Cyanometallates

Scheme 4 Typical halogen bonded motifs involving a partially oxidized TTF molecule such as EDT-TTF-I with halide (top) or cyanometallate (bottom) counter ions...

The substitution and protonation behavior of the rcms-dioxotetra-cyanometalate complexes of Re(V), Tc(V), W(IV), Mo(IV), and Os(VI) have been extensively investigated in the past decade and selected aspects have been reviewed (1, 2). Previous studies demonstrated the use of oxygen-17 NMR in different metal systems (3), including the complex oligomeric Mo(IV) aqueous systems (4), and therefore, since these oxocyano complexes contain an even wider range of nuclei such as 13C, 15N, 170, "Tc, and 183W, they are attractive model complexes to study by multinuclear NMR. Thus, detailed studies on the dynamics therein have been investigated in the past few years (5-8). 

The formal potentials of solid hexa-cyanometalates can also be correlated with the lattice constants, that is, with a parameter that depends mainly on the radii of the two metal ions forming the framework of the compounds. This theoretically derived dependence can be verified when the nitrogen coordinated metal ion and the inserting metal ions are kept constant and the carbon coordinated metal ions are varied, for example, when hexacyanoferrate, hexa-cyanocobaltate, hexacyanomanganate, and so on are compared [53, 55]. The equation... 

Caution. Because of the toxic nature of cyanide, special care should be exercised in these preparations. We make amylnitrite available in the laboratory as an antidote to acute cyanide poisoning. Organic soluble salts of cyanide (and potentially cyanometallates) are especially hazardous contact poisons because they are transported intraveneously through the skin. 

The coordination chemistry of transition metal cyanometallates has been of great and long standing concern because of the fundamental issues related to their electronic structure and reactivity It has been... 

Overall, the review deals mainly with the chemistry in aqueous media, with occasional mention to work in organic solvents. Cyanometallate complexes are known to display profound changes in their electronic structure and reactivity when dissolved in solvents with different acceptor capability, associated with the donor properties of the exposed electron pairs at the cyano ligands (15). These specific interactions are also related to the role of cationic association in the thermodynamics and kinetics of the reactions involving cyano complexes (16). 

Derossi, S., Adams, H., Ward, M. D., Hydrogen-bonded assemblies of ruthenium(II)-biimidazole complex cations and cyanometallate anions structures and photophysics. Dalton Trans. 2007, 33-36. 

The IT behavior of mixed-valence cyanometallates (23-26), Aqueous solutions of[Mo(CN)X, tW(CN)T (Fe(CN)T, and [FVJTd gT ions undergo remarkable color changes upon addition of Fe(IIT), Cu(ll),... 

Figure 3 exhibits some typical electronic spectra of mixed-valence conplexes of the [Mo(CN) Jr ion with various other metal ions. Mixed-valence compounds formed By interaction of Mo(IV), W(IV), Fe(ll), and Rj(ll) cyanometallates with metal ions such as Fe(lll), Cu(II), UO2, and A) belong to the class II of the Robin-Day classification ... 

The change of the redox asymmetry may also be achieved by variation of the inner coordination sphere of the acceptor site of the mixed-valence cyanometallates. Thus, in the case of Cu(ll) it is easily possible to change the redox asynmetry by substitution of the Cu(ll) aquo species by either d-donor or 3T-acceptor ligands. The variation of the redox asynmetry by Ranging the first coordination sphere leads to a shift of Jv1 from about 360 nm ( CCu(en). [Mo(CN)qJ ) to about 660 nmnna (CCufchpJpl CMo(CN7ftX ) as show in Table I. 

The aim of our photochemical investigations of mixed-valence cyanometallates (23, 26. 30. 31) was to study the spectrally sensitized formation of free cyanide by excitation of the IT states of appropriate mixed-valence conpounds. 

The results obtained with cyanometallates are best illustrated by the Scheme 3 ... 

IT excitation of heteronuclear mixed-valence cyanometallates leads to the formation of a vibronically excited valence-isomeric species ( see Figure 6 ) consisting of octacyanomolybdate (V) and the corresponding reduced form of the metal center M. Due to the kinetic lability of[Mo(CN) ] - (32-34) fast cyanide aquation can be expected which conpetes with the back electron... 

Back electron-transfer rate, cyanometallates, 116 Band analysis, excited-state structure, 211,25 Base, effect on doublet excited... 

The cyanometalate box Cs c [Cp Rh(CN)3]4[Mo(CO)3]4 3 is formed in low yield from the reaction of [Cp Rh(CN)3] (Cp = CsMes) and (/ -CeHtMet )Mo(CO)3 in the presence of cesium ions, and it can be crystallized as a Et4N+ salt. The Cs+ ion serves as a template in the self-assembly of the anionic molecular box, which has a cubic Rh4Mo4(/r-CN)i2 core with three exterior carbonyl ligands attached to each Mo and a Cp group to each Rh. The encapsulated Cs+ ion has a formal coordination number of 12 if interaction with the centers of cyano groups is considered (Fig. 20.3.15). 

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