Disorder of (NH₄)₃H(SO₄)₂ in the high-temperature phase I

The highly disordered crystal structure of triammonium hydrogen disulfate, (NH₄)₃H(SO₄)₂, in the high-temperature phase I was studied using single-crystal neutron diffraction. It is known that the O atom involved in hydrogen bonding between neighbouring SO₄ tetrahedra is disordered and takes a split-atom position, building a two-dimensional hydrogen-bond network in the (001) plane. The H atoms in these SO₄-H-SO₄ hydrogen bonds are disordered and hence refined with a split-atom model. Moreover, from the much larger anisotropic mean-square displacements of ammonium protons the NH groups were refined with a reasonable split-atom model, and their motional behaviour was also analysed by rigid-body treatment. Finally, careful consideration was given to show possible supplementary proton migration between the ammonium protons and those of the hydrogen bonds in this high-temperature phase.

Computing details

Data collection: DIF4N (modified Linux version of DIF4); cell refinement: DIF4N; data reduction: PRON (Scherf, 1998); program(s) used to refine structure: Jana2006 (Petricek, Dusek & Palatinus, 2006); molecular graphics: Atoms 5.1; software used to prepare material for publication: Jana2006 (Petricek, Dusek & Palatinus, 2006).

Figures

(I)

Crystal data

HO8S2·3(H4N)	Dx = 1.805 (2) Mg m^−3
Mr = 247.2	Neutron radiation, λ = 0.555 Å
Trigonal, R3m	Cell parameters from 20 reflections
Hall symbol: -R 3;-2"	θ = 8.4–12.0°
a = 5.907 (3) Å	µ = 0.02 mm^−1
c = 22.57 (1) Å	T = 413 K
V = 682.0 (6) Å^3	Cuboid, colourless
Z = 3	3 × 3 × 3 × 0 (radius) mm
F(000) = 95

Data collection

Single-crystal diffractometer HEiDi	Rint = 0.065
Radiation source: nuclear reactor	θmax = 29.9°, θmin = 4.2°
Cu (420) monochromator	h = −10→9
ω scans	k = −8→9
1164 measured reflections	l = −30→40
452 independent reflections	3 standard reflections every 480 min min
133 reflections with I > 3σ(I)	intensity decay: none

Refinement

Refinement on F^2	0 constraints
R[F^2 > 2σ(F^2)] = 0.056	All H-atom parameters refined
wR(F^2) = 0.109	Weighting scheme based on measured s.u.'s w = 1/(σ^2(I) + 0.0004I^2)
S = 1.51	(Δ/σ)max = 0.028
452 reflections	Δρmax = 4.89 e Å^−3
48 parameters	Δρmin = −3.51 e Å^−3
0 restraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
S	0	0	0.4093 (3)	0.052 (2)
N1	0	0	0	0.0569 (18)
N2	0	0	0.1993 (2)	0.0642 (11)
O1	0.0379 (7)	−0.0379 (7)	0.3435 (3)	0.067 (3)	0.3333
O2	0.1348 (2)	−0.1348 (2)	0.57103 (13)	0.0741 (13)
H1	0.464 (2)	−0.464 (2)	−0.0023 (12)	0.063 (6)*	0.1667
H4	0.0542 (17)	−0.0542 (17)	0.1620 (6)	0.093 (7)	0.3333
H5	0.1381 (19)	−0.0321 (17)	0.2122 (4)	0.126 (7)	0.5
H3	0.041 (4)	−0.041 (4)	−0.031 (2)	0.087 (15)*	0.1667
H2	−0.0884 (12)	0.0884 (12)	−0.0230 (8)	0.116 (8)	0.5

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S	0.062 (3)	0.062 (3)	0.031 (4)	0.0311 (15)	0	0
N1	0.058 (2)	0.058 (2)	0.055 (3)	0.0290 (11)	0	0
N2	0.0581 (12)	0.0581 (12)	0.077 (2)	0.0290 (6)	0	0
O1	0.074 (5)	0.074 (5)	0.050 (3)	0.033 (3)	0.0020 (15)	−0.0020 (15)
O2	0.0814 (15)	0.0814 (15)	0.0809 (17)	0.0568 (16)	−0.0015 (7)	0.0015 (7)
H4	0.088 (8)	0.088 (8)	0.091 (9)	0.034 (7)	0.027 (5)	−0.027 (5)
H5	0.079 (7)	0.096 (8)	0.210 (9)	0.050 (7)	0.002 (5)	0.038 (5)
H2	0.119 (8)	0.119 (8)	0.139 (14)	0.079 (9)	−0.015 (5)	0.015 (5)

Geometric parameters (Å, º)

S—O1	1.535 (9)	N1—H2^ii	1.042 (12)
S—O1^i	1.535 (9)	N1—H2^vi	1.042 (12)
S—O1^ii	1.535 (9)	N1—H2^vii	1.042 (12)
S—O2^iii	1.449 (3)	N1—H2^viii	1.042 (12)
S—O2^iv	1.449 (3)	N2—H4	1.009 (14)
S—O2^v	1.449 (3)	N2—H4^i	1.009 (14)
N1—H3	0.82 (4)	N2—H4^ii	1.009 (14)
N1—H3^i	0.82 (4)	N2—H5	0.970 (13)
N1—H3^ii	0.82 (4)	N2—H5^i	0.970 (15)
N1—H3^vi	0.82 (4)	N2—H5^ii	0.970 (10)
N1—H3^vii	0.82 (4)	N2—H5^ix	0.970 (13)
N1—H3^viii	0.82 (4)	N2—H5^x	0.970 (15)
N1—H2	1.042 (12)	N2—H5^xi	0.970 (10)
N1—H2^i	1.042 (12)
O1—S—O2^iii	122.5 (4)	H2—N1—H2^i	97.4 (10)
O1—S—O2^iv	100.2 (3)	H2—N1—H2^ii	97.4 (10)
O1—S—O2^v	100.2 (3)	H3^vi—N1—H2	89 (2)
O1^i—S—O2^iii	100.2 (3)	H3^vii—N1—H2	131 (2)
O1^i—S—O2^iv	100.2 (3)	H3^viii—N1—H2	131 (2)
O1^i—S—O2^v	122.5 (4)	H2^i—N1—H2^ii	97.4 (9)
O1^ii—S—O2^iii	100.2 (3)	H4—N2—H5	76.0 (9)
O1^ii—S—O2^iv	122.5 (4)	H4—N2—H5^i	130.6 (8)
O1^ii—S—O2^v	100.2 (3)	H4—N2—H5^ii	110.1 (8)
O2^iii—S—O2^iv	111.0 (3)	H5—N2—H5^i	111.4 (8)
O2^iii—S—O2^v	111.0 (3)	H5—N2—H5^ii	111.4 (10)
O2^iv—S—O2^v	111.0 (3)	H5^i—N2—H5^ii	111.4 (10)

Symmetry codes: (i) −y, x−y, z; (ii) −x+y, −x, z; (iii) y, x, −z+1; (iv) x−y, −y, −z+1; (v) −x, −x+y, −z+1; (vi) y, x, −z; (vii) x−y, −y, −z; (viii) −x, −x+y, −z; (ix) −y, −x, z; (x) −x+y, y, z; (xi) x, x−y, z.