Isolation and Characterization of a Polymeric Lanthanum Citrate

The first lanthanide citrate coordination polymer with the formula [La(Hcit)(H2O)] n (Hcit3- = C(OH)(COO-)(CH2COO-)2) was prepared from La2O3 and citric acid at pH = 2.2−2.5 under hydrothermal conditions at 120 °C. The compound was characterized by elemental analysis, IR, TG-DTA, and X-ray crystallography. It is thermally stable up to 158 °C and insoluble in common solvents. The compound crystallizes in the monoclinic space group C2/c with a = 16.765(3) Å, b = 8.822(2) Å, c = 14.048(3) Å, β = 120.64(3)°, and Z = 8. The structure consists of chains of La(III) cations bridged by O−C−O groups with pendant Hcit anions forming a pillar structure. The Hcit ligand is involved in six La−O bonds to five different La centers in a very compact 3D structure.