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Mixed-valence complexes spectrum

There are at least two ways in which detailed information about electron-vibrational coupling strengths can be obtained for mixed-valence complexes. Both are based on the fact that such coupling will be reflected in modifications of the vibrational spectrum. Thus, for example, coupling to antisymmetric modes in a symmetric ion will modify intensities and frequencies of the modes involved. [Pg.320]

The difficulties of interpretation presented by some of these complexes are well illustrated by the sequence of ferrocene derivatives (VIII to X). The spectrum of VIII shows a near-infrared absorption as expected for a mixed valence complex, but the band has a shoulder, and at low temperatures is resolved into two bands. Complex IX has a well-defined band almost certainly ascribable to intervalence transfer, but complex X with a similar molecular structure has no such... [Pg.201]

Studies of the intervalence charge-transfer spectrum in solid-state inorganic materials and dinuclear mixed-valence complexes have given analogous information, less controversially. At low temperatures, the variation of spectral bandwidth is given by ... [Pg.1206]

An intervalence electron-transfer band, not present in the Fe analogue, was observed in the room temperature electronic spectrum at 13 800cm . Mossbauer spectra indicated distinct Fe" and Fe " sites at 17K while at 300 K a single absorption was observed. The thermal barrier to electron transfer in the trimer was estimated as about 470 cm. Triiron clusters of this type, in the presence of zinc powder, acetic acid, aqueous pyridine and oxygen, are reported " to effect the oxidation of saturated hydrocarbons. The exchange interactions in the series of complexes [Fe2 M 0(02 CMe)spyj] py (M = Mg, Mn, Co, Ni or Zn) which, M = Ni excepted, are isomorphous with the mixed valence complex referred to above have been measured. [Pg.229]

The ESR spectrum of the fully reduced anion, PV2 Wio04o (Figure 7), has the 15-hne pattern ((g) = 1.95, (a) = 53 G) expected for the interaction of the unpaired electrons with two vanadium nuclei. Observation of the half-field (Am, = 2) transition in the spectrum of the solid potassium salt confirms the triplet state of the species responsible for the spectrum in Figure 7. It seems very likely that those isomers (1,2 and 1,6 with V-O-V groups) which are responsible for the 15-line spectrum of the mixed valence complex would have antiferromagnetically coupled spins in the fully reduced anion. The remote isomers with vanadium atoms separated by O-W-0 (1,4 and 1,5) or O-W-O-W-O (1,11) sequences are therefore probably responsible for the triplet state ESR spectrum. Further ESR and magnetic susceptibihty measurements are planned on individual isomers. [Pg.93]

One of the most powerful methods of evaluating the properties of mixed-valence complexes is spectroelectrochemistry. A key experiment is to reversibly cycle a dinuclear complex through fully oxidized, mixed-valence and fully reduced states. A near IR absorption band that appears only in the electronic spectrum of the mixed-valence state is strong evidence for an intervalence transition. Determination of the nature of the mixed-valence state can also be achieved by spectroelectrochemical methods. [Pg.240]

Oxidation of dinuclear Pd(II) complexes by one electron is predicted to afford dinuclear Pd(II)/Pd(III) mixed valence complexes with a Pd-Pd bond order of 0.5 (Fig. 20) [92]. Dinuclear Pd(II)/Pd(III) mixed valence complexes have been detected by EPR spectroscopy, although, similar to mononuclear systems, the unpaired electron is not always metal-centered [87,93], Two examples of dinuclear Pd(ll)/Pd(lll) complexes bearing a metal-centered unpaired electron have been reported [94, 95]. In 1988, Bear reported the EPR spectrum of tetrahridged dinuclear complex 38, prepared by electrochemical oxidation of 37 (Fig. 22a) [95]. In 2007, Cotton reported the only crystaUographically characterized mixed valence Pd (ll)/Pd(ni) complex (40 Fig. 22b) [94]. Both 38 and 40 are paramagnetic and have EPR spectra consistent with a metal-based oxidatimi. The metal— metal distance in 40 is 0.052 A shorter than the corresponding distance in Pd(ll) complex 39, consistent with a Pd-Pd bond order of 0.5. [Pg.141]


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See also in sourсe #XX -- [ Pg.330 , Pg.331 ]




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