Crystal structure of sodium di­hydrogen arsenate

Ring, J.; Lindenthal, L.; Weil, M.; Stöger, B.

doi:10.1107/S2056989017013470

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Volume 73| Part 10| October 2017| Pages 1520-1522

https://doi.org/10.1107/S2056989017013470

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Crystal structure of sodium dihydrogen arsenate

Joseph Ring,^a Lorenz Lindenthal,^a Matthias Weil ^b ^* and Berthold Stöger ^c

^aTU Wien, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria, ^bInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, TU Wien, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria, and ^cX-Ray Centre, TU Wien, Getreidemarkt 9, A-1060 Vienna, Austria
^*Correspondence e-mail: matthias.weil@tuwien.ac.at

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 18 September 2017; accepted 20 September 2017; online 25 September 2017)

Single crystals of the title compound, Na(H₂AsO₄), were obtained by partial neutralization of arsenic acid with sodium hydroxide in aqueous solution. The crystal structure of Na(H₂AsO₄) is isotypic with the phosphate analogue and the asymmetric unit consists of two sodium cations and two tetrahedral H₂AsO₄⁻ anions. Each of the sodium cations is surrounded by six O atoms of five H₂AsO₄⁻ groups, defining distorted octahedral coordination spheres. In the extended structure, the sodium cations and dihydrogen arsenate anions are arranged in the form of layers lying parallel to (010). Strong hydrogen bonds [range of O⋯O distances 2.500 (3)–2.643 (3) Å] between adjacent H₂AsO₄⁻ anions are observed within and perpendicular to the layers. The isotypic structure of Na(H₂PO₄) is comparatively discussed.

Keywords: crystal structure; isotypism; sodium arsenate; hydrogen bonding.

CCDC reference: 1575494

1. Chemical context

Arsenic acid is triprotic and thus can form various salts, depending on the degree of deprotonation (H₂AsO₄⁻, HAsO₄²⁻, AsO₄³⁻), the condensation grade of the anion (mono-, di-, tri-, polyarsenate, etc) and the amount of water incorporated in the crystal. With respect to sodium arsenates, numerous crystal structures have been determined so far, including arsenic in tetrahedral and/or in octahedral coordination by oxygen atoms. Arsenate structures with arsenic exclusively in tetrahedral coordination resemble those of the related phosphates and in some cases show isotypism with them (marked by an asterisk): Na_3.25(AsO₄)(OH)_0.25(H₂O)₁₂* (Tillmanns & Baur, 1971 ), Na₄(AsO₄)OH (zur Loye et al., 2015 ), Na₂(HAsO₄)(H₂O)₇* (Baur & Khan, 1970 ; Ferraris et al., 1971 ), Na(H₂AsO₄)(H₂O) (Ferraris et al., 1974 ), Na₃(H₂As₃O₁₀) (Driss & Jouini, 1990 ), Na₄As₂O₇ (Leung & Calvo, 1973 ), Na(AsO₃) (Liebau, 1956 ) and Na₅(AsO₅) (Haas & Jansen, 2001 ). Arsenate structures with arsenic in (complete or partial) octahedral coordination include Na(H₂As₃O₉) (Driss, Jouini, Durif et al., 1988 ), Na₃(H₅As₄O₁₄) (Driss & Jouini, 1989 ), Na(HAs₂O₆) (Dung & Tahar, 1978 ), Na₂As₄O₁₁ (Driss, Jouini & Omezzine, 1988 ) and Na₇As₁₁O₃₁ (Guesmi et al., 2006 ). A detailed discussion of the structural principles and crystal chemical characteristics of arsenates with arsenic in octahedral coordination was given some time ago by Schwendtner & Kolitsch (2007 ).

Besides the Na:As 1:1 phase Na(H₂AsO₄)(H₂O) another 1:1 phase, Na(H₂AsO₄), has been reported but without an additional water molecule (Fehér & Morgenstern, 1937 ). To our surprise, a detailed structural investigation of this salt has not yet been reported. Therefore, we started crystal growth experiments and determined its structure and report here on the results.

