-C(27B) 101.7(6)
C(26)-S(1)-C(27B) 95.7(8)
23
C(27A)-S(1)-C(27B) 147.5(10)
C(1)-O(1)-Eu(1) 141.9(4)
C(1)-O(2)-Eu(1)#1 135.2(4)
C(9)-O(3)-Eu(1) 88.5(4)
C(9)-O(4)-Eu(1) 96.1(4)
C(17)-O(5)-Eu(1)#1 168.7(4)
C(17)-O(5)-Eu(1) 83.5(4)
Eu(1)#1-O(5)-Eu(1) 106.35(14)
C(17)-O(6)-Eu(1) 101.9(4)
C(25)-O(7)-Eu(1) 131.7(5)
S(1)-O(8)-Eu(1) 131.2(3)
O(2)-C(1)-O(1) 126.0(5)
O(2)-C(1)-C(2) 118.9(6)
O(1)-C(1)-C(2) 115.1(6)
O(4)-C(9)-O(3) 121.4(6)
O(4)-C(9)-C(10) 117.3(6)
O(3)-C(9)-C(10) 121.3(6)
O(4)-C(9)-Eu(1) 57.9(3)
O(3)-C(9)-Eu(1) 65.2(3)
C(10)-C(9)-Eu(1) 164.5(5)
O(6)-C(17)-O(5) 123.0(6)
O(6)-C(17)-C(18) 118.4(7)
O(5)-C(17)-C(18) 118.7(7)
O(6)-C(17)-Eu(1) 53.3(3)
O(5)-C(17)-Eu(1) 71.3(3)
C(18)-C(17)-Eu(1) 164.3(5)
Table 6. Selected bond lengths (Å) and angles (deg) for 5
Tb(1)-O(4)#1 2.303(5)
Tb(1)-O(5) 2.361(4)
Tb(1)-O(8) 2.364(5)
Tb(1)-O(6) 2.377(4)
Tb(1)-O(3) 2.382(4)
Tb(1)-O(1) 2.396(4)
Tb(1)-O(7) 2.422(6)
Tb(1)-O(2) 2.575(5)
Tb(1)-C(1) 2.823(7)
Tb(1)-O(4) 2.869(5)
Tb(1)-C(9) 2.957(7)
S(1)-C(26A) 1.43(3)
S(1)-O(8) 1.525(6)
S(1)-C(27) 1.713(12)
S(1)-C(26B) 1.850(18)
24
O(1)-C(1) 1.251(8)
O(2)-C(1) 1.256(8)
O(3)-C(9) 1.279(9)
O(4)-C(9) 1.250(9)
O(4)-Tb(1)#1 2.303(5)
O(5)-C(17) 1.246(8)
O(6)-C(17)#1 1.276(8)
O(7)-C(25B) 1.354(9)
O(4)#1-Tb(1)-O(5) 73.52(16)
O(4)#1-Tb(1)-O(8) 147.96(18)
O(5)-Tb(1)-O(8) 138.38(17)
O(4)#1-Tb(1)-O(6) 78.93(17)
O(5)-Tb(1)-O(6) 130.36(16)
O(8)-Tb(1)-O(6) 78.69(17)
O(4)#1-Tb(1)-O(3) 123.32(18)
O(5)-Tb(1)-O(3) 81.55(16)
O(8)-Tb(1)-O(3) 74.62(19)
O(6)-Tb(1)-O(3) 80.28(17)
O(4)#1-Tb(1)-O(1) 87.96(18)
O(5)-Tb(1)-O(1) 75.43(18)
O(8)-Tb(1)-O(1) 97.0(2)
O(6)-Tb(1)-O(1) 144.05(17)
O(3)-Tb(1)-O(1) 133.49(17)
O(4)#1-Tb(1)-O(7) 78.03(19)
O(5)-Tb(1)-O(7) 135.6(2)
O(8)-Tb(1)-O(7) 74.1(2)
O(6)-Tb(1)-O(7) 74.48(19)
O(3)-Tb(1)-O(7) 142.9(2)
O(1)-Tb(1)-O(7) 70.08(18)
O(4)#1-Tb(1)-O(2) 130.73(16)
O(5)-Tb(1)-O(2) 69.65(16)
O(8)-Tb(1)-O(2) 73.64(17)
O(6)-Tb(1)-O(2) 150.33(17)
O(3)-Tb(1)-O(2) 82.23(17)
O(1)-Tb(1)-O(2) 52.05(16)
O(7)-Tb(1)-O(2) 107.3(2)
O(4)#1-Tb(1)-C(1) 107.91(19)
O(5)-Tb(1)-C(1) 66.90(18)
O(8)-Tb(1)-C(1) 88.21(19)
O(6)-Tb(1)-C(1) 162.60(19)
O(3)-Tb(1)-C(1) 107.4(2)
O(1)-Tb(1)-C(1) 26.12(18)
O(7)-Tb(1)-C(1) 91.0(2)
O(2)-Tb(1)-C(1) 26.41(18)
O(4)#1-Tb(1)-O(4) 74.17(15)
