Note Molecular complex from two different binuclear copper 1,4,5,8-naphthalenetetracarboxylate complexes Devendra Singh, Jubaraj B. Baruah ⇑ Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India article info Article history: Received 4 January 2012 Received in revised form 12 March 2012 Accepted 4 April 2012 Available online 13 April 2012 Keywords: Copper complex Tetracarboxylate Dinuclear complex Multiple complexes in single crystal Channel formation Fluorescence abstract Two different binuclear copper complexes [Cu 2 (Phen) 4 (NTC)] (A) and [Cu 2 (Phen) 2 (NTC)(H 2 O) 4 ](B) form a stable molecular complex having a composition [Cu 4 (Phen) 6 (NTC) 2 (H 2 O) 4 Á22H 2 O] (1) (where Phen = 1,10 phenanthroline and H 4 NTC = 1,4,5,8-naphthalenetetracarboxylic acid). Different p-interactions as well as intermolecular hydrogen bonding interactions between the two complexes A and B result in the forma- tion of 3D channel like structures of approximate 18 14 Å dimension are filled by lattice water mole- cules. Moreover, 3D network of complex A itself makes the required space in the crystal lattice to accommodate 1D zigzag chains of complex B. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Multicarboxylate ligands have been extensively studied [1–8] for the construction of polymeric structures. The use of symmetri- cal 1,4-benzenedicarboxylate [9], 1,3,5-benzenetricarboxylate [10], 1,3,5-cyclohexanetricarboxylate [11], 1,2,4,5-benzenetetracarb- oxylate [12] and benzene-hexacarboxylate [13] have resulted in many interesting complexes [14]. Surprisingly, structural studies on the metal complexes of 1,4,5,8-naphthalenetetracarboxylate (NTC) have received less consideration [15–21] because they form insoluble materials. NTC complexes of copper (II) are known in the literature and they formed generally polymeric structures [20,21]. However, the introduction of additional aromatic N-donor chelat- ing ligands may inhibit the formation of polymeric framework. While studying the role of 1,10-phenanthroline as ancillary ligand of copper(II) NTC complex, we observed formation of a novel molecular complex in which two different dinuclear metal carbox- ylate complexes of NTC in a single crystal in the form of host– guest. The results on the structural characterization and physico- chemical properties of the complex are described here. 2. Experimental 2.1. Synthesis of the copper complex A mixture of Phen (270 mg, 1.5 mmol) and H 4 NTC (140 mg, 0.5 mmol) with Cu(OAc) 2 ÁH 2 O (200 mg, 1 mmol), respectively, was stirred at room temperature in a mixed solvents of DMF and methanol (1:3, 15 ml) for an hour. A blue–green precipitate ob- tained from the reaction mixture, was filtered, and washed with methanol. The green block crystals of 1 were obtained by crystal- lizing the precipitate from a mixed solvent of pyridine and water (3:1). Isolated yield: 45% (with respect to copper); Anal. Calc. for C 100 H 116 Cu 4 N 12 O 46 : C, 48.50; H, 4.69; N, 6.79%. Found: C, 49.82; H, 4.45; N, 6.86%. IR (KBr, cm 1 ): 3415 (s), 2923 (w), 1580 (s), 1518 (w), 1426 (m), 1413 (m), 1335 (m), 1213 (w), 1105 (w), 1034 (w), 852 (w), 774 (w), 722 (w). Crystal parameters of 1: Crys- tal system, Triclinic; Space group, P 1; a (Å), 13.7139(7); b (Å), 13.9154(7); c (Å), 15.0719(8); a (°), 91. 135(3); b (°), 112.034(3); c (°), 99.564(3); V (Å 3 ), 2618.5(2); Z, 1; Density/mg m 3 , 1.497; Absorption coefficient/mm 1 , 0.898; F(0 0 0), 1200; Total no. of reflections, 23,784; Reflections, I >2r(I), 6563; Maximum 2h (°), 50.00; Ranges (h, k, l); 16 6 h 6 16, 14 6 k 6 16, 17 6 l 6 17; completeness to 2h (%), 98.7; Data/Restraints/Parameters, 9110/0/ 725; Goodness-of-fit (F 2 ), 0.983; R indices [I >2r(I)], 0.0463; R indices (all data), 0.0641. 3. Results and discussion The reaction of Phen and H 4 NTC with copper(II) acetate mono- hydrate, followed by crystallization from mixed solvents of pyri- dine and water, yields the copper(II) molecular crystal, 1, [Cu 4 (Phen) 6 (NTC) 2 (H 2 O) 4 Á22H 2 O] (Scheme 1). The complex 1 crystallizes in triclinic P 1 space group. The complex is composed of combination of two binuclear copper(II) complexes [Cu 2 (Phen) 4 (NTC)] (A) and [Cu 2 (Phen) 2 (NTC)(H 2 O) 4 ] (B) with 0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2012.04.012 ⇑ Corresponding author. Tel.: +91 361 2582311; fax: +91 361 2690762. E-mail address: [email protected](J.B. Baruah). Inorganica Chimica Acta 390 (2012) 37–40 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Transcript
