A conformational study of bis-, tris- and tetrakis-pyrazolylmethane. Crystallography, L.S.R., dipole moments and theoretical calculations

Rosa Maria Claramunt, Jose Elguero, Maria Jose Fabre, Concepcion Foces-Foces, Felix Hernandez Cano, Irmina Hernandez Fuentes, Carlos Jaime, Concepcion López

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Abstract

Theoretical calculations (MM2 and MNDO) have been carried out on several conformations of bis-, tris- and tetrakispyrazolylmethane. The potential surface thus obtained has been compared with experimental results both in solution (lanthanide shift reagents, dipole moments) and in the solid state (crystallography). The structure of tetrakispyrazolylmethane (3) was determined by X-ray diffraction. The compound crystallizes in the C2/c space group, with a cell of dimensions 29.5117(14), 6.9815(2), 13.8903(4) Å and 105.237(3)°. The molecule presents an approximate S4(4) axis such as N12, N22, N32 and N42 form a distorted tetrahedron. The calculated conformations of minimum energy are consistent with dielectric measurements. The structure of 3 in the solid state lies 5.0 kcal.mol-1 above the minimum as a result of the crystal field. To explain the LSR results, a coordination with two pyrazole nuclei has to be assumed. The presence of a metal (LSR, organometallic complexes) strongly modifies the conformation: in these conditions, bidentated and tridentated structures are observed. © 1989.
Original languageEnglish
Pages (from-to)7805-7816
JournalTetrahedron
Volume45
Issue number24
DOIs
Publication statusPublished - 1 Jan 1989

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