Cyano complexes structures

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... 

Structural models, which are synthesized to imitate features of the proposed structure of the active site. These may be used to demonstrate the chemical conditions, which allow such structures to exist, to investigate their chemical properties and to give a better understanding of the spectroscopic characteristics of the native proteins. Examples of these include the mixed carbonyl/cyano complexes of iron, used to verify the infrared spectra to the hydrogenases (Fig 7.4) (Lai et al. 1998) and the nickel-thiolate complexes which have low redox potentials like the hydrogenases (Franolic et al. 1992). 

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-... 

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). 

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... 

Thermal deamination of tris(ethylenediamine)chromium(III) complexes is a standard preparative method for cis- and trans-diacidobis(ethylenediamine) complexes421,422 and the thermal behaviour of the starting materials has been related to their crystal structures.423 The cyano complex cis-[Cr(CN)2(en)2]C104 in DMSO undergoes stepwise reduction III— 11 — I at the DME. The standard redox potential for the Cr /Cr11 couple is -1.586 V (versus SCE). 

The low stability of two-coordinate complexes with respect to other possible structures is well illustrated by (he cyano complexes. Although sifver(f> and gold( ) form discrete bislcyano) complexes, solid KCufCNk possesses a chain structure in which the coordination number of the copperfl) is 3. 

In oxazole (167) (95MI5) and isoxazole (168) [88ZN(B)328] N-M coordination prevails. The possibility of O coordination (169) is less likely. Examples of the C-coordinated derivatives of oxazole (170) and isoxazole (171) are known [89JOM(372)287]. The complexes of composition CrL2 based on 3-methyl-5-phenyl- and 3,5-diphenylisoxazole were assigned a polymeric structure with the -coordinated framework (78ZOB418). The other example is the interaction of the cyano complexes [M(CN) (cp)(dppe)] (M = Fe, Ru) or [Fe(cp)(dppe)(CNH)]Br with gem-dicyano-epoxide to afford the oxazol-2-yl complexes with the C-coordination mode... 

The cyano complex [Au(CN)fCNMe)] has been prepared by treating [Au(CN)2] with methyl iodide (136), and its near-linear structure was elucidated from X-ray crystallographic studies. 

There are two aspects of the structural chemistry of cyano complexes that we shall discuss here the coordination of the metal atom, and relative values of interatomic distances and vibrational stretching frequencies.1 The correlation between the distances and frequencies and the very limited available thermodynamic data is considered briefly at the end of the section. 

The diphenylpyridine complex 55 has been converted into a number of complexes that show interesting structural or photophysical properties phosphine derivatives are covered in Section IV.A. Thus, the corresponding cyano complex, synthesised... 

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