Inorganica Chimica Acta 390 (2012) 37–40
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier .com/locate / ica
Note
Molecular complex from two different binuclear copper1,4,5,8-naphthalenetetracarboxylate complexes
Devendra Singh, Jubaraj B. Baruah ⇑Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India
a r t i c l e i n f o
Article history:Received 4 January 2012Received in revised form 12 March 2012Accepted 4 April 2012Available online 13 April 2012
Keywords:Copper complexTetracarboxylateDinuclear complexMultiple complexes in single crystalChannel formationFluorescence
0020-1693/$ - see front matter � 2012 Elsevier B.V. Ahttp://dx.doi.org/10.1016/j.ica.2012.04.012
Two different binuclear copper complexes [Cu2(Phen)4(NTC)] (A) and [Cu2(Phen)2(NTC)(H2O)4] (B) form astable molecular complex having a composition [Cu4(Phen)6(NTC)2(H2O)4�22H2O] (1) (where Phen = 1,10phenanthroline and H4NTC = 1,4,5,8-naphthalenetetracarboxylic acid). Different p-interactions as well asintermolecular hydrogen bonding interactions between the two complexes A and B result in the forma-tion of 3D channel like structures of approximate 18 � 14 Å dimension are filled by lattice water mole-cules. Moreover, 3D network of complex A itself makes the required space in the crystal lattice toaccommodate 1D zigzag chains of complex B.
� 2012 Elsevier B.V. All rights reserved.
1. Introduction was stirred at room temperature in a mixed solvents of DMF and
Multicarboxylate ligands have been extensively studied [1–8]for the construction of polymeric structures. The use of symmetri-cal 1,4-benzenedicarboxylate [9], 1,3,5-benzenetricarboxylate [10],1,3,5-cyclohexanetricarboxylate [11], 1,2,4,5-benzenetetracarb-oxylate [12] and benzene-hexacarboxylate [13] have resulted inmany interesting complexes [14]. Surprisingly, structural studieson the metal complexes of 1,4,5,8-naphthalenetetracarboxylate(NTC) have received less consideration [15–21] because they forminsoluble materials. NTC complexes of copper (II) are known in theliterature and they formed generally polymeric structures [20,21].However, the introduction of additional aromatic N-donor chelat-ing ligands may inhibit the formation of polymeric framework.While studying the role of 1,10-phenanthroline as ancillary ligandof copper(II) NTC complex, we observed formation of a novelmolecular complex in which two different dinuclear metal carbox-ylate complexes of NTC in a single crystal in the form of host–guest. The results on the structural characterization and physico-chemical properties of the complex are described here.
2. Experimental
2.1. Synthesis of the copper complex
A mixture of Phen (270 mg, 1.5 mmol) and H4NTC (140 mg,0.5 mmol) with Cu(OAc)2�H2O (200 mg, 1 mmol), respectively,
ll rights reserved.
: +91 361 2690762.
methanol (1:3, 15 ml) for an hour. A blue–green precipitate ob-tained from the reaction mixture, was filtered, and washed withmethanol. The green block crystals of 1 were obtained by crystal-lizing the precipitate from a mixed solvent of pyridine and water(3:1). Isolated yield: 45% (with respect to copper); Anal. Calc. forC100H116Cu4N12O46: C, 48.50; H, 4.69; N, 6.79%. Found: C, 49.82;H, 4.45; N, 6.86%. IR (KBr, cm�1): 3415 (s), 2923 (w), 1580 (s),1518 (w), 1426 (m), 1413 (m), 1335 (m), 1213 (w), 1105 (w),1034 (w), 852 (w), 774 (w), 722 (w). Crystal parameters of 1: Crys-tal system, Triclinic; Space group, P�1; a (Å), 13.7139(7); b (Å),13.9154(7); c (Å), 15.0719(8); a (�), 91. 135(3); b (�), 112.034(3);c (�), 99.564(3); V (Å3), 2618.5(2); Z, 1; Density/mg m�3, 1.497;Absorption coefficient/mm�1, 0.898; F(000), 1200; Total no. ofreflections, 23,784; Reflections, I > 2r(I), 6563; Maximum 2h (�),50.00; Ranges (h, k, l); �16 6 h 6 16, �14 6 k 6 16, �17 6 l 6 17;completeness to 2h (%), 98.7; Data/Restraints/Parameters, 9110/0/725; Goodness-of-fit (F2), 0.983; R indices [I > 2r(I)], 0.0463; Rindices (all data), 0.0641.
