Supramolecular Interactions between Finite Tapes of Water Molecules

Article pubs.acs.org/crystal

Supramolecular Interactions between Finite Tapes of Water Molecules and Hydrated Metal Ions To Produce Infinite TwoDimensional Cationic Layers of Water Molecules Geeta Hundal,*,†,‡ Maninder Singh Hundal,‡ Young Kyu Hwang,† and Jong San Chang*,†,§ †

Research Center for Nanocatalysts, Korea Research Institute of Chemical Technology (KRICT), P.O. Box 107, Yusung, Daejeon 305-600, Republic of Korea ‡ Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, Punjab, India § Department of Chemistry, Sungkyunkwan University, Suwon 440-476, Republic of Korea S Supporting Information *

ABSTRACT: A supramolecular self-assembly of finite tapes of lattice water molecules with the coordinated water molecules of hydrated metal ions forms 2D cationic layers of water molecules in the coordination complex [Ni(H2O)6][Ni(Pydi)2(H2O)2]·4H2O (Pydi = 2,5-pyridinedicarboxylate). It reveals yet another unique mode of the cooperative association of water molecules. The anionic layers have a well-known 2D, nonporous metal− organic framework formed by the assistance from H-bonding of coordinating water molecules.

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well.7a In the same year, Marc Henry5 calculated the H-bond strengths in water clusters inside supramolecular architectures from inorganic and hybrid organic−inorganic molecules. Broadly speaking these clusters may also be considered as having the same classification as above, albeit on a much bigger scale. For discrete rings like Muller’s “giant molecular ball” of 59 water molecules, for example,8 icosahedral water cluster of 280 molecules,9 a chiral snub cube of 8 water molecules,10 clathrate hydrates of 46 water molecules forming a dodecahedral cage,11 and infinite ladder like chains of water molecules,12 etc. are described. Although there are many examples known of rings and 1D chains, 2D sheets of water molecules are relatively scarce especially in inorganic and hybrid organic−inorganic assemblies. The first structurally characterized 2D clathrate reported in a coordination complex has a planar array of metal complexes sandwiched between 2D sheets of H-bonded water molecules.13a Another example has an assembly of helical water columns arranged into an infinite 2D layer motif.13b An L12(6) is found in a nickel(II) borate complex,13c while an L6(6)6(7)10(8) layered arrangement was observed in an erbium complex of fumaric acid.13d Here we present a supramolecular arrangement of alternating cationic and anionic layers in a coordination complex [Ni(H2O)6][Ni(Pydi)2(H2O)2]·4H2O (Pydi = 2,5-pyridinedicarboxylate) where the anionic layers have a 2D, nonporous metal−organic framework formed due to

INTRODUCTION Water being ubiquitous and nature’s best solvent, a thorough understanding of its theoretical, structural, spectroscopic, and thermodynamic aspects is imminent1 and has been of utmost interest to the scientific community.2 As supramolecular assemblies, water molecules may just act as fillers by accommodating the interstitial voids3 or be a part of the selfassembled architecture themselves.4 The inter- and intramolecular H-bonds in various water clusters have been found to lie between −9 and −32 kJ mol−1 and −10 to −100 kJ mol−1, respectively, and for both, the data invariably depends on the O···O cutoff being considered.5 Therefore, the major role to understanding water cluster chemistry is played by X-ray crystallography with theoretical and neutron diffraction studies being the other players. The key factor lies in a careful examination of their solid state structures with a critical view of the H-bond parameters and symmetry elements present in various H-bonded networks in diverse chemical environments.6 One of the aims of these structural studies on water clusters has been to accurately characterize them as various structural motifs. Infantes and Motherwell in their seminal paper7a have beautifully described them as the following motifs with their symbols and percent occurrences given in parentheses: discrete chains (D, 61.1), discrete rings (R, 8.5), infinite chains 1D excluding rings (C, 19.9), infinite 1D tapes (T, 4.6), infinite 2D layers (L, 2.1), and 3D infinite networks (N, 1.0), based upon 1430 well refined hydrated organic structures from CSD. The numbers of various motifs found in organic crystals were updated in a later report.7b They found the same patterns in their brief inspection of 3700 organometallic compounds as © 2013 American Chemical Society

Received: September 11, 2013 Revised: November 26, 2013 Published: November 27, 2013 172

dx.doi.org/10.1021/cg401358p | Cryst. Growth Des. 2014, 14, 172−176

Crystal Growth & Design

Article

H-bonding of coordinating water molecules with carboxylic groups, whereas cationic 2D layers are formed by the selfassembly of finite tapes of lattice water molecules with the hydrated metal ions. The latter reveals yet another unique mode of the cooperative association of water molecules forming a 2D layer.

