Other Mixed-Valence Materials

It was then proposed by TSK that the interpretation and assignment of CS2TCNQ2, could be extended to the other mixed valence TCNQ compounds, even if their electrons are not localized. In these materials, the localized picture of the excitations at the top of Fig. 2 can only be used as a crude guide the... 

In mixed valence materials macroscopic and microscopic measurements indicate the coexistence of two adjacent valence states of the lanthanide atom. There are two types of such solids. In one the two valence states occur on crystallographically distinguishable sites (inhomogeneously mixed valence). The main interest is in the other type, where the lanthanide atoms occupy only sites with identical point symmetry (homogeneously mixed valence). Such solids are certain intermetallic compounds and related sufficiently dilute lanthanide alloys and certain elements. 

Other Inorganic Compounds Prussian Blue represents another type of inorganic mixed valence electrochromic materials. This material is known in three states ... 

The electrochemical and spectroscopic data indicates that sites on these polymers can communicate with each other, in the electron transfer sense, on a relatively short time scale and without the formation of stable mixed valence clusters. Electronic tranport via hopping or tunnelling and modulated by means of neighboring molecular group collisions would be consistent with these requirements. The relative molecular nonspecificity of this mechanism suggests that other polymeric materials would show similar effects and this has been seen for thin films of poly — (vinylferrocene) and poly — (nitrostyrene). 

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. 

Based on the strength of the electronic coupling between the metals, Robin and Day [105] have developed a system in which mixed-valence compounds are broadly distinguished in three classes. In a very weakly coupled or Class I material, only the properties of the individual mononuclear species are observed due to the lack of communication ( = 0). In the other extreme, a Class III com-... 

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