Hydrogen-Bonded Assembly of Water and Chloride in a 3D Supramolecular Host
CRYSTAL GROWTH & DESIGN 2006 VOL. 6, NO. 1 36-39
Ananta Kumar Ghosh,† Debajyoti Ghoshal,† Joan Ribas,‡ Golam Mostafa,*,§ and Nirmalendu Ray Chaudhuri*,† Department of Inorganic Chemistry, Indian Association for the CultiVation of Science, Kolkata 700 032, India, Departament de Quı´mica Inorga` nica, UniVersitat de Barcelona, Diagonal, 647, 08028-Barcelona, Spain, and Department of Physics, JadaVpur UniVersity, JadaVpur, Kolkata-700 032, India ReceiVed August 17, 2005; ReVised Manuscript ReceiVed October 31, 2005
ABSTRACT: The hydrogen-bonded water-chloride assembly {[(H2O)14Cl2]2-}n, which is stabilized in a template of metal organic supramolecular host (MOSH) {[Cu4(phen)4(adi)(OH)2Cl2]2+}n(adi ) adipate dianion; phen ) 1,10-phenanthroline), was isolated. DFT calculations corroborate the X-ray crystal structure of the hydrogen-bonded water-chloride assembly. The variable temperature magnetic study also corroborates the single-crystal structure. Nature adores functional self-assembly, which relies on weak interactions rather than on covalent interactions.1,2 Self-assembly possesses a reversible and self-correcting cooperative process that responds to changes in environmental conditions (solvent, pH, temperature, concentration, etc.). Consequently, these assemblies often build host complexes that are very efficient for uptake and release of guests under controlled conditions.1 As ion transportations are of fundamental importance in many chemical as well as biological processes,3,4 new strategies for ion isolation or recognition in self-assembled complexes are essential for both basic and applied studies.5 Self-assembly is a unique approach for building such ion channels. We are still in a stage of infancy about the knowledge of the factors that control the formation of the ion clusters in such channels.3 During our ongoing research6 on self-assembly, we have isolated a water-chloride assembly {[(H2O)14Cl2]2-}n in a template of metal organic supramolecular host (MOSH) {[Cu4(phen)4(adi)(OH)2Cl2]2+}n (adi ) adipate dianion; phen ) 1,10-phenanthroline). Here the MOSH is stabilized by π-π interactions, and this is a unique example of the directed synthesis using π-π interactions. Moreover, to the best of our knowledge, this is the first example of a water-chloride assembly with 14 water molecules. The variable temperature magnetic study of the complex is also reported, and this is explained in light of the crystal structure. Reaction of cupric chloride dihydrate, adipic acid, sodium hydroxide, and 1,10-phenanthroline in a water-methanol medium and on slow evaporation of the resulting solution yields deep blue single crystals of [Cu4(phen)4(adi)(OH)2Cl2]Cl2‚16H2O (1). The elemental analysis and other characterization, viz., IR and TGA, support this formulation. The X-ray structure determination7 of 1 reveals in a unit cell that two [Cu(phen)]2+ units are linked by µ-chloro and µ-hydroxo to form a dimeric unit [Cu2(phen)2(OH)(Cl)]2+, which is bridged by adipate to form a tetranuclear adduct. Thus, each adipate is linked to four Cu(II) centers. The ORTEP drawing of this tetranuclear entity is shown in Figure 1 and the selected bond lengths and angles are reported in Table 1. The coordination around each Cu(II) center is a distorted square pyramidal. Two nitrogen atoms from phen (N1, N2), one oxygen atom from bridging hydroxyl (O2), and one oxygen from adipate (O1) occupy the basal sites with Cu1-L distances (L ) O or N) ranging from 1.923(4)-2.028(5) Å. The coordinated chloride occupies the apical position with a Cu1-Cl1 distance 2.604(2) Å. Here the copper atom deviates from the basal mean plane by 0.201(1) Å. The bite angle of chelating phen ligand * To whom correspondence should be addressed. (N.R.C.) Fax.: 91-33-2473 2805. E-mail:
[email protected]. (G.M.) E-mail:
[email protected]. † Indian Association for the Cultivation of Science. ‡ Universitat de Barcelona. § Jadavpur University.