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EXPERIMENTAL PROCEDURES

Methods and Materials Used. All chemicals used were purchased from Sigma and were used without purification. The FTIR spectra were recorded with a Nicolet FTIR spectrometer (IMPACT 420 DSP) in the spectral range from 4000 to 400 cm−1. Thermogravimetric (TG) analysis was carried out in a thermogravimetric analyzer (TA Instruments, Universal V4.5A) under a dry nitrogen flow of 100 mL/min. UV−vis was carried out on a SHIMADZU UV-2501PC spectrophotometer having a range from 800 to 250 nm. Synthesis of the Complex. [Ni(H2O)6][Ni(Pydi)2(H2O)2]· 4H2O was formed by mixing basic nickel carbonate (0.375 g, 1 mM) and 2,5-pyridinedicarboxylic acid (0.167g, 1 mM) in 1:1 water/ ethanol mixture (30 mL) and heating at 80 °C with stirring for 30 min. Green colored precipitates were formed, which were insoluble in any solvent. The precipitates were removed by filtration leaving a green colored filtrate, which was concentrated to half of its volume and left for crystallization by slow evaporation. Small green colored, block type crystals appeared after almost 2 months. Selected IR (KBr, cm −1): 3359 νO−H, 1612 (s) νasymOCO, 1394, 1367 (s) νsymOCO, 1484 (w) νCC, 1288 νC−N, 1041 νC−O, 767 δOCO. X-ray Crystal Data for [Ni(H2O)6][Ni(Pydi)2(H2O)2]·4H2O. C14H30N2Ni2O20, M = 663.77, 0.35 × 0.20 × 0.15 mm3, λ = 0.71069 Å, triclinic, P1̅, a = 7.1646(4) Å, α = 109.4850(10)°, b = 11.6664(6) Å, β = 96.911(2)°, c = 16.2037(8) Å, γ = 99.708(2)°, V = 1235.60(11) Å3, Z = 2, Dc = 1.784 g cm−3, μ = 1.633 mm−1, F(000) = 688, 2θmax = 57°, reflections collected 20752, independent reflections 6107 (R(int) = 0.0211). X-ray data were collected on a Bruker’s ApexII CCD diffractometer. The crystal lost shine on exposure, so the data were collected at 100 K in paratone oil. The data were corrected for Lorentz and polarization effects, and empirical absorption corrections were applied using SADABS from Bruker. The structure was solved by direct methods using SIR-9214a and refined by full-matrix least-squares refinement methods based on F2 using SHELXL-97.14b All nonhydrogen atoms were refined anisotropically. The hydrogens of the Py ring were fixed geometrically, while the hydrogens of water molecules were located from difference Fourier synthesis and were well refined isotropically using a riding model (Ueq(H) = 1.2Ueq(C)) and distances restrained to 0.82(2) Å. All calculations were performed using Wingx package.15 The refinement shows some spotted residual peaks with the highest electron density of 3.10 e Å3 being close to O2W and O1W. The model ignoring all residual electron density peaks does not show any voids in the crystal structure, which clearly shows that there is no meaningful residual electron density left. A final refinement of 418 parameters with 25 restraints gave R1 = 0.0582, wR2 = 0.1907 for the observed 5498 reflections [I > 2 σ(I)] and R1 = 0.0627, wR2 = 0.1937 for all data.

Figure 1. The ORTEP diagram of the molecule at 50% probability.

