Standard heat of formation of tris(acetylacetonato)chromium(III) at 25° and the metal–oxygen bond energy

Abstract

The standard heat of formation of tris(acetylacetonato)chromium(III) has been evaluated at 25°via an empirical thermochemical cycle; ΔH°_f=–366·48 ± 0·67 kcal./mole. Enthalpy changes at 25° for the following processes have also been obtained: Cr_(g)+ 3C₅H₈O_2(g)= Cr(C₅H₇O₂)_3(g)+H_2(g); ΔH=–169·1 ± 1·1 kcal./mole, Cr_(g)+ 3C₅H₇O_2(g)= Cr(C₅H₇O₂)_3(g); ΔH=–327·8 ± 8·7 kcal./mole, Cr³⁺_(g)+ 3C₅H₇O₂^–_(g)= Cr(C₅H₇O₂)_3(g); ΔH=–1480 kcal./mole. The heterolytic and homolytic metal–oxygen bond-energy parameters are given; E′_Cr–O= 247; E″_Cr–O= 55 ± 1·5 kcal./mole. (The conversion factor used was 1 kcal. = 4184·0 joules.)