Syntheses and Crystal Structures of Metal Complexes with 2, 2

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Syntheses and Crystal Structures of Metal Complexes with 2,2′-Biimidazole-like Ligand and Chloride: Investigation of X-H · · · Cl (X ) N, O, and C) Hydrogen Bonding and Cl-π (imidazolyl) Interactions

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 7 2282–2290

Yong-Rui Zhong, Man-Li Cao, Hao-Jun Mo, and Bao-Hui Ye* MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen UniVersity, Guangzhou 510275, China ReceiVed October 8, 2007; ReVised Manuscript ReceiVed March 6, 2008

ABSTRACT: Six complexes containing the 2,2′-biimidazole-like ligand and chloride, namely, trans-[Ni(H2biim)2(H2O)2]Cl2 (1), trans-[Co1.5(H2biim)3(H2O)3]Cl3 (2), [Zn(H2biim)2Cl]Cl (3), [Ni2(H2bbim)4(bbim)]Cl2 (4), [Co(H2bbim)3]Cl2 · 2H2O (5), and [Zn2(Hbbim)2(bbim)0.5Cl] (6) (where H2biim ) 2,2′-biimidazole, H2bbim ) 2,2′-bibenzimidazole) have been synthesized by the reactions of the H2biim or H2bbim ligand with the metal chloride salts. The structures of the complexes were determined by singlecrystal X-ray diffraction analyses, and the results revealed that the distances of N · · · Cl varied from 3.10 to 3.29 Å and the angles of N-H · · · Cl varied from 148 to 169°, O · · · Cl varied from 3.09 to 3.16 Å, O-H · · · Cl varied from 151 to 178°, C · · · Cl varied from 3.49 to 3.69 Å, and C-H · · · Cl varied from 122 to 167°. The chloride may act as a multi hydrogen bonded acceptor varying from 3 to 6, resulting in an important collective contribution to cohesion. The data observed in this study seem to suggest that a variety of X-H · · · Cl (X ) N, O, and C) synthons identified here play a crucial role in the formation and further stabilization of supramolecular architecture, for instance, to link the discrete (0D) or low-dimensional (1D) entities into high-dimensional frameworks. In particular, the coplanar [(H2O)2Cl2]2- guests are encapsulated in the cavities formed by four [Co(H2bbim)3]2+ cations and stabilized via accepting 6-fold hydrogen bonds from three H2bbim ligands in 5. The distance between the chloride anion and the imidazolyl ring (Cl · · · centroid, 3.30 Å and 80°) demonstrates the possible existence of Cl · · · π (imidazolyl) charge-assisted interactions because the coordination of a positively charged Co(II) ion greatly enhances the electron-deficient character of the imidazolyl ring and provides sufficient polarization to produce an anion-π charge-assisted interaction. Introduction Noncovalent interactions have received much interest in crystal engineering of supramolecular architecture. A convenient and efficient approach to crystal engineering is the synthesis of reliable synthons that can control the dimensionality of the molecular architecture. Classical hydrogen bonding and π-π stacking have played an important role in crystal engineering and have been investigated in much detail,1–6 while the studies of other weak interactions, such as the halogen bonds and the halogen-π contacts, have received attention only in more recent years.7–9 The X-H · · · Cl (X ) N, O, and C) hydrogen bonds have been well appreciated in crystal engineering because they have shown the capability of playing a decisive role in supramolecular architecture and the function of organic solid materials.7,8,10 However, the investigation of X-H · · · Cl hydrogen bonding using inorganic supramolecular synthons is relatively rare.11 On the other hand, the noncovalent interactions between the organic halogen and aromatic system have been well documented on the basis of analyses of Crystal Structure Data.12 The chemistry of noncovalent anion-π charge-assisted interactions are much less developed, although many enzyme–substrates and cofactors are anions.13 This may be attributed to the repulsive interactions between the electron-donating character of the anions and the aromatic π-systems. Importantly, the NMR experiments have first demonstrated the interactions between the electron-poor aromatic moieties and the anions.14–16 Furthermore, theoretical calculations have also indicated the existence of the noncovalent interactions between the anions and the electron-deficient * To whom correspondence should be addressed. Fax: (86)-20-84112245. Tel: (86)-20-84112469. E-mail: [email protected].

aromatic systems, such as fluorobenzene derivatives,17 fluorostriazine,18 and s-tetrazine derivatives,19 and tetrafluoroethene.20 Recently, several crystallographic evidence have also supported such interactions between the anions and the electron-deficient aromatic systems, such as cryptophane,16 1,3,5-triazine ring,21,22 pyridine,22 a 1,2,4,5-tetrazine,23 pyrazine and pyrimidine.24 The importance of the nature of these interactions comes from the potential application of electron-deficient aryl hosts as an anion receptor in biological systems and medicine.22a,23 One of the challenges for the investigation of such noncovalent interactions is to design appropriate chemical systems incorporating the X-H donor and sufficient π-acidity to accept the chloride anion. We select 2,2′-biimidazole (H2biim) and 2,2′bibenzimidazole (H2bbim) as the primary ligands because they are bifunctional: the imino moieties can be coordinated to a metal ion acting as the first coordination sphere and the amino N-H and C-H groups, as the second coordination sphere, may donate multifold hydrogen bonds to one or two chloride anions,25 extending the structure into a high-dimensional network. The most interesting and important features are (i) the H2biim and H2bbim ligands are coordinated to metal ions in the well-defined geometries; they often form cavities bounded by arene rings, which may be used as anion receptors;26 (ii) the coordination of a positively charged metal ion will greatly enhance the electron-deficient character of the imidazolyl ring and provide sufficient polarization to produce anion-π chargeassisted interactions. Although the imidazolyl group is a side chain of amino acid, no theoretical or experimental investigations of Cl-π interactions are yet available for the imidazolyl ring.27 In this contribution, six complexes containing the metal-H2biim/H2bbim ligand and chloride, namely, trans[Ni(H2biim)2(H2O)2]Cl2 (1), trans-[Co1.5(H2biim)3(H2O)3]Cl3

