Methodological Approach Based on Structural Parameters, Vibrational Frequencies, and MMFF94 Bond Charge Increments for Platinum-Based Compounds

In this work, we
performed a comprehensive benchmark study for
the ground state of five small- and medium-sized platinum derivatives,
PtH, PtCl, [PtCl4]2–, [Pt(NH3)4]2+, and cis-[Pt(NH3)2Cl2], in the gas phase and two cisplatin
polymorphs in the solid phase. The benchmark encompassed 16 density
functionals, including nonhybrids, hybrids, and double hybrids. Furthermore,
Hartree–Fock (HF) and Post-HF by Møller–Plesset
MP2 methods were also tested. Additionally, 11 basis sets were explored,
comparing relativistic all-electron and RECP approaches. Our results
indicate that the methodologies best suited for predicting structural
parameters do not excel in predicting vibrational frequencies and
vice versa. In the context of this theoretical framework, we also
examine the derivation of partial atomic charges and bond charge increments
(bci) as fundamental parameters within the MMFF94 classical force
field. Our results show that the partial atomic charges of CHELPG
present a slight charge fluctuation in Pt for all investigated levels
of theory, and this behavior reproduces well the soft acid definition
for Pt2+, giving the best description of the chemical environment
of platinum in the cisplatin complex. The average calculated bci values
effectively capture the atomic charge variations in the chemical environment
of Pt in the investigated species. The developed bci optimization
tool, based on MMFF94, was implemented using a Python code made available
at https://github.com/molmodcs/bci_solver. This methodology will be further implemented in the DockThor receptor–ligand
docking program, allowing future molecular docking validations involving
ligand compounds containing Pt atoms.