Ammonium cation complexes

Pickard, F.C., Dunn, M.E., Shields, G.C. Comparison of model chemistry and density functional theory thermochemical predictions with experiment for formation of ionic clusters of the ammonium cation complexed with water and ammonia atmospheric implications. J. Phys. Chem. A 2005,109(22), 4905-10. 

NMR spectral techniques are widely used to study complexation of macrocycles as well as the thermodynamic and kinetic quantities that describe host-guest interactions. Measurements of the free energy of activation for complex dissociation (AG. ) at the H NMR coalescence temperature, have been done using a variable temperature H NMR procedure . The method is advantageous for ammonium cations because the dissociation rate for most crown ether-ammonium cation complexes is within the H NMR time scale and only a small amount of sample (3-5 mg) is required. 

Cl anion. X-ray investigations confirm the inclusion of the anion in the macrobicyclic cavity. Ligand 13 described above for the ammonium cation complexation is able to complex, in its tetraprotonated form, the CP anion, a high CP/Br selectivity being observed for this compound. An x-ray structure of the complex [CP C con-... 

The ability to form stable complexes with metal salts is another unique property of the crown ethers. The metal salts described previously include Group I and II elemental as well as in group III. O In addition, ammonium cation complexed with cyclic polyether has also been reported.It is interesting to note that the presence of cyclic polyethers strongly increase the solubility of metal salts in nonpolar solvents. This property can drastically affect the structure and reactivity of ion pairs 25 and also affect the rate of the reactions.26, 27... 

Simplest examples are prepared by the cyclic oligomerization of ethylene oxide. They act as complexing agents which solubilize alkali metal ions in non-polar solvents, complex alkaline earth cations, transition metal cations and ammonium cations, e.g. 12—crown —4 is specific for the lithium cation. Used in phase-transfer chemistry. ... 

The existence of half-salt complex cations formed by the association of an ammonium cation B", with a neutral molecule, B, has also been postulated. 

It resembles tetracyanoethylene in that it adds reagents such as hydrogen (31), sulfurous acid (31), and tetrahydrofuran (32) to the ends of the conjugated system of carbon atoms suffers displacement of one or two cyano groups by nucleophilic reagents such as amines (33) or sodiomalononittile (34) forms TT-complexes with aromatic compounds (35) and takes an electron from iodide ion, copper, or tertiary amines to form an anion radical (35,36). The anion radical has been isolated as salts of the formula (TCNQ) where is a metal or ammonium cation, and n = 1, 1.5, or 2. Some of these salts have... 

Not long thereafter, Tarnowski and Cram reported the first example of a hinged bis-crown ether. The compound was prepared in the usual Williamson reaction by heating a mixture of 2,2, 3,3 -tetrahydroxy-l, r-binaphthyl with pentaethylene glycol ditosylate and KOH in aqueous THF solution. The product (mp 159.5—161°) shown in Eq. (3.30) was obtained in 30% yield. This compound was shown to complex bis-ammonium cations of several varieties . 

The N-coordinated compound [AuCljL] (L= l-ethyl-2-phenylimidazole) with silver tetrafluoroborate gives the cycloaurated species 102, which on further reaction with triphenylphosphine and sodium tetrafluoroborate or ammonium hexafluorophosphate forms the cationic complexes 103 (X = BF., PF,) (00JCS(D)271). 

Fe-HS )jds has been postulated to lead to easier anodic dissolution than that through (Fe-014)3 5. This effect of hydrogen sulphide is thought to be responsible for the acceleration of corrosion of iron observed with some inhibitive sulphur compounds, e.g. thioureas , at low concentrations, since hydrogen sulphide has been identified as a reduction product. However, the effects of hydrogen sulphide are complex, since in the presence of inhibitors such as amines , quaternary ammonium cations , thioureas ", ... 

According to investigations performed by Pakhomov and Kaidalova [204], the crystal structure of NF NbC consists of infinite chains made up of distorted octahedral ions (NbOF4 ) linked by oxygen atoms. Ammonium cations, NH/, occupy the spaces between the chains, as shown in Fig. 30. The packing of the structural units in the NH4NbOF4 crystal can be described as a CsCl type structure in which CF ions are replaced by Nb02F4 complexes and Cs" ions are replaced by ammonium ions. 

The conductivity of a number of bromine containing complexes with different quaternary ammonium cations was studied by Gerold (see Ref. 156]) with respect to the dependence on temperature and bromine... 

More definitive formulas are available from eight X-ray crystallographic reports, as listed in Table XI, which reveals closely related structures by virtue of potassium and ammonium cations being essentially interchangeable. Most are constructed from a complex of Bi3+... 

It is worth mentioning at this point that according to Normant et al. (1975) simple polyamines such as tetramethylethylenediamine (TMEDA) are even more active than [2.2.2]-cryptand in the benzylation of acetates in acetonitrile under liquid-solid conditions. These authors suggested that the activity was due to salt solubilization by cation complexation and not to formation of a quaternary ammonium ion since the latter showed no activity. This statement, however, is not in line with the results of Cote and Bauer (1977), who were unable to detect any interaction between K+ and TMEDA in acetonitrile. Furthermore, Vander Zwan and Hartner (1978) found Aliquat 336 (tricaprylylmethylammonium chloride) to be almost as effective as TMEDA in this reaction (Table 30). It might well be, however, that in amine-catalysed benzylation reactions the quaternary salt formed in situ acts both as a reactant and as a phase-transfer catalyst, since Dou et al. (1977) have shown that the benzyltriethylammonium ion is a powerful benzylation agent. 

The charge delocalization or the polarizability difference explains the selectivity behaviour in cases of high polarizability differences (complex versus aqueous metal ion) or in a homologous series of ions (either inorganic cations or ammonium cations). The smaller hydration status of all types of interlamellarly adsorbed cations is ascribed to the mutual stabilization by charge delocalization over the planar oxygens and exchangeable cations and is caused by the electrostatic interaction forces. 

While examining the coordination properties of new di- and triaza-crown ether ligands containing multiple ferrocene moieties (Fig. 13) we discovered using H and 13Cnmr titration that these systems form selectively 1 1 complexes with ammonium cations (Beer et al., 1993c). 

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