bond distances for all of them. The stereochemistry around the nickel(II) ion in the anionic complex is octahedral with the two Pydi and two water molecules being trans to each other. The two Pydi are coordinating in a bidentate coordination mode forming five-member chelate rings with the help of pyridine N atoms. This coordination mode is similar to that found earlier in Pydi complexes of Co(II) and Cu(II),16a mixed ligand complexes of Co(II)16b and Cu(II)17 with Pydi and proton transfer complexes of many metal ion complexes, including Ni(II) ion, of Pydi.18 The two Ni−N and Ni−O bond distances are 2.063(4), 2.076(4) and 2.050(3), 2.041(3) Å, whereas the two Ni−O(water) distances in the anion are 2.032(3) and 2.054(3) Å, which are comparable to those found earlier.19 Both the pyridine rings are planar and the coordinating and noncoordinating carboxylate groups make dihedral angles of 4.7(4)° and 6.5(4)° and 4.4(4)° and 9.3(3)°, respectively, with them. The chelate rings are almost planar with a maximum deviation of 0.03 and 0.05 Å for C6 and C13 and have an interplanar angle of 4.1(1)° between them. The hexaaquonickel(II) cation also has an octahedral environment around the metal ion. The Ni−O (water) bond lengths in the cation range from 2.042(3) to 2.069(3) Å. The extensive H-bonding interactions involving the anionic and cationic complexes and the lattice water molecules create an interesting and unique crystal structure for the compound. Various kinds of strong (O−H···O) H-bonding interactions are seen between moieties, for example, cation···anion, anion··· anion, lattice water···lattice water (called lattice···lattice hereafter), anion···lattice water, and lattice water···cation. These interactions and the consequent supramolecular structures formed may be described stepwise, that is, first the formation of a nonporous, 2D metal−organic framework by the anions, then a 2D framework of water molecules employing the cations and the lattice water molecules, both parallel to the ac plane, and finally a stacking of these two networks in alternate cationic/ anionic layers perpendicular to the b* axis. Metal−Organic Framework of Anions. The framework is formed due to pure anion···anion interactions. Both coordinated water molecules, O1W and O2W, act as double H-bond donors toward the carboxylate oxygens O4 and O8 of

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RESULTS AND DISCUSSION X-ray Crystal Structure. Figure 1 shows the final model of the molecular structure, which has an anionic complex [Ni(Pydi)2(H2O)2]2− and a cationic complex ion [Ni(H2O)6]2+ and four lattice water molecules in the asymmetric unit. Both Ni2 and Ni3 of the two hexaaquonickel(II) complex cations shown in Figure 1 are lying at the center of symmetry; therefore their total contribution to the asymmetric unit is one [Ni(H2O)6]2+ entity, thus balancing the charges on the overall coordination complex [Ni(H2O)6][Ni(Pydi)2(H2O)2]·4H2O. In the anion [Ni(Pydi)2(H2O)2]2−, all four carboxylate groups are fully deprotonated as is evident from the nearly equal C−O 173



Article

discrete chains parallel to the c axis (Figure 3), which are found in adundance in CSD (796 examples).7b The average H-bond distance of 2.753(5) Å is comparable to that found in hexagonal ice Ih (2.76 Å) at 90 K19a and is shorter than that in bulk liquid water (2.85 Å).19b The OW···OW···OW bond angles vary from 95.6° to 103.6° and are close to the tetrahedral angle found in ice Ih and Ic. The OW···OW···OW···OW torsion angle of −169.2° shows them to be forming a trans conformation. Now these centrosymmetric D4 chains, displaying cation···lattice interactions, form H-bonds with the coordinated water molecules of the hexaaquonickel(II) cations where O3W Hbonds to both O9W and O12W. Although Infantes et al.7 defined the clusters found in the case of organic molecules only and would treat coordinated water molecules of metal− organics in a different way, in fact metal coordinated water molecules are rejected in their searches, since this report, the same classification is practiced almost invariably in metal organics as well, including the coordinated water molecules.13d,20 Therefore, the present water clusters may better be described as forming well-known R6 rings in the chair conformation consisting six centrosymmetric water molecules O3W···O9W···O12W···O3W ···O9W···O12W (Figure 4).

the centrosymmetrically related molecules (Table S1, Supporting Information) and create a 2D, brick work like metal− organic framework parallel to the ac plane (Figure 2). This

Figure 2. Metal−organic framework of centrosymmetric anions, only water···carboxylate H-bonding interactions have been shown for clarity.

framework is reinforced by rather long water···water (O1W··· O2Wd 3.268(5) Å) interactions forming H-bonded dimers of water molecules. These two water molecules accept H-bonds from the phenylene carbons C3 and C10 to support the framework. This framework shows stacking down the a axis, and both kinds of pyridine rings (Py1 C1 to C5, N1 and Py2 C8 to C12, N2) stack on to themselves. This allows π···π interactions between them with centroid to centroid distance of 3.50 Å for Py1···Py1i and 3.614 Å for Py2···Py2ii (see Table S1, Supporting Information, for symmetry abbreviations). A similar type of framework has been found in many proton transfer coordination complexes of Pydi,16 one of them18 even has the same anion, [Ni(pydi)2(H2O)2]2−, as presented here. Self-Assemblies of Water Molecules To Form Cationic Layers. The association of all four lattice water molecules O9W, O10W, O11W, and O12W constitutes lattice···lattice interactions. The O12W acts as H-bond donor to O10W and in turn behaves as H-bond acceptor to O9W. Similarly O11W behaves as H-bond donor for O10W (Table S1, Supporting Information). Thus, four of them comprise H-bonded D4

Figure 4. Formation of a H-bonded 2D network of water molecules in the ac plane constructed consecutively from finite D4−R6−D4 linear chains of H-bonded water molecules, one such motif shown as red balls in ball-n-stick representation; lattice water in purple, coordinated water of cations in blue, nickel(II) ion in cyan.