Figure 1. ORTEP drawing of the tetranuclear building block of 1. Table 1. Selected Bond Lengths (Å) and Angles (deg) for Complex 1a Cu1-Cl1 Cu1-O2 Cu1-N2 Cl1-Cu1-O2 Cl1-Cu1-N2 O1-Cu1-N1 O2-Cu1-N1 N1-Cu1-N2 Cu1-O1-C13 Cu1-N1-C12 Cu1-N2-C10
2.604(2) 1.923(4) 2.005(5) 85.39(16) 95.15(14) 155.17(18) 93.9(2) 81.7(2) 129.1(4) 111.7(4) 128.6(4)
Cu1-O1 Cu1-N1 Cl1-Cu1-O1 Cl1-Cu1-N1 O1-Cu1-O2 O1-Cu1-N2 O2-Cu1-N2 Cu1-Cl1-Cu1* Cu1-O2-Cu1* Cu1-N1-C1
1.962(4) 2.028(5) 97.93(13) 105.82(14) 95.14(19) 89.14(18) 175.6(2) 70.82(6) 103.4(3) 129.7(4)
a Symmetry code: * ) x, 1 - y, z; ** ) 1 - x, y, -z; *** ) 1 - x, 1 - y, -z.
(N1-Cu1-N2) is 81.7(2)°, whereas the hydroxo and chloride bridging angles (Cu1-O2-Cu1* and Cu1-Cl1-Cu1*; * ) x, 1 - y, z) are 103.4(3)° and 70.82(6)°, respectively. The maximum deviation of 0.034(5) Å of the N2 atom from the mean plane calculated from 14 atoms (C1 f C12, N1, N2) of phen ligands shows that it is almost planar. The adipate bridging angle in complex 1 (Cu1-O1-C13) is 129.1(4)°. The separation of two copper atoms in the dinuclear entity (Cu1-Cu1*) is 3.018(1) Å. The long bridging adipate dianion results in a long Cu-Cu distance of 10.971(1) Å in 1. The aromatic rings of phen ligand of tetrameric units undergo intermolecular face-to-face π-π interactions and a metal-π interaction with copper atoms from the adjacent tetrameric unit (Figure 2, Table 2). These two noncovalent interactions are responsible for the stabilization of the overall supramolecular threedimensional (3D) structure (Figure 3; Figures S1-S4, Supporting
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Crystal Growth & Design, Vol. 6, No. 1, 2006 37
Figure 2. π-π and metal-π interactions between the adjacent tetrameric units [color code: green, copper; blue, nitrogen; red, oxygen of adipate and hydroxyl; yellow, bridging chloride; gray solid lines stand for coordinate bond; orange dotted lines indicate π-π interactions and blue solid lines indicate metal-π interactions.] Table 2. π-π Interactions (Face-to-Face) and Metal-π Interactions in Complex 1a ring(i) f ring(j)/metal
distance between the (i,j) ring centroids (Å)
R1 f R2i R1 f R2ii R1 f R3i R2 f R1i R2 f R1ii R2 f R3ii R3 f R1i R3 f R2ii R3 f R3i R3 f R3ii R3 f Cu(1)i
3.568(4) 4.336(4) 3.797(4) 3.567(4) 4.337(4) 3.791(4) 3.796(4) 3.791(4) 4.389(4) 3.537(4) 3.791(1)
dihedral angle (i,j) (deg) 1.95 1.95 0.97 1.95 1.95 1.00 0.97 1.00 0.00 0.00
distance of centroid(i) from ring (j) (Å) 3.420 3.437 3.434 3.406 3.346 3.394 3.422 3.412 3.403 3.401 3.358
a Symmetry code: (i) ) 1/ - x, 1/ - y, - z; (ii) ) 1/ - x, 1/ - y, 1 2 2 2 2 - z. R(i)/R(j) denotes the ith/jth rings of phen: R(1) ) N(1)/C(1)/C(2)/ C(3)/C(4)/C(12); R(2) ) N(2)/C(10)/C(9)/C(8)/C(7)/C(11); R(3) ) C(4)/ C(5)/C(6)/C(7)/C(11)/C(12).
