Structure, magnetism and catecholase activity of the first dicopper(II) complex having a single μ-alkoxo bridge

Pyridine-2,6-dimethanol (H2L), which is a versatile donor has a neutral, monoanionic and dianionic coordination behaviour with two different coordination modes viz. tridentate and bidentate towards Cu(II), leading to three different geometric environments around Cu(II) centers. The single crystal X-ray structure reveals two different Cu(II) complexes with H2L: in the first case ClO4- forms a polymer through intermolecular H-bonding, [Cu(H2L)(HL)]ClO4 (1) while the other one is the first report of a mono mu-alkoxo bridged dicopper(II) complex, [Cu(H2L)(HL) Cu(L)]+(2). The crystallographic asymmetric unit of 2 contains a mononuclear cation [Cu(H2L)(HL)]+ and a dinuclear [Cu(H2L)(HL) Cu(L)]+ unit along with two perchlorate anions, formulated as [Cu(H2L)(HL)][Cu-2(H2L)(HL)(L)] (ClO4)(2). The magnetic characterization of 2 shows a very weak antiferromagnetic coupling between the Cu(II) centers in the dinuclear unit. This is the first report on the magnetic characterization of the first mono alkoxo-bridged dinuclear Cu(II) complex and, hence needs further examples to firmly establish magneto-structural correlations. The efficient catecholase activity of 2 (k(cat) -2.08 x 10(4) h(-1)) is attributed to the presence of a mono mu-alkoxo bridge, which holds two Cu(II) centers similar to 3.26 angstrom apart and possibly facilitates the binding of catecholate during the electron transfer reaction. Moreover, the Cu-2 center is square planar, and provides one free position for coordination by the substrate molecule.