Prussian blue bridging cyanides

Inspecting the structure of vitamin B12, one recognizes the cyanide bound to Co111 in native Bi2. Whereas metal bridging cyanides are one of the longest known structural features in inorganic chemistry (Prussian Blue), this cyanide has never... 

Fig. 12.47 Portion of Ihe crystal structure of Prussian blue showing the bridging by ambidentate cyanide ions. Circles represent iron(II) (O). iron(UI) (O), and oxygen in water ( ). The remaining interstitial or "zeoiitic" water in the cubic sites has been omitted for clarity, as hove most of the cyanide ious. In addition, some of the cyanide ions are replaced by water molecules coordinated to iron(III), and there are also vacancies in the structure. [Modified from Buser, H. J. Schwarzenbach, D. Petter, W. Ludi, A. Inorg. Chem. 1977, 16. 2704-2710. Reproduced with permission.]...

A large number of polymeric complexes is known containing ambidentate cyanide bridging groups. These are related to Prussian blue, which is formed by the addition of ferric salts to ferrocyanides ... 

While bifunctionality is known for the halogens and many pseudohalogens, it is most pronounced for cyanide and influences the structures, properties and chemistry of many of its derivatives. Cyanide bridges were present in the first recorded synthetic inorganic complex, Prussian blue (ca. 1700), and cyanide linkage isomers were often proposed in the old literature but reasonable evidence for the existence of linkage isomers and the structure of Prussian blue is very recent. 

Prussian blue, Fe4[Fe(CN)6]3xH20, consists of a cubic lattice of alternating Fe2+ and Fe3+ ions connected with cyanide bridges (Figure 8.3). The [Fe(CN)6]4 sites are 75 % occupied and the exposed Fe3+ ions are coordinated with H2O. Dehydration and hydration by moisture is reversible hence, Prussian blue is a porous solid albeit one with very small pores. To increase pore size, the [Fe(CN)6]4 complexes were replaced with octahedral [Rer TeACNAJ4 clusters (Figure 8.4). This cluster displays an octahedral array of N donors on a sphere about 4 A larger in diameter than the mononuclear complex. Reaction of Fe3+ with the cluster in... 

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