Synthesis and Structural Characterization of Copper(I) and Copper(II) Complexes with an Ambivalent Phenanthroline-Type Ligand

Abstract

The new phenanthroline ligand 2-(p-methoxyphenyl)-9-(5′-methylpyridin-2′-yl)-1,10-phenanthroline L has been synthesized and shown to form four-coordinate Cu^I(L)₂ (1) and six-coordinate Cu^II(L)₂ (2) complexes. Their structures have been determined by X-ray crystallography: (1) C₅₀H₃₈CuN₆O₂.BF₄, triclinic, space group P ^-1, a12·924(3), b 14·567(4), c 12·649(3) Å , α 105·57(2), β 107·68(2), γ 104·00(2)°; (2) C₅₀H₃₈CuN₆O₂.2PF₆, monoclinic, space group P 2₁/c, a 17·701(5), b 19·285(5), c 14·93(4) Å, β 98·20(2)°. In solution, cyclic voltammetry measurements indicate for the copper(I) and copper(II) complexes a very fast rearrangement of the pyridine substituent with the change of the oxidation state. Surprisingly, the X-ray data show two different coordination modes for the ligand around the copper(I) ion, the 1,10-phenanthroline nucleus being either mono- or bi-dentate. In solution, since the ¹H n.m.r. spectra obtained even at several temperatures display only one set of signals, it is proposed that a fast equilibrium takes place between two coordination modes of the phenanthroline