Hydrogen bonding ammonia complexes

Barnes, A, J., and Wright, M. P, Strongly hydrogen-bonded molecular complexes studied by matrix-isolation vibrational spectroscopy. Part 3. Ammonia-hydrogen bromide and amine-hydrogen bromide complexes, J. Chem. Soc., Faraday Trans, 2 82, 153-164 (1986). 

A. J. Barnes, T. R. Beech, and Z. Mielke, /. Chem. Soc. Faraday Trans. 2, 80, 455 (1984). Strongly Hydrogen-Bonded Molecular Complexes Studied by Matrix Isolation Vibrational Spectroscopy, Part 1. The Ammonia-Hydrogen Chloride Complex. 

The Nl-Bl separation is consistent with an elongated single bond, while the N3-H2 and N3-N2 separations are indicative of hydrogen bonding. This complex also mediates Nj-centered redox reactivity, and in the presence of CoCp 2 and collidinium hydrochloride as a reductant and proton donor, respectively, ammonia was confirmed as a reduction product. The side-on binding mode and N-N bond scission reaction is of potential relevance to the Nj-fixation cycles since hydrazine is a known byproduct of N2 reduction to ammonia by V-nitrogenase [37]. Future work on this scaffold will target redox transformations of other small molecule substrates amenable to reductive activation, for instance, CO2, N2, and CO, and seek to elucidate the intimate role of each Lewis partner to effect substrate activation. 

The cupro and lyocell processes are based on the application of direct dissolution systems. The copper ammonia complex is prepared from copper sulphate and sodium carbonate with sodium and ammonium hydroxides, as presented in the equation in Fig. 4.3. The dissolution process is carried out for cuprammonium via weakening the intra/intermolecular hydrogen bonds and complex formation. Cupro and especially lyocell processes consume lower amounts of water, but a similar magnitude of energy. 

Ammonia is very soluble in water because the NH3 molecules can form hydrogen bonds to H20 molecules. Ammonia is a weak Bronsted base in water it is also a reasonably strong Lewis base, particularly toward d-block elements. For example, it reacts with Cu2+(aq) ions to give a deep-blue complex (Fig. 15.4) ... 

When hot, ammonia and compounds, which contain nitrogen-hydrogen bonds eg ammonium salts and cyanides react violently with chlorates and alkaline perchlorates. Diammonlum sulphate, ammonium chloride, hydroxyl-amine, hydrazine, sodamide, sodium cyanide and ammonium thiocyanate have been cited. So far as hydrazine is concerned, the danger comes from the formation of a complex with sodium or lithium perchlorate, which is explosive when ground. Many of these interactions are explosive but the factors which determine the seriousness of the accident are not known. 

The RAHB effect may be illustrated by the ubiquitous C=0- -H—N hydrogen bond of protein chemistry. As shown in Section 5.2.2, the simplest non-RAHB prototype for such bonding, the formaldehyde-ammonia complex (5.31c), has only a feeble H-bond (1.41 kcalmol-1). However, when the carbonyl and amine moieties are combined in the resonating amide group of, e.g., formamide, with strong contributions of covalent (I) and ionic (II) resonance structures,... 

Two additional systems in which hydrogen bonds are expected to play a dominant role, ammonia-water complex and 2-aminoethanol, were calculated ab initio and by the new MM3 force field. Two ammonia-water complexes were considered, one with an N... H—O bridge (32) and the other with an O... H—N bridge (33). As expected from the relative H-donor/H-acceptor properties of nitrogen and oxygen, 32 was calculated... 

TABLE 15. Energetic and structural parameters for two ammonia-water complexes (32 and 33) as calculated ab initio (6-31G + BSSE correction) and by the MM3 force field augmented with a directional hydrogen bonding potential function0. Reproduced by permission of John Wiley Sons Ltd from Ref. 30b... 

Fig. 6. Potential energy curve relative to the interconversion between ionic and covalent structure for the NHs-HCl complex (NH3 + HCl —> NH4 + C ). dNH represents the distance between the ammonia molecule nitrogen and the hydrogen of the HCl fragment involved in hydrogen bond along the axis (dNH ci HCi)- TZVP standard basis was employed. Energies and distances are in a.u.

The stoichiometric composition of the halogenoborane complexes is 1 1, as a rule. However, in some cases, 2 1 and 4 1 complexes are also obtained (Table 4). In the latter instances additional ligands are bonded to the 1 1 complex through hydrogen bonds.2,11 55 With ammonia only the 1 1 complex is stable, whereas (H20)2-BF3 is more stable than H20-BF3. BF3 produces 2 1 complexes of similar stability with alcohols and carboxylic acids.2,55,57 At low temperatures some tertiary amines give complexes with halogenoboranes and complexes of... 

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 activation parameters for the ethylenediamine complexes of rhodium(III) and iridium(III) are also in keeping with an essentially dissociative mechanism. The observation that AHt(k-t) is larger than AHt(k 2) for iridium(III) has been rationalized in terms of stabilization of the aquahydroxo species by intramolecular hydrogen bond formation. Similarly, the observation for the rhodium(III) system that AHl(k ) < AHt(k-2) for ammonia, whereas A// (, ) AHt(k 2) for ethylenediamine may, in part, by rationalized in terms of the observed differences in the degree of intramolecular hydrogen bond stabilization of the aqua hydroxo species in the two systems [ZCH(en) > J h(NH3) see Table XXI]. 

The reaction between ammonia and methyl halides has been studied by using ab initio quantum-chemical methods.90 An examination of the stationary points in the reaction potential surface leads to a possible new interpretation of the detailed mechanism of this reaction in different media, hr the gas phase, the product is predicted to be a strongly hydrogen-bonded complex of alkylammonium and halide ions, in contrast to the observed formation of the free ions from reaction hr a polar solvent. Another research group has also studied the reaction between ammonia and methyl chloride.91 A quantitative analysis was made of the changes induced on the potential-energy surface by solvation and static uniform electric fields, with the help of different indexes. The indexes reveal that external perturbations yield transition states which are both electronically and structurally advanced as compared to the transition state in the gas phase. 

For attack of F on acrylic acid, first a hydrogen bonded complex is formed which then proceeds to the transition state and then to a stable carbanion. The methyl in the methacrylic acid reduces stabilization of the carbanion as predicted. Subsequent studies using ammonia as the nucleophile indicated that attack proceeded by a rate-determining intramolecular proton transfer from the nucleophile to the ligand, assisted by a discrete water molecule that acts as a catalyst17. They predicted that acrolein underwent 1,4-addition, acrylic acid either 1,2- or 1,4-addition and acrylonitrile 1,2-addition. 

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