Spectroscopic, magnetic, and structural properties of diaquadimethanolbis-(N-tosylvalinato)copper(II) and its 2,2′-bipyridine adduct

Abstract

Binary copper(II) compounds of N-tosylvalinate (tosyl = toluene-p-sulphonyl) of formula [{Cu(tsvalO)₂(H₂O)}₂]·4H₂O and [Cu(tsvalO)₂(H₂O)₂(MeOH)₂] were separated. The structure of the latter consists of discrete [Cu(tsvalO)₂(H₂O)₂(MeOH)₂] units in which the copper atom, lying on the symmetry centre, is surrounded by two carboxylic oxygens and two water molecules centrosymmetrically related. Two methanol molecules complete the co-ordination which is elongated tetragonal bipyramidal. The spectroscopic properties are consistent with a CuO₆ chromophore. From its spectroscopic and magnetic properties, a dimeric structure with strong antiferromagnetic exchange (|2J|= 322 cm^–1) is inferred for [{Cu(tsvalO)₂(H₂O)}₂]·4H₂O. The structure of [{Cu(tsvalO)₂(bipy)}₂](bipy = 2,2′-bipyridine) consists of two crystallographically independent dimeric units. In both dimers the co-ordination is distorted tetragonal pyramidal with bipy nitrogens and two carboxylate oxygens of the amino acids in the equatorial plane. In dimer (I) the apex of the pyramid is occupied by a bridging carboxylate oxygen which is basal to the centrosymmetric copper atom in the dimer. In dimer (II) the two copper atoms are connected by two tosylvalinate ions each bridging via an unidentate carboxylate and a sulphonic oxygen. Intermolecular ring-stacking interactions between bipy ligands belonging to two different dimers are present. The large Cu ⋯ Cu′ separation, Cu–O–Cu′ angle, and the e.s.r. spectra suggest that only very weak exchange interactions may be present.