Synthesis, crystal structure, and quasi-reversible dioxygen binding of [Cu2(tpmc)]X2[tpmc = 1,4,8,11-tetrakis(2′-pyridylmethyl)-1,4,8,11-tetra-azacyclotetradecane; X = ClO4, PF6, or CF3SO3]

Abstract

Dicopper(I) complexes of tpmc [1,4,8,11-tetrakis(2′-pyridylmethyl)-1,4,8,11-tetra-azacyclotetradecane] have been synthesized. The complexes reacted with dioxygen at low temperature (below –60 °C) to form two species of adduct quasi-reversibly, which were characterized by Resonance Raman spectra (¹⁶O–¹⁶O stretching at 820 and 771 cm^–1 and Cu–¹⁶O stretching at 529 and 491 cm^–1 which shifted to lower energy when ¹⁸O₂ was substituted for ¹⁶O₂). From an acetone solution of the dioxygen adducts bis(pyridine-2-carboxylato)copper(II) was isolated. The molecular structure of the dicopper(I) complex [Cu₂(tpmc)][CF₃SO₃]₂ was determined by X-ray diffraction analysis. The complex crystallizes in the monoclinic space group P2₁/n with a= 14.341(4), b= 15.392(4), and c= 9.700(2)Å, β= 93.95(2)°, and Z= 2, and the structure was refined to R= 0.055 and R′= 0.058. The complex cation has a centre of symmetry and each copper atom is co-ordinated by one nitrogen of the macrocyclic ring and two pendant pyridyl nitrogens forming a distorted trigonal plane with a Cu ⋯ Cu separation of 6.739(2)Å.