Cyano bridged dinuclear Cu(II) complexes

Abstract

The reaction of [CuL(OH2)]2+, where L is one of the tripodal tetradentate ligands, tris(2-pyridylmethyl)amine (tpa) or tris(2-aminoethyl)amine (tren), with cyanide ions, has yielded two cyano-bridged dinuclear copper(II) complexes with composition, [{Cu(tpa)}2(CN)][ClO4]3 (1) and [{Cu(tren)}2(CN)][ClO4]3·H2O (2), and a mononuclear complex, [Cu(tpa)(CN)][ClO4]·3H2O (3). Room temperature single-crystal X-ray studies on 1, the mono(DMF) hemihydrate of 2 and the hemihydrate of 3, have confirmed that the Cu(II) centers in each complex adopt geometries that are close to trigonal bipyramidal (TBP), a feature of Cu(II) complexes of such tripodal tetradentate ligands. The tertiary amine nitrogen is located in an axial position trans to the cyano ligand and the other ligand nitrogens are located within the equatorial plane. In the dinuclear complexes the Cu-CN-Cu bridging moieties deviate slightly from linearity and give the complex a slightly bowed appearance. The Cu⋯Cu distances are ca. 5 Å and the Cu(II) atoms are displaced by ca. 0.3 Å away from the equatorial plane towards the cyano group. Variable temperature magnetic susceptibility studies have confirmed that the cyano bridges mediate antiferromagnetic coupling between the Cu(II) centers with J values of −53.2 and −87.1 cm−1 for 1 and 2, respectively. These values are typical of axially connected TBP cyano Cu(II) complexes and are larger than those found for related complexes connected at equatorial coordination sites.