Creutz-Taube cation

In the above example, Cl is transferred between metal centres such transfer is often (but not necessarily) observed. In the reaction between [Fe(CN)g] and [Co(CN)5], the intermediate 25.4 (which is stable enough to be precipitated as the Ba salt) is slowly hydrolysed to [Fe(CN)6] and [Co(CN)5(H20)] without transfer of the bridging ligand. Common bridging ligands in inner-sphere mechanisms include halides, [OH], [CN], [NCS] , pyrazine (25.5) and 4,4 -bipyridine (25.6) pyrazine acts as an electron-transfer bridge in the Creutz-Taube cation and related species (see structure 22.57 and discussion). 

Two curiosely related organometallic and organic examples include the discovery [17,18] of the first stable organometallic analogue (Fig. 1) of the mixed-valent Creutz-Taube ion and the isolation in crystalline form of a simple monocyclic radical cation (Fig. 2) [19,20]. 

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