The heat of formation of tris(acetylacetonato)manganese(III) and the manganese–oxygen bond energy

Abstract

The standard heat of formation of tris(acetylacetonato)manganese (III) has been determined at 25° by reaction calorimetry: ΔH°_fMn(C₅H₇O₂)_3(c)=–332·1 ± 0·7 kcal./mole. Enthalpy changes for the following hypothetical gaseous reactions at 25° have been derived: Mn³⁺(g)+ 3C₅H₇O₂–(g)= Mn(C₅H₇O₂)₃(g)(ΔH_f.i.=–1475 kcal./mole) and Mn(g)+ 3C₅H₇O₂(g)= Mn(C₅H₇O₂)(g)(ΔH_f.r.=–263 kcal./mole).

The heterolytic (E′) and homolytic (E″) manganese–oxygen bond-energy parameters are E′_Mn–O= 246 kcal./mole and E′_Mn–O= 44 kcal./mole.

The homolytic bond energy appears to provide the better basis for the comparison of M^III–O bond energies in the first transition-series metal acetylacetonates.