[en] Three novel metal polyphosphides, α-SrP₃, BaP₈, and LaP₅, were prepared in BN crucibles by the reaction of the respective stoichiometric mixtures under a high pressure of 3 GPa at 950-1000 deg. C. Their crystal structures were determined from single-crystal X-ray data (α-SrP₃: space group C2/m, a=9.199(6) A, b=7.288(3) A, c=5.690(3) A, β=113.45(4) deg. , Z=4, R₁/wR₂=0.0684/0.1180 for 471 observed reflections and 22 variables; BaP₈: space group P-1, a=6.762(2) A, b=7.233(2) A, c=8.567(2) A, α=86.32(2) deg. , β=84.31(2) deg. , γ=70.40(2) deg. , Z=2, R₁/wR₂=0.0476/0.1255 for 2702 observed reflections and 82 variables; LaP₅: space group P2₁/m, a=4.885(1) A, b=9.673(3) A, c=5.577(2) A, β=105.32(2) deg. , Z=2, R₁/wR₂=0.0391/0.1034 for 1272 observed reflections and 31 variables). α-SrP₃ is isostructural with SrAs₃ and the crystal structure consists of two-dimensional puckered polyanionic layers _∞²[P₃]^2- that stack along the c-axis yielding channels occupied by Sr²⁺ counterions. BaP₈ crystallizes in a new structure type which contains a three-dimensional infinite polyanionic framework _∞³[P₃]^2-, with large channels hosting the barium cations. LaP₅ is a layered compound containing _∞²[P₅]^3- polyanionic layers separated by La³⁺ ions. All three compounds exhibit expected diamagnetic behaviors