Abstract
The La-poor part of the ternary La-Ni-Si system has been explored leading to the discovery and structural characterization of four new polar intermetallic compounds. LaNi(5)Si(2) [BaAu(5)Ga(2) type, oP64, space group Pnma, a = 7.8223(7) Å, b = 6.3894(6) Å, c = 17.843(2) Å, V = 891.8(2) Å(3), Z = 8] features a diamond (lonsdaleite)-like homoatomic Ni framework and is the first Ni representative of a larger family of compounds typically formed by aurides. La(2)Ni(8)Si(3) [Eu(2)Ni(8)Si(3) type, tP52, P4(2)/nmc, a = 10.0278(3) Å, c = 7.5047(4) Å, V = 754.65(6) Å(3), Z = 4] is characterized by homoatomic Ni(4) tetrahedra and rectangles. LaNi(5)Si(3) [SrNi(5)P(3) type, oS36, Cmcm, a = 3.722(2) Å, b = 11.759(5) Å, c = 11.622(3) Å, V = 508.7(3) Å(3), Z = 4] is governed by extensive heteroatomic bonding and characterized by homopolyhedral packing. La(3)Ni(4)Si(2) [Ce(3)Ni(4)Si(2) type, mC36, C2/c, a = 15.819(1) Å, b = 6.0068(5) Å, c = 7.4918(6) Å, β = 103.163(5)°, V = 693.17(10) Å(3), Z = 4] is a new member of homologous series that includes La(3)Ni(3)Si(2) and La(3)Ni(3.5)Si(2). We conclude that the similar radii and electronegativities of Ni and Si are the reason for the incredible diversity of compositions and structures in this system.