Charge Transfer in Be-Ru Compounds.

During the investigation of the binary system Be-Ru two new phases - Be7 Ru4 and Be12 Ru7 - with similar compositions (63.6 at. % Be and 63.2 at. % Be, respectively), are discovered. They both represent new structural prototypes. The phases are located between Be2 Ru (Fe2 P-type structure) and Be3 Ru2 (U3 Si2 -type structure) in the phase diagram. This explains why their crystal structures, solved and refined from single crystal X-ray diffraction data, are described as 2D intergrowth of Fe2 P and U3 Si2 motives. The calculated electronic density of stats (DOS) reveals pronounced minima in the vicinity of the Fermi level for both compounds. Position-space analysis of chemical bonding exhibits the formation of three- and four-atomic polar bonds, involving both, Ru and Be, atoms, and a strong charge transfer from Be to the more electronegative Ru.