Structural and magnetic characterization of a novel series of dinuclear Cu(II) complexes bridging by 2,5-pyrazine dicarboxylate

摘要

A new series of dinuclear 2,5-pyrazine dicarboxylato-bridged copper(II) complexes were synthesized and characterized by spectroscopic techniques. The complexes have the general structural formula [Cu-2(L)(2)(mu-pyzdc)](ClO4)(2)center dot nH(2)O where L = TPA, n = 2 (1); L = pmedien, n = 2 (2); L = aepn, n = 3 (3); L = dpt, n = 2 (4); L = Medpt, n = 0 (5); L = dien, n = 0 (6) and L = MeDPA, n = 2 (7) with TPA = tris(2-pyridylmethyl)amine, pmdien = N,N,N',N '',N ''-pentamethyldiethylenetriamine, aepn = N-(2-aminoethyl)-1,3-diaminopropane, dpt = dipropylene-triamine, Medpt = 3,3'-diamino-N-methyldipropylamine, dien = diethylenetriamine, MeDPA = N,N-di(2-pyridylmethyl)methylamine. In these complexes, the bridging nature of the 2,5-pyrazine dicarboxylato ligand (pyzdc) was confirmed by single-crystal X-ray crystallography. The structure of the TPA complex 1 consists of mu-pyzdc bridging two Cu(II) centers in a bis(monodentate) bonding fashion through a single oxygen atom supplied by each carboxylate group of the bridged pyzdc in a distorted trigonal bipyramidal geometry achieved by the four nitrogen atoms from the TPA ligand. In the complexes 25 derived from tridentate amines, the bridged pyzdc acts as a bis( bidentate) ligand in a distorted square pyramidal geometry achieved by one nitrogen and one carboxylate-oxygen of pyzdc, and by the three N- atoms of the amine coligands. The intradimer Cu center dot center dot center dot Cu distances in the complexes 2-5 are in the range 6.97-7.45 angstrom and in it is 10.96 angstrom in 1. The corresponding intermolecular distances are even shorter (5.34-7.99 angstrom). The susceptibility measurements at variable temperatures over the 5-300 K range reveal weak antiferromagnetic coupling with J values ranging from -0.61 to -4.78 cm(-1).