Electronic and Resonance Raman Spectra of Some New Mixed-Valence Compounds of Pt and Pd with a Metal-Halide Chain

Papavassiliou, George C.; Layek, D.

doi:10.1515/znb-1980-0606

Cited by 11 publications

(3 citation statements)

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“…This can be generalized to a multimode description. Already there is quite a sizable body of data accumulating on the resonance Raman spectroscopy of mixedvalence systems (49,50). Some show the long overtone progres sion anticipated for very strong coupling (and hence large Δ) to a mode.…”

Section: Evaluation Of Coupling Strengthsmentioning

confidence: 99%

Parameters of Electron-Transfer Kinetics

Hush

1982

Mechanistic Aspects of Inorganic Reactions

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Over the last two decades, there has been a considerable increase in experimental information about the rates of electron transfer processes, particularly in solution in ionizing solvents. The main features (enthalpies, free energies and entropies of activation) of a large class of these reactions have been broadly understood for about the same length of time. It is interesting to note that the results of very early calculations of outer-sphere reaction rates and their tempera ture dependence frequently agree with recent more detailed estimates. In order to assess the appli cability of different approaches, and thus to discriminate between them, it is desirable to have as much detailed information as possible about the relevant basic parameters. These include, for example, electron coupling or overlap energies, electron-phonon coupling strengths, vibrational frequencies, and spin coupling data. A brief survey is given of the types of experiment which may provide this information. With such data, discussions on matters such as the applicability of Golden Rule perturbation approaches, electronic adiabaticity, the role of nuclear tunnelling, etc., can be put on firmer ground, and some of the outstanding theoretical issues awaiting reso lution are outlined.The theory of homogeneous electron transfer processes, as well as of the closely-related electron exchanges with metallic electrodes, has been the subject of considerable study.The proposal by Hush and by Marcus that these processes are, for simple systems, either usually electronically adiabatic or 0097-6156/82/0198-0301$09.00/0

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Section: Evaluation Of Coupling Strengthsmentioning

confidence: 99%

Parameters of Electron-Transfer Kinetics

Hush

1982

Mechanistic Aspects of Inorganic Reactions

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“…1 In addition to contributing to an understanding of the electronic factors of general E-H bond activation and oxidative addition to a metal center, the complexes are important as models for catalysts in hydrosilation reactions. 2 The X-ray and neutron diffraction structures,1,3"5 29Si NMR shifts and couplings,1 and •To whom correspondence should be addressed. 0020-1669/90/1329-0975S02.50/0 reaction chemistry6"8 and rates9 of these complexes are interpreted in some cases in terms of a three-center-two-electron Mn«-H-E T h i s c o n t e n t i s bond in the complex, as represented schematically in A.…”

Section: Introductionmentioning

confidence: 99%

Electronic structure factors of silicon-hydrogen bond activation by transition metals. Valence photoelectron spectra of (.eta.5-C5H4CH3)Mn(CO)(PMe3)HSiCl3 and (.eta.5-C5H4CH3)Mn(CO)(PMe3)HSiHPh2 (Me = CH3, Ph = C6H5)

Lichtenberger¹,

Rai-Chaudhuri²

1990

Inorg. Chem.

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between atoms in bonds.32 Orbital u3 has nodes between atom pairs 1 and 2 and pairs 3 and 4, and the 2-3 interaction is bonding, again different from the 5c scheme. Thus we would expect the 4c hypervalent bond to be significantly weaker than the 3c or 5c hypervalent bonds. In the 4c bond, nodes occur between atoms in the occupied orbitals whereas, in the 3c and 5c bond, nodes occur at atoms in these orbitals. The above simple model assumes that the atoms are of equal electronegativity. However, in [ FKrNCH]+ the atoms are clearly not of equal electronegativity. Furthermore, the C-H bond is of the right energy for mixing, which complicates the analysis. The presence of a triple bond between C and N is also a complicating factor, as this increases the s component (sp hybridization) in the C-N u bond, which would be part of the 4c hypervalent bond. Examination of Figure 1 shows that the orbitals do not delocalize as extensively as suggested by our model for the 4c hypervalent bond due to the large electronegativity differences. Furthermore, the s and p orbitals are clearly mixed. The highest occupied u orbital, u6, is similar to orbital u2/ of the 4c bond with the largest population on N and the next highest population on F. Because of the large s character in the C N u bond, this orbital is very low in energy and the C-H u bond mixes with the Kr-F u bond instead of mixing with the C-N u bond as one would expect from the 4c hypervalent bond. The C N u bond is mixing, instead, with the (32) Arduengo, A. J.; Burgess, E. M. J . Am. Chem. SOC. 1977, 99, 2376.Kr valence s orbital. Thus the bonding of the u,' orbital of the 4c bond is dispersed over a range of CT orbitals, Another model for this bonding would involve considering both the C-N and C-H bonds as "spectators" and dealing only with a normal 3c,4e hypervalent bond centered at Kr based on the Kr-F bond and the lone pair on N. In this case, u6 of [FKrNCH]' is like u2" of the 3c,4e bond. There is essentially a node at Kr, and the population is not equally distributed between N and F. The u4 orbital of the complex then corresponds to u," of the 3c,4e bond. A complication for this model is that the 3c,4e bond preferentially places the least electronegative atom in the center. Clearly, "Kr+" is not the least electronegative atom. In order for it to lower its electronegativity in order to participate in the hypervalent bond, charge transfer occurs from the C-H region to the Kr to lower its positive charge and hence its electronegativity. This is actually observed in the population analysis and is consistent with the resonance structure shown above.All of our results are consistent with some type of covalent bonding interaction in [FKrNCH]+ being present. However, as the above discussion points out, there is no clear choice between the 3c and 4c hypervalent bond models. Rather, the bonding description for the interaction of [FKr]+ with N C H has components of both models present. The results do show that the bonding between Kr and N is not a simple covalent u bond betwe...

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“…Resonance Raman spectra of mixed valence compounds with a M(II)-X-M(IV) chain (where M = Pt or Pd and X = Cl, Br or I) were reported in a number of papers , The spectra have been observed in a poly crystalline [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] or in singlecrystal form [17][18][19][20][21][22], [9]. The main feature of the spectra is the strong resonance enhancement of the -X-M(IV)-X--symmetric stretching vibration in the chain.…”

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confidence: 99%