O(5)-Tb(1)-O(4) 66.28(15)
O(8)-Tb(1)-O(4) 116.71(16)
O(6)-Tb(1)-O(4) 66.88(15)
O(3)-Tb(1)-O(4) 49.18(17)
25
O(1)-Tb(1)-O(4) 140.87(17)
O(7)-Tb(1)-O(4) 135.71(18)
O(2)-Tb(1)-O(4) 116.98(15)
C(1)-Tb(1)-O(4) 130.04(17)
O(4)#1-Tb(1)-C(9) 98.8(2)
O(5)-Tb(1)-C(9) 75.45(18)
O(8)-Tb(1)-C(9) 94.2(2)
O(6)-Tb(1)-C(9) 68.91(18)
O(3)-Tb(1)-C(9) 24.85(19)
O(1)-Tb(1)-C(9) 146.78(18)
O(7)-Tb(1)-C(9) 143.1(2)
O(2)-Tb(1)-C(9) 102.36(18)
C(1)-Tb(1)-C(9) 124.1(2)
O(4)-Tb(1)-C(9) 24.72(18)
C(26A)-S(1)-O(8) 91(2)
C(26A)-S(1)-C(27) 87.2(13)
O(8)-S(1)-C(27) 106.0(5)
C(26A)-S(1)-C(26B) 164(3)
O(8)-S(1)-C(26B) 101.7(6)
C(27)-S(1)-C(26B) 98.5(8)
C(1)-O(1)-Tb(1) 96.4(4)
C(1)-O(2)-Tb(1) 87.9(4)
C(9)-O(3)-Tb(1) 103.6(4)
C(9)-O(4)-Tb(1)#1 170.6(5)
C(9)-O(4)-Tb(1) 81.6(4)
Tb(1)#1-O(4)-Tb(1) 105.83(15)
C(17)-O(5)-Tb(1) 142.4(4)
C(17)#1-O(6)-Tb(1) 133.3(4)
C(25B)-O(7)-Tb(1) 132.3(6)
S(1)-O(8)-Tb(1) 130.7(3)
O(1)-C(1)-O(2) 121.4(6)
O(1)-C(1)-C(2) 117.6(6)
O(2)-C(1)-C(2) 120.9(7)
O(1)-C(1)-Tb(1) 57.5(3)
O(2)-C(1)-Tb(1) 65.7(4)
C(2)-C(1)-Tb(1) 165.7(5)
O(4)-C(9)-O(3) 123.6(6)
O(4)-C(9)-C(10) 118.7(7)
O(3)-C(9)-C(10) 117.6(6)
O(4)-C(9)-Tb(1) 73.7(4)
O(3)-C(9)-Tb(1) 51.5(3)
C(10)-C(9)-Tb(1) 163.7(5)
26
CHAPTER III
RESULTS AND DISCUSSION
Our interest in LigAH2 stemmed from its highly conjugated aromatic backbone which
can impart rigidity on resulting frameworks. Although LigAH2 was implied as an intermediate
in the literature,27,28 to the best of our knowledge it has not been documented in the design of
MOFs. Copper(I) catalyzed Ullmann coupling of 4,4’-diiodobiphenyl with excess amount of
acetylacetone yields the desired LigAH2 in 40% yield (Scheme 1). Synthetic protocol employed
in the current study was modified from previously reported procedure by Jiang et. al.25
O
O
O
O
H H
I
I
O O
+ K2CO3, 10% mol CuI, 20% mol L-proline
THF/DMSO, 90oC
Scheme 1: Synthesis of LigAH2 via Ullmann coupling
Figure 6: Crystal structure of LigAH2 with the acidic hydrogen shown (in pink) being chelated
by the acac moiety.
Crystal structure indicates that LigAH2 exists in the enol form in the solid states with the
exchangeable proton shared in between two oxygen atoms (Figure 6). The dihedral angle
between an acac plane and the adjacent phenyl plane is ~79º.
