Grygoriy Dmytriv

The ternary boride MgNi2B6 (magnesium dinickel hexaboride) crystallizes as a new representative of the CeCr2B6 structure type. The Mg and Ni atoms occupy sites with mmm and mm2 symmetry, respectively. The B atoms occupy two sites with m.. and m2m symmetry. The 14-membered polyhedron around the Mg atom is a hexagonal prism, with two adjacent lateral faces centred by Mg atoms. The Ni atoms are encapsulated in 10-vertex polyhedra. The trigonal prismatic coordination is typical for both B atoms.

The ternary germanide Mg5.57Ni16Ge7.43 (cubic, space group Fm m, cF116) belongs to the structural family based on the Th6Mn23-type. The Ge1 and Ge2 atoms fully occupy the 4a (m m symmetry) and 24d (m.mm) sites, respectively. The Ni1 and Ni2 atoms both fully occupy two 32f sites (.3m symmetry). The Mg/Ge statistical mixture occupies the 24e site with 4m.m symmetry. The structure of the title compound contains a three-core-shell cluster.

Abstract Crystal structures of MgCoGa, Mg0.74CoGa0.52 and Mg0.49CoGa0.15 phases from the Mg–Co–Ga system were investigated using single-crystal diffraction. These structures belong to the family of so-called Laves phases. Hexagonal MgCoGa crystallizes as a disordered phase within the MgZn2 structure type.