Chemical bonding in compounds of the CuAl(2) family: MnSn(2), FeSn(2) and CoSn(2).

A model for the chemical bonding in the isostructural intermetallic compounds MnSn(2), FeSn(2) and CoSn(2), crystallising in the CuAl(2)-type structure, is developed. The description is based on quantum-chemical calculations applying the electron localisability approach as well as on experimental results obtained from Raman spectroscopy, Hall effect and electrical resistivity measurements on oriented single crystals. The analysis of the chemical bonding reveals four different covalent interactions leading to the formation of interpenetrating 6(3) nets of tin and chains of transition-metal atoms T (T=Mn, Fe or Co) along [001], which are interconnected by three-centre bonds. Polarised Raman measurements on oriented single crystals allowed the determination of the bond strengths, resulting in a bond order of 0.5 within the 6(3) nets, while the three-centre interactions show bond orders of up to 1. Measurements show a metal-like temperature dependence of the resistivity. A comparison of the results with the bonding models obtained for the isostructural compounds CuAl(2), TiSb(2) and VSb(2) reveals the influence of the main-group element on the connectivity pattern.