Thermochemistry of the potassium hexafluorometallates(III) of the elements from scandium to gallium

Abstract

The following standard enthalpies of formation at 25 °C have been determined by solution calorimetry : K₃ScF₆(c), –3 337; K₃TiF₆(c), –3 213; K₃VF₆(c), –3 026; K₃CrF₆(c), –2 977; K₃MnF₆(c), –2 849; K₃FeF₆(c), –2 807; K₃CoF₆(c), –2 634; K₃NiF₆(c), –2 558; K₃CuF₆(c), –2 407; K₃GaF₆(c), –3 001 kJ mol^–1. From these, the corresponding enthalpies of formation from gaseous K⁺, M³⁺, and F^– ions, I, have been calculated. When plotted against the number of 3d electrons on the metal ion, the values of |I| generate the familiar doubled-humped curve predicted by ligand-field theory, but the two humps are somewhat bigger than might have been expected.