10.1021/cg700980v CCC: $40.75  2008 American Chemical Society Published on Web 05/28/2008

Complexes with 2,2′-Biimidazole-like Ligand and Cl

Crystal Growth & Design, Vol. 8, No. 7, 2008 2283

Table 1. Crystal Data and Structure Refinement for 1-6a compound

1

2

3

4

5

6

formula formula weight crystal system space group a/Å b/Å c/Å β/deg V/Å3 Z Dc/g cm-3 µ/mm-1 data/parameter R1 (I > 2σ)a wR2 (all data)b GOF ∆Fmax/∆Fmin (e Å3)

C12H16NiCl2N8O2 433.92 monoclinic P21/c 8.188(5) 8.672(5) 14.513(6) 121.31(2) 880.4(8) 2 1.637 1.430 1694/129 0.0313 0.0899 1.00 0.49/-0.24

C18H24Co1.5Cl3N12O3 651.24 monoclinic C2/m 22.022(1) 12.477(6) 9.648(5) 95.799(9) 2637(2) 4 1.640 1.305 2683/200 0.0817 0.2306 1.00 0.57/-0.98

C12H12ZnCl2N8 404.59 tetragonal P42212 11.0868(7) 11.0868(7) 12.778(2) 90 1570.7(2) 4 1.711 1.915 1518/130 0.0253 0.0686 1.01 0.75/-0.23

C70H48Ni2Cl2N20 1357.56 monoclinic C2/c 13.001(1) 19.287 (2) 25.606 (2) 94.049(2) 6404.8(10) 4 1.408 0.732 6226/424 0.0482 0.0643 0.90 0.77/-0.36

C42H34CoCl2N12O2 868.64 monoclinic P21/c 12.661(1) 20.958(2) 15.475(1) 95.767(2) 4085.4(6) 4 1.412 0.604 7949/548 0.0798 0.2176 1.00 0.59/-0.40

C35H22Zn2ClN10 748.82 monoclinic P21/c 11.883(1) 27.270(3) 10.513(1) 91.630(2) 3405.5(6) 4 1.461 1.528 6637/433 0.0526 0.1070 1.00 0.53/-0.44

a

R1 ) Σ4Fo4 - 4Fc4/Σ4Fo4. b wR2 ) [Σw(Fo2 - Fc2)2/Σw(Fo2)2]1/2.

(2), [Zn(H2biim)2Cl]Cl (3), [Ni2(H2bbim)4(bbim)]Cl2 (4), [Co(H2bbim)3]Cl2 · 2H2O (5), and [Zn2(Hbbim)2(bbim)0.5Cl] (6), have been synthesized. They provide examples of a wide variety of noncovalent interactions such as C-H · · · Cl, N-H · · · Cl, and O-H · · · Cl hydrogen bonds and π-π stacking as well as Cl-π (imidazolyl) charge-assisted interactions. Such secondary, weak interactions lead to the formation of novel, multidimensional supramolecular networks. Experimental Section Materials and Methods. The reagents and solvents employed were commercially available and used as received without further purification. The C, H, and N microanalyses were carried out with a Vario EL elemental analyzer. 1H NMR spectra were recorded on a Varian 300 MHz spectrometer at 25 °C. The H2biim28 and H2bbim29 ligands were synthesized with the published procedures, respectively, and checked with elemental analysis and NMR spectra. Synthesis of trans-[Ni(H2biim)2(H2O)2]Cl2. A methanol solution (10 mL) of H2biim (0.067 g, 0.5 mmol) was added into a methanol solution (10 mL) of NiCl2 · 6H2O (0.119 g, 0.5 mmol) and ina (0.123 g, 1 mmol, ina ) isonicotinic acid). The resultant mixture was stirred for 0.5 h at room temperature. The insoluble components were removed by filtration, and the filtrate was allowed to evaporate at room temperature. The green-colored single crystals suitable for X-ray analysis were obtained from the filtrate after one week. Yield: 0.038 g, 35% based on the H2biim ligand. Anal. Calcd (%) for C12H16NiCl2N8O2: C 33.22, H 3.72, N 25.82; found: C 33.65, H 3.85, N 25.47. Synthesis of trans-[Co1.5(H2biim)3(H2O)3]Cl3. CoCl2 · 6H2O (0.119 g, 0.5 mmol), H2biim (0.067 g, 0.5 mmol) and ina (0.121 g, 1 mmol) were added into an ethanol-aqueous solution (10 mL, 1:1). The resulting mixture was stirred for 20 min at room temperature, then, transferred and sealed in a 23 mL Teflon reactor. The mixture was heated at 150 °C for 3 days and then cooled to room temperature at a rate of 5 °C · h-1. The final solution was filtered, and the filtrate was allowed to evaporate at room temperature. The orange-colored single crystals suitable for X-ray analysis were obtained from the filtrate after one week. Yield: 0.034 g, 32% based on the H2biim ligand. Anal. Calcd (%) for C18H24Co1.5Cl3N12O3: C 33.20, H 3.71, N 25.81; found: C 32.88, H 3.27, N 25.67. Synthesis of [Zn(H2biim)2Cl]Cl. The reaction was carried out using a method similar to that for 1, using ZnCl2 · 2H2O instead of NiCl2 · 6H2O. The filtrate was allowed to evaporate slowly at room temperature. After one week, the pale-yellow block crystals were obtained in 0.023 g, 23% based on the H2biim ligand. Anal. Calcd (%) for C12H12ZnCl2N8: C 35.62, H 2.99, N 27.70; found: C 36.20, H 2.86, N 27.87. Synthesis of [Ni2(H2bbim)4(bbim)]Cl2. NiCl2 · 6H2O (0.119 g, 0.5 mmol), H2bbim (0.176 g, 0.75 mmol), and 4-cyanopyridine (0.104 g, 1 mmol) were added into an ethanol-aqueous solution (10 mL, 1:1). The resulting mixture was stirred for 30 min at room temperature, then,