Figure 3. Channels filled with chloride-water chains in the 3D supramolecular structure of 1 (solvent water and chloride are shown by space-filling model) [color code: green, copper; blue, nitrogen; red, oxygen of adipate and hydroxyl ligand; yellow, chloride; magenta, lattice water oxygen. Gray solid lines stand for coordinate bond; orange dotted lines show hydrogen bonds or π-π interactions and blue solid line indicates metal-π interactions].
Information). Moreover, each unit cell contains 16 solvent water molecules and two free chloride ions. Out of the 16 solvent waters, 14 water molecules and two chloride ions are self-assembled to form a one-dimensional (1D) supramolecular assembly (Figure 4) by O-H‚‚‚Cl and O-H‚‚‚O hydrogen bonding (Table 3). Two lattice water molecules did not take part in the formation of the assembly. In the chain there is a periodic repetition of a fourmembered ring and a 14-membered ring. The four-membered ring comprised of two water molecules and two chlorides generates a
cyclic motif R22(8) in Etter’s graph notation.8 In contrast, the 14membered ring comprised of two chlorides and 12 water molecules 2 generates two cyclic motifs R10 12(24) and R2(8). The large motifs (24) are generated from known water tetrameric cluster9 R10 12 precursors with cyclic motifs, R44(8). These self-assembled waterchloride chains are arranged in the channels formed by a π-interacted 3D supramolecular metal organic host. The structure of the water-chloride chain formed here is comparable to the structure of a self-assembled chain of water.10 It is most important to stabilize a water-chloride self-assembly in a supramolecular host rather than a template generated by a covalent bond, as most of the interactions occurring in living systems are weak and dynamic. A DFT calculation11 with B3LYP12 potential using the basis set 6-31G(d,p) was performed on a part of the supramolecular chloridewater assembly, [(H2O)20Cl4]4-, assuming C2h symmetry. The optimized assembly (Figure S5, Supporting Information) is in accordance with the X-ray crystal structure of the hydrogen-bonded assembly. The ca. 3.39 Kcal binding energy stabilizes the supramolecular assembly. Thermogravimetric analysis (Figure S6, Supporting Information) of complex 1 using 7.6454 mg in air shows that dehydration starts at ∼50 °C and is completed at ∼180 °C showing a 1.3592 mg weight loss, which corresponds to 16 water molecules (ca. 1.3908 mg) present. The range of temperature for dehydration suggests that the association of water molecules in a self-assembled template is quite strong. The IR spectra of 1 exhibit a broad band centered at 3400 cm-1, which may be assigned an O-H stretching frequency pertaining to the water-chloride assembly.13 X-ray powder diffraction patterns (Figure S7, Supporting Information) of the compound before and after water expulsion show major changes. Therefore, the loss of water from the lattice suggests a breakdown of the 3D structure. The magnetic properties of complex 1 in the form of χMT versus T plots (χM is the molar magnetic susceptibility for two CuII ion) are shown in Figure 5. The value of χMT at 300 K is 0.92 cm3mol-1 K, which is practically constant up to 50 K. Upon further lowering of the temperature, there is a rapid decrease of the χMT value to 0.70 cm3 mol-1 K at 2 K, indicating a small antiferromagnetic coupling between CuII ions. Although complex 1 is a tetranuclear entity formed by two dimeric Cu2 units linked by a long dicarboxylate ligand, in a first approach, we have fitted the magnetic data as dinuclear, with the Bleaney-Bowers14 formula using the Hamiltonian H ) -JS1S2 and assuming that the magnetic interaction through the adipate is negligible. The best-fit parameters are J ) -1.06 ( 0.02 cm-1, g ) 2.21 ( 0.02, and R ) 4.0 × 10-5 (R is the agreement factor defined as ∑i[(χmT)obs - (χmT)calc]2/∑i[(χmT)obs]2), which