Thermochemistry of Cobalt(III) β-Diketonates

The standard molar enthalpies of formation of the crystalline complexes of cobalt(III) with 1-phenyl-1,3-butanedione (Hbzac), 2,2,6,6-tetramethyl-3,5-heptanedione(Hdpm), and 1,1,1-trifluoro-2,4-pentanedione (Htfac) were determined, at 298.15 K, by solution-reaction calorimetry: ΔfH°m[Co(bzac)3,cr]=−877.1±8.7kJ·mol−1 ΔfH°m[Co(dmp)3,cr]=−1708±12kJ·mol−1 ΔfH°m[Co(tfac)3,cr]=−3191±15kJ·mol−1 The enthalpies of sublimation of Co(dpm)3 and Co(tfac)3, at 298.15 K, determined by high-temperature microcalorimetry were 126±3 and 114±2 kJ·mol−1, respectively. From the enthalpies of formation of the gaseous complexes, the average molar bond-dissociation enthalpies, 〈D〉(Co–O), were derived.