Inorganica Chimica Acta 376 (2011) 598–604

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Inorganica Chimica Acta

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1D coordination network formed by a cadmium based pyridyl urea helical monomer

Kinkini Roy, Mark D. Smith, Linda S. Shimizu ⇑Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States

a r t i c l e i n f o a b s t r a c t

Article history:Received 26 April 2011Received in revised form 19 July 2011Accepted 22 July 2011Available online 30 July 2011

Keywords:Cadmium coordinationHelical polymerSolution studiesDiffusion NMR

0020-1693/$ - see front matter � 2011 Elsevier B.V. Adoi:10.1016/j.ica.2011.07.034

⇑ Corresponding author.E-mail address: shimizul@chem.sc.edu (L.S. Shimiz

Herein, we report the metal complexation properties of a macrocyclic ligand (L) that contains three pyr-idines as well as three urea groups. Linear and strand like ligands are typically used to afford helical coor-dination polymer. Our reported macrocyclic ligand (L) has remarkable flexibility and can twist upondative bond formation. Two macrocyclic ligands complex with three cadmium atoms to form a helicatemonomeric structure [Cd3L2(H2O)6(CH3CN)2]6+, which extends to a 1D polymeric structure via hydrogen-bonding. We also investigated the binding property of this new ligand in solution by NMR and UV–Visspectroscopy. These results together with diffusion NMR studies suggest that in solution this ligand alsoforms an oligomeric complex with cadmium.

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1. Introduction

Design of helical coordination polymers [1] has received tre-mendous attention due to the potential applications of these poly-mers in catalysis [2], nonlinear optics [3], luminescence [4] andchiral separation [5]. Two types of ligands are commonly employedto afford helical coordination polymers. One type includes strandlike ligands [6] or linear ligands [7] (Fig. 1a) that are preorganizedto twist upon dative bond formation to generate helicity. Alterna-tively, there are bridging ligands that are conformationally re-stricted into twisted helical structures (Fig. 1b) [8]. Commonorganic ligands used in coordination polymers include pyridineN-donors and carbonyl O-donors [9]. Pyridines and bipyridinesare particularly attractive as they not only can form metal com-plexes but also associate via aromatic stacking interactions [10].Macrocyclic ligands are typically less flexible and are not usuallyamenable for constructing helical polymers [11]. Our group has re-cently synthesized tripyridyl tris-urea macrocycle (Fig. 1c), whichhas programmed flexibility [12]. Here we report that this macrocy-clic ligand is able to twist and bind Cd2+ to form a 2:3 complex thatfurther assemble into a 1D helical polymeric structure. These heli-cal polymeric units formed a 2D network by p–p aryl stackinginteraction between pyridine p clouds of adjacent chain. We alsoinvestigated the binding affinity of this macrocyclic ligand in solu-tion by NMR and UV–Vis titrations. The binding stoichiometry insolution was compared to that of the solid-state structure. Subse-quent diffusion NMR data also suggests that in dilute solution thisligand forms an oligomeric complex with cadmium.

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u).

In previous work, we reported the synthesis, structure, andbinding properties of pyridyl urea macrocycle 1 with alkali metalcations (Li+, Na+, and K+) [12]. This 24 member macrocycle consistsof three pyridine units as well as three ureas protected as triazin-anone groups. It was crystallized as the dichloromethane solvate(Fig. 2a) [12]. The free ligand was not planar. Three pyridine nitro-gens and one of the triazinanone tertiary nitrogens face roughly inthe same direction. The three carbonyls point approximately out-wards and do not define any binding site. The ‘‘hard’’ alkali cationsusually prefer ‘‘hard’’ lewis bases. Thus, we expected that the mac-rocycle would adjust its conformation to form a binding site for thecation. The low quality crystals of 1�NaClO4 diffracted sufficientlyto establish general structure connectivity [12]. Upon complexa-tion of NaClO4, the macrocycle dramatically flips its conformation,turning all the carbonyl groups inward to coordinate with the Na+

ions (Fig. 2b). The sodium ion was indeed more oxophilic and pre-ferred to form shorter stronger interactions with the carbonyl oxy-gens of ligand 1 as well as to the oxygens of the perchlorate ion[12]. Fig. 2b highlights the ligand structure in 1�NaClO4 with theNa+, perchlorate and water omitted to accentuate the cavityformed by the inward facing carbonyl oxygens [12]. Ligand 1 isflexible enough to twist and reorient the potential oxygen and pyr-idine binding sites. The reciprocity among rigidity and flexibility isan important issue in supramolecular chemistry and is an area thatwe are starting to explore.

