Investigation in the Ga-rich side of the Mn–Ga system: Synthesis and crystal structure of MnGa4 and MnGa5−x (x ∼ 0.15)

Crystalline compounds MnGa4 and MnGa5−x were successfully prepared by direct synthesis from the elements. The crystal structure of MnGa4 was solved and refined in the cubic Im 3 ¯  m space group, a = 5.5941(2) Å, Z = 2. The compound MnGa5−x was found under two variants: MnGa4.96, tetragonal, P4/mnc with a = 6.3395(2), c = 10.0275(7) Å and MnGa4.83, triclinic, P 1 ¯ with a = 6.3047(5), b = 9.9441(9), c = 18.901(2) Å, α = 90.382(7), β = 90.766(6), γ = 90.356(7) °. The latter can be viewed as a superstructure deriving from the tetragonal form by tripling one parameter of the cell. The structures of MnGa4 and MnGa5−x are built on the basis of a three-dimensional packing of Mn@Ga8 units, cubic in MnGa4 and square antiprismatic in MnGa5−x. In the latter these units are more or less distorted and capped by an extra gallium atom.