Complexation of palladium(II) with thiocyanate - a spectrophotometric investigation

A spectrophotometric investigation into the complexation of palladium(II) with thiocyanate revealed the existence of five coordinated palladium(II) complexes. Molar absorbance spectra as well as formation constants were calculated for all five complexes. Complex-formation of Pd(II) with thiocyanate has been investigated by spectrophotometry at 25 degrees C and an ionic strength of 1.0 M. The formation constants, beta(n), for the palladium(II) thiocyanate complexes [Pd(SCN)(n)(H2O)(4-n)](2-n) (n = 0-4), have been determined and the values are: log beta(1) = 8.14, log beta(2) = 15.46, log beta(3) = 21.94, and log beta(4) = 27.42. These complexes are generally accepted to be square planar. However, a five-coordinate species, i.e. [Pd(SCN5](3-), with a formation constant of log beta(5) = 31.94 seems to exist and is proposed to be square pyramidal. Molar absorption spectra for all the complexes in question have been obtained.