The unexpected flexibility of 1 led us to investigate this macro-cycle as a ligand for Cd2+. Cadmium (II) has different coordinationpreferences and a propensity to coordinate with both N and O con-taining ligands. This tendency has been exploited to generate novelmetal-organic frameworks [13], for example CdCl2 formed helicalcoordination complexes with ligands such as N,N-bispyridin-4-ylmethylsuccinamide [14]. In addition, Cd(II) can be readily

http://dx.doi.org/10.1016/j.ica.2011.07.034mailto:shimizul@chem.sc.eduhttp://dx.doi.org/10.1016/j.ica.2011.07.034http://www.sciencedirect.com/science/journal/00201693http://www.elsevier.com/locate/ica

Fig. 1. Comparison of the structure of different types of ligands. (a) Linear strand like ligand that can be preorganized in presence of Pb2+ and can generate helicity [7]. (b)Polyheterocyclic strand that is preorganized to helical shape enforced by the pyridine–pyrimidine helicity codon [8]. (c) Macrocyclic ligand 1 that consists of three pyridineunits as well as protected urea [12].

Fig. 2. Comparison of the free ligand 1 versus the conformation it adopted in the 1�NaClO4 complex. (a) X-ray crystal structure of the free ligand crystallized fromdichloromethane. (b) Side view of the ligand 1 from the X-ray crystal structure of ligand 1� NaClO4 complex. Upon complex formation the macrocycle dramatically flipped itsconformation to afford an interior binding cavity.

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substituted for Zn2+ in metalloproteins and blocks their function, aproperty that is associated with its toxicity in biological systems[15]. The detection and remediation of cadmium from the environ-ment is of great importance [16]. Given literature precedence, weset out to test the ligating ability of pyridines and ureas in ligand1 for the transition metal cation Cd2+.

2. Experimental

2.1. Materials

Triazinanone was prepared as previously described [17]. Allchemicals were purchased from Aldrich and used without furtherpurification. 1H NMR and 13C NMR spectra were recorded on Var-ian Mercury 400. UV–Vis absorption studies were carried out usinga Shimadzu UV–Vis spectrophotometer with 50 and 10 mm preci-sion cells made of Quartz Suprasil 300.

2.2. Synthesis

Ligand 1 was prepared as previously described [12]. A suspen-sion of LiH (220 mg, 27.8 mmol) and 5-tert-butyltetrahydro-1,3,5-triazin-2(1H)-one (720 mg, 4.64 mmol) in THF (200 mL)was heated under reflux for 6 h and then allowed to cool to roomtemperature. A solution of 2,6-bis(bromomethyl)pyridine (1.22 g,4.64 mmol) in THF (200 mL) was added drop wise over a 60 minperiod. The resulting mixture was heated under reflux for 80 hand then cooled to 0 �C. Ice-cold water (250 mL) was carefullyadded to destroy excess LiH, and the organic solvent removed invacuo. The aqueous mixture was extracted with CH2Cl2

(3 � 100 mL). The aqueous layer was stirred with 1 N NaOH(100 mL) for 30 min. After 30 min the aqueous layer was re-ex-tracted with CH2Cl2 (2 � 150 mL). The combined organic layerwas washed with water (2 � 100 mL), dried with MgSO4 and evap-orated under reduced pressure. Silica gel chromatography (CHCl3/MeOH 9:1) of the residue afforded ligand 1 (0.29 g, 24.0%).