27
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
190 240 290 340Wavelength(nm)
Absorb
ance
LigAH2
LigA2-
Figure 7: UV-vis absorption profile of LigAH2 (dash line) and sodium salt of LigA2- (solid line)
UV-vis measurement of LigAH2 (Figure 7) indicates the free ligand has a broad band
absorption with the maximum at 275nm in CHCl3. The free LigAH2 is poorly soluble in MeOH;
however, its sodium salt is. Deprotonation of LigAH2 shifts the absorption maximum at 280nm
towards longer wavelength and also lowers its intensity of absorption.
3.1 Construction of dinuclear Zn(II) complexes of LigA2-.
Slow diffusion of hexanes into DCM solution containing the mixture of Zn(OAc)2.
2H2O, LigAH2 and phenanthroline in a 2:1:2 ratio yielded dinuclear Zn complex 1. Scheme 2
28
illustrates the reaction leading to the formation of complex 1. Zinc (II) acetate was chosen as
the acetate ion can act as a base to deprotonate LigAH2.
N
N
O
O
O
O
H H
Zn(OAc)2.2H2O
+
+
1:1MeOH: DCM
2
O
O
N
N
Zn
O
O
CH3
2
2
Scheme 2: Synthesis of 1
Figure 8: ORTEP drawing of Zn2(LigA)(phen)2 (1) crystallized from DCM/hexanes
The formation of 1 demonstrates the ability of LigA2- to coordinate to Zn(II) centers as a
dianion. Phenanthroline (phen) acts as a capping ligand while acetate ions complete the
coordination sphere of the octahedral Zn centers. Crystals of 1 grown from CH2Cl2/hexanes lose
solvent rapidly. Regrowth of the crystals in a different solvent system (i.e. CHCl3/hexanes)
resulted in a more stable structure. Interestingly, the coordination environment around the Zn
centers has changed from octahedral (Figure 8) to pseudo-trigonal bipyramidal (Figure 9) as the
29
bidentate acetate ions become monodentate upon switching of solvent system. However, the
unbound oxygen atoms on the monodentate acetate are very close to the Zn centers (i.e. 2.646 Å
Zn to O distance).
Figure 9: Crystal structure of 1, Zn2(LigA)(phen2) grown from CHCl3/hexanes.
The structure was found in the centrosymmetric space group C2/c. Within the
asymmetric units, the two Zn centers are related to each other by an inversion center. The
aromatic rings of the ligand are not co-planar, with a dihedral angle of ~43o. The Zn-N bond
lengths are 2.103(7) and 2.162(6) Å which are similar to other Zn reported small molecule with
similar N,N bidentate ligand.30 The distance between Zn to one oxygen atom of the ligand is
shorter than the other (Zn(1)-O(1) 1.981(5) Å and Zn(1)-O(2) 2.017(6)Å. The bite angle of acac
moieties O(1)-Zn(1)-O(2) of the ligand on Zn is 87.7(2)o.
If two capping ligands in 1, either acetate or phen, can be replaced by additional
equivalents of LigAH2 during the self-assembly process, new molecular textures such as
molecular square or 1D zig-zag polymer could be formed. Wang and coworkers has reported
such molecular square complex.31 Using tetraacetylethane dianion as the ligand which is similar
30
to LigAH2, the authors created a distorted Co-containing molecular square structure. However,
attempts to make molecular square from our dinuclear Zn complex failed.
3.2 Construction of 1D Zn-containing coordination polymer
Slow diffusion of Et3N at room temperature generated the 1D coordination polymer
(Scheme 3). Preliminary syntheses indicated a suitable Et3N concentration window lies from
0.0535M to 0.428M Et3N. The structure (Figure 11) was analyzed and refined in the
orthorhombic space group Pna21. The structure cocrystallized with chloroform solvent. There is
unlikely any π-π stacking interactions in the crystal as the separation between two adjacent
aromatic rings is ~ 5.9Å. The repeating unit of the polymer is identified in Figure 12 where the
Zn center is five-coordinated by two halves of the bidentate LigA2- and a methanol molecule.
The geometry at the Zn center is approximate square pyramidal as the angles formed by the
oxygen of MeOH, Zn and acac oxygen range from 95-105o. The bite angles of the acac moieties
onto Zn range from 86.6(4) (i.e. O(8)-Zn(2)-O(9)) to 88.3 (4)o(i.e. O(1)-Zn(1)-O(2)) (Table 3) .
Compound 2 is insoluble in common organic solvents.
