Mixed valence halides

Technetium(II) complexes are paramagnetic with the d5 low-spin configuration. A characteristic feature is the considerable number of mixed-valence halide clusters containing Tc in oxidation states of +1.5 to + 3. This area has been reviewed (42). For convenience, all complexes, except those of [Tc2]6+, are treated together here. EPR spectroscopy is particularly useful in both the detection of species in this oxidation state and the study of exchange reactions in solution. The nuclear spin of "Tc (1 = f) results in spectra of 10 lines with superimposed hyperfine splitting. The d5 low-spin system is treated as a d1 system in the hole formalism (40). 

A number of mixed valence halides exist, such as In2Q3 (In3InmCk), In5Cl9 (InJInJ Clj), and In7Cl9 (In InIUCl9) In11 complexes can be made by the reaction... 

A simple procedure to prepare TICI3 is to bubble CI2 through a suspension of TlCl in acetonitrile . For TlBrs from TlBr, Br2 carried in N2 may be employed. The mixed-valence halides T1 T1" X4 and Tl TF Xe (X = Cl or Br) crystallize from aqueous solutions made by partially oxidizing TlX with the corresponding halogen. The rate of oxidation of Tl by Br2 in aqueous solution depends on the step ... 

Mixed valence halide A metal halide in which the metal atoms are in two different oxidation states (class I the oxidation states can be clearly distinguished)... 

The localized-valence halogen-bridged platinum(II)/platinum(IV) complexes (175) are of interest because of their highly anisotropic electrical and optical properties. The complexes are characterized by broad and intense intervalence bands in their electronic spectra.542 Partial oxidation of [PtCl(dien)]Cl with iodine yields the mixed valence species [PtI(dien)][PtI3(dien)]I2,543 but when 4Me-dien is used, the mixed valence compound is only obtained if it is trapped quickly, before isomerization of the meridional platinum(IV) complex to a facial form.544 Although these species nominally have localized valences, the extent of delocalization increases as the bridging halide... 

Chalcogenides, 5 94-96 berkelium, 28 49, 53-54 lattice energies of, 1 192, 193 ligands, 45 16 Chalcogen(II) compounds binary halides, 35 274—280 complexes with Lewis bases, 35 293-295 halo-chalcogenates(ll), 35 280-288 mixed-valence compounds, 35 288-293 cationic species, 35 291-293... 

There are several interesting families of inorganic mixed-valence compounds that we have not discussed here (see Yvon, 1979 McCarley, 1982). For example, there are metal-cluster compounds such as the Chevrel phases, M,jMo6X8(X = S or Se) and condensed metal-cluster chain compounds such as TlMojScj, TijTe, NaMo O and M PtjO. TTF halides and TTF-TCNQ complexes (Section 1.9) constitute molecular mixed-valent systems in which the mixed valency is associated with an entire molecule the charge on TTF in such compounds is nonintegral. The structure of TTF-Br(, 79 and... 

What makes the TTF-TCNQ family distinct from the other salts of TCNQ with cations, such as alkali metals and tetramethylammonium, is that the charge transfer,/ in the TTF-TCNQ family is incomplete (f < 1). TTF-TCNQ members are also different from the TTF-halides in the TTF-halides, where the charge on each halide atom is unity, partial charge transfer (mixed valency) is realized by the formation of nonstoichiometric materials, while in the TTF-TCNQ family, the composition is stoichiometric (1 1), but mixed valence arises because of partial electron-transfer. 

A mechanism that accounts for the oxidative addition of halocarbons has been proposed for the two d8-d8 dimers (Figure 4) (23). The mechanism involves the oxidative quenching of the triplet excited state of the metal dimer as the primary photoprocess. This gives a radical anion species that dissociates a halide, thereby producing an organic radical. The dissociated halide adds to the partially oxidized metal dimer to form a mixed valence Ir -Ir -X or Pt 1-Pt -X intermediate. This intermediate reacts further with the remaining organic radical (presumably in a second, thermal electron transfer step) to form the final d2-d2 dihalide dimer. 

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