Pentacyano

Further similarity with Mn may be seen in the fact that the vast majority of the compounds of Fe are high-spin. Only ligands such as bipy and phen (already mentioned) and CN , which are high in the spectrochemical series, can induce spin-pairing. The low-spin [Fe(CN)g] , which is best known as its red, crystalline potassium salt, is usually prepared by oxidation of [Fe(CN)6]" with, for instance, CI2. It should be noted that in [Fe(CN)6] the CN ligands are sufficiently labile to render it poisonous, in apparent contrast to [Fe(CN)6]" , which is kinetically more inert. Dilute acids produce [Fe(CN)5(H20)] , and other pentacyano complexes are known. 

The Ni /CN system illustrates nicely the ease of conversion of the two stereochemistries. Although, as already pointed out, there is no evidence of a hexacyano complex, a square pyramidal pentacyano complex is known ... 

Nickel, methyltetrakis(trimethylphosphine)-tetraphenylborate stereochemistry, 1,44 Nickel, pentacyano-isomerism, 1, 206 structure, 1, 40 Nickel, tetracarbonyl-cxchangc reactions, 1,288 Nickel, tetracyano-, 5,67 Nickel, tetrahalo-, 5, 186 Nickel, tetrakis(dinitrogen)-syn thesis... 

Redox Reactivity of Coordinated Ligands in Pentacyano(L)Ferrate Complexes Jose A. Olabe... 

Pentachlorotoluenes, 6 345 Pentacyano complexes, 14 536 Pentacyclopentadiene, 8 224t Pentadecanoic acid, physical properties, 5 29t... 

A further interesting observation from the cyanide exchange study relates to the fact that the exchange rate constants for the equatorial cyanide in the pentacyano complexes compared to the protonated spe-... 

In pentacyano complexes of cobalt(III) the net charge at the coordination center is considerably decreased by the strong coordinate bonds of the five cyano groups. Thus the EPA properties of cobalt(III) are considerably lower in this complex unit, but further stabilization may still be effected by a sixth EPD ligand of high donicity like ammonia. By the reaction... 

Alkali metal salts of such tetracyanonickelate(II) anion may be crystallized from such solutions as hydrates, K2 [Ni(CN)4 3H2O upon evaporation of the solution. In strong cyanide solution, a pentacyano complex anion, red penta-cyanonickelate(ll), [Ni(CN)5] forms. Strong acids decompose cyanonickelate salts, precipitating nickel cyanide. 

Wayne K. Wilmarth It is a pleasure to report the work carried out by Albert Haim and Robert Grassi dealing with substitution reactions of the pentacyano-cobalt(III) complexes. 

The other question concerns the catalytic effect of iodine on the iodination of the pentacyano complex. Did you ever observe the same effect of I2 say on the substitution of bromide, or thiocyanate as well ... 

It has been known for some time, as a result of the work of Prof. Adamson and others, that cobalt (I I) forms a stable pentacyano complex in aqueous solution. However there have been some questions raised about the structure of this species particularly as to whether it is a truly pentacoordinated species or whether there is a loosely held water molecule. 

Dr. Brubaker I have been interested personally in the work that has come from Australia in the last year by Betts and Winfield and others on the oxidation also of the pentacyano with oxygen. Here they find the oxygen binds a proposed intermediate species which may be a monoperoxo monomer, which this group scavenges very well for the pentacyanocobalt(II) and forms the familiar decacyano-/x-peroxyldicobalt(III) complex. So in this case too, the oxidant sticks, not water. 

REDOX REACTIVITY OF COORDINATED LIGANDS IN PENTACYANO(L)FERRATE COMPLEXES... 

The formation of -butyldiazoate by reaction of [Fe(CN)5(NO)]2 with lithium -butyl amide contrasts with the formation of dibutylamine as the main product in the reaction of the same complex with -butylamine (85). This can be explained if the diazoic/diazoate equilibrium shown in Fig. 18 is shifted to the left far enough to form of a diazenido by loss of hydroxide. Attack of -butylamine on the a-carbon of the diazenido species, produces dibutylamine. DFT computed results suggest that the stabilization by complexation of the intermediate diazonium ion (see Fig. 18) is large for the iron-pentacyano complex, in agreement with the fact that no rearrangement products were observed in the reaction of this species with -butylamine (86). The reaction has been proposed as a good route for the preparation of symmetrical, unsymmetrical, and cyclic secondary amines (85). 

When the above factors are put under control, the possibility of changing the ligand L in the pentacyano(L)ferrate complexes adds a further dimension for studying systematic reactivity changes, brought out by the controlled modification of the redox potentials of the Fe(II)-Fe(III) redox couples. In this way, the rates of electron transfer reactions between a series of [Fen(CN)5L]re complexes toward a common oxidant like [Coin(NH3)5(dmso)]3+ showed a variation in agreement with Marcus predictions for outer-sphere electron transfer processes, as demonstrated by linear plots of the rate constants versus the redox potentials (123). 

The chemistry of redox-active ligands L in the pentacyano(L) ferrate(II) and -(III) complexes is of fundamental concern for disclosing... 

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