TY - JOUR
T1 - Structure, hydrogen bonding and thermal expansion of ammonium carbonate monohydrate
AU - Fortes, A. Dominic
AU - Wood, Ian G.
AU - Alfè, Dario
AU - Hernández, Eduardo R.
AU - Gutmann, Matthias J.
AU - Sparkes, Hazel A.
PY - 2014/1/1
Y1 - 2014/1/1
N2 - We have determined the crystal structure of ammonium carbonate monohydrate, (NH4)2CO3·H2O, 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)Å3 [ρcalc = 1281.8(7)kgm-3] at 10K. The single-crystal data collected at 10 and 100K are complemented by X-ray powder diffraction data measured from 245 to 273K, Raman spectra measured from 80 to 263K 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 273K; above 273K, 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 ≃ 30-40kJmol-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 ∼36kJmol-1. The c-axis exhibits negative thermal expansion, but the thermal expansion behaviour of the a and b axes is ormal.
AB - We have determined the crystal structure of ammonium carbonate monohydrate, (NH4)2CO3·H2O, 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)Å3 [ρcalc = 1281.8(7)kgm-3] at 10K. The single-crystal data collected at 10 and 100K are complemented by X-ray powder diffraction data measured from 245 to 273K, Raman spectra measured from 80 to 263K 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 273K; above 273K, 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 ≃ 30-40kJmol-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 ∼36kJmol-1. The c-axis exhibits negative thermal expansion, but the thermal expansion behaviour of the a and b axes is ormal.
KW - ammonium carbonate
KW - density functional theory
KW - neutron diffraction
KW - Raman spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=84915803304&partnerID=8YFLogxK
U2 - 10.1107/S205252061402126X
DO - 10.1107/S205252061402126X
M3 - Article (Academic Journal)
C2 - 25449618
AN - SCOPUS:84915803304
SN - 2052-5192
VL - 70
SP - 948
EP - 962
JO - Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials
JF - Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials
IS - 6
ER -