Mixed valence compounds/clusters

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... 

We discuss here two examples of vibronic effects in polynuclear highly symmetrical transition metal clusters. The existence of degenerate and quasi-degenerate molecular orbitals in their energy spectra results in the Jahn-Teller effect or in the vibronic mixing of different electronic states. We show that both quantum-chemical methods and model approaches can provide valuable information about these vibronic effects. In the case of the hexanuclear rhenium tri-anion, the Jahn-Teller effect is responsible for the experimentally observed tetragonal distortion of the cluster. The vibronic model of mixed-valence compounds allows to explain the nature of a transient in the photo-catalytic reaction of the decatungstate cluster. 

Other Papers.—Various iron species prepared by the vacuum pyrrolysis of acetyl-ferrocene-furfural resins at 400°C have been studied by Mossbauer spectroscopy. These consist of an amorphous glass-like carbon matrix containing free iron atoms, Fe+ ions, iron clusters, superparamagnetic iron, and ferromagnetic iron.333 The effect of pressure of up to 50kbar on the absorption spectra of five iron(m), two iron(n) and one mixed valence compound has been studied. In six of the compounds, but not in basic ferric acetate or soluble Prussian Blue, the observed pressure-induced bands were assigned to d-d transitions of converted iron(n) for the ferric compounds and to spin-forbidden d-d bands for the ferrous compounds. The charge-transfer band from iron(n) to iron(m) in soluble Prussian Blue showed a blue shift at pressures up to 7.2 kbar.334... 

The Iu4 cluster can be completely or partial oxidized with halogen or chalcogen to form 104X4 heterocubanes or mixed-valence compounds. The complex In4[C(SiMe3)3]4 abstracts O from o-nitrosotoluene forming the extremely... 

Cluster Compounds Inorganometalhc Compounds Containing Transition Metal Main Group Elements Coordination Numbers Geometries Electronic Structure of Main-group Compounds Lead Organometallic Chemistry Mixed Valence Compounds Tin Inorganic Chemistry. 

There exist a vast number of discrete, polymetallic coordination clusters both of the metal-metal bonded type and linked by a tremendous variety of bridging ligands, notably carboxylates. Such compounds are not coordination polymers but oligomers and hence can be more soluble, more well-defined and easier to characterise than coordination polymers, for which they can serve as useful model systems. We will discuss discrete, self-assembled complexes of semi-protected metal ions that act as hosts in solution or as 3D capsules in the next chapter and we will not cover these systems in detail here except to note in passing a couple of examples that are of particular interest. One particularly prominent cluster is Muij-acetate, the mixed-valence compound... 

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