Ammonium chloride, crystal structure

The structure amplitude, F. In an ammonium chloride crystal the unit cell is a cube containing one NH4 and one Cl ion. If the centre of a chlorine ion is taken as the corner of the unit cell, then the ammonium ion lies in the centre of the cell (Fig. 110). 

The ammonium chloride crystal forms a particularly simple example of the effect of atomic arrangement on the intensities of the various reflections. The structure amplitude will be treated more generally in a later section,... 

These materials are essentially combustion improvers and tend to have fairly simple formulations (e.g., 3% copper chloride, 7% manganese chloride, 90% ammonium chloride). They are designed to change the crystalline structure within the clinker crystal lattice and raise the clinker eutectic point, thus minimizing the formation of noncombustible clinker, residual ash, and other deposits. Feed rates are approxiimately 0.5 to 2.0 lb per bone-dry ton. 

It should not be inferred that the crystal structures described so far apply to only binary compounds. Either the cation or anion may be a polyatomic species. For example, many ammonium compounds have crystal structures that are identical to those of the corresponding rubidium or potassium compounds because the radius NH4+ ion (148 pm) is similar to that of K+ (133 pm) or Rb+ (148 pm). Both NO j and CO, have ionic radii (189 and 185 pm, respectively) that are very close to that of Cl- (181 pm), so many nitrates and carbonates have structures identical to the corresponding chloride compounds. Keep in mind that the structures shown so far are general types that are not necessarily restricted to binary compounds or the compounds from which they are named. 

Angle factors. The two factors already mentioned—the crystal structure amplitude and the factor for the number of similar planes— give a general idea of the reason for the variation of intensity from one arc to another in the powder photograph of ammonium chloride. We have now to consider the general diminution with increasing angle. 

Octahedral coordination of Tiiv is also present in the titanium silicates ETS-4 and ETS-10. The structure of these materials is reported to be similar to that of zorite, and they can be described as microporous crystals with uniform pores similar in dimensions to classical small- and large-pore zeolites. In ETS-4 and ETS-10, there are two monovalent cations or one divalent cation for each Tilv ion (Kuznicki, 1989, 1990 Kuznicki et al., 1991a, 1991b, 1991c, 1993 Deeba et al., 1994). A recent report of the synthesis of ETS-10 with tetramethyl-ammonium chloride indicates a ratio of monovalent cations to Tilv of 1.6 (Valtchev et al., 1994). The acidic properties of these materials have not been reported. A material modified by the addition of Al3+ has been obtained, ETAS-10, which, after exchange with NH4 salts, exhibits acidic properties but these are due to the presence of Al3+ and not to the Tilv (Deeba et al., 1994). 

Metz, B., Rosalky, J. M., Weiss, R., [3] Cryptates - X-ray crystal-structures of chloride and ammonium ion complexes of a spheroidal macrotricyclic ligand. J. Chem. Soc., Chem. Commun. 1976, 533-534. 

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. 

B. Cetinkaya, M. F. Lappert, G. M. McLaughlin, and K. Turner, Chloromethylene-ammonium Chlorides. Electron-Rich Carbenoids as Precursors to Secondary Carbene Metal Complexes Crystal and Molecular Structure of Trichloro(dimethylamino-methylene)bis(triethylphosphine)rhodium(III), J. Chem. Soc., Dalton Tram. 1974, 1591-1599. 

An interesting example where infrared O-H frequencies were used to correlate structures is for choline chloride dihydrate, which is postulated to have a semi-clathrate hydrate structure by analogy with the known crystal structure of tetraethyl ammonium fluoride pentahydrate [162]. 

Fig. 39 Crystal structures of the inclusion complexes of I8H66+ with fluoride (a) [78], and chloride (d) [79] carbon bound hydrogen atoms have been omitted for clarity, (b, c, e, f) Triangles have been obtained by linking the hydrogen atoms of the secondary ammonium groups of each tren subunit, involved in hydrogen bonding...

M. M. Stasova and B. K. Vain-shtetn. Trudy Inst. Krist. Akad. Nauk S.S.S.R. 1956, No. 12, 18-24. x-ray crystal structure of ammonium chloride. 

The ammonium ion can take the place of a monatomic cation in an ionic crystal struaure. For example, the crystal structure of ammonium chloride, NH4CI, which is found in fertilizers, is very similar to the crystal struaure of cesium chloride, CsCl, which is used in brewing, mineral waters, and to make fluorescent screens. In each structure, the chloride ions form a cubic arrangement with chloride ions at the corners of each... 

Describe the crystal structures of cesium chloride and ammonium chloride. How are they similar, and how are they different ... 

The commonest polymorphic changes of this type are those associated with the onset of free rotation in a crystal structure. Many simple molecular compounds (HC1, HBr and CH4 are examples) show a transition with rising temperature from a complex structure to a simple close-packed arrangement in which the molecules effectively acquire spherical symmetry by free rotation. Similar effects are displayed by a number of ionic crystals containing complex ions of un-symmetrical shape. Thus NaCN, KCN and RbCN have complex structures at low temperatures but transform at higher temperatures to the sodium chloride structure in which the CN ions behave as spherical entities. In some cases rotation may take place only about one axis, so that the molecule or group acquires cylindrical rather than spherical symmetry, and in other cases rotations about different axes may be excited successively at different temperatures. An extreme example of this is ammonium nitrate, in which both cation and anion are capable of... 

---