Local and extended constructions of the bonding in transition metal AB2X2 compounds of ThCr2Si2 and CaAl2Si2 types are contrasted. From the local perspective, in the “inverted” XB4 tetrahedral coordination observed in the CaAl2Si2 structure, the greater topological flexibility of the transition metal (B) d orbitals allow for better adjustment to the strain. Thus the difference between the strength of the 1-fold and the 3-fold B-X bonds is small compared to the main group analogs. From the extended structure point of view, the metal sublattice in the CaAl2Si2 structure is less “dispersive” than in the ThCr2Si2 alternative. Hence, the metals interact better with the ligand sublattice at low (∼d0) and high (∼d10) electron counts. This may be one of the reasons the CaAl2Si2 structure occurs only for d0, d5, and d10 configurations at the transition metal.
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Zheng et al. (1988) studied this question.