Results of an experimental research of phase equilibrium in ternary systems MX2-NR4X-H2O [M = Cd(II), Cu(II), Co(II), Mg(II); X = Cl, Br; R = Me, Et, Bu] at 25°C were reported. A comparative analysis of compositions of solid compounds and regions of their crystallization, which are equilibrium with liquid phase, was conducted. An effect of hydration, association of salts of quaternary ammonium and acido complexation of ions of d-elements on the formation of the complex and double salts in the systems was presented.