Solvation of calcium ion in methanol: Comparison of diffraction studies and molecular dynamics simulation

Molecular dynamics simulation and diffraction (X-ray and neutron) studies were compared on 1 and 2 M methanol solutions of calcium chloride with aiming at the determination of the solution structures. Beyond that, the capabilities of the methods to describe solution structure are discussed. It has been found that diffraction methods are performing very well in determination of Ca2+-O distances (2.39 Å in average). Further on, by applying the X-ray diffraction method ion pairs could be observed easily for higher concentrated solution, but for neutron diffraction study, the most adequate isotope substitution method has to be chosen with care in order to be able to detect ion pairs in solution. The results of molecular dynamic simulation were found to be in general accordance with the experimental findings. The smaller discrepancies between simulation and experimental results are coming from small differences in the ion-methanol and ion-ion distances, and they may be due to both the potential model applied in the simulation and to the experimental uncertainties.