F-H•••F hydrogen bond in diphenylguanidinium hydrogen bifluoride

The crystal structure of C12H14N3+FHF- is reported. The structure contains the strong hydrogen-bonded system, the bifluoride anion F-H . . .F-. The geometry of this anion deviates significantly from linearity but has the H atom in an approximate centered position. The F . . .F distance is 2.293(3) Angstrom, considerably less than twice the van der Waals radius of fluorine, as expected from a very strong hydrogen bond. One of the phenyl rings of the diphenylguanidinium counter ion of the bifluoride anion is oriented syn to the unsubstituted N atom of the guanidine group, the other adopts an anti conformation. The anions and cations are held together by a layered two-dimensional network of hydrogen bonds. Both NH and NH2 groups of the cation are donors towards the fluoride ions, exhausting the potential of diphenylguanidine for hydrogen bonding. (C) 2001 Elsevier Science B.V. All rights reserved.