NMR-STUDY OF THE F-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-F HYDROGEN-BOND- RELATION BETWEEN HYDROGEN-ATOM POSITION AND F-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-F BOND-LENGTH

H-1 and F-19 NMR study of (NH4)(3)BiBr6NH4Br . 2NH(4)HF(2) shows the b ifluoride ion in this compound to be asymmetric with distances r(H-F) = 1.042 +/- 0.002 and R(F-F) = 2.373 +/- 0.008 Angstrom. Existing NMR and neutron diffraction data for the F-H...F hydrogen bond in solids h ave been studied to find a relation between the position of the hydrog en atom and F-H F...bond length. Such a relation has been established and explained in the framework of the two-dimensional dynamic model of the hydrogen bond. The dependencies of r(A-H) on R(A-B) for the O-H.. .O and F-H...F bonds are shown to be similar.