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

Two Cd(HBimc)-based isomers, [Cd(HBimcN)(HBimcT)(H2O)]·3.5H2O·EtOH (1a·3.5H2O·EtOH, H2Bimc=1H-benzimidazole-5-carboxylic acid) and [Cd(HBimcN)(HBimcT)(H2O)] (1b), and two Cu(HMBimc)-based coordination polymers, [Cu(HMBimcN)2(H2O)]·1/2H2O (2·1/2H2O, H2MBimc=2-methyl-1H-benzimidazole-5-carboxylic acid) and [Cu(HMBimcT)2]·2THF·H2O (3·2THF·H2O), were self-assembled from Cd(ClO4)2·6H2O/H2Bimc and Cu(ClO4)2·6H2O/H2MBimc systems, respectively. Compound 1a adopts a ladder-like chain structure, comprised of a hydrogen-bond-stabilized Cd2(HBimcN)2-metallocyclic stair and a 1D straight –(Cd–HBimcT)n– edge, whereas compound 1b exhibits a 2D (4,4)-rhombus layered structure, intercrossed by 1D –(Cd–HBimcN)n– chains and –(Cd–HBimcT)n– chains. Compound 2 shows a 1D double-stranded wave-like chain from two single-stranded wave-like –(Cu–HMBimcN)n– chains and compound 3 adopts a 2D (4,4)-topological layer structure, intercrossed by subunits of 1D –(Cu–HMBimcT)n– chains. Interestingly, a pair of tautomeric HBimc building blocks—normal (N or HBimcN) and tautomer (T or HBimcT)—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.