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

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 single-crystal 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.