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Structure, hydrogen bonding and thermal expansion of ammonium carbonate monohydrate
Author(s) -
Fortes A. Dominic,
Wood Ian G.,
Alfè Dario,
Hernández Eduardo R.,
Gutmann Matthias J.,
Sparkes Hazel A.
Publication year - 2014
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s205252061402126x
Subject(s) - orthorhombic crystal system , hydrogen bond , raman spectroscopy , crystallography , crystal structure , negative thermal expansion , thermal expansion , density functional theory , bond length , neutron diffraction , chemistry , crystal (programming language) , single crystal , materials science , molecule , computational chemistry , physics , organic chemistry , metallurgy , programming language , computer science , optics
We have determined the crystal structure of ammonium carbonate monohydrate, (NH 4 ) 2 CO 3 ·H 2 O, using Laue single‐crystal diffraction methods with pulsed neutron radiation. The crystal is orthorhombic, space group Pnma ( Z = 4), with unit‐cell dimensions a = 12.047 (3), b = 4.453 (1), c = 11.023 (3) Å and V = 591.3 (3) Å 3 [ρ calc = 1281.8 (7) kg m −3 ] at 10 K. The single‐crystal data collected at 10 and 100 K are complemented by X‐ray powder diffraction data measured from 245 to 273 K, Raman spectra measured from 80 to 263 K and an athermal zero‐pressure calculation of the electronic structure and phonon spectrum carried out using density functional theory (DFT). We find no evidence of a phase transition between 10 and 273 K; above 273 K, however, the title compound transforms first to ammonium sesquicarbonate monohydrate and subsequently to ammonium bicarbonate. The crystallographic and spectroscopic data and the calculations reveal a quite strongly hydrogen‐bonded structure ( E HB ≃ 30–40 kJ mol −1 ), on the basis of H...O bond lengths and the topology of the electron density at the bond critical points, in which there is no free rotation of the ammonium cation at any temperature. The barrier to free rotation of the ammonium ions is estimated from the observed librational frequency to be ∼ 36 kJ mol −1 . The c ‐axis exhibits negative thermal expansion, but the thermal expansion behaviour of the a and b axes is ormal.