Anions pseudohalide

A simple and straightforward approach to their synthesis is the reaction between simple metal salts and the alkali metal or complex anion pseudohalides. Mixed ligand complexes can easily be made via addition of a neutral ligand to the anionic complex species (cf. preparation of trans-ML2(NCS)2, e.g. 103). However, all these methods have been well reviewed202 209 and representative examples can be found in the references of Section 13.5.5.3. 

Neutral and anionic Pseudohalide complexes have been reported. While most of the thiocyanates were considered to be N-coordinated, Nh NMR spectra of Nb(NCS)6 were reinterpreted in terms of a mixture of N- and S-coordinated isomers. 

The trivalent [P04] and [As04] ions react similarly. Examples of anions that give insoluble Hg(I) compounds in this way include halides, pseudohalides, halates, carboxylates and sulfate. A trace of HNO3 or HCIO4 is often added to the solution of the Hg(I) nitrate or perchlorate to prevent disproportionation induced by alkali. Table 1 lists common Hg(I) derivatives prepared in this way and includes values of the solubility products of the sparingly soluble Hg(I) compounds where these are measured. A similar reaction is used to prepare HgjCO, from a soluble bicarbonate ... 

Ligand A anionic (e.g., halides, pseudohalides, alkyl, aryl, thiolate, alkoxide) ligand N neutral (e.g., amines, imines, phosphines, carbenes, nitriles, isonitriles, NO, CO) ligand C cationic (e.g., NO+)... 

Notably, the thiocyanide anion as a pseudohalide forms similar complexes with the aromatic jt-acceptors. Indeed, in the recently characterized complex... 

Donor-stabilized compounds with simple, non-functional alkyl substituents R are known mainly for gold in its standard oxidation states +1 and +3, that is, (L)AuR and (L)AuR3, respectively. For the latter, R may be replaced by halide, pseudohalide, or other anionic or neutral ligands leading to compounds of the general formula (L)AuR X3 x. 

Organometallic Nitrogen Compounds of Germanium, Tin, and Lead, 3, 397 Organometallic Pseudohalides, 5, 169 Organometallic Radical Anions, 15, 273 Organometallic Reaction Mechanisms, 4, 267... 

Hydrogen cyanide (Table 15.1) is a colorless, flammable liquid or gas that boils at 25.7°C and freezes at minus 13.2°C. The gas rarely occurs in nature, is lighter than air, and diffuses rapidly. It is usually prepared commercially from ammonia and methane at elevated temperatures with a platinum catalyst. It is miscible with water and alcohol, but is only slightly soluble in ether. In water, HCN is a weak acid with the ratio of HCN to CN about 100 at pH 7.2, 10 at pH 8.2, and 1 at pH 9.2. HCN can dissociate into H+ and CN. Cyanide ion, or free cyanide ion, refers to the anion CN derived from hydrocyanic acid in solution, in equilibrium with simple or complexed cyanide molecules. Cyanide ions resemble halide ions in several ways and are sometimes referred to as pseudohalide ions. For example, silver cyanide is almost insoluble in water, as are silver halides. Cyanide ions also form stable complexes with many metals. 

In Table 6 the differences of free enthalpies of solvation for several anion ligands in a donor solvent D and in AN are given. HMPA shows very weak solvation whereas water is a very strong solvating agent for anions. The free enthalpies of solvation of halide and pseudohalide ions are by 4 to 15 keal/mol more negative than in aprotic donor solvents. 

As shown in the introduction, the DNM anion can be regarded as a resonance stabilized, nonlinear planar pseudohalide, which forms an insoluble, highly explosive brownish silver salt upon addition of silver nitrate to an aqueous solution of 7. The DNM anion is related to the linear fulminate ion (CNO ) and can formally be regarded as the addition product of NO to fulminic acid (HCNO). Starting from CH4, NO containing nonlinear pseudohalides can be derived by successive substitution of H by NO, e.g. H3C(NO)/H2C(NO), H2C(N0)2/HC(N0)2 and HC(NO)3/C(NO)3, whereas the linear pseudohalide CNO is formally formed by replacing three H atoms by one NO unit and deprotonation. 

Carbanions of the type [HjCR ], [HCR R ] and [CR R R ] (R = NO and R R = CN, NO, NO2) can be considered to be resonance-stabilized, nonlinear pseudohalides. All experimentally known resonance-stabilized methanides are reported to be planar or nearly planar (Table 1). While the parent ion, the methanide anion HsC, adopts a pyramidal structure [Afipianar-pyramidai = 9.8 kJmol rf(CH) = 1.099 A, <(HCH) = 109.7° cf. rf(CH) = 1.093 A, <(HCH) = 109.6°] due to the lack of delocalization (no resonance for the p-AO-type lone pair possible) , substitution of one H atom by NO results in a planar anion since the empty jr -orbitals of the NO group are perfectly suitable to delocalize the carbon lone pair. Further substitution of the second H atom again results in planar anions, and the same holds for the third substitution in case of R = CN. In case of R = NO and NO2, the third substitution leads either to a propeller-type structure with only a small distortion from planarity or one NO2 group is twisted by 90°, nevertheless leaving the central carbon in an almost trigonal planar environment . ... 

Most hydrated metal ions are more soluble in water than in ILs. The distribution ratios of some metal ions between aqueous and IL phases may be enhanced in the presence of coordinating anions, such as halides or pseudohalides, capable of modifying the metal complex hydrophobicity, increasing partitioning from water [41]. 

Anionic AuX2 with halide or pseudohalide ligands are well known and have been widely used as a starting materials. The salts Au(SCN)2 have been structurally characterized showing, for alkaline metals, infinite linear chains with alternating... 

This class of compound is represented by the dicyanoiodate(I) anion, involving a pseudohalide rather than an alkyl or aryl ligand. The linear ion, with I—C distance of 2.302 A, has been characterized in the compound K[I(CN)2]C6H12N202, resulting from reaction of an aqueous solution of KCN with an ethanolic solution of ICN. The diimino oxalic acid diethyl ester molecule apparently stabilizes the structure.56... 

When nickel(II) salts containing a coordinating anion (halide and pseudohalide) are reacted with NaBH4 in the presence of np3, trigonal bipyramidal nickel(I) complexes of the type [NiXnp3], in which the coordinating anion occupies die axial position, 39,340 are obtained. When nickel(II) salts with poorly coordinating anions are used, non-stoichiometric hydrido complexes of nickel(II) are obtained (equations 108 and 109). 

Macrocycles with 14-16-membered chelate rings all encircle both high-spin and low-spin nickel(II) in the solid compounds. With anions which have coordination tendency, e.g. halides, pseudohalides and in some cases NOJ, trans octahedral paramagnetic complexes are obtained which are often blue or violet. With anions such as C104, PF6 and BF4 (and I, in some cases) which show little tendency to coordinate, square planar diamagnetic complexes are obtained which are generally yellow. 

Iron-centered paramagnetic complexes formed by reactions between iron salts and nitric oxide in the presence of anionic ligands, and characterized by g = 2.03, were first reported over 20 years ago (22) similar complexes, of the general type [Fe(NO)2X2] +, have subsequently been produced by reactions of iron salts and nitric oxide in the presence of halides and pseudohalides (118), alcohols and alkoxides (119), mercaptides (120, 121), and mercaptopurines and mercaptopy-rimidines (122). 

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