O
O
O
OZn(OAc)2.2H2O + 3/2
slow diffusion
CHCl3/MeOH
O
OO
O
Zn
OCH3
H
n
2
Scheme 3: Synthesis of 2, [Zn(LigA)(CH3OH).2CHCl3]n
31
Figure 11: 1D coordination polymer 2, [Zn(LigA)(CH3OH).2CHCl3]n
Figure 12: ORTEP drawing of the building block of 2
Attempt to extend this 1D polymer into a 2D ladder network by replacing the
coordinating methanol with a pillar ligand such as 4,4’-dipyridyldioxide (dpdo) or 4,4’-bipyridyl
was unsuccessful. Bridging ligand biphenyl-4,4'-diyldimethanol has also been attempted. The
produced crystals, however, are too small for single-crystal diffraction analysis. This self-
assembly strategy (Figure 13) has been reported by Hill et. al. and Kitagawa and coworkers.21, 32
32
Figure 13: Schematic description of the self-assembly of pillar supported structure
The Zn centers in the structure of 2 are clearly running out of coordination sites; adding
additional dimension to create 2D and 3D networks therefore seems a daunting task. As
mentioned previously, using metal clusters as building blocks in constructing metal-organic
framework may solve the problem of limited coordination numbers of metal centers.
Lanthanide metals can be used in place of Zn due to a number of reasons: 1) their flexible
coordination mode, 2) high coordination numbers to allow addition of extra dimensions, 3) their
ease being hydrolyzed even at neutral pH to facilitate formation of metal clusters, 4) their
luminescence properties which can be imparted onto the resulting framework. Compared to
carboxylate ligands, the acac moieties of LigAH2 is bulky and thereby preventing the access of
other ligands to the metal to form multidimensional network. As a result of the aforementioned
rationale, 4,4-(ethyne-1,2-diyl) dibenzoic acid (LigBH2) was chosen as a ligand substituting
LigAH2 in building multidimensional framework. LigBH2 was obtained in good yield (76.6%)
following the reported procedure.4,26 The UV-vis absorption spectra of LigBH2 and its sodium
salt are shown in Figure 14. Free LigBH2 in DMSO shows absorption maxima at 306 nm and
326 nm (bold solid line).
33
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
190 240 290 340 390 440 490
Wavelength(nm)
Absorb
ance
LigBNa2 in DMSO
LigBNa2 in water
Free LigBH2
Figure 14: UV-vis absorption of free LigBH2 (bold solid line) and its salt in different
water and DMSO (dash and thin solid line)
Coordination of LigBH2 to Zn and Eu and Tb under slow diffusion condition at room
temperature leads to the formation of 2D Zn-containing sheet and 3D lanthanide-containing
open frameworks as described in the next sections.
3.3 Construction of 3, a 2D interpenetrating Zn-containing framework
Structure of 3 is composed of paddle-wheel dinuclear Zn carboxylate units (Figure 15
(a)) bridged by LigB2- to form a 2D square grid (Figure 15 (b)). In addition, the dihedral angle
between the two interpenetrating frameworks is approximately 84° (Figure 16). Four one-half of
the LigBH2 bridge the two Zn centers of the paddle wheel unit in a bis-monodenate fashion,
totaling four oxygen atoms around each Zn centers. These fours oxygen atoms forming the base
and one disordered DMSO molecule occupying the apex position of the square pyramidal
complete the five-coordinated environment around each Zn center.
34
(a)
(b)
Figure 15: (a) Structure of the paddle-wheel dinuclear Zn carboxylate units of framework 3; (b)
Structure of the 2D grid of framework 3.
35
Figure 16: 2D interpenetrating, sheet-like structure of 3
The framework crystallizes in the space group Pbca. Each paddle wheel unit shows Zn-
Zn distance of 2.979 (9) Å which is consistent with those observed in reported analogues.9 Such
distance is significantly shorter than that (i.e. 3.515 Å) reported by Allendorf and coworkers but
similar to that (i.e. 2.955(10)) reported by Fang et. al. 24, 34 The distances from Zn to the
carboxylate oxygens are not quite uniform with Zn(1)-O(3) (2.007(3) Å) being the shortest
distance of the four Zn-O bonds. However, these are similar to those reported in Zn paddle-
wheel analogue.34 The axial DMSO molecules are held tightly to the Zn center (Zn(1)-O(5)
1.984(3) Å).
