7 - Thermodynamic properties influenced by crystal field energies

Summary

These observations (non-linear heats of hydration) suggest the following hypothesis: In the absence of crystal-field effects the thermodynamic properties – – would evolve steadily along the transition series.

L. E. Orgel, Journ. Chem. Soc., p. 4756 (1952).

Introduction

One of the most successful applications of crystal field theory to transition metal chemistry, and the one that heralded the re-discovery of the theory by Orgel in 1952, has been the rationalization of observed thermodynamic properties of transition metal ions. Examples include explanations of trends in heats of hydration and lattice energies of transition metal compounds. These and other thermodynamic properties which are influenced by crystal field stabilization energies, including ideal solid-solution behaviour and distribution coefficients of transition metals between coexisting phases, are described in this chapter.

Influence of CFSE on thermodynamic data

Graphical correlations

Crystal field stabilization energies derived spectroscopically from absorption bands in the visible to near-infrared region, including the crystal field spectral measurements of minerals described in chapter 5, are enthalpy terms and, as such, might be expected to contribute to bulk properties such as lattice energies and solvation energies of transition metal compounds. If cations were spherically symmetrical and no preferential filling of 3d orbitals occurred, a given thermodynamic quantity would be expected to display smooth periodic variation in a series of transition metal compounds as a result of contraction of the cations.