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

[Image: see text] 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 La(12.5)Ni(28.0)Si(18.3) (n = 3; a = 28.8686(8), c = 4.0737(2) Å, Z = 3), La(22.1)Ni(39.0)Si(27.8) (n = 4; a = 20.9340(6), c = 4.1245(2) Å, Z = 1), La(32.9)Ni(49.8)Si(39.3) (n = 5; a = 24.946(1), c = 4.1471(5) Å, Z = 1), and La(44.8)Ni(66.1)Si(53.4) (n = 6; a = 28.995(5), c = 4.158(1) Å, Z = 1) crystallize in the hexagonal space group P6(3)/m and can be generalized according to La(n(n+1)+x)Ni(n(n+5)+y)Si((n+1)(n+2)–z) with n = 3–6. Their crystal structures are based on AlB(2)-type building blocks, fused La-centered Ni(6)Si(6) 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. La(n(n+1)+x)Ni(n(n+5)+y)Si((n+1)(n+2)–z) can be considered as a mirror series to the La-rich La((n+1)(n+2))Ni(n(n–1)+2)Si(n(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.