Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)–z: A Symmetric Mirror Homologous Series in the La–Ni–Si System

A series of four homologous silicides have been discovered during systematic explorations in the central part of the La-Ni-Si system at 1000 °C. All compounds La12.5Ni28.0Si18.3 (n = 3; a = 28.8686(8), c = 4.0737(2) Å, Z = 3), La22.1Ni39.0Si27.8 (n = 4; a = 20.9340(6), c = 4.1245(2) Å, Z = 1), La32.9Ni49.8Si39.3 (n = 5; a = 24.946(1), c = 4.1471(5) Å, Z = 1), and La44.8Ni66.1Si53.4 (n = 6; a = 28.995(5), c = 4.158(1) Å, Z = 1) crystallize in the hexagonal space group P63/m and can be generalized according to Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)-z with n = 3-6. Their crystal structures are based on AlB2-type building blocks, fused La-centered Ni6Si6 hexagonal prisms, yielding larger oligomeric equilateral domains with the edge size equal to n. The domains extend along the c axis and show checkered ordering of the cationic and anionic parts, while all their atoms are located on mirror planes. Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)-z can be considered as a mirror series to the La-rich La(n+1)(n+2)Nin(n-1)+2Sin(n+1), where an exchange of the formal cationic and anionic sites, i.e., La and Si, occurs. The La-Ni-Si system is the first system where two such analogous series have been observed.