Synthesis, characterization and crystal structures of Cd(II) and Zn(II) complexes with 2,2′-biimidazole

The reactions of zinc and cadmium salts with 2,2'-biimidazole (H(2)biim) yielded a series of compounds in which the ligand is coordinated in the chelating bidentate mode. ZnCl2 and [Ag(H(2)biim)](NO3) in methanol in a 2:1 proportion produced Zn(H(2)biim)Cl-2, in which the metal has a distorted tetrahedral coordination. A 1:2 ratio led to [Zn(H(2)biim)(2)(CH3OH)(2)](NO3)(2), containing an octahedrally coordinated Zn(II) center with the O-bonded methanol ligands occupying trans positions. The corresponding [Cd(H(2)biim)(2)(CH3OH)(2)](NO3)(2) compound was obtained from CdCl2. By starting with Cd(NO3)(2) and Cd(ClO4)(2) in aqueous media, the related octahedral bis-chelate compounds [Cd(H(2)biim)(2)(NO3)(H2O)](NO3) and Cd(H(2)biim)(2)(ClO4)(2), respectively, were isolated, the apical positions being filled by perchlorate oxygens in the latter case. With Cd(BF4)(2), the glass container participated in the reaction and a tris-chelate complex [Cd(H(2)biim)(3)](2)(SiF6)(BF4)(2) center dot 6EtOH was isolated. The [Cd(H(2)biim)(3)](2+) and SiF62- ions define an extended hydrogen-bonded network, in which BF40 ions surrounded by disordered ethanol molecules occupy large cavities. The two free N-H groups provide H(2)biim with a unique ability to form hydrogen bonds and their interactions with counter anions or other acceptors play a determining role in controlling molecular packing. The IR spectra of all compounds are discussed. (C) 2006 Elsevier B.V. All rights reserved.