Cyclic voltammetric studies of copper(II) complexes with some bis(imidazole)bis(thioether) ligands. The X-ray crystal structure of (1,6-bis-(5(4)-imidazolyl)-2,5-dithiahexane)dichlorocopper(II)

Abstract A variety of copper coordination compounds with an N 2 S 2 donor set, composed of tetradentate bis(imidazole)bis(thioether) ligands, have been synthesized and characterized. The starting solid complexes have the general formula Cu( L )XY, in which X and Y are monoanions: Cl − (both X and Y) or [BF 4 ] − (Y), and the ligands L are bidhx (1, 6-bis-(5-methyl-4-imidazolyl)-2, 5-dithiahexane), bhdhx (1, 6-bis-(5(4)-imidazolyl-2, 5-dithia- hexane) and bidhp (1, 7-bis-(5-methyl-4-imidazolyl)-2, 6-dithiaheptane). These ligands differ only in the length of the bridge between the S atoms and in the presence or absence of a methyl substituent on the imidazole group. The cyclic voltammetric behaviour of four of those complexes, viz. [Cu(bidhx)Cl(BF 4 )] ( A ), [Cu(bhdhx)Cl][BF 4 ( B ), [Cu(bhdhx)Cl 2 ] ( C ) and [Cu(bidhp)Cl 2 ] ( D ), in dimethyl sulfoxide solution under different conditions is described in detail. It was found that [Cu(bidhp)Cl 2 ] decomposes so quickly in solution that its cyclic voltammograms became meaningless. A possible interpretation of the experimental results of the other three complexes, including the influence of coordinated [BF 4 ] − , will be presented and compared with previous results on similar complexes. For these three complexes, half-wave potentials from + 8 to + 120 mV versus SCE (+ 250 to + 360 mV versus SHE) were found, which are within the lower range of redox potentials for blue copper proteins. The compound [Cu(bhdhx)Cl 2 ] (C) crystallizes in the orthorhombic space group Pbca with a = 12.738(3), b = 17.218(4), c = 13.894(7) A, V = 3047(2) A 3 , Z = 8 and consists of molecular units with a [CuN 2 S 2 Cl 2 ] chromophore. Distances in the distorted octahedral geometry are: CuN = 1.96, CuS = 2.52 and 2.84, and CuCl = 2.37 and 2.59 A.