Synthesis, solid-state and solution structures of bis{N,N′-bis[(2-thienyl)methylene]-1,2-diaminoethane}-silver(I) and -copper(I) trifluoromethanesulfonate complexes

Abstract

Reaction of 2 equivalents of the thienyl ketimines [(SC₄H₃)CRN]₂C₂H₄(R = Me or SC₄H₃) with 1 equivalent of M^I(O₃SCF₃)(M = Ag or Cu) resulted in formation of stable [M{[(SC₄H₃)CRN]₂-C₂H₄}₂][O₃SCF₃] complexes. The crystal structures of [Ag{[(SC₄H₃)CMeN]₂C₂H₄}₂][O₃SCF₃] and [Cu{[(SC₄H₃)CN]₂C₂H₄}₂][O₃SCF₃] have been determined. Both unit cells contain discrete anions and, basically isostructural, complex cations. The co-ordination sphere of the metal(I) centre is dominated by four imine N atoms [Ag, 2.329(3); Cu, 2.014(14)–2.110(13)Å] provided by two symmetrically, bidentate co-ordinating [(SC₄H₃)CRN]₂C₂H₄ ligands. Four thiophene S atoms are also in proximity of the metal nucleus [Ag, 3.259(2); Cu, 3.160(8)–3.438(6)Å], but do not co-ordinate. The AgN₄ geometry is flattened, as indicated by the spatial geometry of the four donor atoms, and tends more to square planar than to the usual tetrahedral arrangement. The CuN₄ geometry is slightly compressed from tetrahedral. A characteristic of these complexes is their very low solubility which makes futher spectroscopic studies difficult. Various ¹H NMR experiments have established that the complex cations are isostructural, having a tetrahedral co-ordination geometry similar to that found in the crystals, comprising symmetrically co-ordinating, bidentate ligands. There are no indications that the solution structure is compressed. The solution structure is only kinetically stable at low temperatures (⩽180 K); at more elevated temperatures ligand exchange occurs, which is rapid at ambient temperatures.