Metal-Organic Frameworks Assembled From Erbium Tetramers and 2,5-Pyridinedicarboxylic Acid

Abstract

Two novel three-dimensional lanthanide-organic frameworks, [Er-6(OH)(8)(pydc)(5)(H2O)(3)]center dot 2.5H(2)O (1) and [Er-3(OH)(6)(pydc)Cl] (2) (pydc(2-) is the deprotonated residue of 2,5-pyridinedicarboxylic acid - 2,5-H(2)pydc), were prepared by hydrothermal synthesis into an organic matrix formed by the linker. Individual chains are disposed in the ab plane of the unit cell in a brick-wall fashion and results from the coalescence if cubane-type clusters of Er3+. Compound 2 comprises densely packed cationic [Er-3(OH)(6)Cl](n)(2n+) inorganic layers, constructed by the lateral coalescence of 1D chains identical to those found in 1. These layers are pillared by the organic linkers along the [001] direction of the unit cell yielding the crystal structure of 2. Considering the metallic tetramers and the ligands as framework nodes, compounds 1 and 2 are 7- and 2-nodal networks, respectively. While the former is unprecedented among metal-organic framework (MOF) structures, the latter is reminiscent of the known tcj/hc topological type. The crystal structures and properties of the two compounds have been investigated by (single-crystal and powder) X-ray diffraction, electron microscopy (SEM and EDX), vibrational spectroscopy, CHN elemental analyses, and thermogravimetry. The magnetic properties of 1 also have been investigated.