Cyanide as a ligand

Reedijk, J., Methyl Cyanide as a Ligand, Bronder-Offset, Rotterdam, 1968. 

Here, effectively, the Co " (aq) is being oxidised by the nitrite ion and the latter (in excess) is simultaneously acting as a ligand to form the hexanitrocobaltate(III) anion. In presence of cyanide ion CN. cobalt(II) salts actually reduce water to hydrogen since... 

A species that bonds to a metal cation to form a complex is known as a ligand. Any species that has a lone pair of electrons has the potential to be a ligand, but in this section, we confine our description to a few of the most common ligands ammonia, compounds derived from ammonia, cyanide, and halides. We describe additional examples in Chapter 20 which addresses the chemistry of the transition metals. 

X. Wu, X. Li, F. King, J. Xiao, Angew. Chem. Int. Ed. 2005, 44, 3407. Surprisingly, no direct references to cyanide inhibition of hydrogenation catalysts could be found. For a general reaction showing the swift reaction of a transition metal complex with cyanide as a means to isolate the ligand, see for ex-... 

The most important observation in the pre-steady-state kinetics of the CN system is that after a short lag (100 msec) there is a phase (lasting about 3 sec) where the evolution of H2 is linear and only after these 3 sec does CN reduction occur. This long lag prior to CN reduction would correspond to 18 to 20 electron transfer steps from the Fe protein. More realistically this delay probably involves a CN -induced modification of the enzyme, such as a ligand substitution reaction (this modified state of the enzyme is designated as. E in Figure 21). However, this modification step is too slow to be part of the steady-state cycle for CN reduction. Also, it cannot be a slow activation of the enzyme prior to turnover, since the onset of H2 evolution is the same in both the presence and the absence of CN . Steady-state observations indicate that cyanide binds to a more oxidized form of the MoFe protein than binds N2, but that state cannot be defined because of the long lag phase. 

The main biological and biochemical interest in cobalt concerns vitamin B,2 and a number of its derivatives, such as 5 -deoxyadenosyl cobalamin, which function as coenzyme in a number of rearrangements involving hydrogen shifts and aquocobalamin which is involved in the synthesis of methionine, methane and acetate. Vitamin in its resting state is ESR-inactive since it contains Co , but, when reduced to Co, spectra such as that shown in Figure 4.7 are obtained. This reduced form is referred to as vitamin B,2r it does not have cyanide as a sixth ligand. Its... 

In ferricytochrome c, state III is the physiologically active one, again with histidine-18 and methionine-80 as the heme ligands. These two strong field ligands force the potentially unpaired iron electrons to pair and give the iron a low spin, and the intact methionine-80 bond produces the characteristic 695-nm absorption. Fluoride ion cannot displace methionine from the iron as a ligand, cyanide displaces methionine slowly, and azide and NO do so rapidly. 

The CN anion has a great ability to coordinate as a ligand and to provide a series of complex cyanides which are common in wastewaters from... 

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