Mixed-valence compounds pyrazine bridged

Mixed valency occurs in minerals (e.g. 63 ), metal-chain compounds, dimers and oligomers and metal complexes, and even in organic and biological systems (Brown, 1980 Day, 1981). Among the dimeric and oligomeric metal complexes exhibiting mixed valency, the pyrazine-bridged Ru (II, III) ammine complex. 

In the six-membered diazine systems, (93 95), the most widely investigated ligand is pyrazine (93) in the model pyrazine bridged mixed valence compound (103) (see Mixed Valence Compounds and Creutz-Taube Complex). The coordination chemistry of the aliphatic analog, piperazine (98), is not well developed. 

The most intensively studied diazine is undoubtedly pyrazine (7), present in the so-called Creutz-Taube complex [(H3N)5Ru(pyrazine)Ru(NH3)5] , a well-known mixed-valence compound. Examples of other bridged compounds (11) are the chain compound Cu(N03)2 (pyrazine) and the two-dimensional C0CI2 (pyrazine) (see Figure 8). The synthesis of the corresponding Zn compormd probably proceeds via an intermediate which is immediately converted to the end-product via crystallization, resulting in a unique acoustic emission. ... 

Mixed Oxidation State Ruthenium. In view of the growing number of mixed valence state ruthenium complexes reported, especially Ru compounds, all the pertinent references are collected in this section. The new pyrazine-bridged... 

Luminescent coordination compounds continue to attract considerable attention. Zink recently reported a new mixed-ligand copper(I) polymer that shows interesting photoluminescence (232). The complex [CuCl(L44)Ph3P] consists of a one-dimensional chain lattice of metal ions bridged by both Cl" ions and pyrazine molecules. The compound shows conductivity of less than 10-8 S cm 1. The absorption spectrum of the complex shows a band at 495 nm, which could be interpreted as the promotion of an electron from the valence band to the conduction band. On the basis of resonance Raman spectra, the lowest excited state in the polymer is assigned to the Cu(I)-to-pyrazine metal-to-ligand charge-transfer excited state. 

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