supplementary materials


Acta Cryst. (2008). E64, i57    [ doi:10.1107/S1600536808025336 ]

Barium zinc diarsenate

T. Ðordevic

Abstract top

The title compound, BaZnAs2O7, belongs to the family of isotypic series of compounds adopting the general formula M12+M22+X2O7 (M12+ = Ca, Sr, Ba or Pb; M22+ = Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn or Cd; X = P or As). Suitable single crystals were prepared under hydrothermal conditions. The framework structure is characterized by corner-sharing ZnO5 square pyramids and As2O7 groups where the Zn atoms occupy channels. X-ray diffraction analysis of single crystals twinned by non-merohedry [twin plane is (100)] yielded formula BaZnAs2O7. Raman spectra confirmed the presence of a non-linear As-O-As linkage.

Comment top

Diphosphates with the general formula M1M2P2O7 have been extensively studied during the last years. Among them are a couple of compounds with divalent M1 and M2 atoms (Mihajlović et al., 2004 and references therein). These diphosphates show a variety of crystal structure types that are controlled by the distinct stereochemical behaviour of the M1 and M2 cations. It affects the coordination numbers, the degree of distortion of the coordination polyhedra, and the conformation of the P2O7 groups (Murashova et al., 1991). By comparison much less is known about the structural chemistry of compounds with the formula M12+M22+X2O7 where X = V, Cr, Ge, As, and Si. Prior to this study, the crystal structures of only seven diarsenates M12+M22+As2O7 were known. Six of the first ones are isotypic with the title compound and crystallize in space group P21/n: PbCuAs2O7 (Pertlik, 1986), SrCoAs2O7 (Horng & Wang, 1994), BaCuAs2O7 (Wardojo & Hwu, 1995; Chen & Wang, 1996), BaMgAs2O7, BaCoAs2O7 (Mihajlović et al., 2004) and SrCuAs2O7 (Chen & Wang, 1996). Worthy to note is the five-coordinated M(2) position. CaCuAs2O7 has the same space-group symmetry; however, for the reduced cell the space group setting is P21/c and the structural features are different (Chen & Wang, 1996; Staack & Müller-Buschbaum, 1998).

The crystal structure of BaZnAs2O7 is characterized by a three-dimensional framework formed from corner-sharing square pyramids ZnO5 and As2O7 groups. Within the framework bent chains running parallel to [010] are formed by the ZnO5 and As1O4 polyhedra. They are linked by the As2O4 tetrahedra. Each of the five corners of the square pyramids around the Zn atoms are shared with a different As2O7 group. The Ba position is located within channels parallel to [010] (Fig. 1). The Ba atoms are coordinated by nine oxygen atoms, and the coordination polyhedron can be described as a distorted tricapped trigonal prism. The average <Ba—O> bond length of 2.829 Å compare well to that of BaMgAs2O7, BaCoAs2O7 and BaCuAs2O7 (2.852, 2.829 and 2.852 Å, respectively). The pyroarsenate groups involve two crystallographically non-equivalent AsO4 tetrahedra. As expected, the longest As—O bonds are to the bridging oxygen atoms: <As1—O1> = 1.746 (2) Å and <As2—O1> = 1.751 (3) Å. The bond angles Oterminal—As—Oterminal are significantly larger than Obridging—As—Oterminal. The As1—Obridging—As2 angle is 124.67 (14)°.

In the 1000–800 cm-1 range, Raman spectrum shows the As—O antisymmetric and symmetric stretching modes of the (As2O7)4- groups [904 (sh), 892 (vs), 847 (m), 825 (m)]. The bands at 784 (w) and 585 (s) cm-1 can be assigned to the asymmetric [νas (As—O—As)] and symmetric bridge stretching vibration [νs (As—O—As)], respectively and they are characteristic of the (As2O7)4- group with a non-linear As—O—As bond (Nord et al., 1988). In the region below 450 cm-1 appear the bending modes of the (As2O7)4- groups, and various lattice modes of the compound.

The presence of only two structure types among M12+M22+-diarsenates contrasts with the situation among the M12+M22+-diphosphates where a greater variety of structure types is known; however, it probably reflects to some extent the different number of diphosphates and diarsenates studied so far.

