Synthesis, structure and magnetism of a linear Cu-Cl-Cu entity found in [(Cu(tachH)(tach))(2)(mu-Cl)]

Coordination of cis, trans-1,3,5-triaminocyclohexane (tach) to copper(II) at pH 11 in the presence of chloride ions results in the formation of a mu(2)-chloro-linked dimer of Cu(tach)(2) units, which was characterized by single-crystal X-ray analysis, UV/Vis and IR spectroscopy, elemental analysis and magnetic measurements. Within the Cu(tach)(2) halves, the structurally rigid, chelating tach ligands are oriented syn to each other and each ligand binds to the copper center via two amino groups, forming a near-square planar coordination environment. Under the present reaction conditions, half of the tach ligands are protonated at the pendant, non-coordinated amino group. The Cu(tach)2 halves are joined in a D-2h-symmetric fashion. This complex is of special interest as only few Cull dimers based on a single linear Cu-Cl-Cu motif are known. For the first time a magnetochemical analysis of such a species is provided that characterizes the weak antiferromagnetic intramolecular interactions between the two s = 1/2 Cu-II centers. (c) 2005 Elsevier Ltd. All rights reserved.