The crystal structure of perdeuterated methanol monoammoniate (CD₃OD·ND₃) determined from neutron powder diffraction data at 4.2 and 180 K

Abstract

The crystal structure of perdeuterated methanol monoammoniate, CD3OD·ND3, has been solved from neutron powder diffraction data collected at 4.2 and 180 K. The crystal structure is orthorhombic, space group Pbca (Z = 8), with unit‐cell dimensions a = 11.02320 (7), b = 7.66074 (6), c = 7.59129 (6) Å, V = 641.053 (5) Å3 [ρcalc = 1162.782 (9) kg m−3] at 4.2 K, and a = 11.21169 (5), b = 7.74663 (4), c = 7.68077 (5) Å, V = 667.097 (4) Å3 [ρcalc = 1117.386 (7) kg m−3] at 180 K. The crystal structure was determined by ab initio methods from the powder data; atomic coordinates and anisotropic displacement parameters were subsequently refined by the Rietveld method to Rp < 3% at both temperatures. The crystal comprises a sheet‐like structure in the bc crystallographic plane, consisting of strongly hydrogen bonded elements; these sheets are stacked along the a axis, and adjacent sheets are linked by what may be comparatively weak C—D...O hydrogen bonds. Within the strongly bonded sheet structure, ND3 molecules are tetrahedrally coordinated by the hydroxy moieties of the methanol molecule, accepting one hydrogen bond (O—D...N) of length ∼1.75 Å, and donating three hydrogen bonds (N—D...O) of length 2.15–2.25 Å. Two of the methyl deuterons appear to participate in weak interlayer hydrogen bonds (C—D...O) of length 2.7–2.8 Å. The hydrogen bonds are ordered at both 4.2 and 180 K. The relative volume change on warming from 4.2 to 180 K, ΔV/V, is +4.06%, which is comparable to, but more nearly isotropic (as determined from the relative change in axial lengths, e.g.Δa/a) than, that observed in deuterated methanol monohydrate.

X-ray and neutron powder diffraction analyses of Gly·MgSO4·5H2O and Gly·MgSO4·3H2O, and their deuterated counterparts

“…As is typical of N-HÁ Á ÁO hydrogen bonds, these contacts are longer and more strained than the O-HÁ Á ÁO hydrogen bonds, with angles in the range 140-165 , comparable to those found in solid ammonia and in ammonia hydrates (Hewat & Riekel, 1979;Loveday et al, 1996;Fortes et al, 2003;Fortes, Wood & Knight, 2009;Fortes, Suard et al, 2009;Griffiths et al, 2012).…”

“…Distribution of hydrogen-bond distances and angles in Gly(d 5 )Á-MgSO 4 Á3D 2 O and Gly(d 5 )ÁMgSO 4 Á5D 2 O (black and white filled symbols, respectively) compared with similar types of bonds in other materials characterized by us using neutron powder diffraction methods (grey symbols). Literature data is from Fortes (2006), Fortes, Wood & Knight (2009, 2010, and Fortes, Suard et al (2009).…”

Phase Behaviour of Ices and Hydrates

“…In ammonia-bearing methanol-water mixtures, stoichiometric methanol ammoniates may crystallize (Kargel 1992); both methanol monoammoniate and methanol hemiammoniate are orthorhombic (Fortes et al 2009d, and exhibit much more isotropic thermal expansion than methanol monohydrate.…”

Thermal conductivity of solid ammonia at low temperatures

“…The ammonia in the outer parts of our Solar system, where it appears mostly in the form of solutions with some other basic compounds, has stimulated investigations of the binary solutions. The structures of crystals of ammonia‐monohydrate , ammonia hydrate , and perdeuterated methanol monoammoniate were specified. Also, the solubility of ammonia in liquid methanol was experimentally investigated .…”