New metal-organic frameworks of [M(C ₆H ₅O ₇)(C ₆H ₆O ₇)(C ₆H ₇O ₇)(H ₂O)]. H ₂O (M=La, Ce) and [Ce ₂(C ₂O ₄)(C ₆H ₆O ₇) ₂]. 4H ₂O

Two novel materials, [M(C ₆H ₅O ₇)(C ₆H ₆O ₇)(C ₆H ₇O ₇)(H ₂O)]. H ₂O (M=La(1a), Ce(1b)) and [Ce ₂(C ₂O ₄)(C ₆H ₆O ₇) ₂]. 4H ₂O (2), with a metal-organic framework (MOF) were prepared with hydrothermal reactions and characterized with photoluminescence, magnetic susceptibility, thermogravimetric analysis and X-ray powder diffraction in situ. The crystal structures were determined by single-crystal X-ray diffraction. Compound 1 crystallized in triclinic space group P1 (No. 2); compound 2 crystallized in monoclinic space group P2 ₁/c (No. 14). The structure of 1 is built from a 1D MOF, composed of deprotonated citric ligands of three kinds. Compound 2 contains a 2D MOF structure consisting of citrate and oxalate ligands; the oxalate ligand arose from the decomposition in situ of citric acid in the presence of Cu ^II ions. Photoluminescence spectra of compounds 1b and 2 revealed transitions between the 5d ¹ excited state and two levels of the 4f ¹ ground state ( ²F _5/2 and ²F _7/2). Compounds 1b and 2 containing Ce ^III ion exhibit a paramagnetic property with weak antiferromagnetic interactions between the two adjacent magnetic centers.