Quantum chemical modeling of the thermodynamics of the formation of Au(III), Pd(II), and Pt(II) chloride complexes

Quantitative prediction of physical properties of liquids and equilibrium constants is important for many applications. Computational methods based on either explicit or implicit solvent models can be used to approximate thermodynamics of complexation. A practical method for calculating the stability constant of ( )d(8) chlorocomplexes (PdCl42-, PtCl42-, AuCl4-) in aqueous solution has been developed by using DFT and DLPNO-CCSD with the SMD solvation model and 100 unique explicit water molecules. Stability constants have been calculated by using methods, such as DFT/PBE0-D3, DLPNO-CCSD, DLPNO-CCSD-DK, and DLPNO-CCSD(T), and basis sets, such as def2-TZVPD, def2-TZVPP, ma-def2-TZVP, ma-DKH-def2-TZVP, SARC-TZVP, and SARC-TZVPP. Calculations using DFT/PBEO-D3/def2-TZVPD and DLPNO-CCSD-DK/ma-DKH-Def2-TZVP/SARC-DKH-TZVP with SMD solvation with explicit waters are found to have errors of 2-3 log units relative to experimental data. The best results are obtained by using 8 explicit waters for d(8) aqua complexes, 14 explicit waters for d(8) chlorocomplexes, and 4 explicit waters for chloride ion.