EPR Spectra Of Solutions Of Platinum Superoxo Hydroxo Complexes
EPR Spectra Of Solutions Of Platinum Superoxo Hydroxo Complexes. Komozin P.N., Pankratov D.A., Kiselev Yu.M. //Russian Journal of Inorganic Chemistry. 1999. V. 44. № 12. P. 1945-1951
EPR spectra of platinum superoxo hydroxo complexes in alkaline solutions were studied at various alkali concentrations. The EPR parameters for new platinum complexes were determined; the g-factors and hyperfine coupling constants were interpreted in terms of the ligand field theory. The structure of the platinum coordination sphere in the superoxo hydroxo complexes is discussed based on the EPR data.
In a previous study, dealing with ozonization of the platinum hexahydroxo complex in alkaline solutions with alkali concentrations of 1 to 4 mol/l, we discovered a blue platinum compound, which was classified as a superoxo hydroxo complex. The EPR spectra virtually coincided with those reported in [2] for the derivative of pentavalent platinum resulting from ozonization or electrochemical oxidation of alkaline solutions of hexahydroxoplatinate(IV). Based on the resolved structure of the EPR spectra of solutions of compounds identified as M[PtV(OH)6] (M = Li, K, Rb, Cs), it was concluded [2] that the unpaired electron of Pt(V) is involved in substantial hyperfine coupling (HFC) with the alkali-metal ions. This is surprising, especially for solutions in which the salts are dissociated. The coupling between the unpaired electron and, for example, potassium or lithium nuclei, whose nuclear spin is 3/2, should result in four equidistant components with equal intensities in the EPR spectra; this was not observed in the spectra of frozen solutions reported in [2]. The EPR spectra of paramagnetic platinum (usually Pt(III)) complexes exhibit hyperfine structure (HFS) from the 195Pt isotope (I= 1/2, natural abundance 33.8%): i.e., for each main component of the g-tensor, the spectrum may contain two equidistant satellites, whose intensity is about 25% of the central peak intensity. The spectra reported in [2] cannot be assigned to individual mononuclear platinum(V) complexes, because they have additional components. These facts, together with those reported in paper, indicate that the EPR spectra observed can by no means be attributed to the platinum(V) hydroxo complex and can be due only to the corresponding superoxo complex.
However. some features of these spectra had precluded the possibility of drawing unambiguous conclusions on the structure of the "blue" complex. The same holds true for the "pink" complex, first prepared in work, which is stable in more concentrated solutions of KOH. More detailed investigation of this aspect is the subject of the present study.
Thus, oxidation of platinum(IV) hexahydroxo complexes by ozone, hypochlorite, persulfate, or electric current in solutions yields superoxo hydroxo complexes that are present in different concentrations depending on the alkali concentration and exposure duration.
2. Вurlaku N.Y., Ketrush P.M., Shames A.L. et al. //Mater. Sci. 1991. V.17. Is.4. P.47.
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