The structural and dynamical properties of the cis-(O-Zn-O angle approximate to 90 degrees) and trans-(O-Zn-O angle;: 180 degrees) isomers of the model diaquotriamminezinc(II) complex in aqueous solution have been evaluated using the hybrid quantum mechanical/molecular mechanical molecular dynamics simulation approach at ab initio Hartree-Fock level. In both complexes, the first hydration shell contains five ligands (two water and three ammonia molecules) arranged in a trigonal bipyramidal geometry. In the metastable cis-isomer two different bond lengths of 2.34 and 2.13 angstrom are observed for the Zn-O-ax and Zn-O-eq bonds, respectively. The transisomer shows the maximum of the Zn-O distance at 2.26 angstrom. The Zn-N bond distances in both cases are similar to 2.12 angstrom. A geometrical transformation of the cis-isomer into the trans-isomer was observed after 11.5 ps of simulation, and the trans-isomer then remained stable throughout the whole simulation time of 30 ps. A comparative study for both isomers has been performed in terms of radial distribution functions, coordination number distributions, anaular distribution functions, tilt and 0 angle distributions, ligands' mean residence time, ion-ligand stretching frequencies, and the vibrational and librational motions of water ligands. The results are compared with the data for the previously studied zinc-monoamine and -diamine complexes.