Related literature top

For isostructural diarsenates, see: Pertlik (1986); Horng & Wang (1994); Wardojo & Hwu (1995); Chen & Wang (1996); Mihajlović et al. (2004). For the relationship to the known M12+M22+X2O7 compounds and the presence of non-merohedric twinning, see: Mihajlović et al. (2004). For related literature, see: Staack & Müller-Buschbaum (1998); Mihajlović & Effenberger (2006); Murashova et al. (1991); Nord et al. (1988).

Experimental top

Single crystals of BaZnAs2O7 were obtained as reaction products from mixtures of Ba(OH)2.8H2O (Merck, > 97%), 2ZnO.2CO3.4H2O (Alfa Products), and As2O5 (Alfa Products, > 99.9%). The mixture was transferred into Teflon vessel and filled to approximately 70% of their inner volume with distilled water (pH of the mixture was 2.5). Finally it was enclosed into stainless steel autoclave. The mixture was heated under autogeneous pressure from 293 to 493 K (4 h), held at that temperature (72 h) and rapidly cooled to room temperature. At the end of the reaction the pH of the solvent was 6. BaZnAs2O7 crystallizes as colourless, prismatic crystals up to 0.11 mm in length (yield ca 25%). It was obtained together with colourless, prismatic crystals of Ba(AsO3OH) (yield ca 60%) (Mihajlović & Effenberger, 2006) and uninvestigated amorphous mass yield ca 15%).

Refinement top

Several single crystals of the BaZnAs2O7 were studied with an automatic four-circle X-ray diffractometer equipped with a CCD area detector. Preliminary measurements showed sharp reflection spots and a pseudo-orthorhombic unit cell. However, closer inspections of the recorded CCD frames revealed that at higher diffraction angles some very slight splitting or slight broadening of the reflection spots was evident; this was later found to be due to twinning. The space-group symmetry was confirmed as P21/n based on the extinction rules. It crystal structure was refined starting from the atomic coordinates given for BaCuAs2O7 (Chen & Wang, 1996). Although the structure models appeared to be crystal-chemically correct, the refinements initially converged unsatisfactorily. Distinct discrepancies between measured and calculated structure factors were observed (Fobs2 > Fcalc2) for the most disagreeable reflections). The weighting scheme used by the programme SHELXL97 (Sheldrick, 2008) suggested unexpectedly large values for the second weighting parameters. Furthermore, in the residual electron densities remained unusually high peaks which indicated the presence of 'phantom' atoms apparently mirroring atom positions across the (100) plane. Because of the pseudo-orthorhombic metrics of the unit cells (β close to 90°), non-merohedric twinning with a twin plane parallel to (100) was assumed. The application of the twin matrix (-1 0 0, 0 1 0, 0 0 1) during the refinement procedures reduced the R-values significantly. During the last stages anisotropic displacement parameters were allowed to vary for all atoms.

Computing details top

Data collection: COLLECT (Nonius, 2002); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997; Otwinowski et al., 2003) and WinGX (Farrugia, 1999); program(s) used to solve structure: SIR97 (Altomare et al., 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2000); software used to prepare material for publication: publCIF (Westrip, 2008).

