Ammonium Cyanate Shows N−H···N Hydrogen Bonding, Not N−H···O

Abstract

The transformation of ammonium cyanate into urea, first studied over 170 years ago by Wöhler and Liebig, has an important place in the history of chemistry. To understand the nature of this solid state reaction, knowledge of the crystal structure of ammonium cyanate is a prerequisite. Employing neutron powder diffraction, we demonstrate conclusively that, in the structure of ammonium cyanate, the NH(4)(+) cation forms N-H...N hydrogen bonds to four cyanate N atoms at alternate corners of a distorted cube, rather than our previously proposed alternative arrangement with N-H...O hydrogen bonds to cyanate O atoms at the other four corners.

Ammonium cyanate: a DFT study of crystal structure, rotational barriers and vibrational spectrum

“…Ammonium cyanate NH 4 NCO has long held an interesting position in chemistry. Historically, a link between the organic and inorganic branches of the subject was established by the reaction discovered by Wo¨hler in 1828, in which ammonium cyanate is converted to urea, (NH 2 ) 2 CO [1,2].…”

“…Historically, a link between the organic and inorganic branches of the subject was established by the reaction discovered by Wo¨hler in 1828, in which ammonium cyanate is converted to urea, (NH 2 ) 2 CO [1,2]. However, the structure of crystalline ammonium cyanate was not determined until recently [3,4].…”

“…Recently, the structural properties of crystalline ammonium cyanate have been studied by both X-ray [3] and neutron [4] powder diffraction experiments. The structure is tetragonal, with two formula units per unit cell, and the space group is P4/nmm [4].…”

“…The structure is tetragonal, with two formula units per unit cell, and the space group is P4/nmm [4]. The linear anions lie on the four-fold axes parallel to the c axis and the cations are located at sites of À4 symmetry, with the hydrogen atoms lying on mirror planes.…”

Urea as a hydrogen carrier: a perspective on its potential for safe, sustainable and long-term energy supply

“…11,12 Work is apparently still in progress, with the theory now that solid state transfer to urea occurs by a proton (H + ) jump from ammonium (NH 4 + ) to cyanate (NCO -) along one of the salt's hydrogen bonds, followed by ammonia's nucleophilic attack on the carbon atom of hydrogen cyanate. 12 Aside from this present uncertainty, methods of urea synthesis have been identified and applied both in the laboratory and in industry such that urea is now a widely used commodity. Because of this, its physical properties are known and available in standard literature ( Table 1).…”