Crystal structures of the compounds PrAl2Si2, Pr3Al4Si6 and PrAlSi2

During a search for new compounds crystallizing with the Ce3Al4Si6 and CeAlSi2 structure types, the new compounds Pr3Al4Si6 and PrAlSi2 were found. The crystal structures of these compounds and of PrAl2Si2 (CaAl2Si2-type structure) were refined from X-ray powder diffraction data (PrAl2Si2: P3¯m1, a = 4.2096(2) Å, c = 6.8422(3) Å, Z = 1; Pr3Al4Si6: P3¯m1, a = 4.18050(9) Å, c = 17.9793(5) Å, Z = 1; PrAlSi2: P3¯m1, a = 4.1615(2) Å, c = 11.1312(7) Å, Z = 2). The structures of Pr3Al4Si6 and PrAlSi2 belong to a homologous series of general formula Rm+nAl2nSi2n+2m, where m and n are the numbers of AlB2- and CaAl2Si2-type slabs, respectively.