Thorium(IV) organic frameworks with aromatic polycarboxylate ligands

Abstract

Contrary to the fairly well established structural chemistry of uranium(VI) with aromatic polycarboxylate ligands, the knowledge on thorium(Th) structural chemistry with this family of ligands is very limited. In this paper, we report the synthesis, spectroscopic and thermal studies, and crystal structures of three Th organic frameworks with 1,2,4,5-benzenetetracarboxylate (btca) or 1,4-benzenedicarboxylate (bdc). Both [Th(btca)(DMF)2(H2O)] (1) and [Th(bdc)2(DMF)2] (2) (DMF = dimethylformamide) have two dimensional (2D) layered structures constructed with 9- (1) or 10- (2) fold coordinated Th polyhedrons and µ 4-btca (1) or µ 2-bdc (2) ligands, respectively, with two coordinated DMF molecules in cis- (1) or trans- (2) positions on each Th atom. The third phase, [Th(bdc)2] (3), has a 3D pillared framework built with eightfold coordinated Th polyhedrons and µ 4-bdc ligands. Their vibrational modes have been investigated and correlated to the structures. VT-PXRD confirmed that 3 is thermally robust to 500 °C and the weight loss at ~300 °C is due to the loss of water molecules in the solvent accessible voids in the crystal lattice. Thorium(IV) organic frameworks (TOC): Three new thorium organic frameworks with aromatic polycarboxylate ligands have been synthesized and characterized. 2D layered structures are favored at room temperature and a thermal robust, 3D thorium organic framework has been made under hydrothermal conditions. Their vibrational modes and thermal stabilities have been further investigated.