2. Structural commentary

The crystal structure of Na(H₂AsO₄) is isotypic with that of Na(H₂PO₄) (Catti & Ferraris, 1974 ). The asymmetric unit of Na(H₂AsO₄) comprises two Na⁺ cations and two tetrahedral AsO₂(OH)₂⁻ groups. The Na1⁺ cation shows a narrow Na—O bond-length distribution in the range 2.337 (2) to 2.498 (2) Å with a distorted octahedron as the corresponding coordination polyhedron. The bond-valence sum (Brown, 2002 ) for the Na1⁺ cation amounts to 1.15 valence units. The surrounding of the Na2⁺ cation is much more distorted, with a bond-length range from 2.338 (2) to 2.769 (3) Å under consideration of a sixfold coordination (bond-valence sum 0.92 valence units). There is an additional remote oxygen atom at a distance of 3.000 (3) Å from Na2⁺. Its contribution of 0.04 valence units to the bond-valence sum might be considered as too low for a significant interaction, and therefore the first coordination sphere of Na2⁺ is discussed as that of a considerably distorted octahedron. The two dihydrogen arsenate groups show the usual differences (Weil, 2000 , 2016 ) between As—O and As—(OH) bonds, with two significantly shorter As—O bonds [mean 1.659 (8) Å] and two longer As—(OH) bonds [1.723 (12) Å].

In the crystal structure of Na(H₂AsO₄) the AsO₂(OH)₂ tetrahedra are arranged in layers lying parallel to (010) with the Na⁺ cations approximately on the same level (Fig. 1). Strong, asymmetric hydrogen bonds [O⋯O distances between 2.500 (3) and 2.643 (3) Å, Table 1] between each of the OH groups of the two dihydrogen arsenate tetrahedra and O atoms of adjacent tetrahedra significantly contribute to the crystal packing. These hydrogen bonds are both within a layer and towards adjacent layers (Fig. 1).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H1⋯O8ⁱ	0.85 (2)	1.75 (2)	2.595 (3)	175 (5)
O4—H2⋯O8	0.83 (2)	1.82 (2)	2.643 (3)	178 (4)
O5—H3⋯O1ⁱⁱ	0.85 (2)	1.73 (2)	2.566 (3)	171 (5)
O7—H4⋯O6ⁱⁱⁱ	0.85 (2)	1.66 (2)	2.500 (3)	169 (4)
Symmetry codes: (i) $[x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (ii) x+1, y, z; (iii) -x+2, -y+1, -z+1.

Figure 1
The crystal structure of Na(H₂AsO₄) in a projection along [100]. All atoms are depicted with displacement ellipsoids at the 97% probability level. Dihydrogen arsenate tetrahedra are given in polyhedral representation, Na⁺ cations as single ellipsoids without bonds to surrounding O atoms. H⋯O hydrogen bonds are illustrated with green lines.

The differences between the isotypic arsenate and phosphate structures can mainly be seen in the X—O bond lengths of the anions (X = As, mean of 1.69 Å; X = P, mean of 1.55 Å), with Δ_max(X—O) of 0.15 Å between arsenate and phosphate tetrahedra. The difference with respect to the Na—O distances in the two structures is less pronounced, with Δ_max(Na—O) = 0.10 Å. Relevant bond lengths of the isotypic crystal structures of Na(H₂AsO₄) and Na(H₂PO₄) (Catti & Ferraris, 1974) are compiled in Table 2. A more quantitative comparison of the two crystal structures with the help of the COMPSTRU routine (de la Flor et al., 2016 ) revealed the following values: The degree of lattice distortion (S), i.e. the spontaneous strain (sum of the squared eigenvalues of the strain tensor divided by 3), is 0.0159; the maximum distance (d_max.), i.e. the maximal displacement between the atomic positions of paired atoms, is 0.1920 Å for atom pair O1; the arithmetic mean (d_av) of the distances of all atom pairs is 0.1108 Å; the measure of similarity (Δ) (Bergerhoff et al., 1999 ) is a function of the differences in atomic positions (weighted by the multiplicities of the sites) and the ratios of the corresponding lattice parameters of the structures and amounts to 0.049.

