Synchrotron powder structure of a new layered lanthanide-organic network

Abstract

Abstract The hydrothermal synthesis and detailed structural characterisation of layered materials formulated as [Ln(H2cmp)] · xH2O [where H5cmp = (carboxyme thyl)iminodi(methylphosphonic acid) and x < 1; Ln3+ = Nd3+ (1) and Eu3+ (2)] are reported. Compounds were isolated as microcrystalline powders and the crystal structure of 1 was determined by ab initio methods from high-resolution synchrotron powder X-ray diffraction (PXRD) data collected at the European Synchrotron Radiation Facility (ESRF, Grenoble, France – beam lines BM01a and BM01b). The structure of 2 was refined by conventional PXRD, starting from the atomic coordinates of 1. Materials contain a single Ln3+ metal centre in highly distorted dodecahedral coordination geometry. Connectivity through H2cmp3– anionic ligands leads to undulated tapes of Ln3+ running parallel to the b-axis [closest inter-Ln distances of 4.203(3) and 4.170(3) Å for 1 and 2] which coalesce into layers, 2 ∞[Nd(H2cmp)], extended in the bc plane. The presence of a terminal protonated phosphonate group seems to induce the formation of the layers. Topologically, the structure is a 8-connected uninodal plane net, which can be further envisaged as two periodic self-penetrated (4,4) nets. The photophysical properties of the Eu3+-bearing material were studied at room temperature (with and without vacuum). The two materials have been further stud ied using thermogravimetric analysis (TGA), vibrational spectroscopy (FT-IR) and CHN elemental analyses.