Complex metal-cyano

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Figure 8. Dependence of the BOD-catalyzed oxygen reduction current density on the difference in formal potentials between the O2/H2O couple and a range of cyano-metal complexes (M) for three values of solution pH. Arrows indicate reported values of the BOD formal potential F (Enz) relative to that of O2/H2O. Reproduced with permission from ref 159. Copyright 2003 Elsevier Science B.V.

Cyano metal complex a metal complex that contains one or more bound cyanide ligands... 

The first coordination compound to be synthesized was the cyano metal complex was Prussian blue, [Fe4 Fe(CN)6 3] [see Prussian Blue), made by the Berlin painter Diesbach in 1704. Much of our understanding of coordination chemistry can be attributed to research on cyano metal complexes see Coordination Organometallic Chemistry Principles). 

Cyano metal complexes are commonly formed by the addition of an excess of cyanide ion (usually as an alkali metal salt) to a transition metal complex in water or a polar organic solvent (equation 1). The completely cyanide-substituted metal complex is usually isolated from these reactions, although one or more steps in the reaction may be relatively slow. In certain cases, cyanide substitution is not complete, resulting in partially substituted cyano metal complexes an example is the addition of CN to Pt alkyl compounds, from which [PtR(CN)3] species are isolated. 

Cyano metal complexes can be formed by the oxidative addition (see Oxidative Addition) of cyanogen to a transition metal complex (equation 2). The oxidative addition of (CN)2 usually requires a low-valent, electron-rich metal... 

Cyano metal complexes undergo a variety of oxidation-reduction reactions. One of the most studied is the fast self-exchange reaction of the [Fe(CN)4] /" anions information from this research was instrumental in establishing the outer-sphere mechanism (see Outer-sphere Reaction) for transition metal oxidation-reduction reactions (see Electrochemistry Applications in Inorganic Chemistry). The nature... 

NMR spectroscopy ( C and N) is routinely used in the characterization of cyano metal complexes. The free CN ion exhibits a C NMR shift of 5 166.2, but the C NMR shift in complexes is almost always upfield of this value the N shift is correspondingly downfield. Information on the rates of reactions for cyano metal complexes can be obtained from NMR studies the self-exchange rates for electron transfer in the [Fe(CN)6], [Ru(CN)6] , [Os(CN)6] , and [W(CN)8] couples have been determined by C or N NMR hne-broadening techniques, but cation-catalyzed pathways dominate the observed rate constants. Experiments using sequestered K+ (by either 18-crown-6 or crypt-2.2.2) found an exchange constant for [Fe(CN)6] / of 2.4 x lO LmoL s (25°C, ionic strength 0.2 mol L ) this is two orders of magnitude less than... 

M. Shporer, G. Ron, A. Loewenstein, G. Navon, Study of some cyano-metal complexes by nuclear... 

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