transferred and sealed in a 23 mL Teflon reactor. The mixture was heated at 150 °C for 3 days and then cooled to room temperature at a rate of 5 °C · h-1. The brown block crystals were obtained in 0.081 g, 40% yield based on the H2bbim ligand. Anal. Calcd (%) for C70H48Ni2Cl2N20: C 61.93, H 3.56, N 20.62; found: C 61.60, H 3.28, N 20.12. Synthesis of [Co(H2bbim)3]Cl2 · 2H2O (5). CoCl2 · 6H2O (0.119 g, 0.5 mmol) and H2bbim (0.176 g, 0.75 mmol) were added into an ethanol-aqueous solution (10 mL, 1:1). The resulting mixture was stirred for 30 min at room temperature, then, transferred and sealed in a 23 mL Teflon reactor. The mixture was heated at 150 °C for 3 days and then cooled to room temperature at a rate of 5 °C · h-1. The palered crystals were obtained in 0.162 g, 75% yield based on the H2bbim ligand. Anal. Calcd (%) for C42H34CoCl2N12O2: C 58.02, H 3.91, N 19.34; found: C 58.23, H 4.28, N 19.12. Synthesis of [Zn2(Hbbim)2(bbim)0.5Cl]. The title complex was synthesized using a method similar to that for 4, using ZnCl2 · 2H2O instead of NiCl2 · 6H2O. The brown block crystals were obtained in 0.078 g, 35% yield based on the H2bbim ligand. Anal. Calcd (%) for C35H22Zn2ClN10: C 56.09, H 2.93, N 18.69; found: C 56.23, H 3.28, N 18.32. X-ray Crystallography. Diffraction intensities for the compounds were collected on a Bruker Apex CCD area-detector diffractometer (Mo KR, 0.71073 Å). Absorption corrections were applied by using the multiscan program SADABS.30 The structures were solved with direct methods and refined with the full-matrix least-squares technique with the SHELXTL program package.31 Anisotropic thermal parameters were applied to all the non-hydrogen atoms. The organic hydrogen atoms were generated geometrically (C-H 0.96 Å) and refined with isotropic temperature factors. Hydrogen atoms on oxygen and nitrogen atoms were located from difference maps and refined isotropically; the O-H distances involving the water molecules were refined with an AFIX restraint of 0.85–0.95 Å. Crystallographic data as well as details of data collection and refinement for the complexes are summarized in Table 1. Selected bond lengths and angles are listed in Table 2. The hydrogen bonding parameters are given in Table 3.

Results and Discussion Syntheses. We and others have demonstrated that the main products were [M(H2biim)2(H2O)2](RCO2)m · nH2O (M ) Co2+, Ni2+, Zn2+; RCO2) acetate,32 ina,33 benzodicarboxylate,34 glutarate,35 squarate,35 succinate35) in the reactions of the metal salts with the H2biim ligand in a 1:2 molar ratio in the presence of the monocarboxylic and dicarboxylic acids, due to the strong charge-assisted hydrogen bonding between the H2biim ligand and the carboxylate groups. When we set up the program to observe the weak interactions of the X-H groups and aromatic π-system to the Cl anion, the metal chloride salts were used as the starting materials. We found that the main product changed to [Ni(H2biim)2(H2O)2](Cl)2 when the molar ratio of NiCl2 to

2284 Crystal Growth & Design, Vol. 8, No. 7, 2008

Zhong et al.

Table 2. Selected Bond Lengths (Å) and Angles (°) of 1–6a 1 Ni(1)-O(1W) Ni(1)-N(4) N(1)-Ni(1)-N(4) O(1w)-Ni(1)-N(4) O(1w)-Ni(1)-N(1a) N(1)-Ni(1)-N(1a)

2.094(2) 2.112(3) 80.75(9) 92.06(9) 88.95(8) 180

Ni(1)-N(1) Ni(1)-O(1Wa) O(1w)-Ni(1)-N(1) O(1w)-Ni(1)-O(1wa) O(1w)-Ni(1)-N(4a) N(1)-Ni(1)-N(4a)

2.078(2) 2.094(2) 91.05(8) 180 87.94(9) 99.25(9)

Table 3. Hydrogen Bonding Parameters (Å and °) of 1–6a D-H · · · A

D-H

H· · ·A

O(1W)-H · · · Cl(1) O(1W)-H · · · Cl(1a) N(2)-H · · · Cl(1b) N(4)-H · · · Cl(1b) C(6)-H · · · Cl(1)

0.86(4) 0.72(3) 0.86 0.86 0.93

2.25(4) 2.46(3) 2.39 2.50 2.87

N(2)-H · · · Cl(1) O(2W)-H · · · Cl(1c) O(1W)-H · · · Cl(1b) C(2)-H · · · Cl(1d) O(1W)-H · · · Cl(2c) O(2W)-H · · · Cl(2a) N(6)-H · · · Cl(2) O(3W)-H · · · Cl(3) C(8)-H · · · Cl(3) N(4)-H · · · Cl(3d) O(3w)-H · · · Cl(3e)

