A systematic study of nonlinear optical (NLO) properties of inorganic transition metal (TM) thiometalates and metalates is reported. Polarizabilities (alpha) and second hyperpolarizabilities (gamma) are calculated in solution within the polarizable continuum model. It is found that NLO properties of anionic inorganic complexes can be successfully modeled in solution, when this cannot be done so in the gas phase. Solvent effects are found to significantly increase alpha and gamma. The effects are stronger on gamma (up to 80%) than on alpha (up to 40%) and stronger on TM thiometalates than on metalates. For alpha, solvent effects are found to be more important than electron correlation effects. For gamma, the two effects are similarly important. Solvent effects on alpha and gamma caused by subordinate factors other than the dominant electrostatic solute-solvent interactions were studied and assessed to be negligible. Upon solvation, large TM and ligand modification effects on alpha and gamma are found. One oxo-to-sulfido substitution results in an increase in alpha by 38 au and gamma by 10 000 au.