A new monoclinic structure type for ternary gallide MgCoGa.

The crystal structure of MgCoGa (magnesium cobalt digallide) was solved by direct methods and refined in two space groups as P2/c (standard choice) and P2/n (non-standard choice). The refined lattice parameters for the standard choice are a = 5.1505 (2), b = 7.2571 (2), c = 8.0264 (3) Å and β = 125.571 (3)°, and for the non-standard choice are a = 5.1505 (2), b = 7.2571 (2), c = 6.5464 (2) Å and β = 94.217 (3)°. All parameters for MgCoGa refined to R = 0.027 and wR = 0.042 using 594 reflections. The crystal structure peculiarities of this compound are discussed. Particular attention has been given to relationships with other similar structures, such as YPdSi and FeC. Crystallographic analysis, together with linear muffin-tin orbital electronic structure calculations, reveals the presence of three-dimensional polyatomic nets with partial covalent bonding between the Ga atoms.