Synchrotron powder structure of a new layered lanthanide-organic network

The hydrothermal synthesis and detailed structural characterisation of layered materials formulated as [Ln(H(2)cmp)] center dot xH(2)O [where H(5)cmp = (carboxymethyl)iminodi(methylphosphonic acid) and X < 1; Ln(3+) = 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 H(2)cmp(3-) 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) angstrom for 1 and 2, respectively] which coalesce into layers, (2)(infinity)[Nd(H(2)cmp)], 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 studied using thermogravimetric analysis (TGA), vibrational spectroscopy (ATR-FTIR) and CHN elemental analyses.