Redetermination of (NH4)2HAsO4

Weil, M.

doi:10.1107/S1600536812043565

inorganic compounds

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ISSN: 2056-9890

Volume 68| Part 11| November 2012| Page i82

doi:10.1107/S1600536812043565

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Redetermination of (NH₄)₂HAsO₄

Matthias Weil ^a ^*

^aInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, Vienna University of Technology, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria
^*Correspondence e-mail: mweil@mail.zserv.tuwien.ac.at

(Received 14 October 2012; accepted 20 October 2012; online 27 October 2012)

In comparison with the original determination based on Weissenberg film data [Khan et al. (1970 ). Acta Cryst. B26, 1889–1892], the current redetermination of diammonium hydrogenarsenate(V) reveals all atoms with anisotropic displacement parameters and all H atoms localized. This allowed an unambiguous assignment of the hydrogen-bonding pattern, which is similar to that of the isotypic phosphate analogue (NH₄)₂HPO₄. The structure of the title compound consists of slightly distorted AsO₃(OH) and NH₄ tetrahedra, linked into a three-dimensional structure by an extensive network of O—H⋯O and N—H⋯O hydrogen bonds.

Related literature

For the previous determination of (NH₄)₂HAsO₄, see: Khan et al. (1970). The arsenate compound is isotypic with the phosphate analogue (NH₄)₂HPO₄ (Khan et al., 1972 ), for which another modification with Z′ = 2 has also recently been described (Kunz et al., 2010 ).

Experimental

Crystal data

(NH₄)₂HAsO₄
M_r = 176.01
Monoclinic, P 2₁ /c
a = 11.3426 (4) Å
b = 6.8512 (3) Å
c = 8.1130 (3) Å
β = 113.784 (4)°
V = 576.92 (4) Å³
Z = 4
Mo Kα radiation
μ = 5.82 mm⁻¹
T = 293 K
0.14 × 0.12 × 0.02 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ) T_min = 0.496, T_max = 0.873
6318 measured reflections
1674 independent reflections
1413 reflections with I > 2σ(I)
R_int = 0.033

Refinement

R[F² > 2σ(F²)] = 0.022
wR(F²) = 0.055
S = 1.04
1676 reflections
101 parameters
All H-atom parameters refined
Δρ_max = 0.59 e Å⁻³
Δρ_min = −0.84 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H3N1⋯O2ⁱ	0.87 (3)	1.88 (3)	2.750 (2)	178 (3)
N1—H1N1⋯O3ⁱⁱ	0.91 (3)	1.91 (3)	2.780 (3)	158 (2)
N1—H2N1⋯O3ⁱ	0.89 (3)	2.06 (3)	2.930 (3)	167 (2)
N1—H4N1⋯O3ⁱⁱⁱ	0.92 (3)	1.86 (3)	2.777 (2)	173 (3)
N2—H4N2⋯O2	0.92 (3)	2.00 (3)	2.910 (2)	174 (2)
N2—H2N2⋯O2ⁱ	0.89 (3)	1.93 (3)	2.809 (2)	174 (2)
N2—H1N2⋯O4	0.83 (3)	2.02 (3)	2.840 (2)	171 (3)
N2—H3N2⋯O4^iv	0.85 (3)	1.95 (3)	2.793 (2)	176 (3)
O1—H1O⋯O4^v	0.73 (3)	1.89 (3)	2.613 (2)	171 (4)
Symmetry codes: (i) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (ii) -x+1, -y+1, -z+1; (iii) $[-x+1, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iv) $[-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (v) $[x, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ .

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536812043565/hb6976sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812043565/hb6976Isup2.hkl

checkCIF report

Comment top

(NH₄)₂HAsO₄ is a frequently used precursor material for preparation of arsenate(V) compounds, starting either from (aqueous) solutions or via ceramic routes. The crystal structure of (NH₄)₂HAsO₄ has originally been determined by Khan et al. (1970) based on Weissenberg photographs. In the original study all atoms were refined with isotropic displacement parameters. Since H atoms could not be localized, the authors could make only assumptions with respect to the resulting hydrogen bonding pattern, deduced from N···O and O···O distances. These assumptions included three models: i) the NH₄ ions exhibit rotatory oscillations; ii) the NH₄ ions are in static disorder; iii) each of the two N atoms forms a bifurcated bond in addition to three normal hydrogen bonds (Khan et al., 1970). Somewhat later Khan et al. (1972) showed for the isotypic phosphate analogue (NH₄)₂HPO₄ that dynamic or static disorder can be ruled out for the NH₄ groups and that the ammonium tetrahedra form four classical hydrogen bonds to the PO₃(OH) groups. The current redetermination of the structure of (NH₄)₂HAsO₄ using modern CCD-based data was intended to shed some light on its hydrogen bonding pattern and to compare the results with the phosphate analogue.