0.86 0.75(7) 0.87(13) 0.93 0.75(9) 0.79(7) 0.86 0.74(9) 0.93 0.86 0.66(10)

2.43 2.44(8) 2.26(13) 2.93 2.40(9) 2.37(7) 2.39 2.43(9) 2.93 2.42 2.45(11)

N(2)-H · · · Cl(1) N(3)-H · · · Cl(1) C(5)-H · · · Cl(2)

0.81(3) 0.87(3) 0.95

2.46(3) 2.36(4) 2.81

2.281(1) 2.034(2) 168.4(1) 95.8(1) 96.8(1)

Ni(1)-N(1) Ni(1)-N(5) Ni(1)-N(9) N(1)-Ni(1)-N(3) N(9)-Ni(1)-N(10a) N(1)-Ni(1)-N(7) N(1)-Ni(1)-N(10a) N(3)-Ni(1)-N(7) N(3)-Ni(1)-N(10a) N(5)-Ni(1)-N(10a) N(7)-Ni(1)-N(10a)

2.121(2) 2.094(2) 2.111(2) 79.0(1) 83.3(1) 95.2(1) 96.8(1) 173.7(1) 90.9(1) 169.4(1) 93.3(1)

Co(1)-N(1) Co(1)-N(5) Co(1)-N(9) N(9)-Co(1)-N(11) N(7)-Co(1)-N(9) N(5)-Co(1)-N(9) N(3)-Co(1)-N(11) N(3)-Co(1)-N(7) N(1)-Co(1)-N(11) N(1)-Co(1)-N(7) N(1)-Co(1)-N(3)

2.159(4) 2.160(4) 2.199(3) 77.0(1) 93.75(1) 90.8(1) 89.6(1) 168.8(1) 90.3(1) 94.5(1) 77.6(1)

Zn(1)-N(1) Cl(2)-Zn(1)-N(1a) N(4)-Zn(1)-N(4a) N(1)-Zn(1)-N(4) Cl(2)-Zn(1)-N(4)

N(2)-H · · · Cl(1) N(4)-H · · · Cl(1) N(6)-H · · · Cl(1a) N(8)-H · · · Cl(1a)

0.86 0.86 0.86 0.86

2.30 2.41 2.38 2.29

2.264(2) 95.8(1) 135.7(1) 78.8(1) 112.1(1)

4 Ni(1)-N(3) Ni(1)-N(7) Ni(1)-N(10a) N(5)-Ni(1)-N(7) N(1)-Ni(1)-N(5) N(1)-Ni(1)-N(9) N(3)-Ni(1)-N(5) N(3)-Ni(1)-N(9) N(5)-Ni(1)-N(9) N(7)-Ni(1)-N(9)

2.125(3) 2.128(2) 2.112(2) 79.2(1) 90.3(1) 173.1(1) 98.2(1) 94.3(1) 90.6(1) 91.5(1)

5 Co(1)-N(3) Co(1)-N(7) Co(1)-N(11) N(7)-Co(1)-N(11) N(5)-Co(1)-N(11) N(5)-Co(1)-N(7) N(3)-Co(1)-N(9) N(3)-Co(1)-N(5) N(1)-Co(1)-N(9) N(1)-Co(1)-N(5)

2.123(4) 2.108(4) 2.224(4) 98.5(1) 167.1(1) 78.1(1) 95.7(1) 95.6(1) 165.7(1) 102.4(1)

6 Zn(1)-N(1) Zn(1)-N(7) Zn(1)-N(5b) Zn(2)-N(4) Zn(2)-N(10a) N(1)-Zn(1)-N(7) N(1)-Zn(1)-N(5b) N(3)-Zn(1)-N(8) N(7)-Zn(1)-N(8) N(5b)-Zn(1)-N(8) Cl(1)-Zn(2)-N(9) N(4)-Zn(2)-N(9) N(9)-Zn(2)-N(10a)

2.171(4) 2.006(4) 2.017(3) 2.013(4) 2.032(5) 105.8(1) 92.1(1) 95.7(1) 79.4(1) 89.6(1) 114.2(1) 104.9(1) 86.5(1)

Zn(1)-N(3) Zn(1)-N(8) Zn(2)-Cl(1) Zn(2)-N(9) N(1)-Zn(1)-N(3) N(1)-Zn(1)-N(8) N(3)-Zn(1)-N(7) N(3)-Zn(1)-N(5b) N(5a)-Zn(1)-N(7) Cl(1)- Zn(2)-N(4) Cl(1)-Zn(2)-N(10a) N(4)-Zn(2)-N(10a)

3.098(3) 3.140(3) 3.203(3) 3.297(3) 3.62

169(3) 158(3) 158 155 138

3.221(6) 3.110(8) 3.114(7) 3.84 3.152(8) 3.160(8) 3.201(6) 3.169(10) 3.52 3.206(5) 3.112(10)

154 151(7) 171(11) 167 178(9) 177(7) 157 177(10) 122 153 178(12)

3.184(2) 3.127(2) 3.49

149(3) 148(3) 127

3.125(3) 3.218(2) 3.181(3) 3.104(3)

162 156 156 158

3.092(7) 3.157(4) 3.146(6) 3.101(4) 3.157(5) 3.157(5) 3.119(7) 3.150(7) 2.724(7) 2.760(6)

162(5) 151 161(6) 157 164 163 165(10) 165(8) 167 158

3.141(4) 3.536(5) 3.694(5)

