New 2-methyl benzimidazole based zinc carboxylates: Supramolecular structures, biomimetic proton conductivities and luminescent properties

Abstract

Two new supramolecular zinc frameworks, [Zn(2-MeBIM)2(OAc)2]·3H2O (1) and [[Zn(2-MeBIM)(Pht)(H2O)]·2H2O]n (2) (where 2-MeBIM=2-methyl benzimidazole, OAc=acetate anion and Pht=dianion of phthalate), were crystallized, and structurally examined. Complex 1 has been characterized to be a discrete molecule, composed of OAc and 2-MeBIM ligands. Whereas, the 2 is identified to be a 1D coordination polymer, due to the μ2-1-6 bridging action of Pht ligand. Each Zn(II) on the chain, further possesses one coordinated water, and one 2-MeBIM. Complex 2, additionally exhibits the carboxylate⋯imidazole–zinc triads as well. Hydrogen bonds align the water molecules of the complexes, through which the respective molecular species are integrated into 3D architectures. Supramolecular features of the complexes resemble those of the zinc enzymes, involved in proton transport based mechanistic events. Hence they are regarded as bio-inspired models for proton conducting applications. AC impedance studies, as anticipated, reveal the humidity based proton conduction characteristics of the complexes, with magnitudes comparable to the level of other classical proton electrolytes. Proton conduction and fluorescence behaviors of the complexes are discussed in relation with the X-ray structural aspects. Hence, the present work, perhaps for the first time, reports the functional characteristics of the bio-relevant and environmentally benign model complexes.