Table 2
Comparison of bond lengths (Å) in the title compound and the isotypic phosphate analogue (Catti & Ferraris, 1974)

Bond	Na(H₂AsO₄)	Na(H₂PO₄)
Na1—O3ⁱ	2.337 (2)	2.355 (1)
Na1—O5ⁱⁱ	2.376 (2)	2.406 (1)
Na1—O3ⁱⁱⁱ	2.382 (2)	2.371 (1)
Na1—O7	2.456 (2)	2.501 (1)
Na1—O2^iv	2.459 (2)	2.436 (1)
Na1—O6^iv	2.498 (2)	2.564 (1)
Na2—O8	2.338 (2)	2.334 (1)
Na2—O3^iv	2.371 (2)	2.369 (1)
Na2—O1ⁱⁱ	2.419 (2)	2.433 (1)
Na2—O6ⁱ	2.586 (2)	2.601 (1)
Na2—O2^iv	2.703 (3)	2.600 (1)
Na2—O4ⁱ	2.769 (3)	2.730 (1)
Na2—O7^v	3.000 (3)	2.930 (1)
As/P1—O3	1.6484 (19)	1.499 (1)
As/P1—O1	1.657 (2)	1.508 (1)
As/P1—O4	1.730 (2)	1.592 (1)
As/P1—O2	1.736 (2)	1.597 (1)
As/P2—O6	1.663 (2)	1.523 (1)
As/P2—O8	1.668 (2)	1.519 (1)
As/P2—O7	1.711 (2)	1.562 (1)
As/P2—O5	1.713 (2)	1.572 (1)
Symmetry codes (i) −x + 1, −y + 1, −z + 1; (ii) x, −y + $[{1\over 2}]$ , z − $[{1\over 2}]$ ; (iii) x + 1, y, z − 1; (iv) x, y, z − 1; (v) x − 1, y, z.

3. Synthesis and crystallization

The title compound was prepared following a procedure by Fehér & Morgenstern (1937). An arsenic acid solution (ca 65%_wt) was partly neutralized with diluted NaOH solution using methyl red as indicator. The resulting solution was concentrated by heating. Standing of the solution overnight on a warm plate (ca 313 K) afforded colourless crystals with a lath-like form and maximal edge lengths of 0.5 mm.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. Starting coordinates and labelling of atoms were taken from the isotypic Na(H₂PO₄) structure (Catti & Ferraris, 1974). Hydrogen atoms were clearly discernible from difference maps and were refined with distance restraints d(O—H) = 0.85 (1) Å.

Table 3
Experimental details

Crystal data
Chemical formula	Na(H₂AsO₄)
M_r	163.93
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	7.0528 (14), 13.798 (3), 7.4792 (15)
β (°)	93.02 (3)
V (Å³)	726.8 (3)
Z	8
Radiation type	Mo Kα
μ (mm⁻¹)	9.32
Crystal size (mm)	0.12 × 0.08 × 0.01

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.534, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	11092, 2651, 1890
R_int	0.052
(sin θ/λ)_max (Å⁻¹)	0.758

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.030, 0.059, 1.04
No. of reflections	2651
No. of parameters	125
No. of restraints	4
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.87, −0.86
Computer programs: APEX3 and SAINT (Bruker, 2016 ), SHELXL2016 (Sheldrick, 2015 ), ATOMS (Dowty, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1575494

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2056989017013470/hb7706sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989017013470/hb7706Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX3 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: coordinates taken from isotypic structure; program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Sodium dihydrogen arsenate top

