Rare configuration of tautomeric benzimidazolecarboxylate ligands in cadmium(II) and copper(II) coordination polymers

Abstract

Two Cd(HBimc)-based isomers, [Cd(HBimc N )(HBimc T )(H 2O)]·3.5H 2O·EtOH ( 1a·3.5H 2O·EtOH, H 2Bimc=1 H-benzimidazole-5-carboxylic acid) and [Cd(HBimc N )(HBimc T )(H 2O)] ( 1b), and two Cu(HMBimc)-based coordination polymers, [Cu(HMBimc N ) 2(H 2O)]·1/2H 2O ( 2·1/2H 2O, H 2MBimc=2-methyl-1 H-benzimidazole-5-carboxylic acid) and [Cu(HMBimc T ) 2]·2THF·H 2O ( 3·2THF·H 2O), were self-assembled from Cd(ClO 4) 2·6H 2O/H 2Bimc and Cu(ClO 4) 2·6H 2O/H 2MBimc systems, respectively. Compound 1a adopts a ladder-like chain structure, comprised of a hydrogen-bond-stabilized Cd 2(HBimc N ) 2-metallocyclic stair and a 1D straight –(Cd–HBimc T ) n – edge, whereas compound 1b exhibits a 2D (4,4)-rhombus layered structure, intercrossed by 1D –(Cd–HBimc N ) n – chains and –(Cd–HBimc T ) n – chains. Compound 2 shows a 1D double-stranded wave-like chain from two single-stranded wave-like –(Cu–HMBimc N ) n – chains and compound 3 adopts a 2D (4,4)-topological layer structure, intercrossed by subunits of 1D –(Cu–HMBimc T ) n – chains. Interestingly, a pair of tautomeric HBimc building blocks—normal ( N or HBimc N ) and tautomer ( T or HBimc T )—is simultaneously included in the structures of 1a and 1b, whilst the N - and T -configured HMBimc building blocks are present as separate entities in Cu species, 2 and 3, respectively. The existence of only a tautomer ( T ) mode of the benzimidazolecarboxylate-based ligand in a Cu(II) network is observed for the first time.