The redetermination confirmed the basic features of the original study, however with the unambiguous localization of all H atoms and, as expected, with higher precision and accuracy. Like in (NH₄)₂HPO₄, the ammonium groups show no static or dynamic disorder and four normal N—H···O hydrogen bonds are formed between the constituents. The largest difference between the two determinations pertains to the O···O distance of the O—H···O (O1···O4) hydrogen bond. In the original study this distance was determined as 2.669 (13) Å, whereas it is 2.613 (2) Å in this study. The latter matches very well with 2.615 (1) Å for the phosphate analogue for which all H atoms could be localized (Khan et al., 1972). In the latter study it was suggested that the difference between these O···O distances of the phosphate (2.615 (1) Å) and the arsenate (2.669 (13) Å) structure is a consequence of the different size of the P⁵⁺ and the As⁵⁺ ions. However, the current redetermination of (NH₄)₂HAsO₄ shows that the influence of the different sizes for the phosphate (average P—O distance 1.54 Å) and the arsenate (average As—O distance 1.68 Å) tetrahedra can in fact be neglected.

Fig. 1 shows the structural set-up of the two different NH₄ and the AsO₃(OH) tetrahedra. All tetrahedra show slight angular distortions; the difference in As—O bond lengths for the three As—O bonds (average 1.674 Å) and the longer As—OH bond (1.7291 (15) Å) is normal. The ammonium cations and hydrogenarsenate anions are linked into a three-dimensional network by classical O—H···O and N—H···O hydrogen bonds, the numerical details of which are given in Table 1. The latter are very similar to those of the isotypic phosphate (NH₄)₂HPO₄ (Khan et al., 1972).

For (NH₄)₂HPO₄ another crystalline polymorph has been described, resulting from hydrolysis of the educt, viz. ammonium hexafluoridophosphate (Kunz et al., 2010). It would be interesting to know whether an arsenate polymorph isotypic with the phosphate analogue or another polymorph (NH₄)₂HAsO₄ exist as well.

Related literature top

For the previous determination of (NH₄)₂HAsO₄, see: Khan et al. (1970). The arsenate compound is isotypic with the phosphate analogue (NH₄)₂HPO₄ (Khan et al., 1972), for which another modification with Z' = 2 has also recently been described (Kunz et al., 2010).

Experimental top

Crystals of the title compound were grown from an aqueous solution containing diluted arsenic acid (20%_wt) mixed with a concentrated aqueous solution of ammonia in excess. The solution was kept in a desiccator with CaCl₂ as drying agent. The first crystals, mostly with a plate-like form, appeared approximately after one week.

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

Fig. 1. Projection of the crystal structure along [010]. AsO₄ tetrahedra are red, NH₄ tetrahedra are blue, O atoms are white, and H atoms are grey. Atoms are displayed with displacement ellipsoids at the 50% probability level. H···O hydrogen bonds are displayed with black lines.

Diammonium hydrogenarsenate(V) top

Crystal data top

(NH₄)₂HAsO₄	F(000) = 352
M_r = 176.01	D_x = 2.026 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 2800 reflections
a = 11.3426 (4) Å	θ = 3.6–30.0°
b = 6.8512 (3) Å	µ = 5.82 mm⁻¹
c = 8.1130 (3) Å	T = 293 K
β = 113.784 (4)°	Plate, colourless
V = 576.92 (4) Å³	0.14 × 0.12 × 0.02 mm
Z = 4

Data collection top

Bruker APEXII CCD diffractometer	1674 independent reflections
Radiation source: fine-focus sealed tube	1413 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.033
ω– and ϕ–scans	θ_max = 30.0°, θ_min = 2.0°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −15→15
T_min = 0.496, T_max = 0.873	k = −6→9
6318 measured reflections	l = −11→10

