Cobalt(II) and copper(II) assembling through a functionalized oxamate-type ligand

Two new metal complexes of formula {[Co(Hpcpa)(H2O)(3)](n)center dot 3/2nH(2)O} (1) and [Cu-2(MeHpcpa)(4)(MeOH)(2)] center dot H2O center dot 3.68 MeOH (2) [H(3)pcpa = N-(4-carboxyphenyl)oxamic acid and MeH(2)pcpa = methyl ester derivative of H(3)pcpa] have been synthesized and their structures determined by. X-ray diffraction. 1 is a neutral zigzag chain of cobalt(II) ions bridged by Hpcpa(2-) ligands exhibiting the bidentate/monodentate coordination mode. Each cobalt(II) ion is six-coordinate with three mer positioned water molecules, two oxamate-oxygens from a Hpcpa(2-) ligand and a carboxylate-oxygen from another Hpcpa(2-) group building a somewhat distorted octahedral surrounding. The intrachain cobalt-cobalt separation is 11.326(2) angstrom. The structure of 2 consists of discrete syn-syn tetracarboxylate-bridged dicopper(II) units of the paddle wheel-type, the oxamate fragment of the MeHpcpa ligand being not involved in the coordination. Each copper(II) ion is five-coordinate in a distorted square pyramidal environment with four carboxylateoxygens in the basal plane and a methanol molecule in the apical position. The intradimer copper-copper separation is 2.5974(11) angstrom. The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9-300 K. The magnetic behavior of 1 corresponds to that of a magnetically isolated high-spin cobalt(II) ion with an important orbital contribution. The analysis of its magnetic data through the Hamiltonian, H = -alpha lambda L-Co.S-Co + Delta[L-ZCo(2) - 2/3] + beta H(-alpha L-Co + g(e)S(Co)) leads to the following set of best-fit parameters: alpha = 1.28(1), lambda= -160(5) cm(-1) and vertical bar Delta vertical bar = 400(20) cm(-1). The magnetic properties of 2 showthe occurrence of a strong antiferromagnetic interaction between the two local spin doublets which lead to a ground singlet spin state [J = -315(2) cm(-1), the Hamiltonian being defined as H = -JS(A).S-B]. This value is in the upper range of those previously reported for the large family of tetracarboxylate-bridged dicopper(II) complexes, the exchange pathway being provided by the four carboxylate bridges in the syn-syri conformation mode. (C) 2014 Elsevier Ltd. All rights reserved.