Synthesis of [Cd3L2(H2O)6(CH3CN)2]6+: Ligand 1 (15 mg,0.0192 mM in 3 mL acetonitrile) was stirred with Cd(ClO4)2�6H2O(8.06 mg) in a 1:1 ratio overnight. Slow evaporation of this aceto-nitrile solution of metal ligand complex afforded colorless crystalssuitable for X-ray analysis [Cd3(C42H60 N12O3)2(CH3 CN)2(H2O)6](ClO4)6�(CH3CN)1.4(H2O)8.5.

2.3. Crystal structure determination

X-ray intensity data from a colorless plate crystal were mea-sured at 150(2) K using a Bruker SMART APEX diffractometer(Mo Ka radiation, k = 0.71073 Å) [18]. Raw area detector dataframe processing was performed with the SAINT+ and SADABS pro-grams [18]. Final unit cell parameters were determined by least-squares refinement of 3353 reflections from the data set. Directmethods structure solution, difference Fourier calculations andfull-matrix least-squares refinement against F2 were performedwith SHELXTL [19]. The compound crystallizes in the triclinic system.The space group P�1 was confirmed by the successful solution andrefinement of the structure. The asymmetric unit consists of halfof one [Cd3(C42H60N12O3)2(CH3CN)2(H2O)6]6+ complex located ona crystallographic inversion center, three independent perchlorateanions and several independent included solvent molecules (seebelow). All non-hydrogen atoms were refined with anisotropicdisplacement parameters except where noted below. Hydrogen

Table 1Crystal data and data collection parameters of 1�Cd2+ complex.

T (K) 150(2)Formula C90.80 H159.12 Cd3 C16 N27.40 O44.46Crystal size (mm3) 0.1 � 0.08 � 0.05Formula weight 2896.03Crystal system triclinicSpace group P1�

a (Å) 14.6764(13) Åb (Å) 14.7626(13) Åc (Å) 15.6522(14) Åa (Å) 83.172(2) �b (Å) 73.217(2) �c (Å) 83.243(2) �m (Å3) 3211.3(5)Radiation k (Å) Mo Ka radiation, k = 0.71073Z 1Dcalcd (g cm�3) 1.497l (mm�1) 0.708F (0 0 0) 1497h range of data collection (�) 1.36–23.26Reflections collected 33975Independent reflections 9241[R(int) = 0.1147]Completeness to hmax 100%Goodness-of-fit (GOF) on F2 0.887Final R indices [I > 2r(I)] R1 = 0.0555, wR2 = 0.1170R1 indices (all data) R1 = 0.1087, wR2 = 0.1328

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atoms bonded to carbon were placed in geometrically idealizedpositions and included as riding atoms. The hydrogen atomsbonded to coordinated water molecules O4, O5 and O6 werelocated in difference maps, their coordinates adjusted to gived(O–H) = 0.84 Å and subsequently treated as riding atoms withUiso,H = 1.5Ueq,O. Crystal data and data collection parameters are gi-ven in Table 1.

2.4. NMR studies

Ligand 1 (7.8 mg, 2 mM) was placed directly into a 5 mL volu-metric flask and CD3CN was added to the mark. The solution wasstirred for several hours to ensure that all components were dis-solved. The same ligand solution (2 mL) was used for the prepara-tion of Cd(ClO4)2�6H2O (16.8 mg, 20 mM) in separate 2 mLvolumetric flasks. First the ligand solution (600 lL) was transferredinto the NMR tube, and a spectrum was recorded at room temper-ature. Then aliquots of cadmium salt were added to that solution.Cadmium solution was added until it reached 7 times that of ligandconcentration. The chemical shifts of the aromatic protons were

Fig. 3. Views from the X-ray crystal structures of the metal complex. (a) Structure oconnected by central Cd2+. (b) Detail of the ligand conformation showed the macrocyclimode.

recorded after each addition of guest solution. The association con-stants were determined by nonlinear least-squares fitting analysisof the titration curve for 1:1 binding.

