Y6Mg9Co2 and Y9Mg30Co2: Novel magnesium-rich compounds representing new structure types

The crystal structures of the magnesium-rich Y6Mg9Co2 and Y9Mg30Co2 compounds have been determined from single crystal X-ray diffraction data. Both compounds represent new structure types: Y6Mg9Co2 is orthorhombic, Pnnm, oP34, a = 8.7883 (2), b = 15.9669 (3), c = 5.9984 (2) Å; Y9Mg30Co2 is hexagonal, P63/mmc, hP82, a = 10.1564 (3), c = 22.498 (1) Å. The crystal structures of these compounds are discussed in comparison with each other and with other magnesium containing compounds. Electronic structure calculations revealed that magnesium atoms form Mg4-tetrahedra with significant covalent Mg–Mg interaction (-iCOHP = 0.732 eV for Y6Mg9Co2 and 0.815 eV for Y9Mg30Co2). The ELF and Bader charge analyses confirm that valence electrons localized around Mg atoms present a covalent bonding character. [Display omitted] •New ternary intermetallics Y6Mg9Co2 and Y9Mg30Co2 were obtained.•Crystal chemistry of new Mg-rich intermetallics is analyzed in detail.•Ab initio calculations showed significant covalent Mg–Mg bonding in both structures.