| Abstract
| - The 195Pt chemical shifts of three complexes have been investigated theoretically. Solvent effects were included in static calculations both explicitly, via a continuum solvent model, and via molecular dynamics with a number of explicit solvent molecules. The calculations demonstrate the significance of solvent effects for 195Pt chemical shifts as well as a high sensitivity to small structural changes in the complexes. A successful computation requires a high-level computational model or a well-balanced and well-understood level of error compensation in computationally more efficient models.
- Density functional theory using the zero-order regular approximate two-component relativistic Hamiltonian has beenapplied to calculate the 195Pt chemical shifts for the complexes [PtCl6]2-, [PtCl4]2-, and [Pt2(NH3)2Cl2((CH3)3CCONH)2(CH2COCH3)]Cl. It is demonstrated that, in contrast to recent findings by other authors, platinum chemical shiftcalculations require not only a basis set beyond polarized triple-ζ quality for the metal atom but also, in principle,the consideration of explicit solvent molecules in addition to a continuum model for the first two complexes. Wefind that the inclusion of direct solvent−solute interactions at the quantum mechanical level is important for obtainingreasonable results despite that fact that these solvent effects are rather nonspecific. The importance of solventeffects has also implications on how experimental data should be interpreted. Further, in contrast to several previousstudies of heavy-metal NMR parameters, functionals beyond the local density approximation were required both inthe geometry optimization and the NMR calculations to obtain reasonable agreement between the computed andexperimental NMR data. This comes with the disadvantage, however, of increased Pt−ligand bond distances leadingto less good agreement with experiment for structural data. A detailed analysis of the results for the two chloroplatinatecomplexes is presented. The same computational procedure has then been applied to the dinuclear Pt(III) complex.Chemical shifts have been calculated with respect to both [PtCl6]2- and [PtCl4]2- chosen as the NMR reference,yielding good agreement with experiment. The determination of preferred solvent locations around the complexesstudied turned out to be important for reproducing experimental data.
|
