Solvent Effect on the 195Pt NMR Properties in Pyridonate-Bridged PtIII Dinuclear Complex Derivatives by ab Initio Molecular Dynamics and Localized Orbital Analysis

An ab Initio molecular dynamics investigation of the solvent effect (water) on the structural parameters, electronic structure, 195Pt NMR spin-spin coupling constants (SSCCs) and chemical shifts of a series of pyridonate-bridged PtIII dinuclear complexes is performed using Kohn-Sham (KS) Car-Parrinello molecular dynamics (CPMD) and relativistic hybrid KS NMR calculations. The indirect solvent effect (via structural changes) has a dramatic effect on the 1JPtPt SSCCs. The complexes also present a strong trans influence in solution, where the Pt Pt bond lengthens with increasing axial ligand σ-donor strength. In the diaquo complex, where the solvent effect is more pronounced, the SSCCs averaged for CPMD configurations with explicit plus implicit solvation agree much better with the experimental data, while the calculations for static geometry and CPMD unsolvated configurations show large deviations with respect to experiment. The combination of CPMD with hybrid KS NMR calculations provides a much more realistic computational model that reproduces the large magnitudes of 1JPtPt and 195Pt chemical shifts. An analysis of 1JPtPt in terms of localized orbitals shows that the solvent also causes rearrangements of the electronic structure, localizing the orbitals. The SSCCs are driven by changes in the s character of the natural atomic orbitals of Pt atoms, which affect the Fermi contact mechanism. There is pronounced multicenter bonding along the metal-metal axis of the complexes.