Neutron diffraction and vibrational spectroscopic study of single crystals of KH(D)(CHCl2COO)2

The hydrogen atoms in the short (2.498 Å) hydrogen bonds of potassium hydrogen bis-dichloroacetate are placed asymmetrically with respect to the oxygen atoms. The geometric mass effect (R 0.02 Å) is well within the range observed with this type of hydrogen bond. The thermal ellipsoids of the bridging protons are slightly elongated, the longer axis being at 40 ° with respect to the O(2)-O(4) direction. This coincides with the direction of the transition dipole moment of thev _a OH vibration. The two infrared components of this vibration are rather different, one (A_u) being very broad and intense and the other (B_u) only moderately broad. Thev _a OH/v _a OD ratio is small (1.05).