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)(ΔHf.i.=–1475 kcal./mole) and Mn(g)+ 3C5H7O2(g)= Mn(C5H7O2)(g)(ΔHf.r.=–263 kcal./mole). The heterolytic (E′) and homolytic (E″) manganese–oxygen bond-energy parameters are EMn–O= 246 kcal./mole and EMn–O= 44 kcal./mole. The homolytic bond energy appears to provide the better basis for the comparison of MIII–O bond energies in the first transition-series metal acetylacetonates.

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