3. Results and discussion
The reaction of Phen and H4NTC with copper(II) acetate mono-hydrate, followed by crystallization from mixed solvents of pyri-dine and water, yields the copper(II) molecular crystal, 1,[Cu4(Phen)6(NTC)2(H2O)4�22H2O] (Scheme 1). The complex 1crystallizes in triclinic P�1 space group. The complex is composedof combination of two binuclear copper(II) complexes[Cu2(Phen)4(NTC)] (A) and [Cu2(Phen)2(NTC)(H2O)4] (B) with
Fig. 1. Structure of 1 (ORTEP diagram drawn with 20% thermal ellipsoid) showingtwo different complexes A and B along with guest water molecules in theasymmetric unit of 1. Hydrogen atoms are removed for clarity.
twenty two guest water molecules (Fig. 1). Both the neutral com-plexes A and B possess inversion centre and observed as theirhalves in the asymmetric unit. The inversion centre passes throughthe mid points of the C49–C50A, C46–C46A and C50–C49A bondsof NTC ligand in complex A while through the mid point of C19–C19A bond of NTC ligand in the complex B; bisecting both the com-plexes in exact two halves but in different ways. Coordinationgeometry of both these penta-coordinated complexes can be bestdescribed as distorted square–pyramid (Table S1). The asymmetricunit of complex A consists of one Cu(II) center, surrounded by fourcoordinated nitrogen atoms (Cu2–N3, 2.06(3) Å, Cu2–N4, 2.02(3) Å,Cu2–N5, 2.19(3) Å, Cu2–N6, 1.99(3) Å) of two Phen ligands and onecoordinated oxygen atom (Cu2–O7, 1.96(2) Å) of a the NTC ligandcreating square–pyramidal geometry whereas the square–pyrami-dal geometry around the one Cu(II) center in the asymmetric unitof complex B is satisfied by two coordinated nitrogen atoms (Cu1–N1, 2.03(3) Å and Cu1–N2, 1.99(3) Å) of one Phen ligand, two coor-dinated oxygen atoms (Cu1–O1, 1.96(3) Å, Cu1–O2, 2.23(4) Å) oftwo water ligands and one coordinated oxygen atom (Cu1–O3,1.95(2) Å) of a half of the NTC ligand. In both complexes, four car-boxylate groups of bridged NTC ligands are expected to be innon-planar orientations (Table S2) due to the steric crowded envi-ronment and only one trans carboxylate group present on the eachside of naphthalene ring coordinates to copper centers in mono-dentate coordination mode. The charge neutrality is achieved byfour deprotonated free –COOH groups of two NTC ligands. The IRspectrum of compound 1 (Fig. S1) has the absorption bands ofasymmetric and symmetric vibrations of carboxyl groups at 1580and 1413 cm�1, respectively, confirms the monodentate coordina-tion mode of NTC. The absence of absorption bands at 1730–1690 cm�1 where the –COOH is expected to appear, is indicativeof the complete deprotonation of H4NTC upon its reaction withmetal ion. An intense band at 3415 cm�1 appears due to the O–Hstretching vibrations of coordinated water molecules.
The intermolecular interactions (Table S3) in the crystal latticeof 1, which are responsible for the formation of interesting supra-molecular architecture of 1, can be better described in terms ofinteractions between the units of (i) complex A, (ii) complex B,and (iii) complex A and B. Namely in (i) the oxygen atom of freecarboxylate group of NTC ligand of complex A engages in intermo-lecular bifurcated C34–H34���O9 and C36–H36���O9 hydrogen bondwith the Phen ring of another unit of A (Fig. S2). The coordinatedPhen rings of complex A further interact to each other via interac-tions related to p-interactions (formed by a combination of twoface to face p���p and two edge to face C–H���p interactions;dc22. . .p 3.68 Å and dc24. . .p 3.74 Å). This arrangement makes a2D net of A; this further grows to 3D by interacting with complexB; and allows the formation of large cavities by association of com-plex A, which encapsulate the 1D zigzag chain of complex B(Fig. 2a). The closed packed structure of the complex by omittingwater molecules is shown in Fig. 2b. (ii) The oxygen atom of coor-dinated water interacts with Phen ring via intermolecular C5–H5���O2 interactions. The coordinated Phen rings of complex B donot participate in p-interactions. These interactions make 1D zig-zag chains of B in the lattice which fits inside the cavities formedby network of A. The 1D zigzag chains of complex B further growto 2D sheets through lattice water molecules via O1–H1A���O15,C1–H1���O15 and C8–H8���O13 interactions which make a hexa-meric cluster of water molecules adopting cyclohexane chair con-formation (Fig. 2c). (iii) The oxygen atoms of free carboxylategroups of both the complexes A and B participate in C9–H9���O9and C39–H39���O6 hydrogen bonding with the Phen rings of eachother, respectively (Fig. 2d). Simultaneously, free oxygen atom ofcoordinated carboxylate group of complex B forms bifurcatedC25–H25���O4 and C27–H27���O4 hydrogen bond with the Phenring of complex A. The free oxygen atom of coordinated carboxyl-ate group of A interact with a coordinated water molecule of B viaacceptor O2–H2B���O8 interaction (Fig. 2e). Moreover, C–H���p(dc15���p 3.68 Å) and p���p interactions between the NTC and Phenrings of both complexes, respectively, are also observed in the crys-tal lattice of 1. These interactions between the two complexes inthe crystal lattice of 1, result in the construction of two intercon-nected 2D layers of complexes A and B cross each other to makea 3D hydrogen bonding network. Consequence of this arrangementgenerates 3D channels of approximate 18 � 14 Å dimensions asviewed along b or c axis. The channels created in the crystal latticeof 1 are filled by uncoordinated lattice water molecules. Due puck-ering and encapsulation ability of the two complexes, they interactamong themselves; we could not separate them by repeated crys-tallization from different solvents.
