The synthesis and crystal structures of new 2-aminomethylbenzimidazole Zinc(II) complexes exhibiting luminescence

Two new blue luminescent Zn(II) complexes, [ZnL2(H2O)]Cl-2 center dot H2O (1) and [ZnL2Cl][ZnLCl2] center dot NO3 (2) (L = 2-aminomethylbenzimidazole) have been synthesized and characterized spectroscopically and crystallographically. The structure of complex (1) can be described as a square pyramid. In the complex (2), there are two units [ZnLCl2] (a), and [ZnL2Cl](+) (b), which have a distorted tetrahedral geometry and a slightly distorted trigonal bipyramidal coordination geometry, respectively. In these complexes, significant multiple inter- and intra-molecular hydrogen bonding and pi-pi stacking interactions are shown. These contacts lead to aggregation and supramolecular assembly of complexes (1) and (2) into 3D and 2D frameworks, respectively. Fluorescent analysis in the dilute DMF solution and solid state shows that both complexes exhibit intense emission in blue region. They display high blue luminescence quantum efficiency due to a metal-to-ligand charge transfer (MLCT) and have a bathochromic shift of the emission energy compared with the free ligand L. The emission intensity of complex (2) is higher than that of complex (1).