Nonintegral oxidation

Oxidation numbers are most often, but not always, integers. If there are nonintegral oxidation numbers, there must be multiple atoms so that the number of electrons is an integer. 

A condition where metal ions within a coordination complex or cluster are present in more than one oxidation state. In such systems, there is often complete delocalization of the valence electrons over the entire complex or cluster, and this is thought to facilitate electron-transfer reactions. Mixed valency has been observed in iron-sulfur proteins. Other terms for this behavior include mixed oxidation state and nonintegral oxidation state. 

The relaxation of La2Ni04 to La2Ni04,i8 illustrates a couple of important points. Firstly, the defect and electronic modes of relaxation necessarily work together since the change in oxidation state of NP+ is directly related to the amount of interstitial present. This simultaneous relaxation of both the stretched and the compressed layers is a feature found in many, if not all, of the observed mechanisms for relaxing lattice-induced strain. Secondly, the lattice-induced strain is directly responsible for the crystallization of a stable compound with a fixed, but irrational, composition, involving a fixed, but nonintegral, oxidation state for nickel. 

The magnetic properties and the magnitude of the electrical conductivity thus largely depend on the stacking arrangements in dithiolenes in nonintegral oxidation states. Many structural investigations concern these questions. 

In order to ensure a metallic state, partial filling of the conduction band is required. This may be obtained either through partial oxidation, as in nonintegral oxidation state (NIOS) salts such as KCP (14, 48-52), or through partial charge transfer, as in donor-acceptor (D-A) adducts such as (TTF) -(TCNQ) involving donor (such as TTF) and acceptor (such as TCNQ) molecules (11-13). 

Nonintegral oxidation state Near infrared Nonlinear optical... 

Some compounds in nonintegral oxidation states are also known (see text). cUse of M implies that both the Tc and the Re species are well known. dD. E. Wigley el al, Inorg. Chem., 1989,28, 1769. 

Consistent with the extensive Fe-N 7r bonding, the equivalence of the two irons, the nonintegral oxidation state higher than Fe(III) and the unusual magnetic properties, (TPPFe)2N appears to be a good example of extensive delocalization between a pair of bridged metal ions. 

Metal-chain complexes containing stacked square-planar tetracyanoplatinate groups, [Pt(CN)4]2", are currently of high interest because of their one-dimensional (very anisotropic ) metallic properties. Complexes of this type contain metal-atom chains and often possess a characteristic brilliant, metallic luster. They may be synthesized by oxidation using chemical or electrolytic techniques.1 Although these compounds often appear metallic, they may also be semiconductors. These complexes differ in their Pt-Pt intrachain separations, degree of partial oxidation of the platinum atom (Pt2-1 2 4), electrical conductivity, and metallic color.2 Compounds in this series which contain platinum atoms in a nonintegral oxidation state are known as partially oxidized tetra-cyanoplatinate (POTCP) complexes. Some complexes also possess a metallic luster but are not metallic, as is the case for Tl4(C03)[Pt(CN)4] (see below). 

In recent years there has been increased interest in mixed valent homonu-clear complexes which exhibit unusual electronic properties arising from the rapid electron transfer between the metal sites, such that the metal atoms are in the equivalent nonintegral oxidation state. These complexes may have interesting electrical and magnetic properties via a valence interchange mechanism if interaction occurs between isolated clusters or within an infinite polymer. To date only small isolated oligomers have been characterized. General reviews of the mixed valent complexes are available for the interested reader (198, 355, 455, 468, 534). 

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