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

The copper(II) complexes of formula [Cu2(2,5-dpp)(H2O)4(CF3SO3)4] _ 2H2O (1) and [Cu2(2,5-dpp (H2O)2(tcnoet)4]n (2) [2,5-dpp = 2,5-bis(2-pyridyl)pyrazine and tcnoet_ = 1,1,3,3-tetracyano-2-ethoxypropenideanion] have been prepared and their structures determined by X-ray crystallographicmethods. Compound 1 is a dinuclear complex where the 2,5-dpp molecule acts as a bis-bidentate bridgebetween the two copper centers, the electroneutrality being achieved by four terminally bound triflateanions. Each copper(II) ion presents an elongated octahedral CuN2O4 environment with two nitrogenatoms from 2,5-dpp and two water molecules in the basal plane and two triflate-oxygen atoms in theaxial positions. Compound 2 is a zigzag chain of copper(II) ions with regular alternating 2,5-dpp and doubletcnoet groups as bridges. Each copper(II) ion exhibits an elongated octahedral CuN5O surroundingwith four nitrogen atoms, two from 2,5-dpp, one from a terminally bound tcnoet and the other from abridging tcnoet occupying the equatorial positions and a water oxygen and a nitrogen from a monodentatetcnoet 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 ofthe magnetic properties of 1 and 2 in the temperature range 1.9–295 K reveal a Curie law behaviour for 1and a very weak ferromagnetic interaction for 2. The poor ability of the 2,5-dpp ligand to mediate magneticinteractions between the copper(II) ions in the 2,5-dpp-bridged copper(II) complexes contrast withthe somewhat better ability of the pyrazine ring in related pyrazine-bridged copper(II) complexes.