Crystal data top

Na(H₂AsO₄)	F(000) = 624
M_r = 163.93	D_x = 2.996 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.0528 (14) Å	Cell parameters from 2433 reflections
b = 13.798 (3) Å	θ = 3.1–31.8°
c = 7.4792 (15) Å	µ = 9.32 mm⁻¹
β = 93.02 (3)°	T = 100 K
V = 726.8 (3) Å³	Lath, colourless
Z = 8	0.12 × 0.08 × 0.01 mm

Data collection top

Bruker APEXII CCD diffractometer	1890 reflections with I > 2σ(I)
ω and φ scans	R_int = 0.052
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 32.6°, θ_min = 2.9°
T_min = 0.534, T_max = 0.746	h = −10→10
11092 measured reflections	k = −20→20
2651 independent reflections	l = −11→11

Refinement top

Refinement on F²	Primary atom site location: isomorphous structure methods
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.030	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.059	w = 1/[σ²(F_o²) + (0.020P)² + 0.0156P] where P = (F_o² + 2F_c²)/3
S = 1.04	(Δ/σ)_max = 0.001
2651 reflections	Δρ_max = 0.87 e Å⁻³
125 parameters	Δρ_min = −0.86 e Å⁻³
4 restraints

Special details top

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

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

	x	y	z	U_iso*/U_eq
As1	0.32467 (4)	0.36827 (2)	0.84669 (4)	0.00611 (7)
As2	0.82170 (4)	0.37010 (2)	0.50756 (4)	0.00595 (7)
Na1	0.85834 (16)	0.40338 (8)	−0.00598 (15)	0.0091 (2)
Na2	0.34819 (17)	0.39825 (9)	0.26282 (16)	0.0134 (3)
O1	0.2417 (3)	0.26833 (14)	0.7478 (3)	0.0108 (4)
O2	0.5315 (3)	0.34069 (15)	0.9726 (3)	0.0099 (4)
O3	0.1910 (3)	0.42983 (14)	0.9809 (3)	0.0078 (4)
O4	0.4015 (3)	0.44833 (15)	0.6878 (3)	0.0124 (4)
O5	0.9202 (3)	0.26110 (14)	0.5709 (3)	0.0113 (4)
O6	0.8540 (3)	0.45079 (14)	0.6715 (3)	0.0098 (4)
O7	0.9303 (3)	0.40531 (15)	0.3188 (3)	0.0093 (4)
O8	0.5931 (3)	0.34459 (14)	0.4613 (3)	0.0082 (4)
H1	0.545 (7)	0.2797 (14)	0.970 (6)	0.055 (15)*
H2	0.462 (5)	0.415 (3)	0.619 (5)	0.038 (13)*
H3	1.026 (4)	0.270 (3)	0.627 (6)	0.071 (18)*
H4	0.995 (5)	0.457 (2)	0.332 (6)	0.045 (13)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
As1	0.00551 (13)	0.00631 (14)	0.00645 (13)	0.00067 (11)	−0.00029 (10)	−0.00017 (11)
As2	0.00609 (13)	0.00599 (14)	0.00564 (13)	−0.00119 (11)	−0.00081 (10)	0.00025 (11)
Na1	0.0087 (6)	0.0086 (5)	0.0099 (6)	0.0004 (4)	−0.0002 (4)	0.0003 (4)
Na2	0.0161 (6)	0.0132 (6)	0.0106 (6)	0.0027 (5)	−0.0038 (5)	−0.0001 (5)
O1	0.0101 (10)	0.0078 (10)	0.0141 (11)	−0.0005 (8)	−0.0031 (8)	−0.0037 (8)
O2	0.0077 (10)	0.0068 (9)	0.0147 (11)	0.0005 (8)	−0.0044 (8)	0.0006 (8)
O3	0.0062 (10)	0.0094 (9)	0.0078 (10)	0.0016 (7)	0.0007 (7)	−0.0011 (7)
O4	0.0150 (11)	0.0112 (10)	0.0114 (11)	0.0040 (9)	0.0059 (9)	0.0033 (8)
O5	0.0105 (10)	0.0064 (10)	0.0163 (11)	−0.0006 (8)	−0.0054 (9)	0.0012 (8)
O6	0.0101 (10)	0.0110 (10)	0.0083 (10)	−0.0033 (8)	0.0012 (8)	−0.0034 (8)
O7	0.0122 (10)	0.0091 (9)	0.0070 (9)	−0.0034 (9)	0.0038 (7)	−0.0008 (8)
O8	0.0058 (9)	0.0078 (9)	0.0108 (10)	−0.0011 (7)	−0.0013 (7)	0.0011 (8)