MOF 3 crystals display green luminescence when irradiated with UV radiation. Figure
17 depicts the emission spectra of 3 obtained with different excitation wavelengths. Excitation
spectrum was measured with the detector set to 495nm (Figure 18)
36
0.0E+00
1.0E+06
2.0E+06
3.0E+06
4.0E+06
5.0E+06
6.0E+06
7.0E+06
8.0E+06
9.0E+06
1.0E+07
355 405 455 505 555
Wavelength (nm)
Arb
itra
ry u
nits 345nm
365nm
370nm
372nm
375nm
Figure 17: Emission spectra of MOF 3 under different excitation wavelengths
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
300 350 400 450 500 550 600 650 700
Wavelength (nm)
Arb
itra
ry u
nit
Figure 18: Normalized solid state emission and excitation profile of MOF 3
Luminescence of MOF 3 is essentially ligand-based emission as Zn2+ (d10) is non-
emissive. One potential advantage of MOF possessing such property is that it should readily be
Emission
Excitation
37
tunable by varying the nature of the linker, perhaps by changing the degree of conjugation in the
ligands. 24
3.4 Construction of 4 and 5, 3D open frameworks
What is going to be discussed for 4 will also be applicable to 5 unless otherwise noted.
Solution assembly of EuCl2.6H2O and TbCl2.6H2O with LigBH2 gave rise to 4 and 5,
respectively. Again, slow diffusion with volatile Et3N as the base yielded highly desirable 3D
porous framework whereas hydrothermal attempts resulted in no crystal but fine powder.
Framework or MOF 4 and 5 are isostructural; however, only 4 is luminescent.
X-ray crystallography. Both 4 and 5 crystallize in the monoclinic space group P21/c.
The asymmetric units of 4 and 5 are shown in Figure 19. The bimetallic unit of structure 4 and 5
is shown in Figure 20. A center of inversion runs through the metal-metal bonds in both 4 and
5. Each Eu is nine-coordinated with two LigB2- contributing seven oxygen donor atoms and
MeOH and DMSO each contributes one oxygen donor atom. The coordination geometry around
Eu center is therefore tricapped trigonal prismatic.
There are three types of coordination modes adopted by LigB2-: truly chelating, truly
bridging and simultaneously bridging and chelating (Figure 20). Carboxylate exhibiting the first
coordination mode are O(4)-Eu(1)-O(3) in 4 and O(1)-Tb(1)-O(2) in 5 with the bite angle of
51.90(15)o and 52.05(16)o, respectively. The inter-metallic distances Eu-Eu and Tb-Tb are
comparable, being 4.1381(6) and 4.1386 (9) Å, respectively. For the carboxylate groups acting
intermediate between truly bridging and chelating, their oxygen atoms (i.e. O(5) in 4 and O(4) in
5) are being shared between two metal centers, displaying the longest among metal-carboxylate
oxygen bonds in 4 and 5 (Eu(1)-O(5) (2.809(4) Å) and Tb(1)-O(4) (2.869(5)Å)). In addition, as
observed, the coordination mode at one terminal of a LigB2- molecule is not necessarily the
same as the other terminal of the same ligand. One end of the carboxylate can adopt the syn-syn
bis-monodentate bridging mode while the other end acting as fully chelating. On the contrary, if
38
one carboxylate terminal acts intermediate between chelating and bridging, the other
carboxylate terminal of the same ligand will also adopt the same coordination mode. All of the
carboxylic groups in both 4 and 5 are coplanar with the aromatic rings to which they bound
except for the truly chelating carboxylate, small dihedral angles of 9.69o (in 4) and 6.18o (in 5)
are observed.
The oxygen atoms in the two truly bridging carboxylate groups are largely equidistant
from the metal centers with an average Tb-O distance of 2.3 Å and Eu-O of 2.4 Å. In both 4 and
5, the coordinating DMSO molecules are more tightly bound to the metal than MeOH.
Lanthanides are known to be oxophilic; as a result, DMSO is coordinating to lanthanide metals
via its O rather than S atom.
Figure 19: The asymmetric unit of 4 (left), and 5 (right)
39
Interpenetration observed in 3 has effectively decreased porosity of the framework. On
the contrary, due to the lack of structure interpenetration, 4 and 5 are highly porous with
triangular channels running along the a axis (Figure 21). Non-coordinating DMSO and water
molecules occupying the void of the channel help stabilize the framework.
Powder X-ray Diffraction. Powder X-ray diffraction pattern of 5 is presented in Figure
22. Several features can be noticed from the data. The simulated and found patterns are similar
with slight shift. This could be the result of expansion in the crystal lattice of the measured
sample. In fact, one reality must be keep in mind is that SXRD data are collected at 150 K
whereas PXRD measurements are performed at ambient temperature. Due to such a significant
difference in temperature, it’s hence likely that the pattern simulated from SXRD will be
slightly different from the experimentally obtained pattern. As a result the two most pronounced
Figure 21: Space-filling diagram of the extended structure of 4 showing triangular channel looking down the a axis.
Figure 20: Bimetallic Eu unit showing the versatile coordination modes of the carboxylate groups of LigB2-
40
peaks at 2θ =5.48 and 6.90oon the found patterns can be reasonably assigned as the ones at 2θ =
5.66 and 7.12o in the simulated pattern.
