Crystal structures, bonding and electronic structures of MM'As, a series of new ternary arsenides (M=ZR, Hf; M'=Fe, Co, Ni)

All six new arsenides were prepared by arc-melting of preheated mixtures of the monoarsenides MAs with the 3d metals Fe, Co, and Ni, respectively. The isostructural title compounds all form the Co2Si structure type, in contrast to the corresponding phosphides with ZrNiP occurring in the Ni2In type. The anomalous expansions of the unit cells from ZrCoAs to ZrNiAs (V = 178.5(3) A3 versus V = 182.5(1) A3) and from HfCoAs to HfNiAs (V = 175.03(5) A3 versus V 177.0(1) A3) can be understood based on extended Hueckel calculations of the electronic structure of HfCoAs. (orig.)