Complexes formed by interaction of E(C₆F₅)₃ (E = B, Al, Ga, In) with excess of acetonitrile (AN) were structurally characterized. Quantum chemical computations indicate that for Al(C₆F₅)₃ and In(C₆F₅)₃ the formation of a complex of 1:2 composition is more advantageous than for B(C₆F₅)₃ and Ga(C₆F₅)₃, in line with experimental observations. Formation of the solvate [Al(C₆F₅)₃·2AN]·AN is in agreement with predicted thermodynamic instability of [Al(C₆F₅)₃·3AN]. Tensimetry study of B(C₆F₅)₃·CH₃CN reveals its stability in the solid state up to 197 °C. With the temperature increase, the complex undergoes irreversible thermal decomposition with pentafluorobenzene formation.