Pseudohalide supported mononuclear trans-NiII complexes of cationic and neutral dinitrogen heterocycles

Two mixed ligand complexes trans-[Ni(NCS)4(PpzH)2] (1) and trans-[Ni(NCO)2(Imd)4] (2) (where Ppz = piperazine; Imd = imidazole) were synthesized from one-pot reactions, and their crystal and molecular structures were determined. The reaction of NiCl2·4H2O with piperazine and KSCN in a 1:2:4 mole ratio in aqueous MeOH at room temperature under stirring condition affords 1. Whereas the reaction of NiCl2·6H2O with imidazole and NaOCN in a 1:4:2 mole ratio in aqueous MeOH at room temperature under stirring condition yields 2 quantitatively. The nickel ions are hexacoordinated by six nitrogen donor atoms of two different origin, thiocyanate and piperazinium ions in case of 1 and cyanate ion and neutral imidazole in case of 2, to form tetragonally elongated and quite regular octahedral arrangements. In 1, the average Ni–Nppz distance is 2.198 Å is longer than the average Ni–Nthc distance at 2.070 Å, whereas, in case of 2, the average Ni–Nimd distance at 2.112 Å and is close to the average Ni–Ncyt distance at 2.107 Å. The reactions in other varying stoichiometries failed to provide the hitherto unknown complexes [Ni(NCS)2(Ppz)4] and [Ni(NCO)4(ImdH)2] confirming the ease of protonation on non-bonding of piperazine is more compared to that of imidazole.