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

Two new metal complexes of formula {[Co(Hpcpa)(H2O)3]n·3/2nH2O} (1) and [Cu2(MeHpcpa)4(MeOH)2]·H2O·3.68 MeOH (2) [H3pcpa = N-(4-carboxyphenyl)oxamic acid and MeH2pcpa = methyl ester derivative of H3pcpa] have been synthesized and their structures determined by X-ray diffraction. 1 is a neutral zigzag chain of cobalt(II) ions bridged by Hpcpa2− 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 Hpcpa2− ligand and a carboxylate-oxygen from another Hpcpa2− group building a somewhat distorted octahedral surrounding. The intrachain cobalt–cobalt separation is 11.326(2) Å. 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) Å. 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 = −αλLCo · SCo + Δ[LZCo2 − 2/3] + βH(−αLCo + geSCo) 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 = −JSA·SB]. 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.

The complex formation of Co(II) and Cu(II) ions with the monoethyl ester derivative of the N-(4-carboxyphenyl)oxamic acid yielded different coordination polymers whose structures and variable-temperature magnetic study are presented here.Figure optionsDownload as PowerPoint slide