inorganic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

A sodium calcium arsenate, NaCa(AsO4)

aDepartment of Geological Sciences, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E2, and bDepartment of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen 361005, Fujian Province, People's Republic of China
*Correspondence e-mail: yuanming.pan@usask.ca

(Received 7 October 2011; accepted 24 October 2011; online 2 November 2011)

The title compound, NaCa(AsO4), was synthesized using a hydro­thermal method at 633–643 K. It has a dense structure composed of alternating layers of distorted [CaO6] octa­hedra and layers of [AsO4] tetra­hedra and distorted [NaO6] octa­hedra, stacked along the a axis. The As, Ca and two O atoms lie on the mirror plane at y = 1/4 (i.e. 4c), while the Na atom lies on an inversion centre (1/2, 1/2, 0) (i.e. 4b). Each distorted [CaO6] octa­hedron shares four equatorial common O vertices with four neighboring octa­hedra, forming a layer parallel to (100), whereas each distorted [NaO6] octa­hedron shares two opposite edges with two neighboring ones, forming a chain running along [010]. Each isolated [AsO4] tetra­hedron shares two edges with two different [NaO6] octa­hedra in one [NaO6] chain and a vertex with another chain. Simultaneously the above [AsO4] tetra­hedron located in a four-membered [CaO6] ring shares one edge of its base facet with one [CaO6] octa­hedron and three corners with three other [CaO6] octa­hedra of one [CaO6] layer, and the remaining apex is shared with another [CaO6] layer. [NaO6] octa­hedra and [CaO6] octa­hedra are linked to each other by sharing edges and vertices.

Related literature

For general background, see: Smedley & Kinniburgh (2002[Smedley, P. L. & Kinniburgh, D. G. (2002). Appl. Geochem. 17, 517-568.]); Zhu et al. (2006[Zhu, Y. N., Zhang, X. H., Xie, Q. L., Wang, D. Q. & Cheng, G. W. (2006). Water Air Soil Poll. 169, 221-238.]); Rodríguez et al. (2008[Rodríguez, J. D., Jiménez, A., Prieto, M., Torre, L. & García-Granda, S. (2008). Am. Mineral. 93, 928-939.]). For related structures, see: Graia et al. (1999[Graia, M., Driss, A. & Jouini, T. (1999). Z. Kristallogr. New Cryst. Struct. 214, 1-2.]) for CaNa2(AsO4)3; IJdo (1982)[IJdo, D. J. W. (1982). Acta Cryst. B38, 923-925.] for NaCa(VO4); Ben Amara et al. (1983[Ben Amara, M., Vlasse, M., Le Flem, G. & Hagenmuller, P. (1983). Acta Cryst. C39, 1483-1485.]) for buchwaldite, NaCa(PO4); Bredig (1942)[Bredig, M. A. (1942). J. Phys. Chem. 46, 747-764.] for NaCa(PO4).

Experimental

Crystal data
  • NaCa(AsO4)

  • Mr = 201.99

  • Orthorhombic, P n m a

  • a = 11.486 (2) Å

  • b = 6.6615 (14) Å

  • c = 5.2406 (11) Å

  • V = 400.97 (15) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 9.73 mm−1

  • T = 173 K

  • 0.18 × 0.12 × 0.10 mm

Data collection
  • Bruker SMART CCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Bruker, 2001[Bruker (2001). SAINT, SMART and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.273, Tmax = 0.443

  • 2163 measured reflections

  • 505 independent reflections

  • 498 reflections with I > 2σ(I)

  • Rint = 0.035

Refinement
  • R[F2 > 2σ(F2)] = 0.021

  • wR(F2) = 0.067

  • S = 1.03

  • 505 reflections

  • 42 parameters

  • Δρmax = 0.83 e Å−3

  • Δρmin = −0.74 e Å−3

Data collection: SMART (Bruker, 2001[Bruker (2001). SAINT, SMART and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2001[Bruker (2001). SAINT, SMART and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: DIAMOND (Brandenburg, 2011[Brandenburg, K. (2011). DIAMOND. Crystal Impact GbR, Bonn, Germany.]) and ATOMS (Dowty, 2004[Dowty, E. (2004). ATOMS. Shape Software, Kingsport, Tennessee, USA.]); software used to prepare material for publication: SHELXL97.

