Synthesis, crystal structure, optical and thermal properties of lanthanide hydrogen-polyphosphates Ln[H(PO3)4] (Ln = Tb, Dy, Ho)

Abstract

Lanthanide hydrogen-polyphosphates Ln[H(PO₃)₄] (Ln = Tb, Dy, Ho) were synthesised as colourless (Ln = Tb, Dy) and light pink (Ln = Ho) crystalline powders by reaction of Tb₄O₇/Dy₂O₃/Ho₂O₃ with H₃PO₃ at 380 °C. All compounds crystallise isotypically (P2₁/c (no. 14), Z = 4, a_Tb = 1368.24(4) pm, b_Tb = 710.42(2) pm, c_Tb = 965.79(3) pm, β_Tb = 101.200(1)°, 3112 data, 160 parameters, wR₂ = 0.062, a_Ho = 1363.34(5) pm, b_Ho = 709.24(3) pm, c_Ho = 959.07(4) pm, β_Ho = 101.055(1)°, 1607 data, 158 parameters, wR₂ = 0.058). The crystal structure comprises two different infinite helical chains of corner-sharing phosphate tetrahedra. In-between these chains the lanthanide ions are located, coordinated by seven oxygen atoms belonging to four different polyphosphate chains. Vibrational, UV/Vis and fluorescence spectra of Ln[H(PO₃)₄] (Ln = Tb, Dy, Ho) as well as Dy[H(PO₃)₄]:Ln (Ln = Ce, Eu) and the magnetic and thermal behaviour of Tb[H(PO₃)₄] are reported.