169 137 149

2

Co(1)-N(1) 2.135(5) Co(1)-N(3) 2.137(5) Co(2)-N(5) 2.173(5) N(3)-Co(1)-N(3a) 79.1(2) O(3w)-Co(1)-N(3) 89.2(2) O(2w)-Co(1)-N(1) 89.1(2) O(2w)-Co(1)-N(1a) 89.1(2) O(3w)-Co(1)-N(1) 90.4(2) N(5)-Co(2)-N(5c) 77.5(2) O(1w)-Co(2)-O(1wd) 180 O(1w)-Co(2)-N(5b) 88.8(2) N(5)-Co(2)-N(5d) 102.5(2) 3

Zn(1)-Cl(2) Zn(1)-N(4) N(1)-Zn(1)-N(1a) Cl(2)-Zn(1)-N(1) N(1)-Zn(1)-N(4a)

∠D-H · · · A

1

2 Co(1)-O(3W) 2.089(9) Co(1)-O(2W) 2.057(7) Co(2)-O(1W) 2.084(7) N(1)-Co(1)-N(1a) 78.8(2) N(1)-Co(1)-N(3) 179.5(2) O(2w)-Co(1)-O(3w) 179.3(3) O(2w)-Co(1)-N(3) 91.4(2) O(2w)-Co(1)-N(3a) 91.4(2) N(1)-Co(1)-N(3a) 101.0(2) O(1w)-Co(2)-N(5) 91.3(2) O(1w)-Co(2)-N(5d) 88.8(2) O(1w)-Co(2)-N(5c) 91.3(2)

D· · ·A

2.061(4) 2.260(4) 2.208(2) 2.087(4) 77.9(1) 173.0(1) 115.0(1) 128.5(1) 116.4(1) 112.2(1) 118.7(1) 116.8(1)

a Symmetry codes for 1: a, -x, -y, -z. 2: a, x, 1 - y, z; b, 1 - x, y, 1 - z; c, x, -y, z; d, 1 - x, -y, 1 - z. 3: a, x, y, 2 - z. 4: a, 1 - x, y, 5/2 - z. 6: a, 2 - x, -y, -z; b: x, 1/2 - y, -1/2 + z.

the H2biim ligand was tuned to 1:1, in which the diversely charge-assisted hydrogen bonds X-H · · · Cl formed and connected the [Ni(H2biim)2(H2O)2] unit into a 3D network.

3

4

5 O(2w)-H · · · Cl(2a) N(2)-H · · · Cl(2a) O(1w)-H · · · Cl(2) N(6)-H · · · Cl(2) N(10)-H · · · Cl(1) N(12)-H · · · Cl(1) O(2w)-H · · · Cl(1b) O(1w)-H · · · Cl(1b) N(4)-H · · · O(2w) N(8)-H · · · O(1w)

1.13(7) 0.86 1.06(8) 0.86 0.86 0.86 0.59(7) 0.84(9) 0.86 0.86

2.00(7) 2.38 2.13(8) 2.29 2.31 2.32 2.54(7) 2.33(9) 1.88 1.94

N(2)-H · · · Cl(1) C(23)-H · · · Cl(1d) C(22)-H · · · Cl(1c)

0.86 0.93 0.93

2.29 2.80 2.86

6

a Symmetry code, 1: a, -x, 1/2 + y, -1/2 - z; b, -x, -y, -z. 2: a, 1/2 + x, 1/2 + y, z; b, -1/2 + x, -1/2 + y, -1 + z; c, x, y, -1 + z; d, 1 - x, y, 1 - z; e: 1 - x, y, 2 - z. 4: a, -1/2 + x, -1/2 + y, z. 5: a, 1 + x, y, z; b, 1 - x, -y, 1 - z. 6: c, 2 - x, -1/2 + y, 1/2 - z; d: 1 x, -y, 1 - z.

Moreover, we also examined the reaction under hydrothermal condition. Surprisingly, when the zinc ion was used under the reaction conditions, [Zn(H2biim)2Cl]Cl 3 was obtained as a main product. Unlike complexes 1 and 2, one chloride is coordinated to Zn2+ in 3. These may be attributed to the different properties of the metal ions. When the H2bbim ligand was introduced to replace the H2biim ligand, complex [Co(H2bbim)3]Cl2 was obtained. Interestingly, the M-H2bbim unit can further associate with the second metal ion forming dinuclear or polynuclear complexes via deprotonation under hydrothermal conditions in the presence of 4-cyanopyridine, presumably because 4-cyanopyridine is hydrolyzed to ina and ammonia, which can trap protons from the H2bbim ligand.36 Crystal Structure of 1. The title complex consists of one [Ni(H2biim)2(OH2)2]2+ cation and two chloride anions. As shown in Figure 1a, the Ni(II) ion locates on a symmetry inversion center and is coordinated by four nitrogen atoms from two H2biim ligands [Ni-N(1) ) 2.078(2) and Ni-N(4) )

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Figure 1. Views of (a) the coordination environment of Ni(II) ion containing N-Η · · · Cl hydrogen bonding, (b) the 2D hydrogen-bonded layer on the ac plane (the orange and green balls are chloride anions) and (c) the 3D hydrogen-bonded network along the c-axis in 1. Symmetry codes: a, 1 - x, -y, -z.

