SOLVENT EFFECTS ON THE RELATIVE STABILITY OF THE PDCL2(H2O)(N) AND PDHCL(H2O)(N) CIS AND TRANS ISOMERS

The relative stability of the cis and trans isomers of the PdCl2(H2O)( n) and PdHCl(H2O)(n) complexes with up to six water ligands has been s tudied. Optimized geometries are discussed with particular emphasis on the positions taken by the second sphere water ligands. It is found t hat the empty coordination site above palladium is not as attractive f or the second sphere ligands as might have been anticipated. Two types of hydrogen bonds, of O-H...Pd and O-H...H-Pd were found, which have only recently been detected experimentally. The effect of a water solv ent on the complexes was then studied using a model with a spherical c avity surrounded by a dielectric continuum. Since the cis forms of the complexes have large dipole moments, the dipole term of the solvent r eaction field strongly favours these structures. However, it is found that the quadrupolar terms have an almost equally large effect in the opposite direction, favouring the trans isomer. Even the octapole and hexadecapole moments make non-negligible contributions to the relative stabilities.