The thermogravimetric analysis of 1 (Supplementary materials)shows a 20.15% gradual weight loss of both coordinated and latticewater molecules in the temperature range 50–170 �C (calculated:18.9%). Further weight loss in the temperature range 215–310 �Cis attributed to the decomposition of organic ligands. The phasepurity of 1 is checked by its powder X-ray diffraction pattern,which gives fairly consistent data with the simulated pattern ofsingle crystal X-ray structure suggests that the coordinated watermolecules may not be uniformly distributed. Thus, the small
Fig. 2. (a) Channel formation (along the b axis) by the two interconnected 2D layers of complex A (red) and complex B (blue) in the crystal structure of 1. (b) Space fillingmodel showing the 3D channel network. Water molecules filled inside the channels have been omitted for clarity. (c) 2D nets of complex A showing various weak interactionsbetween the units of complex A in the crystal structure of 1. (d) A part of crystal structure of 1 showing weak interactions between the units of complexes A and B. (e)Formation of 2D sheets of complex B by lattice water molecules which connect the 1D zigzag chains of complex B and water molecules adopt cyclohexane chair conformationin the crystal lattice of 1. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
deviations are attributed to loss of water molecules. The interest-ing feature is the high amount of water holding capacity.
The solid state fluorescence properties of 1 are investigated atroom temperature (kex = 340 nm), suggesting, an intense emissionpeak appears at 457 nm along with two shoulder peaks at 414 nmand 472 nm. These may be assigned as intra-ligand p ? p⁄ transi-tion [22]. Another emission peak appears at 517 nm, which isattributed to the ligand-to-metal charge transfer (LMCT) transition
[22,23]. The solid state emission spectra of both NTC and Phenligands are also recorded (kex = 340 nm in each case) to furtheranalyze the emission behavior of 1. In the emission spectrum of1, it is interesting to note that the emission bands appear due tothe intra-ligand transition, show the characteristic of p ? p⁄
transition of NTC ligand. Three emission bands in the region of414–472 nm, similar to those of 1, are obtained in the emissionspectrum of NTC ligand which clearly confirms that the ligand
centered transition of 1 is the characteristic of NTC ligand and doesnot show any resemblance to p ? p⁄ transition of Phen ligand [23].Strong luminescence of 1 makes it a candidate for potential photo-active material.
There are examples of copper complexes in which two indepen-dent complexes crystallize in single crystal [24,25] but ours is un-ique in terms of self encapsulation and interesting structural andoptical properties. Symmetry nonequivalence in the crystal latticeof 1 originates from the two self interacting binuclear neutral com-plexes A and B in a single crystal is a rare example. The large spacecreated in the 3D packing of A are sufficient enough to accommo-date the 1D zigzag chains of complex B. The 3D channels like spaceof approximate 18 � 14 Å dimension which originate from thepacking of two layers of complexes A and B running perpendicularto each other in the crystal lattice are occupied by lattice watermolecules.
Acknowledgements
The authors thank Department of Science and Technology, NewDelhi (India) for financial support. DS is thankful to Council of Sci-entific and Industrial Research, New Delhi (India) for senior re-search fellowship.
Appendix A. Supplementary material
Tables for selected bond lengths and angles, hydrogen bond andconformational parameters, simulated and experimental PXRDpatterns, IR, UV–Vis and fluorescence spectra, and TGA curve. CCDC802377 contains the supplementary crystallographic data for com-pound 1. These data can be obtained free of charge from The Cam-bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this articlecan be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2012.04.012. Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2012.04.012.
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