Dinuclear copper(II) and copper(I) complexes of tetradentate (N 4)thio-diazine ligands; synthetic, structural, magnetic and electrochemical studies. In situ oxidation of copper(I) complexes to produce dinuclear hydroxo-bridged copper(II) complexes

Abstract

Hydroxo-bridged dinuclear copper(II) complexes of the tetradentate diazine ligand PTPH (1,4-di-(2′-pyridylthio)- phthalazine) [(Cu 2(PTPH)(OH)X 3) (X=Cl ( I), Br ( II)) were synthesized by the aerial oxidation of copper(I) complexes, prepared in situ. A dinuclear copper(I) perchlorate complex of PTPH [Cu 2(PTPH) 2](ClO 4) 2·2CH 3CN ( III) was also isolated, which involved two adjacent tetrahedral copper(I) centers bound between two tetradentate ligands. I crystallizes in the monoclinic system, space group P2 1/ n, with a=11.065(2), b=12.907(6), c=20.053(2) Å, β=90.59(1)°, and four formula units per unit cell. III crystaltizes in the triclinic system, space group P 1 , with a=11.220(4), b=11.397(3), c=10.561(3) Å, α=92.92(2), β=115.32(2), γ=108.22(2)° and two formula units per unit cell. Attempts to synthesize hydroxo-bridged complexes in aqueous medium were unsuccessful, and in basic medium resulted in the decomposition of the ligand. This was confirmed by the preliminary X-ray structure of the product of the reaction of PTPH with CuCl 2 in MeOH/NEt 3, which indicated the ligand fragment to be 1- methoxy-4-(2′-pyridylthio)phthalazine (PTPO) in a unique structural arrangement involving three different mononuclear copper(II) centers in [Cu(PTPO) 2(H 2O)][CuCl 4][Cu(PTPO)Cl 2]·2.8H 2O ( IV). IV crystallizes in the monoclinic system, space group P2 1/ c, with a=15.386(6), b=25.248(7), c=13.95(2) Å, β=110.71(5)° and four formula units per unit cell. The dinuclear copper(II) complexes have low room temperature magnetic moments and variable temperature magnetic measurements show moderately strong antiferromagnetic coupling (−2 J>360 cm −1). Compounds I and II exhibit two-electron reduction steps at positive potentials 0.41–0.43 V (versus SCE) to produce rearranged dinuclear copper(I) species.