Localized mixed-valence complex

Another type of complex for which it is obvious thatQlarge structural changes occur on excitation (probably 0.2-0.3 A) along particular coordinates are the infinite-chain mixed-valence complexes of platinum and palladium (class II, or localized mixed-valence complexes) (11).. These Pti [/PtIV, PdIVPtIV or Pdi [/PdIV... 

Scheme 8. Oxidation or reduction of metallo-stars to localized mixed-valence complexes. Fe centers for which the oxidation state is not indicated in the scheme are Fe11.

Notice that the excited states are similar to those formed from the localized ground states. Again the first transition is of higher energy than the second. Hush has made a theoretical study of these transitions123. He concluded that, in the case of symmetrical delocalized mixed valence complexes, the two XPS peaks will occur at energies... 

The immense amount of spectroscopic work carried out on these complexes, particularly on their electronic, infrared, Raman and resonance Raman spectra (2), has led to Wolffram s red being regarded as the archetypal class II or localized valence complex in which the two metal atoms differ in their oxidation states by two, cf. Prussian blue is so regarded for mixed-valence complexes in which the two metal atoms differ in their oxidation states by one. 

Core vibrational frequencies obtained by Raman or resonance Raman spectrophotometric technique are summarized in Table V (53, 113, 116-118). The p(Pt—Pt) bands for the pop complexes [Pt2(pop)4] " (PtdDa), [Pt2(pop)4X] - (Ptdl,111)2), and [Pt2(pop)4X2] - (Pt(III)2) increase in the order expected from increasing Pt—Pt interaction (53). Resonance Raman spectra have been used frequently for the assignment of the electronic transitions of complexes as listed in the table. Also, observation of the vibrational structure in the low-temperature luminescence spectra coupled with the data in the table has been useful for considering the nature of the transition of these diplatinum complexes. The resonance Raman spectra at the intervalence band of the three mixed-valence complexes, which are stable only in the solid state, indicate that [Pt2(pop)4Cl] is a localized valence species and the bromo and iodo analogues are nearly delocalized valence species (53). 

Lu YH, Quardokus R, Lent CS, Justaud E, Lapinte C, Kandel SA (2010) Charge localization in isolated mixed-valence complexes an STM and theoretical study. J Am Chem Soc 132 13519... 

J.-F. Halet and C. Lapinte, Charge Delocalization vs Localization in Carbon-Rich Iron Mixed-Valence Complexes A Subde Interplay between the Carbon Spacer and the (dppe)Cp Fe Organometallic Electrophore, Coord. Chem. Rev., 2013, 257, 1584. 

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