Ligand steric effect on the coordination mode of nitrite ion: Syntheses and X-ray single crystal structures of trans-[NiL2(ONO)2] and cis-[NiL′2(O2N)](NO2)·H2O [L = 2-(aminomethyl)pyridine and L′ = (2-aminoethyl)pyridine]

The steric effects of the co-ligands originated from the pi-cloud of the pyridine moiety and from increased aliphatic chain length have been utilized to synthesize two different binding modes of nitrite ion. A red-violet nitrito isomer trans-[NiL2(ONO)2] (1) and a blue-violet nitrito (O,O) isomer cis-[NiL′2(O2N)](NO2)·H2O (2) are obtained by adding L and L′ to the methanolic suspension of K4[Ni(NO2)6]·H2O [L = 2-(aminomethyl)pyridine and L′ = 2-(aminoethyl)pyridine]. No other isomer of complex 1 or 2 is yielded in solution irrespective of the nature of the solvent used or in the solid state. They have been characterized by routine physicochemical studies as well as by X-ray single crystal structure analysis.