Spectroscopic Studies of Copper(I) Complexes of 1,8-Di(2-pyridyl)-3,6-dithiaoctane in a Nonaqueous Solvent. The Halide-ion Effect on Their Structure

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Abstract
The complexes of 1,8-di(2-pyridyl)-3,6-dithiaoctane(pdto) with CuX(X=Cl and Br) and [Cu(CH3CN)4]ClO4 have been synthesized in chloroform, methanol, ethanol, and acetone. Their absorption spectra show an intense metal-to-ligand charge-transfer band at 307 nm: This band is assigned to pyridyl nitrogen←Cu. [Cu(pdto)]+ (1) has been prepared from [Cu(CH3CN)4]ClO4, its pdto acting as a four-coordinate ligand. CuX reacts with pdto to yield two complexes: One is 1, and the other is [CuX(pdto)] (2). Both complexes are four-coordinate, but in the 2 one of the two pyridyl groups is dissociated. The complex 2 is unstable and is oxidized by oxygen. Neither complex reacts with CO, indicating the tight binding of pdto with Cu(I). The 1 and 2 are equilibrated in solution. The 1H NMR spectra well demonstrate that 2 is dominant in chloroform and that 1 is the principal form in alcohol, while the 1/2 ratio is 3/7. This solvent-dependence is ascribed to the coordination ability and/or polarity of the solvent.
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