2.5. UV–Vis titration

Titrations were performed by adding small aliquots (5–10 lL) ofCd(ClO4)2�6H2O (10�4 mol L�1) in CH2Cl2 and CH3CN mixed solu-tion (v/v = 1:9) into 2 mL ligand solution (10�6 mol L�1) in CH2Cl2and CH3CN (v/v = 1:9) using a microsyringe. UV–Vis absorptionchanges were monitored during the titration. The difference inabsorbance (DA) of ligand solution in the presence and absenceof the Cd2+ was calculated and this difference was plotted againstthe cadmium concentration. The association constant Ka for thiswas derived by using nonlinear curve fitting.

2.6. Diffusion NMR spectrum

To check whether Cd(ClO4)2�6H2O formed oligomeric complexwith ligand 1 in solution, diffusion NMR experiments were per-formed using a Bruker Avance/DRX 400 NMR. Solutions of the freehost (2 mM) and Cd(ClO4)2�6H2O (2 mM) were prepared in CD3CN.The host:guest complex was prepared by mixing these solution in a2:3 [ligand:cadmium] ratio to give a final concentration of 0.8 mM.The ligand 1 stock solution was diluted to 0.8 mM with CD3CN forthe diffusion experiment on the free ligand. Diffusion coefficient offree ligand 1 was higher than that of 1�Cd2+ complex. The hydrody-namic radii were calculated from the following equation

D ¼ jT=6pgR

where D is the diffusion coefficient; R is the hydrodynamic radius; g isthe viscosity; j is the Constant; RH2O ¼ 8:26; DH2O ¼ 6� 10

�9;log DHost =�8.85; DHost = 10�8.85 = 1.1� 10�9; RLigand 1 = (6� 10�9�1.4)/(1.1� 10�9) = 8.4 Å; ligand 1�Cd complex log DComplex =�9.93;DComplex = 10�9.93 = 1.16� 10�10; RComplex = (6� 10�9� 1.4)/(1.16�10�10) = 72.4 Å.

3. Results and discussion

Ligand 1 (15 mg in 3 mL acetonitrile) was stirred withCd(ClO4)2�6H2O in a 1:1 ratio overnight. Colorless crystals suitablefor X-ray analysis were obtained by slow evaporation from aceto-nitrile solution of 1 in air to yield [Cd3(C42H60N12O3)2(CH3CN)2(-H2O)6](ClO4)6�(CH3CN)1.4(H2O)8.5. The structure of this complexconsists of a centrosymmetric trinuclear [Cd3L2(H2O)6(CH3CN)2]6+

unit in which the macrocycle undergoes a twist fold and formed

f the helical trinuclear ligand 1�Cd2+ complex where two macrocyclic ligands arec ligand underwent conformational adjustment and followed the exo type binding

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a 2:3 complex between macrocycle and metal. The compoundcrystallizes in the triclinic space group P�1. The structure of the tri-nuclear [Cd3L2(H2O)6(CH3CN)2]6+ unit is depicted in Fig. 3a, andconsists of three cadmium ions, two ligands, six non-coordinatingperchlorate molecules, two coordinating acetonitrile groups andseveral water molecules. Selected bond lengths and angles aroundthe cadmium centers are given in Table 1 (SI). The central cadmium(Cd(1)) ion is located on a crystallographic inversion center and issurrounded by two symmetry-equivalent [Cd(2)L] complexes in atrans configuration. The Cd(1) center adopts a pseudo-octahedralcoordination environment and is bonded with four carbonyl oxy-gen and two pyridine nitrogen atoms from two symmetry-equiva-lent macrocyclic ligands. Thus, this central Cd(I) bridges twomacrocyclic ligands, and the N–Cd–N bridge is exactly linear bysymmetry. The equatorial plane can be defined by the four car-bonyl oxygens (Cd(1)–O1 = 2.308(5) Å (x2) and Cd(1)–O(2) = 2.284(5) Å (x2)). The equatorial chelating angles are

Fig. 4. Views from the crystal structure of [Cd3L2(H2O)6(CH3CN)2]6+. (a) Each monomericcomplex OH–O hydrogen bonding (cyan) creates infinite 1D chains along the crystallogHelical arrangement is depicted by space filling model.