Figures top
[Figure 1] Fig. 1. The crystal structure of BaZnAs2O7 in a projection parallel to [010].
[Figure 2] Fig. 2. Atomic displacement ellipsoids at the 50% probability level.
Barium zinc diarsenate top
Crystal data top
BaZnAs2O7F000 = 832
Mr = 464.55Dx = 4.813 Mg m3
Monoclinic, P21/nMo Kα radiation
λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 5551 reflections
a = 5.6260 (10) Åθ = 0.4–35.0º
b = 8.557 (2) ŵ = 20.08 mm1
c = 13.317 (3) ÅT = 293 (2) K
β = 90.01 (3)ºPrismatic, colourless
V = 641.1 (2) Å30.09 × 0.04 × 0.02 mm
Z = 4
Data collection top
Nonius KappaCCD
diffractometer
2807 independent reflections
Radiation source: fine-focus sealed tube2747 reflections with I > 2σ(I)
Monochromator: graphiteRint = 0.040
T = 293(2) Kθmax = 35.0º
φ and ω scansθmin = 1.5º
Absorption correction: multi-scan
(Otwinowski & Minor, 1997)
h = 9→9
Tmin = 0.265, Tmax = 0.690k = 13→13
11068 measured reflectionsl = 21→21
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: full  w = 1/[σ2(Fo2) + (0.0324P)2 + 1.09P]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.022(Δ/σ)max = 0.001
wR(F2) = 0.056Δρmax = 2.21 e Å3
S = 1.06Δρmin = 1.77 e Å3
2807 reflectionsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
102 parametersExtinction coefficient: 0.0037 (3)
Primary atom site location: structure-invariant direct methods
Crystal data top
BaZnAs2O7V = 641.1 (2) Å3
Mr = 464.55Z = 4
Monoclinic, P21/nMo Kα
a = 5.6260 (10) ŵ = 20.08 mm1
b = 8.557 (2) ÅT = 293 (2) K
c = 13.317 (3) Å0.09 × 0.04 × 0.02 mm
β = 90.01 (3)º
Data collection top
Nonius KappaCCD
diffractometer
2807 independent reflections
Absorption correction: multi-scan
(Otwinowski & Minor, 1997)
2747 reflections with I > 2σ(I)
Tmin = 0.265, Tmax = 0.690Rint = 0.040
11068 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.022102 parameters
wR(F2) = 0.056Δρmax = 2.21 e Å3
S = 1.06Δρmin = 1.77 e Å3
2807 reflections
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ba10.21674 (4)0.34610 (2)0.715139 (16)0.01062 (5)
Zn10.66892 (8)0.14866 (4)0.88747 (3)0.01171 (8)
As10.75049 (6)0.03337 (3)0.65727 (2)0.00781 (6)
As20.67177 (6)0.31336 (4)0.51369 (2)0.00760 (6)
O10.7114 (5)0.1140 (3)0.53795 (18)0.0143 (4)
O20.6667 (5)0.1533 (3)0.6483 (2)0.0130 (4)
O31.0297 (5)0.0613 (3)0.6914 (2)0.0175 (5)
O40.5580 (4)0.1208 (3)0.73543 (19)0.0111 (4)
O50.8103 (5)0.3354 (3)0.40399 (19)0.0117 (4)
O60.3801 (5)0.3486 (3)0.5158 (2)0.0114 (4)
O70.8042 (5)0.4073 (3)0.60893 (18)0.0131 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ba10.01013 (8)0.01003 (8)0.01171 (8)0.00076 (5)0.00048 (7)0.00098 (5)
Zn10.01165 (17)0.01094 (16)0.01254 (16)0.00053 (12)0.00077 (14)0.00057 (11)
As10.00859 (13)0.00678 (12)0.00807 (12)0.00043 (9)0.00037 (11)0.00005 (9)
As20.00792 (12)0.00819 (12)0.00668 (11)0.00004 (10)0.00003 (10)0.00028 (9)
O10.0249 (13)0.0089 (9)0.0092 (9)0.0013 (9)0.0022 (9)0.0006 (7)
O20.0166 (11)0.0048 (9)0.0176 (11)0.0001 (8)0.0022 (9)0.0011 (7)
O30.0091 (10)0.0163 (11)0.0270 (13)0.0004 (8)0.0051 (9)0.0005 (10)
O40.0105 (10)0.0133 (10)0.0097 (9)0.0012 (8)0.0021 (7)0.0029 (8)
