Syntheses and coordination studies of 2-(diphenylphosphinomethyl)pyridine N,P dioxide with Co2+, Ni2+, Cu2+ and Zn2+ tetrafluoroborate

Several new coordination complexes of Co2+, Ni2+, Cu2+ and Zn2+ were synthesized by the reaction of their corresponding tetrafluoroborate salts with 2-(diphenylphosphinomethyl)pyridine N,P dioxide, L. All structures were determined by single-crystal X-ray crystallography showing an octahedral environment around the metal centers. Single crystals of M(BF4)2L2(S)2 (M = Co2+, Ni2+ or Zn2+; S = MeOH or CH3CN) were obtained at −5 °C by slow diffusion of ether into solutions of these complexes. When these crystals were re-dissolved in methanol and allowed to grow again at room temperature using the same technique and solvent system, the product obtained presented a 3:1 ratio ligand-to-metal. The complex [Cu(BF4)2L2(MeOH)](BF4), exhibits two units of L, one molecule of MeOH and one counter-anion coordinated to the Cu2+ center. This can be attributed to the steric restrictions generated by the lower symmetry in this complex, a product of significant Jahn–Teller effects, which favors a long range interaction between the metal center and a less coordinative counter-anion, compared to a MeOH unit. A 1:1 ligand-to-metal ratio complex of Ni2+ was also obtained by allowing the starting materials to react for only a short time. Attempts to obtain single crystal of complexes of Co2+, Cu2+ or Zn2+ in a 1:1 ratio were not successful. The resulting 3:1 ligand-to-metal products were fully characterized by elemental analysis, UV–Vis spectroscopy and FT-IR spectroscopy.