Syntheses, spectroscopic, and electrochemical properties of dinuclear copper(II) complexes bridged by a single thiolate sulphur atom; X-ray crystal structures of [Cu2(L1)2(SC6H4Cl-4)][PF6] and [Cu2(L2)2(SC6H4CH3-4)][ClO4]

Abstract

Dinuclear copper(II) complexes [Cu₂(L¹)₂(SR)][PF₆]{L¹= 3,3′-(trimethylenedinitrilo)bis[butan-2-one oximato (1 –)]; R = C₆H₄Cl-4(1), C₆H₄Br-4 (2), or C₆H₄CH₃-4 (3)} and [Cu₂(L²)₂(SR)][ClO₄][L²= difluoro{3,3′-(trimethylenedinitrilo)bis[butan-2-one oximato(2 –)]} borate(1 –); R = C₆H₄CH₃-4 (4), C₆H₄CH₃-2 (5), or C₆H₄Cl-4 (6)] have been prepared. Single-crystal X-ray structure analyses of (1) and (4) reveal that two copper atoms are bridged by a single thiolate-sulphur atom. Complex (1) crystallizes in space group P, with a= 11.230(3), b= 14.079(3), c= 12.540(3)Å, α= 97.04(2), β= 101.59(2), γ= 72.95(2)°, and Z= 2. Complex (4) crystallizes in space group P, with a= 12.329(6), b= 15.447(6), c= 11.018(7)Å, α= 94.45(5), β= 92.22(5), γ= 96.13(4)°, and Z= 2. The structures of (1) and (4) were refined by least-squares methods to R= 0.064 and 0.089 for 4 416 and 2 167 reflections respectively. In dichloromethane complexes (1)–(6) exhibit absorption bands in the region 320—420 nm due to the thiolate sulphur-to-copper(II) charge-transfer transitions. E.s.r. spectra of these complexes showed a half-band signal due to the Cu–Cu interaction around 1 500 G in dichloromethane–toluene (1 : 1 v/v) at 77 K. The dinuclear structure of the complexes is retained not only in very dilute (ca. 10^–5 mol dm^–3) dichloromethane solutions but also in the two successive reduced forms, as confirmed by the absorption spectra and cyclic voltammetry, respectively.