Dicadmium complexes bearing tetradentate formamidinate ligands with triple helical structures

Reactions of Cd(NO3)2·4H2O with bis(2-pyridyl)formamidine (HDpyF) and bis(6-methyl-2-pyridyl)formamidine (HDMepyF) in CH3OH afforded the dinuclear products, [Cd2(DpyF)3][Cd(NO3)4]0.5 (1), and [Cd2(DMepyF)3](NO3) (2), respectively. Their structures were determined by X-ray crystallography. Complex 1 crystallized in two different space groups with different packing solvents. Both the DpyF− and DMepyF− ligands are coordinated to the Cd atoms in new tetradentate fashions, forming two chelating and four bridging bonding modes. Each cadmium metal center of the cations is tris-chelated and strongly distorted from octahedral coordination due to the small bite of the DpyF− and DMepyF− ligands. The molecules of the cations are chiral due to the ligand constraints. They are the first dicadmium complexes bearing formamidinate ligands with triple helical structures.