Mixed-valence complexes/compounds

For 82 complexes of type III, the corresponding absorption band is expected to occur at higher energy because both 7t orbitals of the ligand interact strongly with the metal atoms. Particularly interesting is the very intense band at 14.2 kK in [(NH3)5Ru(82)Ru(NH3)5]Cl4. A comparable band is not found in the related compounds of type Ila structure [e.g., [(CN)5Co(82)Co(CN)5] and aqueous Cr(82)Cr ]. It has been proposed that the central unit in [(NH3)5Ru(82)Ru(NH3)s] is best formulated as Ru —(82) —Ru" (25, 44). 8uch a mixed-valence complex could exhibit the intense band observed 106). 

Electric fleld gradient, 22 214-218 Electroabsorption spectroscopy, 41 279 class II mixed-valence complexes, 41 289, 291, 294-297 [j(jl-pyz)]=+, 41 294, 296 Electrocatalytic reduction, nickel(n) macro-cyclic complexes, 44 119-121 Electrochemical interconversions, heteronuclear gold cluster compounds, 39 338-339 Electrochemical oxidation, of iron triazenide complexes, 30 21 Electrochemical properties fullerene adducts, 44 19-21, 33-34 nickeljll) macrocyclic complexes, 44 112-113... 

The great recent development in electrochemical techniques will certainly be helpful for the study of redox processes of a metal which can occur in so many oxidation states. Multinuclear NMR spectrometers will allow increased use of 51V resonance as a routine method for the characterization of complexes in solution. Other recent developments are the study of polynuclear complexes, metal clusters (homo and hetero-nuclear) and mixed valence complexes, and it can be anticipated that these topics will soon become important areas of vanadium coordination chemistry, although the isolation of compounds with such complex... 

Ostrowetsky studied solutions containing Vv and Vlv and concluded 481 (i) at pH s 10, no mixed-valence complex forms (ii) at 8 pH 10, one forms with a Vlv/Vv ratio of 2, and at least six vanadium atoms a solid, Na3[V2V4VOi5H], was isolated (iii) at 4 s pH s 6.5, six different mixed-valence complexes form but only those with Viv/Vv ratios of 3/7 and 7/3 are stable (iv) a compound containing eight Vv and two Viv transforms into the more stable 7/3 compound in a few minutes (v) all these compounds contain a Vi0 group in the molecule. 

The mixed valence complex Pdn[PdIVF6] has been prepared from the reaction of PdBr2 with BrF3. The relevant bond lengths in this compound are Pdn—F 2.17 A and PdIV—F 1.90 A.306,309,310,317,318 The structures of other hexafluoropalladate(IV) salts are dependent on the counterion (see Table 5). 

These are one of the most studied classes of mixed valence complexes and have been reviewed recently by Keller and by Clark.134,135 They all possess a common structural unit X,MII X"M1V"X,MII, X. Table 5 gives a selection of examples for which electrical conduction studies are available with particular emphasis on results obtained on single crystals. The compounds are arranged depending on the charge of the complex. 

The coordination geometries of MIV in compounds or mixed-valence complexes, in contrast to Mn, tend to exhibit high symmetries the MX4 molecules are tetrahedral and [MXf,]2- units adopt the octahedral (or slightly distorted) configuration. 

There are a number of dinuclear carboxylate complexes of Co" which show interesting magnetic behavior and contain the [Co2(ft-OH2)(RC02)2]2+ or [Co2(/t-X)(/i-RC02)2]+ core (X = OH, Cl, Br), stabilized by chelating nitrogen ligands to complete the octahedral coordination. The latter can be oxidized to mixed-valence ConCom compounds in which the valences are localized.5... 

The low-valent oxides K3[Ni02] and KNa2[Ni02] contain linear [O—Ni1—O]3- units, similar to analogous Fe and Co compounds.17 There are a number of Ni1 complexes with metal-metal bonds of varying lengths, for example, (17-G-XVII) and the mixed-valence complex (17-G-XVIII). 

Mixed Valence Complexes. A number of compounds containing both Cu1 and Cu11 are well established. The sulfides, for example, K3Cu8S6made by heating K2C03, Cu, and S, may have metal-like electrical conductivities and magnetic properties. 

---