2.111(2) Å] arranged trans to each other in the equatorial plane and two aqua ligands [Ni-O(1W) ) 2.094(2) Å] occupying the apical coordination sites to furnish an octahedral geometry. The two rings of each H2biim ligand are almost coplanar with a dihedral angle of 2.9°, and the metal ion is also in the plane. The main distortion of the resulting octahedral coordination geometry originates from the small N(1)-Ni(1)-N(4) bite angle of the chelating ligand (80.7(1)°). The geometry of the [Ni(H2biim)2(OH2)2]2+ cation is comparable to the previously reported values in [Ni(H2biim)2(OH2)2](NO3)237 and [Ni(H2biim)2(OH2)2](ina)2.33Each [Ni(H2biim)2(H2O)2]2+ cation is hydrogen bonded to two chloride anions with distances of N · · · Cl ) 3.203(3) and 3.297(3) Å, and the angle of N-H · · · Cl ) 158° in R12(7) synthon. The average N · · · Cl distance 3.255(3) Å is in the accepted range of N-H · · · Cl hydrogen bonding (2.91–3.62 Å).38 The [Ni(H2biim)2(OH2)2]Cl2 units are further connected to each other via the hydrogen bonds of O(1W)H · · · Cl(1) ) 3.098(3) and O(1W)-H · · · Cl(1a) ) 3.140(3) Å, and C-H · · · Cl(1) ) 3.62 Å, resulting in a 2D layer on the ac plane, as shown in Figure 1b. Furthermore, the layers connect each other via the O(1W)-H · · · Cl and C-H · · · Cl hydrogen bonds into a 3D network (Figure 1c). Interestingly, each chloride anion acts as a 5-fold hydrogen bonded acceptor from four cations via two N-H · · · Cl, two O(1W)-H · · · Cl, and one C-H · · · Cl hydrogen bond (green ball). Therefore, the chloride anions help to sustain the 2D assembly and at the same time the final 3D array. Crystal Structure of 2. As shown in Figure 2a, two crystallographically independent Co(1) and Co(2) ions locate on an asymmetric unit, where the Co(1) locates on a crystallographic center with 0.5 occupancy and the Co(2) is in a special position (1/2, 0, 1/2) with 0.25 occupancy. The geometry of 2 is similar to 1. The Co-N distances are comparable to previously reported values in [Co(H2biim)2(OH2)2]2+;33 however, the average Co-O(W) distance [2.077(7) Å] in 2 is

significantly shorter than those in the reported values [2.1152.175(3) Å].33 This may be attributed to the fact that the formation of stronger hydrogen bonding between the coordinated water and carboxylate group or lattice–water cluster enlongates the Co-O(W) bond in the previous complexes.33b Each [Co(H2biim)2(H2O)2]2+ cation is hydrogen bonded to two chloride anions with the distances of N · · · Cl ) 3.201-3.221 Å, and the angles of N-H · · · Cl ) 153-157° in R12(7) synthon. Interestingly, the Co(1) (violet) and Co(2) (orange) units are respectively connected to each other via the O(W)-H · · · Cl intrachain hydrogen bonds, resulting in 1D Co(1) · · · Co(1) · · · Co(1) (A) and Co(2) · · · Co(2) · · · Co(2) (B) chains with the shortest Co · · · Co distance of 9.648 Å along the c-axis (Figure 2b). Furthermore, these chains assemble in A-A-B fashion into a 2D layer structure via the O(W)-H · · · Cl interchain hydrogen bonds on the ac plane, as shown in Figure 2b. These sheets further assemble into a 3D network via the C-H · · · Cl hydrogen bonds [C(8)-H · · · Cl(3) ) 3.52 and C(2)-H · · · Cl(1d) ) 3.84 Å] as well as the strong π-π interactions with a face-to-face distance of 3.3 Å between the two H2biim ligands of Co(1) units along the b-axis (Figures 2c and S1, Supporting Information). Significantly, the chloride anions Cl(1) and Cl(3) act as 6-fold hydrogen bonded acceptors from five cations through two N-H · · · Cl, two O(1W)-H · · · Cl, and two C-H · · · Cl hydrogen bonds (see Figure S2, Supporting Information), while Cl(2) is a 4-fold hydrogen bonded acceptor (see Figure 2b). It is worth pointing out that the chloride anions link the homocationic units into 1D chains, then into a 3D network via X-H · · · Cl (X ) C, N, and O) hydrogen bonds. Crystal Structure of 3. Although the chemical component and coordination geometries of the title complex are the same as the reported complex (3′) which has been prepared in a different approach, it crystallizes in P42212 space group and is different from 3′ in P21/c,39 and their crystal packings are very distinct. Similarly, each Cl- anion links two [Zn(H2biim)2Cl]+

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Figure 2. Views of (a) the coordination environment of Co(II) ion containing N-Η · · · Cl hydrogen bonding, (b) the 2D hydrogen-bonded layer on the ac plane (the cation containing Co(1) in violet and Co(2) in orange; green, red and yellow balls are Cl(1), Cl(2) and Cl(3), respectively), and (c) the 3D hydrogen-bonding network along the c-axis. Symmetry code, a: x, 1 - y, z; b, 1 - x, y, 1 - z; c, x, -y, z; d, 1 - x, -y, 1 - z.

cation in R12(7) synthon via 4-fold hydrogen bonded with the distances of N · · · Cl ) 3.184(2) and 3.127(2) Å, and the angle of N-H · · · Cl ) 149° (Figure 3a), resulting in a neutral 1D tape-like chain along the c-axis (Figure 3c). Distinguishingly, these tapes assemble into pairs via face-to-face strong π-π interaction (3.35 Å) between the H2biim ligands (Figures 3c and S3, Supporting Information), and the coordination chlorides locate on both sides of the “double chain” in 3. Interestingly, the coordination chlorides further intercalate into the neighboring “double chain” via the interactions of hydrogen bonds of C-H · · · Cl(2) (3.49 Å) and C-H · · · π (the distance of H · · · π ) 2.67 Å, see Figure 3b), resulting in a 3D network (Figure S4, Supporting Information). Therefore, it is the chloride that helps to sustain the 3D array. Crystal Structure of 4. Each Ni(II) ion is coordinated by six nitrogen atoms from two H2bbim ligands [Ni-N ) 2.094(2)-2.128(2) Å] and a bbim2- ligand [Ni-N ) 2.111(2) Å] in a chelating fashion to furnish a distorted octahedral geometry. The bond lengths are comparable to the values [2.093(5)-2.182(5) Å] in [Ni(H2bbim)3]2+.40 The bite angle of Ni-bbim (83.3°) is slightly larger than that of Ni-H2bbim (79.1°). As shown in Figure 4a, the bi-deprotonated ligand bbim2- locates on a symmetry center and bridges the two Ni(H2bbim)2 moieties into a binuclear coordination cation with

