Transition metal cyano complexes

A variety of anionic transition metal cyano-complexes have been intercalated in LDHs and their structure investigated by vibrational spectroscopy [161]. There is general agreement that octahedral complexes such as [Fe(CN)6] and [Fe(CN)6] intercalated in LDHs ahgn themselves with their three-fold axis perpendicular to the sheets, but the spectra are gen-... 

We have recently been examining various inner-sphere adsorbed redox couples with the aim of deducing if such electron delocalization effects are indeed encountered. One type of candidate system is transition-metal cyano complexes. Some representative data for the Fe(CN)63>/1 "couple adsorbed at gold are presented in Figs. 2 and 3. 

Various aspects of the transition metal cyano complexes have been discussed in three authoritative reviews /, 76, 23). The present authors will therefore not attempt to give a comprehensive review of the subject. Instead, we restrict ourselves to the discussion of structural properties of crystalline cyano compounds containing octahedral M (CN)6 groups, where the characteristic construction element is given by the four-atomic sequence N—C—M . M represents a transition metal,... 

A time resolution of approximately 10 ps is possible with the CFMIO method, although at such short times the mixing and chemical reaction take place simultaneously and the analysis becomes more complicated. Nonetheless, the method was used successfully in a study of the reactions of iron(III) and ruthenium(III) polypyridine complexes with several transition metal cyano compounds [3], but each experiment required approximately 300 mL of solution. The measured rate constants for electron transfer exceeded 3 x 10 M s . ... 

Conversely, the calibration for the cyanide determination poses no problem. Free cyanide is found, for example, in untreated liquors from electroplating processes. Since these samples also contain transition metal ions, part of the cyanide exists in complexed form, whereby the various metal cyano complexes differ significantly in their stability. 

A general route leading to cyano-bridged complexes is the elimination of alkali metal cyanide from alkali metal dicyano-(phthalocyaninato)transition-metal(III) complexes M [PcM(CN)2] (see Scheme 12 M =Na, K M=Cr [117], Mn [ll H, Fe [114], Co [124], Rh [127]). The same method can be used to form [PcCo(SCN)] from K[PcCo(NCS)2] [119]. 

Conversely, the cyanide calibration poses no problem. For this purpose, reagent-grade sodium cyanide can be used. Free cyanide is foimd, for example, in untreated wastewater from electroplating processes. Because these samples also contain transition metal ions, part of the cyanide exists in complexed form, so the various metal-cyano complexes differ significantly in their stabiUty. Therefore, the cyanide signal produced amperometrically represents both the free cyanide initially present in the sample as well as the one that is released in the mobile phase via a shift of the complexation equilibrium according to Eq. (3.43). 

A. G. Sharpe, The Chemistry of Cyano Complexes of the Transition Metals Academic Press, Inc., New York, 1976. 

Investigations of cyanides and cyano complexes of Cd and Hg have augmented tremendously since about 1990, after detection of inclusion compounds of Cd(CN)2. A thorough review on transition-metal cyanides especially emphasizes the chemistry of inclusion compounds of both the Hofmann type (frameworks dominated by planar Ni(CN)4 building blocks) and the cyanocad-mate type (frameworks with tetrahedral Cd(CN)4 units).87 The structures of these inclusion compounds, but also of cyanides themselves, often topologically resemble the structures of minerals this aspect ( mineralomimetic chemistry ) is dealt with in a simultaneous survey.88 A more generic review of framework structures, with a section on cyanide inclusion compounds, is also to be mentioned.90... 

The importance of cyanide in the development of the coordination chemistry of virtually all transition-metal elements is illustrated for technetium, where homoleptic cyano complexes are... 

As anticipated above, the reactivity of the cyano complexes of transition metals are strongly influenced by the structure of the medium, namely the nature of the solvent (specific cyano-donor interactions), or the type and concentration of the counterions (15). Both of these factors have a profound influence in the electronic structure, and determine the observed changes in reactivity, particularly in... 

Reactions between 5-cyanotetrazole and transition metals, when performed in boiling acetone, lead to hydrolysis of the cyano group and formation of 5-carbamyl tetrazolate complexes (68). Complexes containing 1- or 5-substituted tetrazolate anions can also be obtained by 1,3-dipolar cycloaddition of organic isonitriles (RNC) (15) or nitriles (RCN) (61), respectively, to coordinated azide ligands [Eqs. (3) and (4)]. 

Most fulminates are very dangerously explosive, but this appears not to be the case for transition metal complexes containing tetraphenylarsonium, tetrapropylammonium or other very large cations. Much recent work on fulminate complexes has involved these compounds, and, as a result of it, the very close analogy with cyano complexes is now established beyond doubt. 

It may be noted that, for d2, d4, d6, rf8 and d ° transition metal ions, octa-, hepta-, hexa-, penta-and tetra-cyano complexes represent the species of maximum coordination number. It should thus be possible, so far as electronic factors are concerned, to prepare an ennea complex of a d° system (e.g. Revl1 or La111). No ennea cyano complex has, however, yet been reported. 

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