Mixed-ligand complexes of palladium(II) with bromide and chloride in acetonitrile

Abstract

A computer and a graphical method are used to evaluate equilibrium constants and extinction coefficients from spectrophotometric data for the system . tPn PdBr42" + nCP = PdClnBr4_n2" + nBr"The measurements were performed in acetonitrile at an ionic strength maintained at 1.5 with tetrabutylammonium halide. The results obtained by both techniques are in reasonably good agreement. The computer-determined values for the constants are log ß = 1.24 ± 0.07, log 7ß2 = 1.84 ± 0.06, log ß3 = 2.50 ± 0.06, and log +04 = 2.39 ± 0.05. These constants yield a distribution of mixed-halide species which approximates that which would be predicted on a statistical basis. The stability of PdCl42~i s 102•4 times greater than that of PdBr42~i n acetonitrile. This is not only an inversion of the relative stability in water but a change of 6.5 orders of magnitude. The measurement of mixed-ligand complexation appears to be a better method of determining the relative stability of simple ligand complexes than measurements involving the individual systems.