Characterization and structural study of lanthanum citrate trihydrate [La(C 6H 5O 7)(H 2O) 2]·H 2O

Abstract

[La(C 6H 5O 7)(H 2O) 2]·H 2O 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)°, Z exp=3.96] with space group P 2 1 / n (14). Direct methods were applied and the model was subsequently least-squares refined ( R B=5.1% and R wP=12.0%). La 3+ is nine-fold coordinated, the LaO 9 forming a mono-capped square antiprism. The basic unit is a binuclear entity of two LaO 9 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 La 3+ in monodentate, bidentate and bridging way. Also the alkoxide group, which carries the proton, is coordinated to La 3+. Two water molecules complete the coordination sphere, while the third one can be found inbetween the La 3+-citrate network.