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.022	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.055	All H-atom parameters refined
S = 1.04	w = 1/[σ²(F_o²) + (0.0304P)²] where P = (F_o² + 2F_c²)/3
1676 reflections	(Δ/σ)_max = 0.001
101 parameters	Δρ_max = 0.59 e Å⁻³
0 restraints	Δρ_min = −0.84 e Å⁻³

Crystal data top

(NH₄)₂HAsO₄	V = 576.92 (4) Å³
M_r = 176.01	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 11.3426 (4) Å	µ = 5.82 mm⁻¹
b = 6.8512 (3) Å	T = 293 K
c = 8.1130 (3) Å	0.14 × 0.12 × 0.02 mm
β = 113.784 (4)°

Data collection top

Bruker APEXII CCD diffractometer	1674 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2009)	1413 reflections with I > 2σ(I)
T_min = 0.496, T_max = 0.873	R_int = 0.033
6318 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.022	0 restraints
wR(F²) = 0.055	All H-atom parameters refined
S = 1.04	Δρ_max = 0.59 e Å⁻³
1676 reflections	Δρ_min = −0.84 e Å⁻³
101 parameters

Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
As1	0.249593 (18)	0.89261 (3)	0.42786 (3)	0.00648 (7)
O1	0.20879 (15)	0.9789 (2)	0.2115 (2)	0.0126 (3)
O2	0.25894 (13)	0.0977 (2)	0.5442 (2)	0.0098 (3)
O3	0.38858 (13)	0.7692 (2)	0.4982 (2)	0.0114 (3)
O4	0.13017 (13)	0.7484 (2)	0.4289 (2)	0.0098 (3)
N1	0.44933 (18)	0.1231 (3)	0.1532 (3)	0.0111 (3)
N2	0.12140 (18)	0.3798 (3)	0.2643 (3)	0.0100 (3)
H1N1	0.494 (3)	0.131 (3)	0.275 (4)	0.017 (7)*
H2N1	0.422 (2)	0.003 (4)	0.114 (4)	0.013 (6)*
H3N1	0.388 (3)	0.209 (4)	0.117 (4)	0.022 (7)*
H4N1	0.509 (3)	0.167 (4)	0.111 (4)	0.016 (7)*
H1N2	0.118 (3)	0.491 (5)	0.302 (4)	0.020 (7)*
H2N2	0.169 (3)	0.392 (3)	0.201 (4)	0.013 (7)*
H3N2	0.046 (3)	0.336 (4)	0.209 (4)	0.022 (7)*
H4N2	0.164 (2)	0.297 (4)	0.358 (4)	0.013 (6)*
H1O	0.186 (3)	0.907 (4)	0.139 (5)	0.032 (10)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
As1	0.00865 (10)	0.00455 (11)	0.00669 (11)	0.00021 (7)	0.00355 (7)	−0.00027 (8)
O1	0.0228 (7)	0.0084 (8)	0.0071 (7)	−0.0016 (6)	0.0064 (6)	−0.0004 (6)
O2	0.0134 (7)	0.0062 (7)	0.0105 (7)	−0.0002 (5)	0.0056 (6)	−0.0026 (6)
O3	0.0102 (6)	0.0113 (7)	0.0131 (7)	0.0031 (5)	0.0051 (6)	0.0011 (6)
O4	0.0111 (6)	0.0068 (7)	0.0119 (7)	−0.0018 (5)	0.0051 (5)	0.0003 (6)
N1	0.0117 (8)	0.0096 (9)	0.0123 (9)	0.0008 (7)	0.0052 (7)	0.0006 (7)
N2	0.0121 (8)	0.0071 (9)	0.0120 (9)	0.0003 (7)	0.0059 (7)	−0.0005 (7)

Geometric parameters (Å, º) top

As1—O2ⁱ	1.6718 (14)	N1—H2N1	0.89 (3)
As1—O3	1.6732 (14)	N1—H3N1	0.87 (3)
As1—O4	1.6793 (14)	N1—H4N1	0.92 (3)
As1—O1	1.7293 (15)	N2—H1N2	0.83 (3)
O1—H1O	0.73 (3)	N2—H2N2	0.89 (3)
O2—As1ⁱⁱ	1.6718 (14)	N2—H3N2	0.85 (3)
N1—H1N1	0.91 (3)	N2—H4N2	0.92 (3)

