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

Abstract

The copper(II) complexes of formula [Cu 2(2,5-dpp)(H 2O) 4(CF 3SO 3) 4] · 2H 2O ( 1) and [Cu 2(2,5-dpp)(H 2O) 2(tcnoet) 4] n ( 2) [2,5-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 CuN 2O 4 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 CuN 5O 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) Å ( 2) whereas that through the double tcnoet bridge is 9.559(1) Å ( 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 1 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.