0
200
400
600
800
1000
1200
1400
1600
1800
3 6 9 12 15 18 21 24 27 30 332 theta
Inte
nsity Simulated
PXRD of 5
Observed
PRXD of 5
Figure 22: Powder X-ray diffraction calculated and found (bold) pattern for framework 5
0
200
400
600
800
1000
1200
1400
1600
1800
2000
3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9
2 theta
Inte
nstity
Calc. PXRD of 5
Found PXRD of 5
Figure 23: Magnified region of 2θ = 3 to 9o in both calculated and found PXRD patterns of 5
41
Figure 23 magnifies the region of 2θ = 3 to 9o for comparison. However, the quite
intense peak at 2θ = 7.62o of found pattern could not be accounted for on the simulated one
suggesting that the sample, while its crystallinity is proven, does contain a second phase. One of
the possibilities is that this peak arises from modified lattice due to the loss of non-coordinating
solvents in the cavities of the framework.
Thermogravimetric analysis. TGA was carried out under a nitrogen atmosphere with a
heating rate and a nitrogen flow rate of 5oC/min and 100 cm3/min, respectively.
Upon isolation, the as-synthesized crystals of 4 and 5 become opaque rapidly. TGA
diagrams of MOF 4 and 5 are shown in Figure 24.
55
60
65
70
75
80
85
90
95
100
105
0 100 200 300 400 500 600
Temperature (oC)
Weig
ht
(%)
3D Tb
3D Eu
Figure 24: TGA of 4 (bold) and under N2 atmosphere and heating rate of 5oC/min
A sample of single crystals of 4 (5.791 mg) shows gradual yet apparent three weight loss
stages in the TGA whose onset points are 80oC, 137oC and 319oC. At 44oC, two water
42
molecules in the cavity have been lost (calcd. 2.28% weight loss; found 2.36% weight loss). At
125oC, all cavity solvents (i.e. 2DMSO and 3H2O) have been lost in addition to the loss of two
coordinating MeOH and 1/2 of one coordinating DMSO (calcd. 20.02%; found 20.05%). From
137oC to 319oC, a loss of 41.67% was observed which corresponds to loss of the remaining 1.5
coordinating DMSO and a concomitant loss of 70% ligand (calcd. 39.8%; found 40.3%). The
framework 4 is thus said to be stable up to 137oC.
TGA of terbium-containing framework shows one fewer weight loss stages compared to
that of Eu framework. The onset points were determined as 61oC and 134oC. The run was
initiated with an isotherm segment for a period of 40 min at room temperature. This helps
confirm that the crystals indeed lose weight even without heating. However, plotting % weight
remained against time (Figure 25), one can notice a plateau from approximately 16.55 to 44.83
min which correspond to 20oC and 32oC. During this interval one can assume that the sample
weight has become more or less stable. At 32oC, a loss of 2.57% was already occurred
corresponding to loss of two water molecules in the cavity (Found 2.3%). Further loss of the
remaining water molecule in the cavity occurred from 32oC-61oC. From 61oC to 134oC, 24.02%
weight loss was observed which corresponds to the loss two DMSO in the cavity as well as two
coordinating MeOH and 0.5 coordinating DMSO. Framework 5 is therefore thought to be stable
up to 134oC.
43
40
50
60
70
80
90
100
0 20 40 60 80 100 120 140 160 180 200
Time (min)
We
ight
(%)
Figure 25: Weight loss of 5 over time (min)
Luminescent properties of 4. The sensitized emission of lanthanide-aromatic
complexes is very common in rare earth chemistry.35 In contrast to the green luminescence
displayed by 3, single crystals of 4 produce red emission under UV irradiation. The solid state
excitation-emission of 4 has been studied at room temperature (Figure 26). The spectra exhibit
sharp emission at 615 nm arising from the 5D0 to 7F2 transition characteristic of Eu(III)
emission.36 As only 4 luminesces, LigB2- is a suitable antenna for Eu(III) ion but not for Tb(III)
ion. The established metal-based emission of MOF 4 might render it useful in the sensing of
small molecules. Aqueous solutions of Cu(NO3)2, MgSO4.7H2O, ZnSO4.H2O, CoCl2.6H2O,
Mn(OAc)2.4H2O, FeSO4.7H2O, Zn(OAc)2.2H2O in addition to common organic solvents and
pentafluorophenol have been tested for MOF 4 inclusion; however, none has shown evidence
for luminescence signal modulation thus far.
