Thermochemistry of thiolato derivatives of manganese carbonyl. The strength of manganese-sulphur bonds

Abstract

Calorimetric measurements of the thermal decomposition of [Mn 2(CO) 8(SR) 2] (RCH 3, C 2H 5) have been made in the temperature range T = 450–550 K. Analyses of the decomposition reactions indicate that the products include the sulphide, R 2S, 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: Δ f H m°([Mn 2(CO) 8(SCH 3) 2], cr) = −(1521 ± 30) kJ mol −1, Δ f H m°([Mn 2(CO) 8(SC 2H 5) 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.