Spin-forbidden transitions in some cis-CrIIIA4B2 ions. A failure of spherical parameterization of the interelectron repulsion integrals

Abstract

The ²E→⁴A₂(O) luminescence and ⁴A₂→²E, ²T₁ absorption spectra of cis-[Cr(en)₂F₂]I, cis-[Cr(en)₂Cl₂]Cl·H₂O, cis-[Cr(en)₂Br₂]Br·H₂O and NH₄[Cr(en)F₄](en = 1,2 diaminoethane, have been measured at temperatures down to 5 K. In each case the two components of the ²E state have been identified and their separation compared with that calculated from the complete weak field matrices of the d³-tetragonal crystal field–inter-electron repulsion–spin-orbit coupling–Trees correction perturbations. For the dichloro- and dibromo- complexes the calculated separation is an order of magnitude smaller than is observed but the discrepancy is less marked for the fluorocomplexes. This is interpreted as evidence for differential metal d-orbital expansion effecting the values of the electron–electron repulsion integrals.