Homologous Lanthanide Nickel Silicides Based on Oligomeric Triangular Blocks: Crystal Structures and Physical Properties

Isostructural series of homologous silicides Lnn(n+1)+xNin(n+5)+ySi(n+1)(n+2)-z (n = 4–6) have been obtained with Ln = Ce, Pr and Gd at 1000 C. All of them crystallize in the hexagonal space group type P63/m, exhibit short unit cell c parameters and variable but strongly correlating a parameters (n = 4: a = 20.795–20.826(9), c = 3.994–4.041(1) Å; n = 5: a = 24.693–24.726(4), c = 4.000–4.066(1) Å, and n = 6: a = 28.716–28.760(1), c = 3.9983–4.0734(3) Å). The crystal structures are represented by fused oligomeric SrPtSb -type blocks – La-centered Ni6Si6 hexagonal prisms forming equilateral domains with the edge size equal to n. The polyanionic triangular motifs and the cationic components alternate along all crystallographic axes. The newly discovered compounds Lnn(n+1)+xNin(n+5)+ySi(n+1)(n+2)-z represent asymmetric higher-n Ni-rich compositional and structural mirrors to the rare reported Ln-rich representatives Ln(n+1)(n+2)Nin(n-1)+2Sin(n+1). Unit cell parameter trends and magnetic measurements suggest the intermediate valence character of the Ce atoms.