Acta Cryst. (2013). E69, o217
[ doi:10.1107/S1600536813000305 ]

meso-4,4'-Difluoro-2,2'-{[(3aR,7aS)-2,3,3a,4,5,6,7,7a-octahydro-1H-1,3-benzimidazole-1,3-diyl]bis(methylene)}diphenol

A. Rivera, D. Quiroga, J. Ríos-Motta, M. Kuceraková and M. Dusek

Abstract: In the crystal structure of the title compound, C₂₁H₂₄F₂N₂O₂, there are two intramolecular O-HN hydrogen bonds involving the N atoms of the imidazolidine ring and the hydroxy groups. The crystal studied was a meso compound obtained by the reaction of the aminal (2S,7R,11S,16R)-1,8,10,17-tetraazapentacyclo[8.8.1.1^8,17.0^2,7.0^11,16]cosane with 4-fluorophenol. The imidazolidine ring has a twisted conformation with a CH-CH-N-CH₂ torsion angle of 44.99 (14)° and, surprisingly, the lone pairs of the N atoms are disposed in a syn isomerism, making the title compound an exception to the typical `rabbit-ear effect' in 1,2-diamines. In the crystal, molecules are linked via C-HF hydrogen bonds, forming chains along the c-axis direction. These chains are linked via another C-HF hydrogen bond, forming a three-dimensional network.

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