a distance of Ni · · · Ni 5.41 Å as the first coordination sphere. The four coordinated H2bbim ligands are arrayed on the periphery of the binuclear unit as the second sphere receptors for anions via hydrogen bonding. Indeed, each binuclear cation is hydrogen bonded to four chloride anions with the distances of N · · · Cl ) 3.104(3)-3.218(2) Å and the angles of N-H · · · Cl ) 156-162°, forming a tetrahedron building unit as shown in Figure 4b. Interestingly, the tetrahedron building units connect each other via sharing the vertex into a 2D layer network on the bc plane (Figure 4c). Where the binuclear cation can be considered as a four-connected node and the chloride can be regarded as a two-linked spacer, resulting in a (4,4) hydrogen bonding net. Furthermore, the sheets further pack into a 3D structure via π-π interactions (see Figure S5, Supporting Information). Therefore, it is the chloride that connects the binuclear units into a 2D layer via N-H · · · Cl hydrogen bonds. Crystal Structure of 5. The Co(II) ion is coordinated by six nitrogen atoms from three H2bbim ligands [Co-N ) 2.108(4)2.224(4) Å] in a chelating fashion to furnish a distorted octahedral geometry. The distances of the Co-N bond are consistent with the previous report in Co(II)-H2bbim complexes [2.054(1)-2.182(2) Å] by Lu et al.40 As shown in Figure 5a, each [Co(H2bbim)3]2+ cation is hydrogen bonded to two chloride anions with the distances of N · · · Cl ) 3.101-3.157 Å and the

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Figure 3. Views of (a) the coordination environment of Zn(II) ion containing the hydrogen bonding with Cl-, (b) the C-Η · · · π and C-Η · · · Cl (green ball) interactions, and (c) a hydrogen-bonded double chain constructed via π-π interaction along the c-axis in 3. Symmetry code, a: x, y, 2 - z.

Figure 4. Views of (a) the coordination environment of Ni(II) ion containing the hydrogen bonding with Cl-, (b) the tetrahedron building unit (orange line) via linking the chloride anions which are hydrogen bonded to the binuclear unit, and (c) the 2D (4,4) hydrogen-bonded net on the bc plane in 4. Symmetry code, a: 1 - x, y, 5/2 - z; b: –1/2 + x, -1/2 + y, z.

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Figure 5. Views of (a) the coordination environment of Co(II) ion containing the hydrogen bonding with Cl- anion and water molecules, (b) the presentation of Cl · · · π (imidazolyl) charge assisted interaction, (c) the “double chain” assembled in “head-to-head” along the a-axis, and (d) the 2D sheet connected via hydrogen bonds, π-π and Cl-π interactions on the ac plane in 5. The green balls are Cl(1) and the yellow balls are Cl(2).

angles of N-H · · · Cl ) 151-164°, and two water molecules with the distances of N · · · O ) 2.724 and 2.760 Å, and the angles of N-H · · · O ) 158 and 164° as a basically structural unit. The Cl(1) and a H2bbim ligand form a R12(7) hydrogen bonding synthon, while the Cl(2) anion is hydrogen bonded to the O(1w) and O(2w) in two R23(9) synthons. The structural units further self-connect into a “single chain” via sharing the Cl(2) anion as an acceptor in hydrogen bonding (see Figure S6, Supporting Information). Furthermore, a pair of “single chains” self-assemble into a “double chain” (zipper like) in a head-to-head fashion (Figure 5c) via hydrogen bonding between the Cl(1) anion and the water molecules [O(2w) · · · Cl(1b) ) 3.119(7) and O(1w) · · · Cl(1b) ) 3.150(7) Å]. The phenyl groups of H2bbim ligand hang on both sites of the “double chain”. Interestingly, they stack together via π-π interactions (3.332

Å) as well as the Cl · · · π charge assisted interactions into a 2D structure (Figure 5d). The most interesting feature of 5 is that two chloride anions and two water molecules, which are coplanar and form a [(H2O)2Cl2]2- R24(8) guest, are encapsulated in the cavities formed by four [Co(H2bbim)3]2+ cations and stabilized via accepting 6-fold hydrogen bonds from the three H2bbim ligands. The Cl anions are 4-fold hydrogen-bonded acceptors and the Cl(2) anion (yellow ball) resides above the imidazolyl ring (Figure 5b), where the distance from the Cl(2) to the centroid of this ring is 3.30 Å and the angle of the Cl · · · centroid axis to the plane of the ring is 80°. As expected, this distance is slightly longer than the values calculated (3.2 Å, 90°)41 and experimentally observed (3.17 Å, 87°)21 from the chloride to the centroid of s-triazine, because the latter is more electron deficient

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Figure 6. Views of (a) the coordination environment of Zn(II) ions containing N-H · · · Cl hydrogen bonding, (b) the 2D herringbone sheet connected via coordination bonds on the bc plane, (c) the 3D structure connected via C-H · · · Cl (green balls) hydrogen bonding along the a-axis, and (d) the four-coordination of Cl- anion via coordination bond, N-H · · · Cl and C-H · · · Cl hydrogen bonding in 6. Symmetry code, a: 2 - x, -y, -z; b: x, 1/2 - y, -1/2 + z; c: 2 - x, -1/2 + y, 1/2 - z; d: 1 - x, -y, 1 - z.

