STRUCTURES AND ENERGETICS OF ZN(NH3)(N)(2-6) - COORDINATION-NUMBER OFZN2+ BY AMMINE() (N=4)

From ab initio studies of Zn(NH3)(n)(2+) complexes (n=4-6), their vari ous minimum energy structures have been identified for the first time. The hexa-ammine-Zn(II) complexes with the coordination numbers (N-c) of 4 to 6 have almost the same enthalpies. But, owing to the entropy e ffect the complex with N-c=4 has the lowest free energy. Nevertheless, the structural stabilities of these complexes are not so different; t hus, the N-c may vary between 4 and 6 according to given molecular env ironments, though N-c=4 is the most favored. This is in accord with th e statistical analysis of the X-ray data of the Zn(II) complexes coord inated by nitrogen-containing ligands.