Microporous La(III) Metal-Organic Framework Using a Semirigid Tricarboxylic Ligand: Synthesis, Single-Crystal to Single-Crystal Sorption Properties, and Gas Adsorption Studies

Two La(III) coordination polymers, {[La(cpia)(2H(2)O)]center dot 4H(2)O}(n) (1) and {[La(cpia)(H2O)(2DMF)}(n) (2) (cpiaH(3) = 5-(4-carboxy-phenoxy)-isophthalic acid, DMF = N,N'-dimethylformamide), have been synthesized under hydro- and solvothermal conditions, respectively. The lattice water molecules in compound I could be partially replaced at RT with different solvent molecules such as ethanol, acetone, and pyridine leading to three new daughter crystals {[La(cpia)(2H(2)O)]center dot 2H(2)O center dot C2H6O}(n) (la), {[La(cpia)(2H(2)O)]center dot 2H(2)O center dot C3H6O}(n) (1b), and {[La(cpia)(2H(2)O)]center dot 2H(2)O center dot C5H5N}(n) (1c) in a single-crystal to single-crystal (SC-SC) manner. All five compounds were further characterized by IR spectroscopy, elemental analysis, X-ray powder diffraction, and thermogravimetry. Each polymer forms a carboxylate-bridged three-dimensional structure with each metal adopting LaO9 geometry. Thermogravimetric analysis (TGA) shows that compound 1 loses water molecules beginning at similar to 80 degrees C and continues until 300 degrees C, and it is thermally stable up to 400 degrees C. All the daughter compounds 1a-1c lose solvent molecules in a stepwise manner and become fully desolvated at 320 degrees C. Like 1, all the daughter crystals are also stable up to 400 degrees C and beyond that it starts to decompose. On the other hand, 2 starts to lose weight continuously beginning at similar to 80 degrees C and breaks down without showing any plateau. The sorption measurements performed on desolvated I show that N-2 molecules are adsorbed at the surface only at 77 K; however, appreciable amounts of CO2 are readily and reversibly incorporated at 273 K.