Tetracyanonickel complex

A tetracyanonickel complex, Na2 [Ni(Q l)4], is a valuable reagent for the conversion of diazonium salts to aryl nitrQes in the Sandmeyer reaction [83, 84]. Addition of the complex to benzenediazonium chloride, at pH 9-11 in a buffer, gave benzonitrile in 59.2% yield. 

ARZU SUNGUR, SEVIM AKYUZ, and J. ERIC D. DAVIES / Vibrational Spectroscopic Studies of 4,4 -Bipyridyl Metal(II) Tetracyanonickelate Complexes and Their Clathrates 491 [383]... 

Vibrational Spectroscopic Studies of 4,4 -Bipyridyl Metal(II) Tetracyanonickelate Complexes and their Clathrates... 

Sungur, A., S. Akyuz amd J. E. D. Davies - Vibrational studies of 4,4 -bipyridyl metal tetracyanonickelate complexes and their clathrates... 

Silva-Avalos J, Richmond MG, Nagappan O, et al. 1990. Degradation of the metal-cyano complex tetracyanonickelate (II) by cyanide-utilizing bacterial isolates. Microbiol 56 3664-3670. 

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. 

The tetracyanonickelate(II) ion is the most extensively studied square planar complex of nickel(II). TTie electronic spectrum is characterized by d-d bands at 31 000-32 000 cm-1 (eM 500-800) and charge transfer bands (eM = 6000-15 000) at 33 000-37 000 cm-1. In Figure 22 the electronic and MCD spectra of K2Ni(CN)4 are shown. In the MCD spectrum of the low energy band (d-d), since C terms are zero because the ground state is lAlg, the presence of the... 

The compounds M(NH3)2Ni(CN)4 (M = Zn or Cd), which consist of two-dimensional polymeric sheets of tetracyanonickelate ions bridged by coordinating diamminemetal(II) cations, function as host lattices for clathration of small aromatic molecules such as thiophene, furan, pyrrole or pyridine IR studies indicate the presence of hydrogen bonding between the host lattice ammonia and the aromatic guest molecules.132,133 A crystal structure determination of the related clathrate Cd(en)Ni(CN)4(pyrrole)2 has been reported.134 Similarly, the complex Cd(py)2Ni(CN)4 consists of polymeric [Cd—Ni(CN)4] layers held together by Cd-bound pyridine.135... 

The precipitate is readily soluble in excess reagent, when a yellow solution appears owing to the formation of tetracyanonickelate(II) complex ions ... 

If the solution of tetracyanonickelate(II) is heated with sodium hypobromite solution (prepared in situ by adding bromine water to sodium hydroxide solution), the complex decomposes and a black nickel(III) hydroxide precipitate is formed (difference from cobalt ions) ... 

The tetracyanonickelate ion is a good example of a thermodynamically stable comi ex that is kinedcally labile. The classic example of the opposite case, i.e., a kin cally in complex that is thomodynainlcally unstab4e, is the hexaammine c< alt(Ill) cation in acid solution. One nught expect it to deccmpose ... 

An excess of potassium tetracyanonickelate(II) is necessary to prevent reduction to potassium tetracyanonickelate(O). The desired nickel (I) complex is the only reduction product if at least a twofold excess of the nickel(II) complex is present. 

In studying ligand exchange reactions, it is often useful to distinguish between the stability of a complex ion and its tendency to react, which we call kinetic lability. Stability in this context is a thermodynamic property, which is measured in terms of the species formation constant Kf (see p. 677). For example, we say that the complex ion tetracyanonickelate(II) is stable because it has a large formation constant Kf 1 X 10 °)... 

The exchange of cyanide ion between the Ni(CN)4 ion and the bulk solution was complete within 30 seconds, which was too fast to be followed properly by the method used. A study of the Ni - Ni(CN)4 exchange was complicated by formation of the precipitate (Ni(CN)2) in the mixture of nickel(II) and tetracyanonickelate ions. The results indicated two non-equivalent metal ions in the solid, which confirmed that its structure is indeed Ni[Ni(CN)4]. The nickel(II) exchange between Ni(CN)4 and four nickel(II) complexes indicated a direct bimolecular interaction. 

The effect of different salts on the visible spectra of tetracyanonickelate(II) has been investigated, in order to elucidate the formation of further complexes, and to solve the discrepancy between two earlier papers, [59BLA/GOL] and [60MCC/JON]. All salts (KCN, KSCN, KI, KBr, KCl, KF, KNO3) added to Ni(CN)J caused an increase in absorbance around 375 - 500 nm, but the effects were rather different. The data qualitatively confirmed the formation of four very weak complexes Ni(CN)5, Ni(CN)4SCN Ni(CN)4l, and to a much lesser extent Ni(CN)4Br. Numerical estimates of their stability were not provided. 

The rates of coordination reactions are characterized by the terms labile (very fast reactions) and inert (very slow reactions). It is important to understand that these terms do not, in any way, indicate the stability of a complex. They describe the kinetics of the interaction of ligands and a central ion complex stability is described by the magnitude of the equilibrium constant of the reaction by which a complex dissociates into its component central ion and ligands. An inert complex is not necessarily stable, that is, it does not necessarily have little tendency to dissociate. For example, the tetracyanomercurate(II) complex, Hg(CN)/", is labile but very stable while the reverse is true for the tetracyanonickelate(II) complex, Ni(CN)/, which is inert and unstable. ... 

Nishikiori. S. Takahashi-Ebisudani. Y. Iwamoto, T. Novel series of clathrate compounds of the three-dimensional metal complex hosts (yV-methyl-l,3-diaminopropane) cad-mium(II) tetracyanonickelate(II), (V,V-dimethyl-1,3-diaminopropane) cadmium(II) tetracyanonickelate(II) and (2-hydroxyethylinethylamine) cadmium(II) tetracyano-nickelate(II). J. Inclusion Phenom. Mol. Recognit. Chem. 1990, 9(2), 101-112. 

Because the complex is an anion, the metal is indicated as nickelate(O). Putting these parts together and naming the cation first, we have potassimn tetracyanonickelate(O). 

Co2+ gives in NM s, PDC 2 and DMSO22 both the scarcely soluble dicyanide, and a pentacyano-complex [Co(CN)5]2 which appears to have a pseudooctahedral structure by coordination of one solvent molecule. Ni2+ gives again scarcely soluble dicyanides and square planar tetracyanonickelates i. 

The vibrational wavenumbers of the Ni(CN)4 group vibrations of the M-Ni-bipy complexes and M-Ni-bipy-G clathrates [G=Toluene, aniline or JV,A -dimethyl-aniline] are given in Table I. The v(CN) and 6(NiCN) vibrational wave-numbers are found to be similar to those of Hofmann type clathrates [6] and the pyridine [7] complex, showing that the M-Ni(CN)4 layers have been preserved. Since we observed only one v(CN) (E ) band in the IR spectrum and the other two v(CN) (4ig and 5i ) bands in the Raman spectrum of the Cd-Ni-bipy complex, we propose a square planar environment around the tetracyanonickelate ion. 

Describe the d-electron distributions of the complexes Ni(NH3)/ and NfiCNlT according to crystal field theory. The tetraamminenickel(II) ion is paramagnetic, and the tetracyanonickelate(ll) ion is diamagnetic. 

Another example, but, acontrario, is provided by the tetracyanonickelate(II) complex [Ni(CN)4] . It is very stable ... 

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