Why is 10Dq so useful for measuring changes of the impurity-ligand distance?

The microscopic origin of the strong dependence displayed by the cubic field splitting parameter, 10Dq, on the metal-ligand distance in transition metal complexes is explored within a realistic molecular orbital framework. Taking as a guide the case of the CrF6 3−Oh complex it is shown that though the admixture of 2s(F−) orbitals in the antibonding eg *(∼ 3z2—r2;x2 – y2) orbital is very small [(Neλs)2 ≅ 5%] it is the main responsible of the law 10Dq α R−n with n close to five. By contrast the admixture of 2p(F−) orbitals though more important [(Neλp[sgrave])2 ≅ 16%] is shown to be no relevant as regards the R dependence of 10Dq. Thus this analysis demonstrates that the R dependence of 10Dq is ultimately related to that displayed by the isotropic superhypefine constant for Oh complexes with unpaired [sgrave]-electrons.