Atomic partial charges for mixed chloroammine chromium(III) complexes fitted to the molecular electrostatic potential

Using the RESP procedure partial atomic charges for six isomers of a series of octahedral complexes [Cr(NH3)6−x(Cl)x](3−x)+ (x = 0, 1, 2, 3) were least-square fitted to the molecular electrostatic potential (MEP) derived from quantum mechanical (QM) calculations with different HF basis sets. The resulting charges are self-consistent, they match MEPs, QM dipole and quadrupole moments, and they reflect fine electronic effects in the coordination sphere (viz. trans and cis influence) offering a possibility to explicitly incorporate some of these electronic features in a molecular mechanics (MM) treatment. RESP derived partial atomic charges (together with other nonobservable quantities, such as atomic dipole moments, and atomic polarizabilities) could thus be parametrized on the basis of a multibody model, which is a prerequisite for any nonadditive MM approach.