Supporting information


Comment top

Arsenic, a highly toxic pollutant in surface and ground waters, poses serious health and environmental problems all around the world (Smedley & Kinniburgh, 2002). One common method for immobilization and remediation of arsenic contamination in aqueous environments is through co-precipitation with calcium by forming various Ca-arsenate compounds (Zhu et al., 2006). To date, more than 20 Ca-arsenate compounds have been reported, but only a few of them have their crystal structures determined (Rodríguez et al., 2008). Knowledge about the crystal structures of Ca-arsenate compounds is important for better understanding their stabilities and potential applications for remediation of arsenic contamination in aqueous environments. Herein we report on the hydrothermal synthesis and crystal structure of a new compound NaCa(AsO4), which is the second sodium calcium arsenate after CaNa2(AsO4)3 (Graia et al., 1999).

The crystal structure of the title compound differs from those of its phosphorus and vanadium counterparts (IJdo, 1982; Ben Amara et al., 1983 & Bredig, 1942). The basic structural features of the title compound include [NaO6] octahedra, [AsO4] tetrahedra and [CaO6] octahedra. Sodium atoms are surrounded by six O-atoms forming distorted [NaO6] octahedra, which share edges to form chains running along [010] (Fig. 1–2). These octahedral chains are linked by isolated [AsO4] tetrahedra to form polyhedral sheets parallel to the (100) plane (Fig. 2). This linkage is made by each [AsO4] tetrahedron sharing edges with two [NaO6] octahedra in one chain and a vertex with another chain. These sheets are then linked together by [CaO6] octahedra via sharing edges and vertices(Fig. 1–3).

Related literature top

For general background, see: Smedley & Kinniburgh (2002); Zhu et al. (2006); Rodríguez et al. (2008). For related structures, see: Graia et al. (1999) for CaNa2(AsO4)3; IJdo (1982) for NaCa(VO4); Ben Amara et al. (1983) for buchwaldite, NaCa(PO4); Bredig (1942) for NaCa(PO4).

Experimental top

Single crystals of NaCa(AsO4) were synthesized using a hydrothermal method. A mixture of 0.5 mmol calcium nitrate Ca(NO3)2.H2O and 0.3 mmol sodium hydrogen arsenate heptahydrate Na2HAsO4.H2O was added to 5 ml of 2M NaOH solution. This mixed solution was then transferred into a 22 ml pressure vessel from Parr Instrument Company and heated to and maintained at a temperature of 633–643 K for 13 days. Solid products were filtered, washed with deionized water, and dried in the air. Crystals with a rectangular morphology were selected with a polarizing microscope for the collection of single-crystal X-ray diffraction data at 173 K.

Structure description top

Arsenic, a highly toxic pollutant in surface and ground waters, poses serious health and environmental problems all around the world (Smedley & Kinniburgh, 2002). One common method for immobilization and remediation of arsenic contamination in aqueous environments is through co-precipitation with calcium by forming various Ca-arsenate compounds (Zhu et al., 2006). To date, more than 20 Ca-arsenate compounds have been reported, but only a few of them have their crystal structures determined (Rodríguez et al., 2008). Knowledge about the crystal structures of Ca-arsenate compounds is important for better understanding their stabilities and potential applications for remediation of arsenic contamination in aqueous environments. Herein we report on the hydrothermal synthesis and crystal structure of a new compound NaCa(AsO4), which is the second sodium calcium arsenate after CaNa2(AsO4)3 (Graia et al., 1999).

The crystal structure of the title compound differs from those of its phosphorus and vanadium counterparts (IJdo, 1982; Ben Amara et al., 1983 & Bredig, 1942). The basic structural features of the title compound include [NaO6] octahedra, [AsO4] tetrahedra and [CaO6] octahedra. Sodium atoms are surrounded by six O-atoms forming distorted [NaO6] octahedra, which share edges to form chains running along [010] (Fig. 1–2). These octahedral chains are linked by isolated [AsO4] tetrahedra to form polyhedral sheets parallel to the (100) plane (Fig. 2). This linkage is made by each [AsO4] tetrahedron sharing edges with two [NaO6] octahedra in one chain and a vertex with another chain. These sheets are then linked together by [CaO6] octahedra via sharing edges and vertices(Fig. 1–3).

