Hydration of platinum(II) complexes:: a molecular mechanics study using atom-based force-field parameters

This work is related to the interaction of water with two platinum(II) complexes, [Pt(NH3)(4)](2+) (denoted 1) and trans-[Pt(OH)(2)(NH3)(2)] (denoted 2). We have considered two approaches of a water molecule to complexes 1 and 2 along the z-axis normal to the platinum(II) coordination plane: approach I, with the water oxygen oriented towards Pt, and approach II, with one water hydrogen directed towards Pt. Calculations have been performed within a molecular mechanics method based upon the interaction potentials proposed earlier by Claverie et al. and subsequently adjusted to results obtained with symmetry - adapted perturbational theory as well as with supermolecule (up to second-order Moller-Plesset, MP2) methods. We discuss some possible simplifications of the potentials mentioned. The results relative to the hydration of Pt complexes 1 and 2 following approach I or II are discussed and compared to recent (MP2) ab initio energy-distance curves that we have recently determined. The MP2 calculations have shown that besides exchange-repulsion contributions, which are very similar in all hydrated complexes, approach I is mainly governed by electrostatics, whereas for approach II both electrostatic and dispersion contributions are important.