Re-investigation of the Er3+-C2O42- -H2O system:: from the classical ceramic precursor to a new nanoporous molecular material potential precursor

This paper focuses on the crystallographic diversity observed for the compounds obtained, by reacting potassium oxalate with Er(III) chloride, in gel media. Three lanthanide and oxalate compounds are described two out of the three are simple lanthanide oxalate complexes while the other one is a mixed lanthanide-alkaline oxalate complex. All three have been structurally characterized. 1, namely Er-2(C2O4)(3)(H2O)(6).4 H2O, crystallizes in the space group P2(1)/c (system monoclinic) with a = 11.3590(2) Angstrom, b = 9.6162(2) Angstrom, c = 9.9401(2) Angstrom, beta = 118.723(9)degrees and Z = 4. Its crystal structure has been found to be identical to the one already reported. It consists of parallel honeycomb-like molecular layers. 2, namely KEr(C2O4)(2).4 H2O, has been found to be isostructural to the Y(III) homologous complex already reported. It crystallizes in the space group I4(1)/amd (tetragonal system) with a = 11.4145(14) Angstrom, c = 8.893(2) Angstrom and Z = 4. Its structure consists of channels along the c axis spreading over the (ab) plane with a square cross section. 3, namely Er-2(C2O4)(3)(H2O)(6).12 H2O, crystallizes in the space group R (3) over bar (trigonal system) with a = 30.8692(10)Angstrom, c = 7.2307(2)Angstrom and Z = 12. This compound has, to the best of our knowledge, never been structurally described. It is the first three-dimensional lanthanide oxalate ever reported. Its crystal structure exhibits channels with hexagonal cross-sections spreading along the c --> axis. The diameter of the channels is as large as 12 Angstrom. They are filled with crystallization water molecules.