Copper(II) complexes of hydroquinone-containing Schiff bases. Towards a structural model for copper amine oxidases

Complexation of the preformed ligand 2,5-dihydroxy-N-{pyridin-2-ylmethyl}-b enzylideneamine (HL1) with hydrated Cu(BF4)(2) afforded [{Cu(mu-L-1)}(2)][B F4](2) 1. The crystal structure of 1 . MeNO2 shows a dimer of near-planar c opper(II) ions, with a bridging apical BF4- anion. Variable temperature sus ceptibility measurements showed the copper(II) ions in 1 to be moderately a ntiferromagnetically coupled. The complexes [CuL2]X (X-=ClO4- 2, NO3- 3, Cl - 4 or NCS- 5) and [CuL3]ClO4 (6; HL2=N-{pyridin-2-ylmethyl}-N'-{2,5-dihydr oxybenzylidene}-1,2-diaminoethane, HL3=N-{pyridin-2-ylmethyl}-N'-{2,4,5-tri hydroxybenzylidene}-1,2-diaminoethane) have been prepared by template conde nsation of N-(pyridin-2-ylmethyl)-1,2-diaminoethane with the appropriate be nzaldehyde derivative and copper salt. The single crystal structure of 2 sh ows a near-planar four-co-ordinate copper(II) centre, with a non-co-ordinat ed ClO4- anion. The chelate ligand backbone is disordered over two orientat ions, which correspond to different patterns of intermolecular hydrogen bon ding in the lattice. UV/vis and EPR data in dmf solution suggest that 2-6 a ll undergo solvolysis to form an identical [CuL(dmf)(x)](+) (x=0-2) species in solution. Cyclic voltammograms of HL1 and 1-6 are complex, and demonstr ate rapid acid-catalysed decomposition of the benzoquinonecarbaldimine liga nd oxidation products.