Characterization and structural study of lanthanum citrate trihydrate [La(C6H5O7)(H2O)2].H2O

Abstract

[La(C6H5O7)(H2O)2]·H2O was synthesized as precursor material for an aqueous solution–gel route to La-containing multimetal oxides. The compound was characterized by means of FTIR, TGA and pycnometry. The crystallographic structure was solved from powder diffraction data. The symmetry is monoclinic [a=17.097(3) Å, b=9.765(2) Å, c=6.3166(8) Å and β=90.42(1)°, Zexp=3.96] with space group P21/n (14). Direct methods were applied and the model was subsequently least-squares refined (RB=5.1% and RwP=12.0%). La3+ is nine-fold coordinated, the LaO9 forming a mono-capped square antiprism. The basic unit is a binuclear entity of two LaO9 polyhedra having one edge in common. These units are connected along the c-axis through citrate molecules. The carboxylate groups of the citrate are coordinated to La3+ in monodentate, bidentate and bridging way. Also the alkoxide group, which carries the proton, is coordinated to La3+. Two water molecules complete the coordination sphere, while the third one can be found inbetween the La3+-citrate network.