Metal-organic frameworks of lanthanide (III) ions with a podand bearing terminal carboxylates: Identification of water clusters of different nuclearity

A new podand bearing one carboxylate group at each terminal and a long linker from the bridgehead nitrogen has been designed and synthesized. It reacts with an aqueous solution of Ln(NO3)3 · 6H2O (Ln = La(III), Ce(III) and Pr(III)) under hydrothermal condition, to give porous metal organic framework structures with the empirical formula, {[La(ptaH)(NO3)] · 4H2O}n (1), {[Pr(ptaH)(NO3)] · 3H2O}n (2) and {[Ce(ptaH)(NO3)] · 3H2O}n (3). Each of the coordination polymers looks like infinite chain of metallocycle with different void spaces. Supramolecularly assembled water molecules of different nuclearity occupy the cavities in these metal-organic framework structures. Crystals of 1 were heated at 150 °C for 3 h to give 1′ which shows movement of metal bound water cluster in the crystalline state. These compounds are characterized by X-ray crystallography, X-ray powder diffraction, TGA, IR spectroscopy and elemental analysis.

Hydrothermally synthesized porous 3D MOF structures look like a continuous array of metallomacrocycles. Water clusters of different nuclearity are present in the large voids. The La(III)-bound acyclic water tetramer moves away from the metal upon heating keeping the crystallinity intact.Figure optionsDownload as PowerPoint slide