Five-co-ordination with ‘hybrid’ ligands. Part V. Cobalt(II) and nickel(II) complexes with tetradentate ligands containing nitrogen and phosphorus or arsenic as donor atoms

Abstract

Four tripod-like ‘hybrid’ ligands (L) with donor sets N₃P, N₃As, N₂P₂, and N₂As₂ have been synthesized. They form cobalt(II) and nickel(II) complexes of general formula [MLX]Y (X = Cl, Br, I, CN, or NCS; Y = BPh₄ or I) and [ML(NCS)₂]. The cobalt(II) complexes are high-spin five-co-ordinate. The nickel(II) complexes with ligands N₃P and N₃As are either high-spin five-co-ordinate or low-spin, probably square-planar. With the ligand N₂P₂, low-spin, five-co-ordinate nickel(II) complexes are formed. The magnetic cross-over point for five-co-ordinate complexes of nickel(II) is found on changing from the N₃PX to the N₂P₂X donor set. In the bisthiocyanato-complexes with N₃P and N₃As the phosphorus and arsenic atom are un-co-ordinated. The octahedral [Ni(N₂As₂)(NCS)₂] complex gives rise to an equilibrium between octahedral and five-co-ordinate species in solution.