Abstract
The elusive crystal structure of the so-called ‘antimonic acid’ has been investigated by means of robust and state-of-the-art techniques. The synergic results of solid-state magic-angle spinning nuclear magnetic resonance spectroscopy and a combined Rietveld refinement from synchrotron X-ray and neutron powder diffraction data reveal that this compound contains two types of protons, in a pyrochlore-type structure of stoichiometric formula (H3O)1.20(7)H0.77(9)Sb2O6. Some protons belong to heavily delocalized H3O+ subunits, while some H+ are directly bonded to the oxygen atoms of the covalent framework of the pyrochlore structure, with O–H distances close to 1 Å. A proton diffusion mechanism is proposed relying on percolation pathways determined by bond-valence energy landscape analysis. X-ray absorption spectroscopy results corroborate the structural data around Sb5+ ions at short-range order. Thermogravimetric analysis and differential scanning calorimetry endorsed the conclusions on the water content within antimonic acid. Additional 0.7 water molecules per formula were assessed as moisture water by thermal analysis.
Highlights
NPD = 1.5947 Å20 40 60 80 100 120 140 (f) Case C scenario Sb5+ O H1+(H3O)1.20(7)H0.77(9)Sb2O6 (λ = 1.5406 Å Cu Kα radiation) with peaks indexed in a face-centred cubic unit cell with a = 10.36052(15) Å. (b,c) Plots from the combined Rietveld refinement from SXRD and NPD data.Experimental, calculated, and difference (b) SXRD and (c) NPD patterns, with Bragg reflection positions marked by vertical green bars. (d–f) Views of the AA pyrochlore final structure (‘Case C’ scenario described in the SupportingInformation)
A peak indexing over a laboratory X-ray powder diffraction (XRD) pattern was performed as shown in Fig. 1a, confirming that AA adopts a cubic pyrochlore-type structure belonging to the Fd3m (# 227, Oh7 ) space group, in agreement with previous reports[3,28]
When O′ is present, two structural groups can be identified within the unit cell: a main covalent framework of B2O6 corner-sharing octahedra, and a sub-lattice A2O′, interspersed in a tetrahedral arrangement
Summary
20 40 60 80 100 120 140 (f) Case C scenario Sb5+ O H1+. Experimental (red crosses), calculated (solid black line), and difference (solid blue line at the bottom) (b) SXRD (λSXRD = 0.44271 Å) and (c) NPD (λNPD = 1.5947 Å) patterns, with Bragg reflection positions marked by vertical green bars. (d–f) Views of the AA pyrochlore final structure Hydronium subunits are constituted by silver (H1) protons bonded to green (O2) oxygens at 1.323(11) Å in a tetrahedral distribution (with 104.0(16)° angles). These atoms present high mobility, with prolate anisotropic ellipsoids oriented along the (x,x,x) main threefold diagonal. These atoms present high mobility, with prolate anisotropic ellipsoids oriented along the (x,x,x) main threefold diagonal. (e) Close up of the statistical distribution of a single cavity wherein the O2 and H1 are distributed at
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
