Syntheses, crystal structures and magnetic properties of di-and trinuclear croconato-bridged copper(II) complexes

摘要

The new croconato-bridged copper(II) compounds [Cu_2(terpy)_2(H_2O)_2(C_5O_5)](NO_3)_2·H_2O (1) and [Cu_3(phen)_5(C_5O_5)_2](CF_3SO_3)_2 (2) [C_5O_5~(2-) = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione; terpy = 2,2':6'.2"-terpyridine; phen = 1,10-phenanthroline) have been prepared, and their crystal structures and variable temperature magnetic susceptibilities determined. The structure of complex 1 consists of croconato-bridged dinuclear [Cu_2(terpy)_2(H_2O)_2(C_5O_5)]~(2+) complex ions, nitrate counter ions and water of hydration. The croconato ligand exhibits an asymmetrical bis-bidentate coordination mode through four of its five oxygen atoms. The two crystallographially independent copper atoms have similar coordination geometries: elongated, distorted octahedral with three terpyridyl nitrogen atoms and one croconate oxygen atom in the equatorial plane, and a second croconate oxygen atom and a water molecule in the axial positions, the stronger axial interaction in each case being to the water molecule. The intramolecular copper-copper separation across the croconate bridge is 6.852(1) A. The structure of complex 2 is built of croconato-bridged trinuclear [Cu_3(phen)_5(C_5O_5)_2]~(2+) complex ions and triflate counter ions. The terminal copper atoms [Cu(1) and Cu(la)] have, to the first approximation, a square pyramidal coordination geometry with one croconate oxygen and three phen nitrogen atoms in equational positions, and a fourth phen nitrogen atom in the apical position. A second semi-coordinated croconate oxygen atom is located in the remaining axial position. The central copper atom [Cu(2)] is elongated octahedral with two croconate oxygen and two phen nitrogen atoms in equatorial positions, and two oxygen atoms,one from each croconate group, in axial positions. The croconate ligand in 2 adopt an unusual asymmetrial bis-bidentate bridging mode involving three adjacent oxygen atoms, the copper-copper separation across this bridge being 4.177(A). Variable temperature magnetic susceptibility measurements show the occurrence of weak [J = - 2.94 cm~(-1) (1)] and intermediate [J = - 47.1 cm~(-1) (2)] intramolecular antiferromagnetic interactions across the bridging croconato. These values are analyzed in the light of their structures and compared with those previously reported for the parent compounds.