The Co2Al9 structure type revisited

The centrosymmetric structure Of Co2Al9 (space group P2(1)/c, Pearson symbol mP22), the isotypic structures of Rh2Al9 and Ir2Al9 and the slightly distorted acentric structures of Rh2Ga9 and Ir2Ga9 (space group Pc) were reinvestigated from single crystal X-ray diffraction data. The structure of Rh2Ga9 represents a new structure type. The difference between the aluminides and the gallides originates in the details of atomic interactions investigated by the electron localization function and band structure calculations.