Figure 3. H-bonded D4 chains (one of them shown as red balls) of uncoordinated water molecules, R6 rings formed of four lattice (purple) and two coordinated water (blue) molecules, and Y shaped D4 chains formed of two coordinated and two lattice water molecules; stem of the Y has been shown as blue dashes. 174



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Spectroscopic Studies. The FTIR of the complex (Figure S2, Supporting Information) has a broad band centered at 3359 cm−1 clearly showing the presence of water molecules. In the complex, sharp bands at 1612 and 1394 cm−1 have been assigned to asymmetric and symmetric vibrations of coordinated carboxylate groups along with a δ (OCO) band at 767 cm−1. A large difference, Δν, between νasymOCO and νsymOCO of 220 cm−1 corroborates a monodentate coordination through the carboxylate groups.22 The electronic spectrum of the complex shows features typical for an octahedral environment around the metal ion. Usually the octahedral Ni(II) complexes exhibit three energy bands23 at 7000−13000, 11000−20000, and 19000−27000 cm−1 corresponding to 3A2g → 3T1g (F) (ν1), 3A2g → 3T2g (F) (ν2), and 3A2g → 3T1g (P) (ν3) transitions. The complex shows a broad ν2 band at 15949 cm−1 (ε 68.5 M−1 cm−1) (Figure S3a, Supporting Information). Another band, being observed at 31348 cm−1 and considered as ν3 band, has a high intensity (ε 870 M−1 cm−1) for a d−d transition (Figure S3b, Supporting Information). It may be due to the covalent nature of the anionic complex and intensity stealing from a nearby, intense CT band. In the spectrum, a spin forbidden transition, 3A2g → 1Eg, is also seen on the low energy side of the ν2 band at 13513 cm−1 (48 M−1 cm−1). In these cases, when Dq/B is close to unity, the ν2 transition is often seen as clear doublet, which may be a consequence of the transition to the 1Eg level gaining intensity because of the interaction with the 3T1g (F) level.24 The TGA of crystals (Figure 6) shows a total weight loss of 82.6% in the temperature range of 45−900 °C. The compound

O9W and O12W of this ring were earlier considered as part of the above-described D4 chains, but in this new description O10W and O11W become part of a “Y” shaped D4 chain formed by H-bonding of central O11W with O7W and O8W from two symmetry related [Ni(H2O)6]2+ moieties (Figure 3). The water clusters hence are forming finite D4−R6−D4 chains. The “Y” shaped D4 here is precisely formed by H-bonding of O10Wd, O8Wi, and O7Wj to O11W in the center. The mean H-bond distance in the ring is 2.736(6) Å; OW···OW···OW bond angles varying between 85.4° and 105.8° and torsion angles OW···OW···OW···OW of 91.0° and −77.5° indicate the well-known chair conformation (206 structures known according to Mascal et al., 7b with 163 in the chair conformation) of the R6 water cluster. A CSD search shows 47 hits for structures that contain water clusters with an R6 motif (in a chair conformation),21 formed through four lattice and two metal coordinated water molecules. Now owing to the combined effect of H-bonded D4−R6−D4 finite chains of water molecules and nickel coordinated water molecules, a supramolecular 2D network of water molecules is generated parallel to the ac plane, which may be better appreciated from Figure 5. Another complex18 of

Figure 5. Space filled representation of H-bonded 2D network of water molecules in the ac plane; lattice water in purple, coordinated water of cations in blue, and nickel(II) ion in cyan.

