Significant Differences in the Energy of X-H/Pt Interactions between Cisplatin and Transplatin Molecules

Abstract

X−H/Pt interactions between cisplatin (cis-[Pt(NH3)2Cl2]) and transplatin (trans-[Pt(NH3)2Cl2]) molecules as hydrogen atom acceptors and CH4, NH3 and H2O molecules as hydrogen atom donors were studied by quantum chemical calculations and analysis of crystallographic data from Cambridge Structural Database (CSD). Results of interaction energies calculations showed that almost in all cases cisplatin molecule forms stronger X−H/Pt interaction compared to transplatin molecule. The strongest calculated interaction is O−H/Pt interaction between cisplatin and a water molecule with the energy ΔEMP2/aug-cc-PVDZ=-5.97 kcal/mol; calculated energy of the strongest transplatin/water interaction is ΔEMP2/aug-cc-PVDZ=-4.43 kcal/mol. Only in case of C−H/Pt interactions translplatin molecule forms slightly stronger interaction compared to cisplatin molecule; the energy of the strongest C−H/Pt interaction involving transplatin molecule is ΔEMP2/aug-cc-PVDZ=-1.20 kcal/mol while for cisplatin energy is ΔEMP2/aug-cc-PVDZ=-1.08 kcal/mol. Interaction energies for geometries with the strongest X−H/Pt interactions were re-calculated at CCSD(T)/CBS level and these results were in excellent agreement with results obtained at MP2/aug-cc-PVDZ level of theory. Electrostatic potentials were calculated and used to explain results of interaction energies calculations. Analysis of geometrical data revealed that cisplatin and transplatin molecules are involved in X−H/Pt contacts in crystal structures.