Geometric parameters (Å, º) top

As1—O3	1.6484 (19)	Na1—O6^iv	2.498 (2)
As1—O1	1.657 (2)	Na2—O8	2.338 (2)
As1—O4	1.730 (2)	Na2—O3^iv	2.371 (2)
As1—O2	1.736 (2)	Na2—O1ⁱⁱ	2.419 (2)
As2—O6	1.663 (2)	Na2—O6ⁱ	2.586 (2)
As2—O8	1.668 (2)	Na2—O2^iv	2.703 (3)
As2—O7	1.711 (2)	Na2—O4ⁱ	2.769 (3)
As2—O5	1.713 (2)	Na2—O7^v	3.000 (3)
Na1—O3ⁱ	2.337 (2)	O2—H1	0.847 (19)
Na1—O5ⁱⁱ	2.376 (2)	O4—H2	0.828 (18)
Na1—O3ⁱⁱⁱ	2.382 (2)	O5—H3	0.847 (19)
Na1—O7	2.456 (2)	O7—H4	0.849 (19)
Na1—O2^iv	2.459 (2)

O3—As1—O1	120.05 (10)	O1ⁱⁱ—Na2—O4ⁱ	157.97 (8)
O3—As1—O4	107.40 (10)	O6ⁱ—Na2—O4ⁱ	73.32 (7)
O1—As1—O4	109.92 (11)	O2^iv—Na2—O4ⁱ	90.18 (7)
O3—As1—O2	105.89 (10)	O8—Na2—O7^v	128.32 (8)
O1—As1—O2	109.06 (10)	O3^iv—Na2—O7^v	72.63 (7)
O4—As1—O2	103.17 (10)	O1ⁱⁱ—Na2—O7^v	74.48 (7)
O6—As2—O8	112.80 (10)	O6ⁱ—Na2—O7^v	52.53 (6)
O6—As2—O7	111.60 (10)	O2^iv—Na2—O7^v	129.53 (8)
O8—As2—O7	111.00 (10)	O4ⁱ—Na2—O7^v	125.50 (7)
O6—As2—O5	110.24 (10)	As1—O1—Na2^vi	131.96 (12)
O8—As2—O5	104.21 (10)	As1—O2—Na1^vii	135.72 (11)
O7—As2—O5	106.56 (10)	As1—O2—Na2^vii	86.99 (8)
O3ⁱ—Na1—O5ⁱⁱ	161.36 (9)	Na1^vii—O2—Na2^vii	109.31 (9)
O3ⁱ—Na1—O3ⁱⁱⁱ	90.20 (7)	As1—O2—H1	107 (3)
O5ⁱⁱ—Na1—O3ⁱⁱⁱ	89.30 (8)	Na1^vii—O2—H1	104 (3)
O3ⁱ—Na1—O7	86.19 (8)	Na2^vii—O2—H1	111 (3)
O5ⁱⁱ—Na1—O7	75.23 (8)	As1—O3—Na1ⁱ	130.46 (11)
O3ⁱⁱⁱ—Na1—O7	83.49 (8)	As1—O3—Na2^vii	101.02 (9)
O3ⁱ—Na1—O2^iv	102.04 (8)	Na1ⁱ—O3—Na2^vii	100.03 (8)
O5ⁱⁱ—Na1—O2^iv	80.75 (8)	As1—O3—Na1^viii	122.85 (11)
O3ⁱⁱⁱ—Na1—O2^iv	166.71 (9)	Na1ⁱ—O3—Na1^viii	89.80 (7)
O7—Na1—O2^iv	102.26 (9)	Na2^vii—O3—Na1^viii	110.53 (9)
O3ⁱ—Na1—O6^iv	79.94 (8)	As1—O4—Na2ⁱ	128.10 (12)
O5ⁱⁱ—Na1—O6^iv	118.47 (8)	As1—O4—H2	105 (3)
O3ⁱⁱⁱ—Na1—O6^iv	83.21 (8)	Na2ⁱ—O4—H2	99 (3)
O7—Na1—O6^iv	160.71 (8)	As2—O5—Na1^vi	134.83 (12)
O2^iv—Na1—O6^iv	93.76 (8)	As2—O5—H3	111 (3)
O8—Na2—O3^iv	156.69 (9)	Na1^vi—O5—H3	113 (3)
O8—Na2—O1ⁱⁱ	86.89 (8)	As2—O6—Na1^vii	122.07 (11)
O3^iv—Na2—O1ⁱⁱ	90.22 (8)	As2—O6—Na2ⁱ	128.58 (11)
O8—Na2—O6ⁱ	122.07 (8)	Na1^vii—O6—Na2ⁱ	90.36 (7)
O3^iv—Na2—O6ⁱ	77.53 (7)	As2—O7—Na1	137.29 (12)
O1ⁱⁱ—Na2—O6ⁱ	126.96 (8)	As2—O7—Na2^ix	126.26 (11)
O8—Na2—O2^iv	92.76 (8)	Na1—O7—Na2^ix	90.85 (7)
O3^iv—Na2—O2^iv	63.95 (7)	As2—O7—H4	114 (3)
O1ⁱⁱ—Na2—O2^iv	81.03 (8)	Na1—O7—H4	102 (3)
O6ⁱ—Na2—O2^iv	132.91 (8)	Na2^ix—O7—H4	61 (3)
O8—Na2—O4ⁱ	73.31 (7)	As2—O8—Na2	137.60 (11)
O3^iv—Na2—O4ⁱ	104.07 (8)

