X-ray study of solid ammonia

Abstract

Ammonia and deutero-ammonia have been studied by single-crystal and powder X-ray methods. There are four molecules in the cubic unit cell, and the space group is confirmed to be P213. The nitrogen parameter obtained by least-squares refinement is equal to 0-0401 for I~H 3 at -102 ° C. and the same for ND 3 at -160 ° C. Cell dimensions, determined by powder methods, are : a = 5.084 A for NH 3 at -196 °C., 5"073 A for ND~ at -196 °C., 5.091 /~ for ND 3 at -160 °C., and 5.138 A for NH 3 at -102 °C. Each ammonia molecule is involved in six hydrogen bonds of approximate length 3.4 A. A possible assignment of the hydrogen atoms to these bonds is given. Electron-density maps give evidence of hydrogen positions with coordinates (0.85, 0.14, 0.99), in agreement with this assignment, but with hydrogen off the bond axis, making the H-N-H angles more nearly tetrahedral.

Ammine Calcium and Strontium Borohydrides: Syntheses, Structures, and Properties

“…The slopes of the straightl ines are 35.6 (R 2 = 0.9964) and 39.5 3 (R 2 = 0.9956), respectively,t hat corresponds to the size of one ammonia molecule, which in solid NH 3 at À80 8Ci sV(NH 3 ) = 33.9 3 . [29] Similarr esultsa re obtained for the series of ammine metal borohydrides based on Mn and Y. [15,16] Structural relationshipbetween amminemetal chlorides and borohydrides 2+ + (M = Ca and Sr).…”

The kinetics and mechanisms of organic reactions in liquid ammonia

“…In the solid phase, Xray diffraction indicates that each ammonia molecule is surrounded by six nearest neighbours though asymmetrical and nonlinear hydrogen bonds and each electron pair on a nitrogen atom can accommodate three hydrogen bonds. 47 While, in the liquid phase, an ammonia molecule is surrounded by an average of 11 molecules close to its boiling point. 48 However, interestingly, infra red spectroscopy of liquid ammonia at room temperature shows that less than 3 hydrogen bonds are formed, 49 in stark contrast with the X-ray results, which suggests that temperature and pressure effects are very important factor for the properties of liquid ammonia.…”

Critical behaviour of the specific heat and the thermal expansion close to the melting point in ammonia solid III

“…Ammonia solid I has four molecules per unit cell in a cubic structure with the space group P 213 [1]- [3], whereas ammonia solid II has two orientationally disordered molecules per unit cell in a hexagonal close-packed structure (hcp) with the space group P 63 /mmc [4]. The third solid phase which exists at 35 kbar at 25 o C, has a face centered cubic (fcc) structure [5].…”

“…Ammonia has three solid phases, namely, I, II and III with the different crystal structures, as determined experimentally [1]- [4]. Ammonia solid I has four molecules per unit cell in a cubic structure with the space group P 213 [1]- [3], whereas ammonia solid II has two orientationally disordered molecules per unit cell in a hexagonal close-packed structure (hcp) with the space group P 63 /mmc [4].…”