For general background, see: Smedley & Kinniburgh (2002); Zhu et al. (2006); Rodríguez et al. (2008). For related structures, see: Graia et al. (1999) for CaNa2(AsO4)3; IJdo (1982) for NaCa(VO4); Ben Amara et al. (1983) for buchwaldite, NaCa(PO4); Bredig (1942) for NaCa(PO4).

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2011) and ATOMS (Dowty, 2004); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The crystal structure of NaCa(AsO4) plotted in projection along [001].
[Figure 2] Fig. 2. The crystal structure of NaCa(AsO4) plotted in projection along a direction near [010].
[Figure 3] Fig. 3. Coordination environment of Ca, Na, As and O atoms, with displacement ellipsoids drawn at the 50% probability level (symmetry codes: (i) -0.5+x, 0.5-y, 0.5-z; (ii) -0.5+x, 0.5-y, 1.5-z; (iii) -0.5+x, y, 1.5-z; (iv) 1-x, 0.5+y, 1-z; (v) 1-x, -y, 1-z; (vi) 1-x,0.5+y, -z; (vii) x, y, -1+z; (viii) x, 0.5-y,-1+z; (ix) 1-x, -0.5+y, -z; (x) 0.5+x, 0.5-y, 0.5-z; (xi) 1-x, -0.5+y, 1-z; (xii) 0.5+x, 0.5-y, 1.5-z; (xiii) x, 0.5-y, z; (xiv) x, y, z+1).
sodium calcium arsenate top
Crystal data top
NaCa(AsO4)F(000) = 384
Mr = 201.99Dx = 3.346 Mg m3
Orthorhombic, PnmaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2nCell parameters from 2163 reflections
a = 11.486 (2) Åθ = 3.6–28.2°
b = 6.6615 (14) ŵ = 9.73 mm1
c = 5.2406 (11) ÅT = 173 K
V = 400.97 (15) Å3Prism, colorless
Z = 40.18 × 0.12 × 0.10 mm
Data collection top
Bruker SMART CCD area-detector
diffractometer
505 independent reflections
Radiation source: fine-focus sealed tube498 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.035
1200 images,Δω=1°, Exp time: 15 s. scansθmax = 28.2°, θmin = 3.6°
Absorption correction: multi-scan
(SADABS; Bruker, 2001)
h = 1514
Tmin = 0.273, Tmax = 0.443k = 58
2163 measured reflectionsl = 66
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.021 w = 1/[σ2(Fo2) + (0.0474P)2 + 0.5926P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.067(Δ/σ)max = 0.001
S = 1.03Δρmax = 0.83 e Å3
505 reflectionsΔρmin = 0.74 e Å3
42 parametersExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.017 (2)
Crystal data top
NaCa(AsO4)V = 400.97 (15) Å3
Mr = 201.99Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 11.486 (2) ŵ = 9.73 mm1
b = 6.6615 (14) ÅT = 173 K
c = 5.2406 (11) Å0.18 × 0.12 × 0.10 mm
Data collection top
Bruker SMART CCD area-detector
diffractometer
505 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2001)
498 reflections with I > 2σ(I)
Tmin = 0.273, Tmax = 0.443Rint = 0.035
2163 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02142 parameters
wR(F2) = 0.0670 restraints
S = 1.03Δρmax = 0.83 e Å3
505 reflectionsΔρmin = 0.74 e Å3
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
xyzUiso*/Ueq
As10.59797 (3)0.25000.56866 (7)0.0046 (2)
Na10.50000.50000.00000.0088 (3)
Ca10.28059 (6)0.25000.49344 (14)0.0053 (2)
O10.4611 (2)0.25000.6849 (5)0.0075 (5)
O20.6038 (2)0.25000.2482 (6)0.0068 (6)
O30.66769 (14)0.0513 (3)0.7038 (3)0.0068 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
As10.0014 (3)0.0050 (3)0.0073 (3)0.0000.00013 (11)0.000
Na10.0076 (7)0.0087 (7)0.0101 (7)0.0027 (6)0.0003 (6)0.0014 (6)
Ca10.0017 (4)0.0051 (4)0.0091 (4)0.0000.0002 (2)0.000
O10.0017 (10)0.0096 (12)0.0111 (12)0.0000.0023 (9)0.000
O20.0042 (12)0.0100 (13)0.0062 (13)0.0000.0012 (8)0.000
O30.0056 (8)0.0048 (8)0.0099 (8)0.0014 (6)0.0024 (7)0.0000 (7)
Geometric parameters (Å, º) top
As1—O21.681 (3)Na1—O3v2.4970 (18)
As1—O11.686 (2)Na1—O3vi2.4970 (18)
As1—O3i1.7015 (17)Ca1—O12.304 (3)
As1—O31.7015 (17)Ca1—O3vi2.3346 (19)
Na1—O1ii2.3873 (19)Ca1—O3vii2.3346 (19)
Na1—O1iii2.3874 (19)Ca1—O2viii2.393 (3)
Na1—O22.426 (2)Ca1—O3ix2.4393 (19)
Na1—O2iv2.426 (2)Ca1—O3x2.4393 (19)
O2—As1—O1113.48 (12)O2iv—Na1—O3vi81.96 (8)
O2—As1—O3i113.41 (8)O1—Ca1—O3vi87.93 (6)
O1—As1—O3i106.76 (8)O1—Ca1—O3vii87.93 (6)
O2—As1—O3113.41 (8)O3vi—Ca1—O3vii118.57 (10)
O1—As1—O3106.76 (8)O1—Ca1—O2viii173.87 (10)
O3i—As1—O3102.14 (12)O3vi—Ca1—O2viii88.94 (6)
O1ii—Na1—O289.08 (7)O3vii—Ca1—O2viii88.94 (6)
O1iii—Na1—O290.92 (7)O1—Ca1—O3ix101.26 (7)
O1ii—Na1—O2iv90.92 (7)O3vi—Ca1—O3ix87.52 (4)
O1iii—Na1—O2iv89.08 (7)O3vii—Ca1—O3ix152.85 (7)
O1ii—Na1—O3v67.60 (7)O2viii—Ca1—O3ix83.86 (7)
O1iii—Na1—O3v112.40 (7)O1—Ca1—O3x101.26 (7)
O2—Na1—O3v81.96 (8)O3vi—Ca1—O3x152.85 (7)
O2iv—Na1—O3v98.04 (8)O3vii—Ca1—O3x87.52 (4)
O1ii—Na1—O3vi112.40 (7)O2viii—Ca1—O3x83.86 (7)
O1iii—Na1—O3vi67.60 (7)O3ix—Ca1—O3x65.72 (8)
O2—Na1—O3vi98.04 (8)
Symmetry codes: (i) x, y+1/2, z; (ii) x, y, z1; (iii) x+1, y+1, z+1; (iv) x+1, y+1, z; (v) x, y+1/2, z1; (vi) x+1, y+1/2, z+1; (vii) x+1, y, z+1; (viii) x1/2, y, z+1/2; (ix) x1/2, y+1/2, z+3/2; (x) x1/2, y, z+3/2.

