Ammonium iodide, crystal structure

The novel highly substituted spiro[4.4]nonatrienes 98 and 99 are produced by a [3+2+2+2] cocyclization with participation of three alkyne molecules and the (2 -dimethylamino-2 -trimethylsilyl)ethenylcarbene complex 96 (Scheme 20). This transformation is the first one ever observed involving threefold insertion of an alkyne and was first reported in 1999 by de Meijere et al. [81]. The structure of the product was eventually determined by X-ray crystal structure analysis of the quaternary ammonium iodide prepared from the regioisomer 98 (Ar=Ph) with methyl iodide. Interestingly, these formal [3+2+2+2] cycloaddition products are formed only from terminal arylacetylenes. In a control experiment with the complex 96 13C-labeled at the carbene carbon, the 13C label was found only at the spiro carbon atom of the products 98 and 99 [42]. 

Figure 6. X-ray crystal structure of the iodide cryptate of the macrotricyclic quaternary ammonium receptor 16." ...

Ammonium chloride [12123-02-9], NH Q, ammonium bromide [12124-97-9], NH Br, and ammonium iodide [12027-06-4], NH I, are crystalline, ionic compounds of formula wts 53.49, 97.94, and 144.94, respectively. Their densities d systematically follow the increase in formula weight 1.53, 2.40, and 2.52. AH three exist in two crystal modifications (10) the chloride, bromide, and iodide have the CsQ structure below temperatures of 184.5, 137.8, and — 17.6°C, respectively each reversibly transforms to the NaQ. stmcture at higher temperatures. 

Analogical molecular structure is possessed by other simple compounds such as potassium iodide, ammonium chloride, sodium hydroxide, barium nitrate, ammonium acetate and so on. In all these compounds there is a transfer of one or several electrons from one element to the other, positive and negative ions being thus formed, that are hold together in a crystal by electrostatic attraction. A bond of this kind is no genuine chemical bond in tbe correct meaning of the term, but is just,a result of Coulomb forces of attraction between opposite charges. 

Ammonium fluoride, NH4F, crystallizes with a structure different from those of the other ammonium (and alkali) halides. The chloride, bromide, and iodide have the CsCl structure at temperatures below 184 3°, 137-8 , and — IT S C respectively, and the NaCl structure at temperatures above these transition points, but NH4F crystallizes with the wurtzite structure, in which each N atom forms N-H—F bonds of length 2-71 to its four neighbours arranged tetrahedrally around it. This is essentially the same structure as that of ordinary ice. 

Ionic liquids (ILs) with their outstanding solvent properties, that is, high conductivity, tunable polarity, zero volatility, and high thermal stability, are of growing interest in different fields of application including as a solvent component in microemulsions [6,7]. Thus, the tunable polar properties are of special interest. Therefore, ILs can be used as polar [8-11] as well as nonpolar solvents [12,13], Moreover, ILs can show amphiphilic behavior [14] and are called IL sirnfactants [15], Their physical properties can be adjusted in a characteristic way by varying the molecular structure of ILs. Since the ILs are sterically mismatched ions, they hinder crystal formation. Different cations, for example, ammonium, phosphonium, sulfonium, imidazolium, pyridinium, or pyrrolidinium, with different anions, for example, chloride, bromide, iodide, fluoroborate, or fluorophosphates, can be selected for a broad range of combinations [6]. 

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