Synthesis, Structures and Quantum Chemistry Study on the Multidentate Ligands of Pyrazole

Three kinds of bis(pyrazol-1-yl)alkane derivatives were synthesized by the reaction of tetrabromoethane, pyrazole and 4-iodo-1H-pyrazole in the KOH-DMSO system: 1,1,2,2-tetra(1H-pyrazol-1-yl)ethane (1), 1,1,2,2-tetrakis(4-nitro-1H-pyrazol-1-yl)ethane (2), 1,1,2,2-tetrakis(4-iodo-1H-pyrazol-1-yl)ethane (3). The compounds were characterized by elemental analysis, IR spectrum, H-1 NMR and C-13 NMR, and the crystal structures of compounds 2, 3-1, 3-2 were characterized by the X-ray diffraction technology (the compounds 3-1 and 3-2 are two different crystal structures of compound 3). Furthermore, with the Gaussian09 quantum chemistry package, the stabilities and charge distribution of the compounds were studied by the B3LYP method of density functional theory. By comparing the results between quantum calculation and X-ray diffraction, we found that they are fairly consistent.