The structure of a dinuclear copper(I) complex of a Schiff-base ligand containing a copper–copper bond

Abstract

The copper(I) complex [Cu₂L²₂][ClO₄]₂·H₂O [L²= 2,6-di(2′-methoxyethyliminomethyl)pyridine] has been prepared by reaction of [Cu(MeCN)₄][ClO₄] with the open-chain Schiff base ‘N₃O₂’ ligand L² derived from the condensation of one molecule of 2,6-diformylpyridine with two molecules of 1-amino-2-methoxyethane. Crystals of [Cu₂L²₂][ClO₄]₂·H₂O are monoclinic with a= 20.221 (8), b= 16.239(7), c= 11.345(8)Å, β= 102.2(1)°, Z= 4, and space group P2₁/n. In the dimeric cation the two copper atoms are directly linked by a Cu–Cu bond of length 2.626(1)Å. In contrast to other metal complexes of pyridyldi-imine ligands the inequivalent copper atoms in the present structure are not bonded to all three nitrogen atoms of the same trimethine group and, moreover, all four imine groups are severely twisted out-of-plane with respect to their respective pyridine rings. Each copper atom is strongly bonded to two imino-nitrogen atoms, one from each ligand molecule. Cu(1) is also weakly bound to two ether oxygens, one from each ligand. The remaining two ether oxygen atoms are not co-ordinated. An unusual feature of the structure is that the pyridine nitrogen atoms appear to act as (asymmetric) bridges between the metal centres [Cu(1)–N, 2.693(6), 2.676(6)Å; Cu(2)–N, 2.237(6), 2.204(6)Å]. I.r. and ¹H n.m.r. spectra in CD₃CN of the free ligand and complex are compared. Evidence from electronic spectra suggests that the integrity of the dimeric unit is largely retained in solution.