Experimental details

Crystal data
Chemical formulaNaCa(AsO4)
Mr201.99
Crystal system, space groupOrthorhombic, Pnma
Temperature (K)173
a, b, c (Å)11.486 (2), 6.6615 (14), 5.2406 (11)
V3)400.97 (15)
Z4
Radiation typeMo Kα
µ (mm1)9.73
Crystal size (mm)0.18 × 0.12 × 0.10
Data collection
DiffractometerBruker SMART CCD area-detector
Absorption correctionMulti-scan
(SADABS; Bruker, 2001)
Tmin, Tmax0.273, 0.443
No. of measured, independent and
observed [I > 2σ(I)] reflections
2163, 505, 498
Rint0.035
(sin θ/λ)max1)0.664
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.021, 0.067, 1.03
No. of reflections505
No. of parameters42
Δρmax, Δρmin (e Å3)0.83, 0.74

Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2001), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2011) and ATOMS (Dowty, 2004).

 

Acknowledgements

This project was supported by the fund from the Natural Science and Engineering Research Council (NSERC) of Canada.

References

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First citationZhu, Y. N., Zhang, X. H., Xie, Q. L., Wang, D. Q. & Cheng, G. W. (2006). Water Air Soil Poll. 169, 221–238.  Web of Science CrossRef CAS Google Scholar

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