Thermochemistry of Thiolato Derivatives of Manganese Carbonyl - the Strength of Manganese-Sulfur Bonds

Calorimetric measurements of the thermal decomposition of [Mn-2(CO)(8)(SR)(2)] (R = CH3, C2H5) have been made in the temperature range T = 450-550 K. Analyses of the decomposition reactions indicate that the products include the sulphide, R(2)S, and manganese(II) sulphide. Using drop microcalorimetric methods, values were determined for the standard molar enthalpies of formation at 298 K of the crystalline compounds: Delta(f)H(m)(o)([Mn-2(CO)(8) (SCH3)(2)],Cr) -(1521 +/- 30) kJ mol(-1), Delta(f)H(m)(o)([Mn-2 (CO)(8)(SC3H5)(2)],cr) = -(1555+/-30) kJ mol(-1). These are combined with molar enthalpies of sublimation and other standard enthalpy contributions to provide an estimate of the Mn-S bond enthalpy contribution D(Mn-SR)= (162+/-5) kJ mol(-1). A group disruption model is also considered.