84.34(16) and 95.66(16)�, which are close to the ideal chelating an-gle of 90� for an octahedron. Two pyridyl nitrogens occupy the ax-ial sites, with Cd(1)–N(4) = 2.402(6) Å (x2) and N4–Cd1–N4⁄ = 180�. The other unique cadmium center (Cd(2)) displays adistorted octahedral geometry where one pyridyl sp2 nitrogenatom and three water molecules form the equatorial coordinationplane. The equatorial Cd–O distances range from 2.220(5) to2.328(6) Å and the Cd–N distance is 2.385(6) Å. The angles at themetal atoms deviate significantly from 90� and are 99.15(19)� forO(5)–Cd(2)–N(12), and 82.90(19)� for O(5)–Cd(2)–O(6). Theremaining axial coordination sites are occupied by a urea carbonyloxygen atom with Cd(2)–O(3) = 2.290(5) Å and one acetonitrilemolecule with Cd(2)–N(13) = 2.321(7) Å. To achieve this geometricarrangement the macrocycle twists leading to a folded conforma-tion where two pyridine nitrogens and the urea carbonyls in be-tween them are facing to the side of the central cadmium(Fig. 3b). Although the alkali metals prefer the endo coordination

unit is bridged by hydrogen bonding in an end to end mode to form a 1D chain. Interraphic ½1; �10� direction. Intra complex OH–N hydrogen bonds are also shown. (b)

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mode the Cd2+ atom prefers an exo coordination mode and sits outof the macrocyclic cavity. The other pyridine nitrogens and twoadjacent urea carbonyls face to the opposite side of the central cad-mium. A monomer turn unit consists of two ligands connected bythe central cadmium (Cd1) and the two additional cadmiums (Cd2and Cd2⁄) related by inversion.

Hydrogen bonding between the monomer turn units leads to aninfinite 1D polymeric chain structure. Each monomeric unit formshydrogen bonds via water molecules attached to the peripheralcadmium atoms (Cd2 and Cd2⁄) and the urea carbonyls of a neigh-boring monomer in an end-to-end mode to form a 1D chain run-ning along the crystallographic ½1 �10� direction (Fig. 4a). Thecadmium coordination induces a helical 1D coordination polymerswith the pitch length of 19.54 Å. Two macrocycle molecules coor-dinate three cadmiums and forms helicates. This helical arrange-ment is emphasized in the skeletal space filling diagrampresented in Fig. 4b that shows the cadmium atoms as well as che-lating oxygen and nitrogens.

Fig. 5 highlights the interconnected network formed by the fur-ther assembly of these helices. The 1D polymeric structures sup-port an overall 2D network through aromatic p–p interactionsbetween symmetry-equivalent pyridyl rings of adjacent 1D chains.Inversion-symmetry-related pyridyl rings {N8, C23–C27} of twoneighboring monomers are mutually parallel with an interplanarspacing of 3.239(3) Å, and a centroid–centroid separation of3.508(4) Å. The p. . .p interactions link the H-bonded chains intolayers parallel to the crystallographic (001) plane.

Fig. 5. Crystal view down the chain direction of nine chains. This 2D network is formeddefined by p–p interactions are horizontal in the figure.

