title: meso-4,4'-Difluoro-2,2'-{[(3aR,7aS)-2,3,3a,4,5,6,7,7a-octa-hydro-1H-1,3-benzimidazole-1,3-di-yl]bis-(methyl-ene)}diphenol.
abstract: In the crystal structure of the title compound, C(21)H(24)F(2)N(2)O(2), there are two intra-molecular O-H⋯N hydrogen bonds involving the N atoms of the imidazolidine ring and the hy-droxy groups. The crystal studied was a meso compound obtained by the reaction of the aminal (2S,7R,11S,16R)-1,8,10,17-tetra-aza-penta-cyclo-[8.8.1.1(8,17).0(2,7).0(11,16)]cosane with 4-fluoro-phenol. The imidazolidine ring has a twisted conformation with a CH-CH-N-CH(2) 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-H⋯F hydrogen bonds, forming chains along the c-axis direction. These chains are linked via another C-H⋯F hydrogen bond, forming a three-dimensional network.
authors: Facultad de Ciencias, Departamento de Química, Universidad Nacional de Colombia, Sede Bogotá, Cra 30 No. 45-03, Bogotá, Código Postal 111321,  Colombia.
authors: Augusto
authors: A
authors: Rivera
authors: Diego
authors: D
authors: Quiroga
authors: Jaime
authors: J
authors: Ríos-Motta
authors: Monika
authors: M
authors: Kučeraková
authors: Michal
authors: M
authors: Dušek