44
0
0.2
0.4
0.6
0.8
1
1.2
310 360 410 460 510 560 610 660 710
Wavelength (nm)
Arb
itra
ry u
nit
Emission
Excitation
Figure 26: Solid state excitation-emission spectrum of MOF 4
45
CHAPTER IV
CONCLUSION AND FUTURE OUTLOOK
It has been an ongoing challenge to absolutely predict the network topology of the
designed MOFs; nevertheless, various novel and interesting molecular textures have been
synthesized with the use of appropriate ligands and metals and characterized. The products
obtained represent both transition metal-based (i.e. 3) and lanthanide-based MOFs (i.e. 4, 5).
The results obtained demonstrated that building highly ordered and multidimensional networks
from discrete molecular units is indeed an attractive approach since it allows one-pot reactions
at room temperature.11 The constituents of a framework can be designed or chosen to transfer
desired physical properties onto the framework. The work in this thesis has provided an example
of, using emissive lanthanide metals to impart luminescence properties onto the framework. Of
the structures attained, 2D Zn-containing and 3D Eu-containing frameworks exhibit
luminescence properties and have solvents occupying their cavities. The ability for these
frameworks to function as useful host-guest systems is therefore very probable. Potentially, they
could selectively entrap deleterious compounds (pollutants, toxicants, ect.) and report the
presence of these compounds through luminescence signal modulation. For such useful
functions to become practical, further investigation is required.
Modification of the as-synthesized framework might lead to new properties. The existence
of a C≡C triple bond in LigB2- can serve as a starting point for further functionalizing of the
current framework to explore new reactivities. Furthermore, transition metal-carbonyl
complexes (e.g. Cr(CO)3) can be anchored at the benzene rings constituting most of the internal
surface in a η6 fashion. Due to rich photochemistry of these transition metal complexes, the CO
group can be replaced by N2 or H2. The numbers of aromatic rings incorporated in the attained
frameworks are twice as many as those in the system reported by Long et. al.. 37 While MOF 3-5
46
might be too heavy to function as practical hydrogen storage materials, they can serve as
potential catalysts and as rigid matrix for reactions otherwise can only be performed in gas
phase and supercritical fluids
47
REFERENCES:
1) (a) Dodziuk, H, Introduction to Supramolecular Chemistry, 2002, Kluwer Academic
Publishers, Netherlands, p1, 25-26. (b) Menger, F.M., 2002, PNAS, 99 (8), 4819-4822
2) Lindoy, L.F., Atkinson, I.M., Editor Stoddart, J.F., 2000, Self-Assembly in
supramolecular systems, RSC, UK, p4, 6
3) Jones, W., Rao., C.N.R., 2002, Supramolecular organization and materials design,
Cambridge University Press, p 214, 391
4) Fasina, T. M., Collings, J.C., JBurke, . M., Batsanov, A. S., Ward, R. M., Albesa-Jové,
D., Porrès, L., Beeby, A., Howard, A. K., Scott, A. J. , Clegg, W., Watt, S. W., Viney,
C.., Marder ,T. B., 2005, J. Mater. Chem., 15, 690 – 697
5) Janiak, C., 2003, Dalton Trans., 2781-2804
6) Carrano, C.J., Santillan, G.A., 2008, Inorg. Chem., ASAP article
7) Eddaoudi, M., Moler, D.B, Li,H., Chen, B., Reineke, T. M., O’Keeffe, and Yaghi, O.M,
2001, Acc. Chem. Res., 34, 319-330
8) Kim, J., Chen, B. , Reineke, T. M., Li, H., Eddaoudi, M., Moler, D.B., O’Keeffe, M.,
and Yaghi, O.M. ,2001, JACS, 123, 8239-8247
9) Eddaoudi, M., Kim, J., Vodak, D., Sudik, A., Wachter, J., O’Keeffe, M., Yaghi, O.M.,
2002, PNAS, 99, 4900-4904
10) Yang, Y., Jiang, G., Li, Y.-Z., Bai, J., Pan, You, X.-Z., 2006, Inorg. Chim., Act., 359,
3257-3263
11) Yaghi, O.M., and Rowsell, J.L.C., 2005, Angew. Chem. Int. Ed., 44, 4670-4679
12) (a) Qiu, S.-L., Fang, Q., Zhu, G, Jin, Z, Xue, M. Wei, X. Wang, D,, 2007, Cryst.
Growth Des., 7(6), 1035-1037. (b) Wang, X.-L, Qin, C., Wang, E.-B., Su, Z.-M., Xu, L.,
Batten, S., R., 2005, Chem. Commun., 4789-4791
13) Feng S., and Xu, R., 2001, Acc. Chem. Res, 34, 239-324
48
14) Klinowski, J., Paz, F.A.A., Khimyak,Y.Z., Bond, A.D., and Rocha, J., 2002., Eur. J.
