The complex formed between HCOO- and HOH is examined by ab initio methods using a 4-31+G* basis set. A number of minima are located in the potential energy surface, the most stable of which is of C2, geometry wherein both protons of HOH participate in H bonds. The barrier impeding proton transfer between OH- and HCOO- rises with increasing intermolecular separation for each of the arrangements studied. As the OH- anion moves toward the C-0 axis of HCOO-, the equilibrium position of the bridging proton is shifted toward the former group, paralleling earlier observations for the pair of neutral subunits HCOOH and HOH. On the other hand, HCOO- and HCOOH behave in different fashion with respect to motions of the hydroxyl group out of the carboxyl plane. These patterns are explained simply on the basis of differing ion-dipole interactions, as are small differences in the optimal geometries and proton-transfer behavior of the various arrangements of the two subunits.
- hydrogen bonding,