THERMODYNAMIC STUDIES OF RELATIVE STABILITIES OF BIS- AND TRIS-PHOSPHINE COMPLEXES OF NICKEL(2) CYANIDE IN SOLUTION

Thermodynamic data are reported for the four-coordinate-five-coordinate equilibria Ni(PR3)2(CN)2 + PR3⇄ Ni(PR3)3-(CN)2 (where PR3 = P(C2H5)3, P(C3H7)3, P(C4H9)3, P(C2H5)2C6H5, PC2H5(C6H5)2) in ethanol, n-hexane, and dichloroethane. The stability order for the complexes Ni(PR3)3(CN)2, measured by the equilibrium constants at 20° in ethanol, is P(C3H7)3 ~ p(C4H9)3 < P(C2H5)3 < PC2H5(C6H5)2 « P(C2H5)2C6H5. It is shown that the values of the enthalpy changes ΔH°, determined spectrophotometrically by measuring the equilibrium constants at different temperatures, provide a fairly good measure of the growing covalency of the bonds on formation of the five-coordinate complexes. © 1969, American Chemical Society. All rights reserved.