High-pressure synthesis and structural characterization of three new polyphosphides, α-SrP3, BaP8, and LaP5

Abstract Three novel metal polyphosphides, α -SrP 3 , BaP 8 , and LaP 5 , were prepared in BN crucibles by the reaction of the respective stoichiometric mixtures under a high pressure of 3 GPa at 950–1000°C. Their crystal structures were determined from single-crystal X-ray data ( α -SrP 3 : space group C 2 /m , a =9.199(6) A, b =7.288(3) A, c =5.690(3) A, β =113.45(4)°, Z =4, R 1 / w R 2 =0.0684/0.1180 for 471 observed reflections and 22 variables; BaP 8 : space group P−1 , a =6.762(2) A, b =7.233(2) A, c =8.567(2) A, α =86.32(2)°, β =84.31(2)°, γ =70.40(2)°, Z =2, R 1 / w R 2 =0.0476/0.1255 for 2702 observed reflections and 82 variables; LaP 5 : space group P 2 1 /m , a =4.885(1) A, b =9.673(3) A, c =5.577(2) A, β =105.32(2)°, Z =2, R 1 / w R 2 =0.0391/0.1034 for 1272 observed reflections and 31 variables). α -SrP 3 is isostructural with SrAs 3 and the crystal structure consists of two-dimensional puckered polyanionic layers ∞ 2 [P 3 ] 2− that stack along the c -axis yielding channels occupied by Sr 2+ counterions. BaP 8 crystallizes in a new structure type which contains a three-dimensional infinite polyanionic framework ∞ 3 [P 3 ] 2− , with large channels hosting the barium cations. LaP 5 is a layered compound containing ∞ 2 [P 5 ] 3− polyanionic layers separated by La 3+ ions. All three compounds exhibit expected diamagnetic behaviors.