Ni2+ with Pydi, having the same anion [Ni(pydi)2(H2O)2]2−, has a different overall crystal structure because the cation in that case is a protonated amine instead of hexaaquonickel(II) ion. The presence of hydrated metal ions as cations in the present case is responsible for the formation of this unique crystal arrangement. Self-Assembly of Ionic Sheets. Finally the lattice···anion and cation···anion interactions assemble these cationic and anionic 2D sheets to run parallel to each other, alternately in a direction perpendicular to the b axis. O9W and O10W H-bond to the carboxylate oxygens of Py1 whereas O11W and O12W are bonded to Py2, giving a total of six lattice ···anion interactions. The cation−anion interactions are dominated by H-bonds between the coordinated water molecules of cations and the carboxylate oxygens of anions. All of them, except the O7W act as H-bond donors to the carboxylate oxygens. O7W and O8W behave as H-bond acceptors from phenylene C1, thus forming weak C−H···O type of anion···cation interactions, which further support the assembly. Finally O4W···O2W generates a water···water H-bond between the coordinated water molecules of two ionic layers (Figure S1, Supporting Information).

Figure 6. Weight loss (%) of the complex with temperature.

starts losing water at 45.3 °C, and up to 339 °C, there is a 32.7% weight loss, which corresponds to the loss of all 12 water molecules in the compound. This loss agrees well with the calculated value of 32.5% for these water molecules. A major component of the organic molecules is lost between 340 and 492 °C accompanied by a 33.5% weight loss. Between 492 and 800 °C, the remaining part of the organic component is lost to give a total of 49.9% loss (calculated 49.5%) between 340 and 800 °C to finally give NiCO3 as a residue. The loss of water molecules is sequential. Between 45 and 76 °C, the weight loss corresponds to two water molecules, 5.9% (calcd 5.4%), which may be due to two of the lattice water molecules. From 77 to 154 °C, six water molecules, probably of the cation, are lost, weight loss 16.8% (calcd 16.3%). Between 154 and 340 °C, the remaining four water molecules are lost. The powder XRD of the crystal matched well with that of the generated one from the crystal structure (Figure S4, Supporting Information) but 175