Inorg. Chem., 2823-2828
15) Yaghi, O.M., Davis, C.E., Li, G., Li, H., 1997, JACS, 119, 2861-2868
16) Chae, H.K, Kim, J. S, Go, Y., Eddaoudi, M., Matzger, A.J., O’Keeffe, M, Yaghi, O.M.,
2004, Nature, 427, 523
17) http://www.iupac.org/publications/pac/1985/pdf/5704x0603.pdf. Access Jan 12 08
18) Han, S.S, Deng, W.-Q., Goddard, W.A., 2007, Angew. Chem., Int, Ed., 46, 6289-6292
19) Rosi, N.L., Eckert, J., Eddaoudi, M., Vodak, D.T., Kim, J., O’Keeffe, M., Yaghi, O.M.,
2003, Science, 300, 1127
20) (a) Evans, O.R., Ngo, H.L., Lin, W., 2001, JACS, 123, 10395-10396. (b) Gomez-Lor,
B., Gutierrez-Puebla, E., Iglasias, M., Monge, A., Ruiz-Valero, C., Snejko, N., 2002,
Inorg. Chem., 41, 2429-2432
21) Hill, C.L, Han, J.W., 2007, JACS, 129, 15094-15095
22) Chen, B., Liang, C., Yang, J., Contreras, D. S., Clancy, Y.L., Lobkovsky, E.B., Yaghi,
O.M., Dai, S., 2006, Angew.Chem. Int. Ed., 45, 1390-1393
23) Wang S., Seward, C., 2004, Encyclopedia of Supramolecular Chemistry, Marcel Dekker
Inc., New York, p816-820
24) Bauer, A.C., Timofeeva, T.V., Settersten, T.B., Patterson, B.D., Liu, V.H, Simmons,
B.A., Allendorf, M.D., 2007, JACS, 129, 7136-7144
25) Jiang, Y., Wu, N., Wu, H., He, M., 2005, Synlett, 18, 2731-2734
26) Mio, M. J.; Kopel, L. C.; Braun, J. B.; Gadzikwa, T. L.; Hull, K. L.; Brisbois, R. G.;
Markworth, C. J.; Grieco, P. A., 2002,Org. Lett., 4, 3199-3202
27) Ramirez, F., Bhatia, S.B., Patwardhan, A.V., Smith, C.P., JOC, 1967, 3547-3553
28) Yu, S.-Y., Huang, H.-P., Li, S.-H., Jiao, Q., Li, Y.-Z., Wu, B., Sei, Y., Yamaguchi, K.,
Pan, Y.-J., Ma, H.-W., Inorg. Chem. 2005, 44, 9471-9488
49
29) Fanta, P. E., 1946, Chem. Rev. 38, 139-196
30) Li, C.-B, Fang, W.,Dong,E.-J., Liu, B., Li, Y.-W., 2007, Acta Cryst., E63, m150–m152
31) Zhang, Y.; Wang, S.; Enright, G. D.; Breeze, S. R., 1998, JACS, , 120, 9398-9399
32) (a) Maji, T.K., Uemura, K., Chang, H.-C., Matsuda, R., Kitagawa, S., 2004, Angew.
Chem., Int. Ed., 43, 3269-3272. (b) Kitaura, R., Fujimoto, K., Noro, S.-i, Kondo, M,
Kitagawa, S., 2002, Angew. Chem., Int. Ed., 42, 133-135
33) Pigue, C. and Bunzli, J.G, Chem. Rev., 2002, 102, 1897-1928
34) Fang, Q., Zhu, G., Xue, M., Sun, J., Sun, F., Qiu, S., 2006, Inorg. Chem., 45, 3582-3587
35) Reineke, T.M., Eddaoudi, M., Fehr, M., Kelley, D., Yaghi, O.M., 1999, JACS, 121,
1651-1657
36) de Lill, D. T., de Bettencourt-Dias, A., Cahill, C. L., 2007, Inorg. Chem., 46, 3960-3965
37) Kaye, S.S., Long, J.R., 2008, JACS, 130, 806-807
50
APPENDIX
SELECTED SPECTRA
51
O O
O O
HH
1 H-N
MR
52
O O
O O
HH
13C
-NM
R
53
CO
OC
H3
H3C
OO
C
1 H-N
MR
54
CO
OH
HO
OC
1 H-N
MR
55
CO
OH
HO
OC
13C
-NM
R