Electronic Spectra Including Charge Transfer

In nondonor solvents such as hexane, the iodine color remains essentially the same violet, but in benzene and other rr-electron solvents it becomes more red-violet, and in good donors such as ethers, alcohols, and amines the color becomes distinctly brown. The solubility of I2 also increases with increasing donor character of the solvent. Interaction of the donor orbital of the solvent with the 9a orbital results in a lower occupied bonding orbital and a higher unoccupied antibonding orbital. As a result, the TTg ---- CT transition for I2 + donor (Lewis base) has a higher energy and an ab- 

The charge-transfer phenomenon also appears in many other adducts. If the charge-transfer transition actually transfers the electron permanently, the result is an oxidation-reduction reaction—the donor is oxidized and the acceptor is reduced. The sequence of reactions of [Fe(H20)6] (the acid) and aquated halide ions (the bases) 

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Electron transfer [Eq. (1)] would occur at a rate near the diffusion limit if it were exothermic. However, a close estimate of the energetics including solvation effects has not been made yet. Recent support of the intermediacy of a charge transfer complex such as [Ph—NOf, CP] comes from the observation of a transient (Amax f 440 nm, t =2.7 0.5 ms) upon flashing (80 J, 40 ps pulse) a degassed solution (50% 2-propanol in water, 4 X 10 4 M in nitrobenzene, 6 moles 1 HCl) 15). The absorption spectrum of the transient is in satisfactory agreement with that of Ph—NO2H, which in turn arises from rapid protonation of Ph—NOf under the reaction conditions ... 

We have utilized the embedded cluster DV scheme to study the electronic structure of the Y(Ni] IMI)B2C superconductors (M=Fe, Co, and Ru), with 71 atom variational clusters centered on the substitutional site [109] as shown in Fig. 13. Bonding within the RC plane is found to be highly ionic, while B-C and Ni-B bonding structures are analyzed as typically covalent. In addition, the strong overlap between atoms in the transition metal plane has typical metallic character. Thus the entire spectrum of chemical bonding including ionic, covalent, and metallic structures is found within this peculiar crystal structure. The Ni-B slab is found to be electron-rich, as the result of charge transfer from the RC planes. 

Electronic transitions in the absorption spectra of Pt(II) complexes include ligand-field (LF) and charge-transfer (CT) bands and perhaps 5d-6p transitions e.g., the absorption spectrum of aq [PtCl ] displays well-separated LF and CT transitions with a maximum at 480 nm (molar absorbtivity, e = 15 M cm ) assigned to a triplet LF absorption, two maxima at 394 nm (e = 57) and 337 nm (e = 62) assigned to singlet LF absorption, and intense bands 200-250 nm (e > 10 ) to LMCT transitions ". The luminescence of K lPtCl ] in ice occurs from the lowest LF-triplet state, and the molecular geometry of this excited state (ES) may be (distorted T j) rather than D41, (square planar), which is particularly relevant to the photochemistry of Pt(II) complexes. 

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