In a mixture of solvents S1 and S2 a cation Mz+ forms “solvatomers” of the type M(S1)i(S2)k‐iz+, where k is the coordination number of the cation and i = 0 to k. The rate of substitution of a solvating molecule by a ligand LzL depends in general on the specific solvatomer and on the solvent molecule being substituted. – Kinetic measurements are reported on systems with the cations Be2+, Al3+, and Ni2+, the ligands sulfate, rhodanide and acetate and the solvent pairs water‐dimethylsulfoxide, water‐N‐methylformamide, water‐hexamethylphosphoric triamide, water‐formamide and methanol‐dimethylsulfoxide. – Some rules concerning the kinetic behaviour of such systems have been developed. In particular, an explanation is presented for the different kinetics observed with tetrahedrally coordinated complexes (k = 4) and with octahedrally coordinated ones (k = 6).