Next we sought to evaluate whether this ligand forms com-plexes with Cd2+ in solution. Specifically, we wanted to comparethe binding stoichiometry in solution with what was observed insolid-state. Previously, we observed the solution complexes of thisligand 1 with alkali tetrafluoroborate salts including LiBF4, NaBF4and KBF4 [12]. This ligand bound Li+ and Na+ to form stable discrete1:1 complex in solution. It showed the greatest affinity for LiBF4with a binding constant of �105 M�1 in CD3CN. 1H NMR (CD3CN)studies of the free ligand 1 showed that the twelve methylene pro-tons adjacent to pyridine nitrogen of ligand afforded one singlet at4.31 ppm. The twelve methylene protons in the triazinanone ringafforded a signal at 4.47 ppm of equal intensity. This suggests thateither the ligand has a symmetrical rigid conformation or few flex-ible conformations that are interchangeable on the NMR timescale. Proton NMR studies were performed to further investigatethe formation of a cadmium complex in solution. The ligand wastitrated with cadmium perchlorate keeping the ligand concentra-tion constant. The proton NMR spectra were recorded after eachaddition. Titration of ligand (5.01 mM in acetonitrile) with varyingamount of Cd(ClO4)2�6H2O solution (20 mM in CD3CN) resulted anupfield–downfield–upfield migration pattern (Fig. 6). First, all thetriazinanone methylene protons moved upfield by 0.1 ppm fol-lowed by the downfield shift by 0.15 ppm. This behavior suggestsmultiple binding events. The largest shift was observed for thetwo aromatic protons adjacent to pyridine nitrogen. Those protonsafforded one doublet at 7.11 ppm and migrated steadily downfieldby 0.4 ppm.

by p–p aryl stacking interaction between pyridine p cloud of adjacent chain. Layers

Fig. 6. NMR titration studies with ligand in solution: partial 1H NMR spectrum(400 MHz, CD3CN) of ligand 1 after addition of CdClO4 (from bottom to top) 0.00,0.2, 0.7, 1.00, 1.30, 1.50 equiv of Cd2+ ([1] = 5.01 mM). The pyridine aromaticprotons moved downfield with increasing Cd2+ concentrations, a trend that stopsafter addition of 1.5 equiv of Cd(ClO4)2�6H2O.

Fig. 7. Binding studies with ligand 1. (a) Titration curves of ligand 1 solution(10�6 M) in CH2Cl2/CH3CN (1:9) at 298 K upon addition of aliquots ofCd(ClO4)2�6H2O. (b) JOB plot for ligand 1 and Cd(ClO4)2�6H2O in CH2Cl2/CH3CNmixed solvent (v/v 1:9). The total concentration of 1 and metal salts was keptconstant at 2.5 � 10�5 mol L�1.

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We turned to UV–Vis spectroscopy to more accurately accessthe binding events. The UV–Vis spectrum of free ligand solution(10�6 mol L�1) in CH2Cl2/CH3CN (v/v = 1:9) displayed absorptionmaxima at 224 nm (Fig. 7). The wavelength and shape of theabsorption band remained invariant over the concentration range2.1 � 10�6–2.1 � 10�5 M suggesting that the ligand did not aggre-gate in dilute solution. Upon addition of cadmium perchlorate(10�4 mol L�1) in CH2Cl2/CH3CN solution (v/v = 1:9) into 2 mL li-gand the main absorption of free ligand was red shifted from 224to 237 nm suggesting the formation of charge transfer complex.An isosbestic point was observed in the titration curve. Host–guestbinding stoichiometry was measured by continuous variation plots(JOB plot) [20]. The absorbance at 224 nm was used to construct aJOB plot (Fig 7b). The JOB plot shows two lines intercept at a moleratio of 0.6. This indicates 2:3 stoichiometries between the ligandand Cd2+, which is consistent with the crystal structure. The steepintersecting lines also suggest a high association constant. We esti-mated association constant as �106 M�1. An increase in the base-line absorption was observed with increasing [Cd2+], a possibleindication of oligomer formation. Taken together the UV titrationdata and the JOB plot indicate that ligand 1 and Cd2+ form a stablecomplex in solution with a binding stoichiometry similar to what isobserved in the solid state.

We turned to diffusion NMR experiment using a BPP-LED pulsesequence to further probe the complex formation and to estimateand compare the hydrodynamic radii of free ligand and ligand�Cd2+complex. Diffusion NMR experiments were carried out on a0.8 mM solution of ligand in CD3CN and on a 2:3 mixture of 1 toCd(ClO4)2�6H2O in CD3CN (0.8 mM 1). Even at this lower concentra-tion, no free ligand was observed, consistent with a high associa-tion constant (see Supplemental Information). The calculatedhydrodynamic radius of the complex was 9 times higher than thefree ligand (8.4 Å versus 72.5 Å). These measurements indicate thata stable oligomeric complex is also formed in solution.