O2ⁱ—As1—O3	113.29 (7)	H1N1—N1—H4N1	103 (2)
O2ⁱ—As1—O4	111.04 (7)	H2N1—N1—H4N1	112 (2)
O3—As1—O4	110.62 (7)	H3N1—N1—H4N1	105 (2)
O2ⁱ—As1—O1	102.46 (7)	H1N2—N2—H2N2	105 (2)
O3—As1—O1	110.40 (7)	H1N2—N2—H3N2	110 (3)
O4—As1—O1	108.67 (7)	H2N2—N2—H3N2	116 (3)
As1—O1—H1O	117 (3)	H1N2—N2—H4N2	111 (3)
H1N1—N1—H2N1	114 (2)	H2N2—N2—H4N2	107 (2)
H1N1—N1—H3N1	110 (2)	H3N2—N2—H4N2	108 (2)
H2N1—N1—H3N1	113 (3)

Symmetry codes: (i) x, y+1, z; (ii) x, y−1, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H3N1···O2ⁱⁱⁱ	0.87 (3)	1.88 (3)	2.750 (2)	178 (3)
N1—H1N1···O3^iv	0.91 (3)	1.91 (3)	2.780 (3)	158 (2)
N1—H2N1···O3ⁱⁱⁱ	0.89 (3)	2.06 (3)	2.930 (3)	167 (2)
N1—H4N1···O3^v	0.92 (3)	1.86 (3)	2.777 (2)	173 (3)
N2—H4N2···O2	0.92 (3)	2.00 (3)	2.910 (2)	174 (2)
N2—H2N2···O2ⁱⁱⁱ	0.89 (3)	1.93 (3)	2.809 (2)	174 (2)
N2—H1N2···O4	0.83 (3)	2.02 (3)	2.840 (2)	171 (3)
N2—H3N2···O4^vi	0.85 (3)	1.95 (3)	2.793 (2)	176 (3)
O1—H1O···O4^vii	0.73 (3)	1.89 (3)	2.613 (2)	171 (4)

Symmetry codes: (iii) x, −y+1/2, z−1/2; (iv) −x+1, −y+1, −z+1; (v) −x+1, y−1/2, −z+1/2; (vi) −x, y−1/2, −z+1/2; (vii) x, −y+3/2, z−1/2.

Experimental details

Crystal data
Chemical formula	(NH₄)₂HAsO₄
M_r	176.01
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	293
a, b, c (Å)	11.3426 (4), 6.8512 (3), 8.1130 (3)
β (°)	113.784 (4)
V (Å³)	576.92 (4)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	5.82
Crystal size (mm)	0.14 × 0.12 × 0.02

Data collection
Diffractometer	Bruker APEXII CCD diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2009)
T_min, T_max	0.496, 0.873
No. of measured, independent and observed [I > 2σ(I)] reflections	6318, 1674, 1413
R_int	0.033
(sin θ/λ)_max (Å⁻¹)	0.703

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.022, 0.055, 1.04
No. of reflections	1676
No. of parameters	101
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.59, −0.84

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ATOMS (Dowty, 2006), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H3N1···O2ⁱ	0.87 (3)	1.88 (3)	2.750 (2)	178 (3)
N1—H1N1···O3ⁱⁱ	0.91 (3)	1.91 (3)	2.780 (3)	158 (2)
N1—H2N1···O3ⁱ	0.89 (3)	2.06 (3)	2.930 (3)	167 (2)
N1—H4N1···O3ⁱⁱⁱ	0.92 (3)	1.86 (3)	2.777 (2)	173 (3)
N2—H4N2···O2	0.92 (3)	2.00 (3)	2.910 (2)	174 (2)
N2—H2N2···O2ⁱ	0.89 (3)	1.93 (3)	2.809 (2)	174 (2)
N2—H1N2···O4	0.83 (3)	2.02 (3)	2.840 (2)	171 (3)
N2—H3N2···O4^iv	0.85 (3)	1.95 (3)	2.793 (2)	176 (3)
O1—H1O···O4^v	0.73 (3)	1.89 (3)	2.613 (2)	171 (4)

Symmetry codes: (i) x, −y+1/2, z−1/2; (ii) −x+1, −y+1, −z+1; (iii) −x+1, y−1/2, −z+1/2; (iv) −x, y−1/2, −z+1/2; (v) x, −y+3/2, z−1/2.

Acknowledgements

The X-ray centre of the Vienna University of Technology is acknowledged for providing access to the single-crystal diffractometer.

References

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