Molecular structure and linkage isomerization of isothiocyanato(3-thiapentane-1,5-dithiolato)oxorhenium(V) complex

The properties of isothiocyanato(3-thiapentane-1,5-dithiolato)oxorhenium(V) [ReO(SSS)NCS, (1a), (3+1) type], where isothiocyanato occupies the fifth position, have been studied. Two linkage isomers, i.e., ReO(SSS)NCS (1a) and ReO(SSS)SCN (1b), were found to be formed during syntheses. The sufficient quantities of 1a were isolated in the solid state, and characterized by X-ray crystallography and IR spectroscopy. From 1H and 15N NMR measurements, it was found that 1a is in equilibrium with 1b in liquid state. In the solvents with low dielectric constant View the MathML source(ε´) such as CH2Cl2, only 1a isomer was detected, while in the solvents with high View the MathML sourceε´ such as CH3CN, both 1a and 1b isomers were observed. We have obtained the equilibrium constant (Kiso) for the linkage isomerization reaction in CD3CN by measuring 15N NMR spectra at various temperatures. The values of Kiso at 25 °C, the standard enthalpy (ΔH∘), and the standard entropy (ΔS∘) for the isomerization equilibrium were evaluated as 0.409, 14.4 kJ mol−1, and 40.9 J K−1 mol−1, respectively.