Solid and ethanolic solution state behavior of N-tosylglycinatecopper(II) system

In the copper(II) ionN-tosylglycinate system, in both the solid state and in aqueous solution, it was suggested that the ligand presents the properties of both L-α-amino acids [1] and their N-acetyl or N-benzoyl-derivatives [2] depending on the pH of the media [3]. In this paper we report an investigation on the same system in ethanolic solution in order to compare the coordination behavior of this amino acid with those of N-acetyl and N-benzoyl-amino acids also in this media. From ethanolic solution two compounds of formula [Cu(TsglyH)2]n (green) and Na2[Cu(Tsgly)2] (blue) (TsglyH and Tsgly = N-tosylglycinate monoanion and dianion, respectively) were isolated. In the latter complex, which is similar to a compound previously separated from aqueous solution, the ligand acts as bidentate through the carboxylate oxygen atom and the deprotonated sulphonic nitrogen atom. For the green compound the crystal structure was also determined. Crystals are monoclinic, space group P21/n, with Z = 4 in a unit cell of dimensions: a = 24.655(3), b = 7.697(2), c = 12.378(3) A, and β = 87.34(8)°, and R = 0.052. The structure (Fig.1) is built up of one dimensional polymeric chains of binuclear units, showing the cupric acetate structure, linked via CuO (sulphonic) bonds. Its magnetic and spectroscopic properties are interpreted on the basis of the crystal structure. The exchange integral (−2J) is 353 ± 4 cm−1. In ethanolic solution at metal ion concentrations similar to those normally found in biological systems, by polarographic measurements, for CNaOH/CComplex ratios between 1 and 3 the Cu(TsglyH)2 species is the only present, while for ratios greater than 4 the Cu(Tsgly)2−2 prevails. The main conclusions from this work are: In ethanolic media the N-tosylglycine parallels the behavior in aqueous solution, even if more complicated equilibria are present in this last solvent. The separation of only two solid compounds from ethanol with respect to the four from aqueous solution also confirm this. These results, and those previously observed for the N-acetyl and N-benzoyl-amino acids [2], suggest as a general rule that the ethanolic media enhances the behavior as simple carboxylate ligands of these amino acids, favouring the separation of compounds which possess dimeric arrangement of the copper(II) acetate type with strong antiferromagnetic exchange. Nevertheless, in the N-tosylglycinatecopper(II) ion system in ethanolic solution in the experimental conditions (i.e. at metal ion concentrations close to those of biological systems), there is no evidence for a binuclear species.