In summary, we have synthesized Cd2+ coordinated helicalcomplex from a macrocyclic ligand containing three pyridinegroups connected by triazinanone units. This ligand is flexible en-ough to allow the metal binding sites to freely rotate and favors thestructure that can best accommodate the guest. Complexation ofCd2+ with the ligand resulted in a twist in the macrocyclic ligandto afford an exo coordination mode. Two macrocyclic ligandstogether with three cadmium atoms formed a helical unit that

extended to a 1D polymeric structure through hydrogen bonds.The solid-state structure demonstrated that the metal binding siteis flexible and able to access multiple conformations. We are nowbeginning to explore large metals that should also show preferencefor exo coordination of this macrocyclic ligand.

Acknowledgments

The authors acknowledge support for this work from the NSF(CHE-1012298) and University of South Carolina, Office of Re-search and Health Sciences.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.ica.2011.07.034.

References

[1] (a) G.F. Swiegers, T.J. Malefetse, Chem. Rev. 100 (2000) 3483;(b) T. Yamamoto, T. Yamada, Y. Nagata, M. Suginome, J. Am. Chem. Soc. 132(2010) 7899;(c) S.-T. Wu, Y.-R. Wu, Q.-Q. Kang, H. Zhang, L.-S. Long, Z. Zheng, R.-B. Huang, L.-S. Zheng, Angew. Chem., Int. Ed. 46 (2007) 8475;(d) H.-J. Kim, E. Lee, H.-S. Park, M. Lee, J. Am. Chem. Soc. 129 (2007) 10994;(e) M. Ikeda, Y. Tanaka, T. Hasegawa, Y. Furusho, E. Yashima, J. Am. Chem. Soc.128 (2006) 6806;(f) M.J. Zaworotko, Chem. Soc. Rev. 23 (1994) 283;

http://dx.doi.org/10.1016/j.ica.2011.07.034

604 K. Roy et al. / Inorganica Chimica Acta 376 (2011) 598–604

(g) S.R. Batten, R. Robson, Angew. Chem., Int. Ed. 37 (1998) 1460;(h) B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629;(i) O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature423 (2003) 705;(j) S. Kitagawa, R. Kitaura, S.-I. Noro, Angew. Chem., Int. Ed. 43 (2004) 2334.

[2] T. Kaczorowski, I. Justyniak, T. Lipinska, J. Lipkowski, J. Lewinski, J. Am. Chem.Soc. 131 (2009) 5393.

[3] Y. Li, Z.-X. Zhang, K.-C. Li, W.-D. Song, Q.-S. Li, Inorg. Chem. Commun. 10 (2007)1557.

[4] Q. Zhu, T. Sheng, R. Fu, C. Tan, S. Hu, X. Wu, Chem. Commun. 46 (2010) 9001.[5] (a) U. Knof, A. von Zelewsky, Angew. Chem., Int. Ed. 38 (1999) 302;

(b) P. Belser, S. Bernhard, E. Jandrasics, A. von Zelewsky, L. DeCola, V. Balzani,Coord. Chem. Rev. 159 (1997) 1.

[6] (a) D.-R. Xiao, E.B. Wang, H.-Y. An, Y.-G. Li, Z.-M. Su, C.-Y. Sun, Chem. Eur. J. 12(2006) 6528;(b) X.-J. Luan, X.-H. Cai, Y.-Y. Wang, D.-S. Li, C.-J. Wang, P. Liu, H.-M. Hu, Q.-Z.Shi, S.-M. Peng, Chem. Eur. J. 12 (2006) 6281.

[7] (a) A.-M. Stadler, N. Kyritsakas, J.-M. Lehn, Chem. Commun. (2004) 2024;(b) S. Ulrich, A. Petitjean, J.-M. Lehn, Eur. J. Inorg. Chem. 13 (2010) 1913.