indicate weak antiferromagnetic coupling between the CuII centers. The reduced magnetization curve for one copper(II) ion (inset of Figure 5) shows that the saturation value is achieved at 5T (almost 1 Nβ, as expected for one quasi-isolated copper ion). The Brillouin curve assuming g ) 2.21 (the value deduced from the fit) is slightly above the experimental one, corroborating the global weak antiferromagnetic coupling. Each copper(II) is linked by one carboxylate in cis-cis equatorial-equatorial conformation and by an oxo group in an equatorialequatorial position. The chloride atom in very long apical-apical (2.60 Å) configuration impedes any noticeable magnetic interaction. Thus, the two equatorial-equatorial pathways are the most important. The syn-syn carboxylate configuration is antiferromagnetic and when there is only one carboxylate, the coupling is always very small (ca. -1/-2 cm-1).15 On the other hand, the Cu-O-Cu coupling depends on the angle; when it is close to 90° ferromagnetic coupling occurs and when it is close to 180° the more antiferromagnetic coupling is observed.14 Here in 1, the Cu-O-Cu angle (103.4°) could give small ferromagnetic coupling, which is compensated by the antiferromagnetic coupling created by the synsyn carboxylate bridge. We have demonstrated the stabilization of the water-chloride assembly in a supramolecular host. As such assemblies are observed
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Figure 4. 1D supramolecular assembly of chloride-water cluster running along the a-axis. [color code: magenta, lattice water oxygen; yellow, lattice chloride; cyan, hydrogen; orange dotted line is for hydrogen bonds]. Table 3. Hydrogen Bonding Interactions (Å, °) of Complex 1a D-H‚‚‚A
D-H
H‚‚‚A
D‚‚‚A
2σ] used for solution and refinement by full-matrix least squares on F2 using SHELX-97 (G. M. Sheldrick, Program for the solution and refinement of crystal structures, University of Gottingen, Germany, 1997) package. During refinement C15 atom is found to be symmetry imposed disordered over two positions. So its occupancy was fixed at 0.5. The atoms C13 and C14 were located on a mirror plane. These atoms (C13, C14, C15) constituted the 2-fold disordered adipate ligand. The non-hydrogen atoms were refined anisotropically. Final R ) 0.0562, Rw ) 0.1850; H atoms of water molecules were located by difference Fourier and were kept fixed. Other H atoms were treated by a riding model; maximum and minimum residual electron densities were 1.37 and -0.79 e Å-3, respectively. (8) Etter, M. C.; MacDonald, J. C.; Bernstein, J. Acta Crystallogr. 1990, B46, 256.
Communications (9) (a) Chacko, K. K.; Saenger, W. J. Am. Chem. Soc. 1981, 103, 1708. (b) Zabel, V.; Saenger, W.; Mason, S. A. J. Am. Chem. Soc. 1986, 108, 3664. (10) Pal, S.; Sankaran, N. B.; Samanta, A. Angew. Chem., Int. Ed. 2003, 42, 1741. (11) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon, M. S.; Jensen, J. H.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su, S. J.; Windus, T. L.; Dupuis, M.; Montgomery, J. A. PC GAMESS version 6.4. J. Comput. Chem. 1993, 14, 1347. (12) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (13) Neogi, S.; Savitha, G.; Bharadwaj, P. K. Inorg. Chem. 2004, 43, 3771.
Crystal Growth & Design, Vol. 6, No. 1, 2006 39 (14) Kahn, O. Molecular Magnetism, VCH: New York, 1993. (15) Bu¨rger, K. S.; Chaudhuri, P.; Wieghardt, K. Inorg. Chem. 1996, 35, 2704. (16) (a) Eisenberg, D.; Kauzmann, W. The Structure and Properties of Water; Oxford University Press: New York, 1969. (b) Ludwig, R. Angew. Chem., Int. Ed. 2001, 40, 1808. (c) Keutsch, F. N.; Saykally, R. J. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 10533. (17) Mangani, S.; Ferraroni, M. Supramolecular Chemistry of Anions; A. Bianchi, A., Bowman-James, K., Garcia-Espan˜a, E., Eds.; Wiley: New York, 1997; p 63.
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