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 groupP63/mand can be generalized
according to Lan(n+1)+xNin(n+5)+ySi(n+1)(n+2)–zwithn= 3–6. Their crystal
structures are based on AlB2-type building blocks, fused
La-centered Ni6Si6hexagonal prisms, yielding
larger oligomeric equilateral domains with the edge size equal ton. The domains extend along thecaxis
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)–zcan 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.