Crystal structure and photoluminescence properties of lanthanide diphosphonates

Abstract

Three lanthanide diphosphonates, [H₃N(CH₂)₄NH₃]Ln[hedpH][hedpH₂] (Ln = La, Eu, Tb; hedp = 1-hydroxyethylidenediphosphonate), have been synthesized under hydrothermal conditions with 1,4-diaminobutane as the template. The structure of the La compound has been determined by single-crystal X-ray diffraction, crystallizing in the space group P-1. Powder XRD shows that the three compounds are isostructural. The crystal structure consists of polymeric La[hedpH][hedpH₂] single chains built up from vertex-sharing LaO₇ polyhedra and CPO₃-tetrahedra. The chains are cross-linked by strong hydrogen bonds to form a three-dimensional network with large channels containing the template cations. The photoluminescence properties of the Eu and Tb materials have been investigated by photoluminescence spectroscopy, including steady-state emission and excitation spectra, and measurement of the lifetimes of the excited states.