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

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1···O8^vi	0.85 (2)	1.75 (2)	2.595 (3)	175 (5)
O4—H2···O8	0.83 (2)	1.82 (2)	2.643 (3)	178 (4)
O5—H3···O1^ix	0.85 (2)	1.73 (2)	2.566 (3)	171 (5)
O7—H4···O6^x	0.85 (2)	1.66 (2)	2.500 (3)	169 (4)

Symmetry codes: (vi) x, −y+1/2, z+1/2; (ix) x+1, y, z; (x) −x+2, −y+1, −z+1.

Comparison of bond lengths (Å) in the title compound and the isotypic phosphate analogue (Catti & Ferraris, 1974) top

Bond	Na(H₂AsO₄)	Na(H₂PO₄)
Na1—O3ⁱ	2.337 (2)	2.355 (1)
Na1—O5ⁱⁱ	2.376 (2)	2.406 (1)
Na1—O3ⁱⁱⁱ	2.382 (2)	2.371 (1)
Na1—O7	2.456 (2)	2.501 (1)
Na1—O2^iv	2.459 (2)	2.436 (1)
Na1—O6^iv	2.498 (2)	2.564 (1)
Na2—O8	2.338 (2)	2.334 (1)
Na2—O3^iv	2.371 (2)	2.369 (1)
Na2—O1ⁱⁱ	2.419 (2)	2.433 (1)
Na2—O6ⁱ	2.586 (2)	2.601 (1)
Na2—O2^iv	2.703 (3)	2.600 (1)
Na2—O4ⁱ	2.769 (3)	2.730 (1)
Na2—O7^v	3.000 (3)	2.930 (1)
As/P1—O3	1.6484 (19)	1.499 (1)
As/P1—O1	1.657 (2)	1.508 (1)
As/P1—O4	1.730 (2)	1.592 (1)
As/P1—O2	1.736 (2)	1.597 (1)
As/P2—O6	1.663 (2)	1.523 (1)
As/P2—O8	1.668 (2)	1.519 (1)
As/P2—O7	1.711 (2)	1.562 (1)
As/P2—O5	1.713 (2)	1.572 (1)

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

Acknowledgements

The X-ray centre of TU Wien is acknowledged for financial support of this study.

