Magnetism and structure in a series of halogen and hydroxo-bridged binuclear copper(II) diazine complexes. Structure of a dibromobridged derivative [Cu2(C14H10N4S2)Br4]

Abstract

The ligand PTP (3,6-bis(2-pyridylthio)pyridazine) generates both hydroxo- and halogeno-bridged, square-pyramidal, binuclear copper(II) complexes ([Cu2(PTP)X4] (X = Cl (I), Br (II)); [Cu2(PTP)(OH)X3] (X = Cl (IV), Br (V)), which are antiferromagnetically coupled. The hydroxo-bridged derivatives are more strongly coupled than those with just halogen bridges and within each pair of complexes substantially increased spin exchange is observed for the bromo-derivatives (−2J = 130.5 ± 0.4 (I), 243.5 ± 0.3 (II), 294 ± 3 (IV), 326 ± 6 (V) cm−1). A related halogen-bridged derivative [Cu2(PAP46Me)Cl4] (III) (PAP46Me = 1,4-di(4,6-dimethyl-2-pyridylamino)phthalazine) exhibits much weaker spin exchange associated with the diminished superexchange capacity of the phthalazine bridge compared with pyridazine (−2J = 55 ± 0.1 cm−1). An X-ray study on [Cu2(PTP)Br4] reveals an asymmetric tribridged structure involving a pyridazine and two bromo-bridges with a copper–copper separation of 3.318(3) Å, one relatively short terminal copper–bromine bond (2.375(3), 2.398(3) Å), and a short and long copper–bromine bridging contact (2.380(3), 2.801(3); 2.414(3), 2.766(3) Å) per copper. The complex formed green crystals with a = 11.1042(18), b = 15.6554(10), c = 12.6058(14) Å, β = 113.485(11)°, P21/c, Z = 4, Rf = 0.045.