Article

1374. (i) Screenivasulu, B.; Vittal, J. J. Angew. Chem., Int. Ed. 2004, 43, 5769. (j) Mukherjee, A.; Saha, M. K.; Nethaji, M.; Chakravarty, A. R. Chem. Commun. 2004, 716. (k) Wakahara, A.; Ishida, T. Chem. Lett. 2004, 33, 354. (l) Zhao, B.; Cheng, P.; Chen, X.; Cheng, C.; Shi, W.; Liao, D.; Yan, S.; Jiang, Z. J. Am. Chem. Soc. 2004, 126, 3012. (m) Zhang, J.-P.; Lin, Y.-Y.; Huang, X.-C.; Chen, X.-M. Inorg. Chem. 2005, 44, 3146. (n) Oxtoby, N. S.; Blake, A. J.; Champness, N. R.; Wilson, C. Chem.−Eur. J. 2005, 11, 1. (o) Barbour, L. J.; Orr, G. W.; Atwood, J. L. Nature 1998, 393, 671; Chem. Commun. 2000, 859. (4) Desiraju, G. R. J. Chem. Soc., Chem. Commun. 1991, 426. (b) Lloyd, G. O.; Atwood, J. L.; Barbour, L. J. Chem. Commun. 2005, 1845. (5) Henry, M. ChemPhysChem 2002, 3, 607. (6) Pal, S.; Sankaran, N. B.; Samanta, A. Angew. Chem., Int. Ed. 2003, 42, 1741−1743 and references 1−17 therein.. (7) (a) Infantes, L.; Motherwell, S. CrystEngComm 2002, 4, 454. (b) Mascal, M.; Infantes, L.; Chisholm, J. Angew. Chem., Int. Ed. 2006, 45, 32−36. (8) Müller, A.; Krickemeyer, E.; Bögge, H.; Schmidtmann, M.; Peters, F. Angew. Chem. 1998, 110, 3567−3571; Angew. Chem., Int. Ed. 1998, 37, 3359−3363. (9) Chaplin, M. Biophys. Chem. 1999, 83, 211−221. (10) MacGillivray, L. R.; Atwood, J. L. Nature 1997, 389, 469−472. (11) Gutt, C.; Asmussen, B.; Press, W.; Johnson, M. R.; Handa, Y. P.; Tse, J. S. J. Chem. Phys. 2000, 113, 4713−4721. (12) Custelcean, R.; Afloroaei, C.; Vlassa, M.; Polverejean, M. Angew. Chem. 2000, 112, 3224−3226; Angew. Chem., Int. Ed. 2000, 39, 3094− 3096. (13) (a) Miyamoto, R.; Hamazawa, R. T.; Hirotsu, M.; Nishioka, T.; Kinoshita, I.; Wright, L. J. Chem. Commun. 2005, 4047−4049. (b) Langford, S. J.; Woodward, C. P. CrystEngComm 2007, 9, 218− 221. (c) Janiak, C.; Scharmann, T. G. J. Am. Chem. Soc. 2002, 124, 14010−14011. (d) Michaelides, A.; Skoulika, S.; Bakalbassis, E. G.; Mrozinski, J. Cryst. Growth Des. 2003, 3, 487−492. (14) (a) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J. Appl. Crystallogr. 1993, 26, 343. (b) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112. (15) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837. (16) (a) Ç olak, A. T.; Yeşilel, O. Z.; Pamuk, G.; Günay, H.; Büyükgüngör, O. Polyhedron 2011, 30, 1012−1022. (b) Ç olak, A. T.; Ç olak, F.; Yeşilel, O. Z.; Akduman, D.; Yilmaz, F.; Tümer, M. Inorg. Chim. Acta 2010, 363, 2149−2162. (17) Lu, J. Y.; Schauss, V. CrystEngComm 2002, 4, 623−625. (18) Ç olak, A. T.; Akduman, D.; Yeşilel, O. Z.; Büyükgüngör, O. Z. Kristallogr. 2009, 224, 207−212 and refs 8−12 therein. (19) (a) Kuhs, W. F.; Lehman, M. S. J. Phys. Chem. 1983, 83, 4312. (b) Head-Gordon, T.; Hura, G. Chem. Rev. 2002, 102, 2651. (20) (a) Ghosh, S. K.; Bhardwaj, P. K. Inorg. Chem. 2003, 42, 8250− 8254. (b) Supriya, S.; Manikumari, S.; Raghavaiah, P.; Das, S. K. New J. Chem. 2003, 27, 218−220. (21) CSD refcode file R6_search.gcd (Supporting Information). (22) (a) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th ed.; John Wiley & Sons: New York, 1986, p 191. (b) Djordjevic, C.; Lee, M.; Sinn, E. Inorg. Chem. 1989, 28, 719−723. (c) Tsaramyrsi, M.; Kaliva, M.; Salifoglou, A.; Raptopoulou, C. P.; Terzis, A.; Tangorlis, V.; Giapintzakis, J. Inorg. Chem. 2001, 40, 5772−5779. (d) Deacon, G. B.; Philips, R. J. Coord. Chem. Rev. 1980, 33, 227−251. (23) (a) Lever, A. B. P. Inorganic Electronic Spectroscopy; Elsevier: Amsterdam, 1984. (b) Lever, A. B. P. J. Chem. Educ. 1968, 45, 711− 712. (24) (a) Holmes, G.; Mc Clure, D. S. J. Chem. Phys. 1957, 26, 1686− 1694. (b) Jorgensen, K. Acta Chem. Scand. 1955, 9, 1362−1377.

also shows that the crystallinity of the complex decreases as it dries up and loses water molecules.

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CONCLUSIONS In summary, we have shown that a hydrated metal ion has the ability to form supramolecular interactions with lattice water molecules and demonstrate yet another unique mode of the cooperative association of water molecules, forming 2D cationic layers of water molecules. In the formation of this layered structure, only strong H-bonds between water molecules, with well refined hydrogen atoms have been considered. The intramolecular interactions among the six water molecules in [Ni(H2O)6]2+ have not been included despite their short O···O distances because of their bond angles being close to 90°, which nonetheless will further corroborate this 2D layered structure. Such structural studies are helpful in understanding the nature and role of various water clusters in biological systems, where assorted metal ions are involved in diverse biological functions in an aqueous environment.

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ASSOCIATED CONTENT

S Supporting Information *

FTIR and UV−vis spectra and XRPD of the complex, and crystallographic information in cif format. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data have been deposited with CCDC as supplementary publication with CCDC reference number 960068.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail address: [email protected] (G. Hundal). *E-mail address: [email protected] (J.-S. Chang). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Korea CCS R Center (KCRC) under a grant number NRF-2013036006. Dr. Geeta Hundal gratefully acknowledges KOFST for awarding Brain Pool fellowship at KRICT, South Korea. The authors are thankful to Prof. Lourdes Infantes from CSIC, Madrid, Spain, for the useful comments and suggestions which helped in analyzing the crystal structure critically.

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REFERENCES

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Supramolecular Interactions between Finite Tapes of Water Molecules

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