[8] (a) K.T. Potts, M. Keshavarz, S.F. Tham, K.A. Raiford, A.C. Gheysen, H.D. Abruna,Inorg. Chem. 32 (1993) 5477;(b) N. Dalla-Favera, J. Hamacek, M. Borkovec, D. Jeannerat, F. Gumy, J.-C.G.Bunzli, G. Ercolani, C. Piguet, Chem. Eur. J. 14 (2008) 2994.

[9] C.-F. Chow, S. Fujii, J.-M. Lehn, Angew. Chem., Int. Ed. 46 (2007) 5007.[10] (a) C.R. Wilson, O.Q. Munro, Acta Crystallogr., Sect. C 66 (2010) o513;

(b) D.L. Reger, R.F. Semeniuc, M.D. Smith, Cryst. Growth Des. 5 (2005) 1181.

[11] (a) J.-H. Cho, R. Sarangi, H.-Y. Kang, J.-Y. Lee, M. Kubo, T. Ogura, E.I. Solomon,W.-W. Nam, J. Am. Chem. Soc. 132 (2010) 16977;(b) A. Roca-Sabio, M. Mato-Iglesias, D. Esteban-Gomez, E. Toth, A. de Blas, C.Platas-Iglesias, T. Rodriguez-Blas, J. Am. Chem. Soc. 131 (2009) 3331.

[12] K. Roy, C. Wang, M.D. Smith, P.J. Pellechia, L.S. Shimizu, J. Org. Chem. 75 (2010)5453.

[13] (a) B. Liu, Y.-C. Qiu, G. Peng, L. Ma, L.-M. Jin, J.-B. Cai, H. Deng, Inorg. Chem.Commun. 12 (2009) 1200;(b) T. Ezuhara, K. Endo, Y. Aoyama, J. Am. Chem. Soc. 121 (1999) 3279.

[14] (a) Z. Zhang, M. Pi, T. Wang, C.-M. Jin, J. Mol. Struct. 992 (2011) 111;(b) Q. Zhu, T. Sheng, R. Fu, C. Tan, S. Hu, X. Wu, Chem. Commun. (2010) 9001.

[15] (a) A. Terrón, J.J. Fiol, A. García-Rasoa, M. Barceló-Oliver, V. Moreno, Coord.Chem. Rev. 251 (2007) 1973;(b) Y.H. Jin, A.B. Clark, R.J.C. Slebos, H. Al-Refai, J.A. Taylor, T.A. Kunkel, M.A.Resnick, D.A. Gordenin, Nat. Genet. 34 (2003) 326.

[16] (a) D. Les�tan, C. Luo, X.-d. Li, Environ. Pollut. 153 (2008) 3;(b) N.M. Dickinson, A.J.M. Baker, A. Doronila, S. Laidlaw, R.D. Reeves, Int. J.Phytoremediation 11 (2009) 97.

[17] A.R. Mitchell, P.F. Pagoria, C.L. Coon, E.S. Jessop, J.F. Poco, C.M. Tarver, R.D.Breithaupt, G.L. Moody, Propellants Explos. Pyrotech. 19 (1994) 232.

[18] SMART Version 5.630, SAINT+ Version 6.45 and SADABS Version 2.05, BrukerAnalytical X-ray Systems, Inc., Madison, Wisconsin, USA, 2003.

[19] G.M. Sheldrick, SHELXTL Version 6.14, Bruker Analytical X-ray Systems, Inc.,Madison, Wisconsin, USA, 2000.

[20] K.J. Hirose, Inclusion Phenom. Macrocyclic Chem. 39 (2001) 193.

1D coordination network formed by a cadmium based pyridyl urea helical monomer1 Introduction2 Experimental2.1 Materials2.2 Synthesis2.3 Crystal structure determination2.4 NMR studies2.5 UV–Vis titration2.6 Diffusion NMR spectrum

3 Results and discussionAcknowledgmentsAppendix A Supplementary materialReferences