References

Baur, W. H. & Khan, A. A. (1970). Acta Cryst. B26, 1584–1596. CrossRef CAS IUCr Journals Web of Science
Bergerhoff, G., Berndt, M., Brandenburg, K. & Degen, T. (1999). Acta Cryst. B55, 147–156. Web of Science CrossRef CAS IUCr Journals
Brown, I. D. (2002). The Chemical Bond in Inorganic Chemistry: The Bond Valence Model. Oxford University Press.
Bruker (2016). APEX3 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.
Catti, M. & Ferraris, G. (1974). Acta Cryst. B30, 1–6. CrossRef CAS IUCr Journals Web of Science
Dowty, E. (2006). ATOMS. Shape Software, Kingsport, Tennessee, USA.
Driss, A. & Jouini, T. (1989). J. Solid State Chem. 78, 130–135. CrossRef CAS
Driss, A. & Jouini, T. (1990). Acta Cryst. C46, 1185–1188. CrossRef CAS IUCr Journals
Driss, A., Jouini, T., Durif, A. & Averbuch-Pouchot, M.-T. (1988). Acta Cryst. C44, 1507–1510. CrossRef CAS IUCr Journals
Driss, A., Jouini, T. & Omezzine, M. (1988). Acta Cryst. C44, 788–791. CrossRef CAS Web of Science IUCr Journals
Dung, N.-H. & Tahar, J. (1978). Acta Cryst. B34, 3727–3729. CrossRef IUCr Journals
Fehér, F. & Morgenstern, G. (1937). Z. Anorg. Allg. Chem. 232, 169–178.
Ferraris, G., Jones, D. W. & Sowden, J. M. (1974). Atti R. Accad. Sci. Torino, Cl. Sci. Fis., Mat. Nat. 108, 507–527.
Ferraris, G., Jones, D. W. & Yerkess, J. (1971). Acta Cryst. B27, 354–359. CrossRef IUCr Journals
Flor, G. de la, Orobengoa, D., Tasci, E., Perez-Mato, J. M. & Aroyo, M. I. (2016). J. Appl. Cryst. 49, 653–664. Web of Science CrossRef IUCr Journals
Guesmi, A., Nespolo, M. & Driss, A. (2006). J. Solid State Chem. 179, 2466–2471. Web of Science CrossRef CAS
Haas, H. & Jansen, M. (2001). Z. Anorg. Allg. Chem. 627, 1013–1016. CrossRef CAS
Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3–10. Web of Science CSD CrossRef CAS IUCr Journals
Leung, K. Y. & Calvo, C. (1973). Can. J. Chem. 51, 2082–2088. CrossRef CAS Web of Science
Liebau, F. (1956). Acta Cryst. 9, 811–817. CrossRef IUCr Journals Web of Science
Loye, K. D. zur, Latshaw, A. M., Smith, M. D., Chance, W. M. & zur Loye, H. C. (2015). J. Chem. Crystallogr. 45, 20–25.
Schwendtner, K. & Kolitsch, U. (2007). Acta Cryst. B63, 205–215. CrossRef IUCr Journals
Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals
Tillmanns, E. & Baur, W. H. (1971). Acta Cryst. B27, 2124–2132. CrossRef IUCr Journals
Weil, M. (2000). Z. Naturforsch. Teil B, 55, 699–706. CAS
Weil, M. (2016). Cryst. Growth Des. 16, 908–921. CSD CrossRef CAS
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. Web of Science CrossRef CAS IUCr Journals