Effect of temperature on formation of two new lanthanide metal-organic frameworks: Synthesis, characterization and theoretical studies of Tm(III)-succinate

Two new metal-organic frameworks (MOFs) have been synthesized under different hydrothermal conditions and characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and elemental analysis. Compound 1, crystallized in space group P1̄ with the formula [Tm2(L)3(H2O)2]·H2O, (H2L=succinic acid), has triclinic cell parameters of a=7.61780(10), b=10.58050(10), c=12.71030(10), α=95.3130(10), β=107.4370(10), γ=111.0960(10) and a cell volume of 888.446(16) Å3. Compound 2, crystallized in space group I2/a with the same formula, is monoclinic, with cell parameters of a=13.77020(10), b=7.63170(10), c=17.2410(2), β=101.303(10) and a cell volume of 1776.72(3) Å3. The results of this work indicate that a flexible succinate ligand that provides several modes of coordination can lead to different conformations, depending on the temperature used in the reaction. In the theoretical part of this study, semiempirical quantum chemistry methods using AM1, PM3 and PM6 models are employed to predict the structure of MOFs, calculate the geometric and crystallographic parameters, and make comparisons with experimental data.