New metal-organic frameworks of [M(C6H5O7)(C6H6O7)(C6H7O7)(H2O)] center dot H2O (M=La, Ce) and [Ce-2(C2O4)(C6H6O7)(2)] center dot 4H(2)O

Abstract

Two novel materials, [M(C6H5O7)(C6H6O7)(C6H7O7)(H2O)] center dot H2O (M=La(1a), Ce(1b)) and [Ce-2(C2O4) (C6H6O7)(2)] center dot 4H(2)O (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 P (1) over bar (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 (F-2(5/2) and F-2(7/2)). Compounds 1b and 2 containing Ce-III ion exhibit a paramagnetic property with weak antiferromagnetic interactions between the two adjacent magnetic centers. (C) 2012 Elsevier Inc. All rights reserved.