F-H center dot center dot center dot 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 ge ometry of this anion deviates significantly from linearity but has the H at om in an approximate centered position. The F . . .F distance is 2.293(3) A ngstrom, 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 biflu oride anion is oriented syn to the unsubstituted N atom of the guanidine gr oup, the other adopts an anti conformation. The anions and cations are held together by a layered two-dimensional netwo rk of hydrogen bonds. Both NH and NH2 groups of the cation are donors towar ds the fluoride ions, exhausting the potential of diphenylguanidine for hyd rogen bonding. (C) 2001 Elsevier Science B.V. All rights reserved.