An electronhyphen;gas study of the bonding, structure, and octahedral ligandhyphen;field splitting in transitionhyphen;metal halides

摘要

We present a discussion of the structure and the ligandhyphen;field splitting parameter 10Dqfor somed1titanium (III) halides. Our approach is based on an ionic model allowing for the inclusion both of electrostatic and of nonhyphen;Coulombic repulsive contributions. The pointhyphen;Coulombic forces are treated exactly using the Madelung constant for each specific crystal. Only the metalndash;ligand and ligandndash;ligand shorthyphen;range repulsions are taken to be of importance, and are calculated using the electronhyphen;gas model. Our results show that for the chloride the model is poor and hence that covalency is essential for understanding the heavier halides. For the fluoride systems, however, we obtain values for the bond distances, and the lattice energy for the trifluoride, which are accurate within five per cent of experiment. As previous approaches have shown, we find the negative sign for 10Dqwhen only the purely electrostatic interaction is included. We show in addition that overlap repulsion provides the major part of the balance which corrects the ordering of theegandt2gstates. We conclude that for fluorides at least the ionic model is an excellent startinghyphen;point for an understanding of their properties.