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

Abstract Two new metal complexes of formula {[Co(Hpcpa)(H 2 O) 3 ] n ·3/2 n H 2 O} ( 1 ) and [Cu 2 (MeHpcpa) 4 (MeOH) 2 ]·H 2 O·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) A. 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 carboxylate-oxygens in the basal plane and a methanol molecule in the apical position. The intradimer copper–copper separation is 2.5974(11) A. 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  = − αλ L Co  ·  S Co  +  Δ [L ZCo 2  − 2/3] +  βH (− α L Co  +  g e S Co ) leads to the following set of best-fit parameters: α  = 1.28(1), λ  = −160(5) cm −1 and | Δ | = 400(20) cm −1 . The magnetic properties of 2 show the 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  = − J S 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–syn conformation mode.