Copper(II) complexes with 2,5-bis(2-pyridyl)pyrazine and 1,1,3,3-tetracyano-2-ethoxypropenide anion: Syntheses, crystal structures and magnetic properties

The copper(II) complexes of formula [Cu-2(2,5-dpp)(H2O)(4)(CF3SO3)(4)] center dot 2H(2)O (1) and [Cu-2(2,5-dpp)(H2O)(2)(tcnoet)(4)](n) (2) 12,5-dpp = 2,5-bis(2-pyridyl)pyrazine and tcnoet(-) = 1,1,3,3-tetracyano-2-ethoxypropenide anion] have been prepared and their structures determined by X-ray crystallographic methods. Compound 1 is a dinuclear complex where the 2,5-dpp molecule acts as a bis-bidentate bridge between the two copper centers, the electroneutrality being achieved by four terminally bound triflate anions. Each copper(II) ion presents an elongated octahedral CuN2O4 environment with two nitrogen atoms from 2,5-dpp and two water molecules in the basal plane and two triflate-oxygen atoms in the axial positions. Compound 2 is a zigzag chain of copper(II) ions with regular alternating 2,5-dpp and double tcnoet groups as bridges. Each copper(II) ion exhibits an elongated octahedral CuN5O surrounding with four nitrogen atoms, two from 2,5-dpp, one from a terminally bound tcnoet and the other from a bridging tcnoet occupying the equatorial positions and a water oxygen and a nitrogen from a monodentate tcnoet in the axial sites. The values of the copper-copper separation across 2,5-dpp are 6.763(1) (1) and 6.754(1) angstrom (2) whereas that through the double tcnoet bridge is 9.559(1) angstrom (2). The investigation of the magnetic properties of 1 and 2 in the temperature range 1.9-295 K reveal a Curie law behaviour for I and a very weak ferromagnetic interaction for 2. The poor ability of the 2,5-dpp ligand to mediate magnetic interactions between the copper(II) ions in the 2,5-dpp-bridged copper(II) complexes contrast with the somewhat better ability of the pyrazine ring in related pyrazine-bridged copper(II) complexes. (C) 2009 Elsevier Ltd. All rights reserved.