than imidazolyl ring. The comparable distances (3.3 Å) have also been observed between the halogens and the aromatic rings.42 Moreover, this distance is shorter than those reported from the chloride to the centroid of pyridine rings (3.46-3.69 Å, 75-82°).22a Although no theoretical or experimental investigation of Cl · · · π (imidazolyl) interaction is yet available,27 the observation gives evidence that the chloride anion interacts with the imidazolyl ring. It should be noted that the coordination of a positively charged Co(II) ion much enhances the electrondeficient character of imidazolyl ring and provides sufficient polarization to produce an anion-π charge assisted interaction. Crystal Structure of 6. Two crystallographically independent Zn(1) and Zn(2) ions locate on an asymmetric unit. The Zn(1) ion is coordinated by five nitrogen atoms from three Hbbim ligands, two of them are in chelating mode [Zn(1)-N(1) ) 2.171(4), Zn(1)-N(3) ) 2.061(4), Zn(1)-N(7) ) 2.006(4), and Zn(1)-N(8) ) 2.260(4) Å] and one is in monodentate mode [Zn(1)-N(5b) ) 2.017(3) Å], resulting in a distorted trigonal bipyramidal structure [N(1)-Zn(1)-N(8) ) 173.0(1), and N(3)-Zn(1)-N(5b) ) 128.5(1)°, τ ) 0.75],43 as shown in Figure 6a. The Zn(2) is four coordinated by three nitrogen atoms from one bbim2- ligand [Zn(2)-N(9) ) 2.087(4), and Zn(2)-N(10a) ) 2.032(5) Å], one Hbbim- ligand [Zn(2)-N(4) 2.013(4) Å], and one chloride anion [Zn(2)-Cl(1) ) 2.208(2) Å] to furnish a tetrahedral geometry. The bond distances of metal ion to imidazolyl ring [N(1) and N(8)] are longer than

those of metal ion to imidazolate ring [N(3), N(5), and N(7)]. This may be attributed to the fact that the nitrogen atoms of imidazolyl and imidazolate rings have different coordination abilities, and the N(1) and N(8) atoms are located on the axial position. This phenomenon was also observed in Co(II)Hbiim44 and Co(II)-Hbbim complexes.40 There are two ligands Hbbim- and biim2- in 6. Each Hbbimligand is simultaneously coordinated to one metal atom in a chelating mode through the imino nitrogen atoms of both imidazolyl rings and in a monodentate mode to another metal atom through the deprotonated amino nitrogen atom of the imidazolate ring as a tridentate ligand. A search of CSD reveals that this coordination mode is rare.26a,40,44,45 The bridging imidazolate group connects the two adjacent Zn(1) ions into a helical chain along the c-axis. The metal-metal distances along the c-axis are 5.92 Å, which is comparable to the previous observations (5.97 and 5.96 Å).44 Furthermore, each bbim2ligand coordinates to two Zn(2) as a spacer, which connects a pair of helical chains containing Zn(1) into a 2D herringbone architecture on the bc plane as shown in Figures 6b and S7, Supporting Information. The chloride anions hang on both sites of the layer, and further interact with the C(23)-H groups from the neighboring layers via C-H · · · Cl hydrogen bonding, resulting in a 3D structure (Figure 6c). It should be noted that the chloride anion is four-coordinated with two intralayer hydrogen bonded acceptors [(N(2)-H · · · Cl(1) ) 3.141(4) and

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C(22)-H · · · Cl(1c) ) 3.694(5) Å) and one interlayer hydrogen bonding [C(23)-H · · · Cl ) 3.536(5) Å] (Figure 6d). Conclusion The careful selection of metal-H2biim/H2bbim coordination units allowed us to exploit predominantly X-H · · · Cl (X ) N, O, and C) noncovalent charge assisted interactions and to construct supermolecular networks. The chloride anion may act as a multiacceptor varying from 3 to 6, resulting in an important collective contribution to cohesion. The data observed here seem to suggest that a variety of X-H · · · Cl (X ) N, O, and C) synthons play a crucial role in the formation and stabilization of supramolecular architecture, for instance, to link the discrete (0D) or low-dimensional (1D) entities into high-dimensional frameworks. The distances of N · · · Cl vary from 3.10 to 3.29 Å, O · · · Cl from 3.09 to 3.16 Å, and C · · · Cl from 3.49 to 3.69 Å. On the other hand, a coplanar [(H2O)2Cl2]2- guest is encapsulated in cavity formed by four [Co(H2bbim)3]2+ cations and stabilized via accepting 6-fold hydrogen bonds form three H2bbim ligands. The distance from chloride anion to the imidazolyl rings demonstrates the possible existence of Cl · · · π (imidazolyl) charge assisted interactions. It should be noted that the coordination of a positively charged Co(II) ion much enhances the electron-deficient character of the imidazolyl ring and provides sufficient polarization to produce anion-π charge assisted interactions. The work presented here is expected to stimulate research interests in the use of halide complexes as building blocks in crystal engineering. Acknowledgment. This work was supported by the NSF of China (No. 20771104) and Guangdong Province (No. 20623086), the Doctoral Programs Foundation of Ministry of Education of China (No. 20070558009), and the National Foundation for Fostering Talents of Basic Science (No. J0730420). Supporting Information Available: The structural Figures of the complexes 2–6; X-ray crystallographic file in CIF format for 1-6. This material is available free of charge via the Internet at http://pubs.acs.org.

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