Taube-Creutz compound

There has been intense interest in the process referred to as intervalence electron transfer in mixed-valence (oxidation state) species ever since the initial preparation of the Taube-Creutz compound ... 

If there is no interaction between the metals in the mixed valence product, then statistics predicts that = 4. However, if the product is stabilized by electronic coupling between M" and M ", then should be larger. For the Taube-Creutz compound = 3x 10 . This method has been used in a review by Ward where values in the range of 10 -10 suggest a strong interaction and values <10 indicate a weak one. Cautions about this method have been expressed by D Alessandro and Keene and by LeSuer and Geiger." ... 

The Creutz-Taube compound (named after its discoverers), [(NH3)5Ru(pyrazine)Ru(NH3)5]5+ is the middle member of a redox-related series, formally containing one ruthenium(II) and one ruthenium(III) (Figure 1.14) the interest lying in whether the two ruthenium centres are identical, whether the valencies are trapped or whether there is partial delocalization. 

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. 

Not only well-separated and intense bands from carbonyl stretching but also other vibrational absorption features lying at lower frequencies may be used to investigate the molecular symmetry and thus the valence situation in complexes like the Creutz-Taube ion or related osmium compounds. 

There is by now an extensive chemistry of mixed-valence compounds where the distinguishing feature is the existence, at least in a formal sense, of different oxidation states within the same compound.The first deliberate synthesis of a discrete metal-based mixed-valence ion was the Creutz and Taube ion, (NH3)5Ru(pz)Ru(NH3)5 + (pz is pyrazine). A number of examples of this type are known based on metal complexes and organometallics, e.g. [(C5H5)Fe(C5H4CsH4)Fe-(CsHs)]" or chemically linked organics such as (3), especially for d -d cases involving Ru " and Ru . - ... 

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. ... 

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