Copper co-ordination to thioether ligands: crystal and molecular structures of bis(2,5-dithiahexane)copper(II) bis(tetrafluoroborate) and bis(3,6-dithiaoctane)copper(I) tetrafluoroborates

Abstract

The crystal and molecular structures of two copper–thioether complexes, (1) bis(2,5-dithiahexane)copper(II) bis(tetrafluoroborate) and (2) bis(3,6-dithiaoctane)copper(I) tetrafluoroborate, have been determined by single-crystal X-ray diffraction techniques, from diffractometer data. The red crystals of (1) are monoclinic, a= 8.082(3), b= 10.282(3), c= 11.893(4)Å, β= 115.3°, space-group P2₁/c, with Z= 2. The colourless crystals of (2) are orthorhombic, a= 14.581(2), b= 13.421(2), and c= 10.781(2)Å, space-group Pna2₁, with Z= 4. Both structures were refined by full matrix least-squares methods, to R 0.057 [1 238 independent reflections; (1)] and 0.082 [1 177 independent reflections; (2)]. The co-ordination geometry in (1) is distorted octahedral with four equatorial Cu–S bonds [mean 2.317(2)Å], and two axial Cu–F bonds [2.579(5)Å]. In (2) it is distorted tetrahedral, mean Cu–S 2.303(5)Å. The [BF₄]^– group is not co-ordinated to the copper(I) atom and is disordered. The close similarity between the Cu^II–S and Cu^I–S bond lengths may be of relevance to the co-ordination in some copper-containing redox proteins, where the thioether side-chain of the amino-acid methionine is a potential ligand.