TY - JOUR
T1 - A conformational study of bis-, tris- and tetrakis-pyrazolylmethane. Crystallography, L.S.R., dipole moments and theoretical calculations
AU - Claramunt, Rosa Maria
AU - Elguero, Jose
AU - Fabre, Maria Jose
AU - Foces-Foces, Concepcion
AU - Cano, Felix Hernandez
AU - Fuentes, Irmina Hernandez
AU - Jaime, Carlos
AU - López, Concepcion
PY - 1989/1/1
Y1 - 1989/1/1
N2 - 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.
AB - 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.
U2 - 10.1016/S0040-4020(01)85795-1
DO - 10.1016/S0040-4020(01)85795-1
M3 - Article
SN - 0040-4020
VL - 45
SP - 7805
EP - 7816
JO - Tetrahedron
JF - Tetrahedron
IS - 24
ER -