Aqueous solution cyano complexes

Jones and Penneman " made an extensive infrared study of the equilibria of cyano complexes in aqueous solution. (For aqueous infrared spectroscopy, see Sec. 111-9.) Figure 111-35 shows the infrared spectra of aqueous silver cyano complexes obtained by changing the ratio of Ag to CN" ions. Table 111-35 lists the frequencies and extinction coefficients from which equilibrium constants can be calculated. Chantiy and Plane studied the same equilibria using Raman spectroscopy. 

Electroplating. Aluminum can be electroplated by the electrolytic reduction of cryoHte, which is trisodium aluminum hexafluoride [13775-53-6] Na AlE, containing alumina. Brass (see COPPERALLOYS) can be electroplated from aqueous cyanide solutions which contain cyano complexes of zinc(II) and copper(I). The soft CN stabilizes the copper as copper(I) and the two cyano complexes have comparable potentials. Without CN the potentials of aqueous zinc(II) and copper(I), as weU as those of zinc(II) and copper(II), are over one volt apart thus only the copper plates out. Careful control of concentration and pH also enables brass to be deposited from solutions of citrate and tartrate. The noble metals are often plated from solutions in which coordination compounds help provide fine, even deposits (see Electroplating). 

The most important low-spin octahedral complex of Mn is the dark-red cyano complex, [Mn(CN)6] , which is produced when air is bubbled through an aqueous solution of Mn and CN . [MnXs] (X = F, Cl) are also known the chloro ion, at least when combined with the cation [bipyH2] +, is notable as an example of a square pyramidal manganese complex. 

Iron(II) and (III) cyano complexes provide very interesting mechanistic chemistry. The Fe(CN)5H20 ion is a popular substrate for study. It is easily prepared in situ by the dissolution of solid Na3[Fe(CN)jNH3] for 15 minutes at 25°C in aqueous solution. For a large variety of entering groups Y (unspecified charge) a D mechanism is favored (Prob. 18) ... 

The classical homoleptic cyanido complex of Tc , the seven-coordinate, yellow-orange complex [Tc(CN)7]" (397), is formed from [Tcle] and an aqueous KCN solution after 24 h of heating under reflux. Careful exclusion of O2 is required, otherwise appreciable amounts of cyano complexes in higher oxidation states are formed. The iodide acts as a reducing agent, since the... 

Fig. 14a-e. Proton NMR spectra of 5% aqueous sodium dodecyl sulphate (a) in aqueous solution in absence of any paramagnetic complex, (b) in presence of biscyano hemin (0.1 mM (c) in presence of aqua (hydroxo) hemin, (d) in presence of hydroxo (pyridinato) hemin and (e) in presence of cyano (pyridinato) hemin (Taken from Ref. 67)... 

The superoxo-containing species [(NC)6Co(/u.-02)Co(CN5]5 can be reduced with thiols such as 2-aminoethanethiol or L-cysteine (175), and the reduction reaction is catalyzed by copper(II) ions in aqueous solution. When copper(II) is present, the role of the thiol is to reduce cop-per(II) to copper(I), which then reacts with the superoxo species through an inner-sphere mechanism. Conversely, when the superoxo complex [(H3N)5Co(/x-02)Co(NH3)5]5+ is reduced with thiol (176), the reaction follows an outer-sphere mechanism, as would be expected. Ascorbic acid also reduces both complexes (177), but only the reduction of the cyano-containing complex exhibits copper(II) catalysis. 

The salt T1CN can be prepared by the reaction of thallium(I) acetate and KCN in aqueous solution,279 but there is no evidence for the formation of cyano complexes in aqueous solution.280... 

Osmyl complexes with miscellaneous donors.The cyano complex K2[0s02(CN)4] is made from the action of aqueous KCN solution on OsO4.S05 There are a number of osmyl complexes with sulfur donors. Reaction of Os04 with sodium sulfite in alkali gives Na2[0s02(S03)4] 506 Raman and IR spectra suggest that the sulfite is S rather than O bonded. 7 There are complexes with thiourea, e.g. 

The M(CN)j ions in aqueous solution are photochemically converted, through several intermediates, into isolable species long believed to be [M(CN)4(OH)4]4 but more recently shown to be 6-coordinate, trans-dioxo complexes [M02(CN)4]4. A cyano complex reported for Mo111 is KtMo(CN)7-2H20, which readily oxidizes... 

Reduction of KRe04 with H2NNH2 in the presence of KCN forms two unusual nitrido-cyano complexes, pink K2[ReN(CN)4]-H20 and yellow K3[ReN(CN>5], which can be easily interconverted. Addition of MeOH to an aqueous solution of either complex produces the tetracyano derivative, whereas addition of xs KCN causes the precipitation of the pentacyano compound. 

The oxidation of thiols in the form of L-cysteine, penicillamine, and thioglycollic acid by [Mo(CN)g] in aqueous acidic solution also formed disulfides as final products 111). The reactions show a second-order substrate dependence, and the rates are found to decrease with increasing hydrogen ion concentration. This is attributed to the deprotonation of the —SH and —COOH groups in these thiols prior to electron transfer. The reactions are interpreted in terms of outer-sphere activation. An explanation for the second-order dependence on thiol concentration involves ion association between the cyano complex and a protonated form of the thiol, followed by reaction of this complex with a second thiol molecule. 

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