Thermochemistry of alkaline-earth phenoxides

The standard molar enthalpies of formation of some alkaline-earth metal phenoxides were determined by reaction–solution calorimetry. The results obtained at T = 298.15 K were as follows: ΔfHm∘[M(OR)2,cr]/kJ·mol-1=-(837.9±7.5)[Mg(OPh)2];−(837.4±7.2)[Ca(OPh)2];-(888.1±7.2)[Ca(O-2,6-Me2Ph)2],-(828.8±7.3)[Sr(OPh)2];-(808.6±7.3)[Ba(OPh)2];-(880.7±7.3)[Ba(O-2,6-Me2Ph)2]. Together with an appropriate Born–Haber cycle, these results allow the calculation of lattice energies for the [M(OR)2] compounds. The thermochemical radii of the anions OR− were obtained using the Kapustinskii equation and the lattice energies previously determined. A set of lattice energies and standard molar enthalpies of formation for alkaline-earth metal phenoxides [M(OR)2, M = Mg, Ca, Sr, Ba; R = OPh, 2,6-Me2OPh], was presented. Estimates for these properties for unmeasured compounds were made based on a model first applied to aliphatic alkaline metal alkoxides.