O50.0094 (10)0.0162 (10)0.0096 (10)0.0000 (8)0.0035 (8)0.0014 (7)
O60.0087 (10)0.0145 (10)0.0110 (10)0.0005 (7)0.0000 (8)0.0022 (8)
O70.0172 (10)0.0110 (9)0.0111 (9)0.0013 (9)0.0075 (8)0.0008 (7)
Geometric parameters (Å, °) top
Ba1—O3i2.641 (3)Zn1—O7vi2.071 (3)
Ba1—O3ii2.674 (3)Zn1—O6vii2.082 (3)
Ba1—O42.734 (3)Zn1—O42.132 (3)
Ba1—O7ii2.768 (3)As1—O31.652 (3)
Ba1—O62.809 (3)As1—O21.669 (2)
Ba1—O2iii2.821 (3)As1—O41.678 (2)
Ba1—O4iii2.889 (3)As1—O11.746 (2)
Ba1—O5iv3.002 (3)As2—O51.667 (3)
Ba1—O5v3.157 (2)As2—O61.669 (3)
Zn1—O2i1.989 (2)As2—O71.676 (2)
Zn1—O5iv2.034 (3)As2—O11.751 (2)
O3i—Ba1—O3ii154.69 (6)O5iv—Ba1—O5v151.15 (6)
O3i—Ba1—O493.77 (8)O2i—Zn1—O5iv115.47 (11)
O3ii—Ba1—O469.23 (8)O2i—Zn1—O7vi145.21 (11)
O3i—Ba1—O7ii124.18 (8)O5iv—Zn1—O7vi97.87 (11)
O3ii—Ba1—O7ii77.40 (8)O2i—Zn1—O6vii85.52 (11)
O4—Ba1—O7ii140.60 (7)O5iv—Zn1—O6vii118.44 (11)
O3i—Ba1—O6105.27 (9)O7vi—Zn1—O6vii87.17 (10)
O3ii—Ba1—O691.37 (8)O2i—Zn1—O490.21 (11)
O4—Ba1—O682.47 (7)O5iv—Zn1—O479.64 (10)
O7ii—Ba1—O677.89 (8)O7vi—Zn1—O486.10 (10)
O3i—Ba1—O2iii96.19 (9)O6vii—Zn1—O4161.45 (10)
O3ii—Ba1—O2iii77.12 (8)O2i—Zn1—Ba1viii142.43 (9)
O4—Ba1—O2iii118.34 (7)O5iv—Zn1—Ba1viii59.85 (7)
O7ii—Ba1—O2iii71.81 (8)O7vi—Zn1—Ba1viii48.98 (7)
O6—Ba1—O2iii149.22 (8)O6vii—Zn1—Ba1viii130.97 (7)
O3i—Ba1—O4iii67.32 (8)O4—Zn1—Ba1viii52.43 (7)
O3ii—Ba1—O4iii123.92 (8)O2i—Zn1—Ba177.81 (9)
O4—Ba1—O4iii157.94 (3)O5iv—Zn1—Ba151.31 (7)
O7ii—Ba1—O4iii60.91 (7)O7vi—Zn1—Ba1120.23 (7)
O6—Ba1—O4iii112.59 (7)O6vii—Zn1—Ba1150.26 (7)
O2iii—Ba1—O4iii56.12 (7)O4—Zn1—Ba144.28 (7)
O3i—Ba1—O5iv82.60 (8)O3—As1—O2115.24 (14)
O3ii—Ba1—O5iv72.34 (8)O3—As1—O4112.25 (14)
O4—Ba1—O5iv55.22 (7)O2—As1—O4106.77 (13)
O7ii—Ba1—O5iv132.28 (8)O3—As1—O1108.22 (15)
O6—Ba1—O5iv137.57 (7)O2—As1—O1106.10 (13)
O2iii—Ba1—O5iv66.11 (8)O4—As1—O1107.88 (13)
O4iii—Ba1—O5iv108.88 (7)O5—As2—O6117.03 (14)
O3i—Ba1—O5v70.18 (8)O5—As2—O7113.66 (13)
O3ii—Ba1—O5v135.12 (8)O6—As2—O7109.72 (13)
O4—Ba1—O5v133.79 (7)O5—As2—O1102.27 (12)
O7ii—Ba1—O5v62.59 (7)O6—As2—O1107.34 (13)
O6—Ba1—O5v62.25 (7)O7—As2—O1105.74 (12)
O2iii—Ba1—O5v106.58 (7)As1—O1—As2124.67 (14)
O4iii—Ba1—O5v52.15 (7)
Symmetry codes: (i) −x+3/2, y+1/2, −z+3/2; (ii) x−1, y, z; (iii) −x+1/2, y+1/2, −z+3/2; (iv) x−1/2, −y+1/2, z+1/2; (v) −x+1, −y+1, −z+1; (vi) −x+3/2, y−1/2, −z+3/2; (vii) x+1/2, −y+1/2, z+1/2; (viii) −x+1/2, y−1/2, −z+3/2.
Acknowledgements top

The author gratefully acknowledges financial support by the Austrian Science Foundation (FWF) (Grant T300—N19).

references
References top

Altomare, A., Cascarano, C., Giacovazzo, C., Guagliardi, A., Moliterni, A. G. G., Burla, M. C., Polidori, G., Camalli, M. & Spagna, R. (1997). SIR97. University of Bari, Italy.

Chen, T. C. & Wang, S. L. (1996). J. Solid State Chem. 121, 350–355.

Dowty, E. (2000). ATOMS for Windows. Shape Software, Kingsport, Tennessee, USA.

Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838.

Horng, J.-C. & Wang, S.-L. (1994). Acta Cryst. C50, 488–490.

Mihajlović, T. & Effenberger, H. (2006). Z. Kristallogr. 331, 770–781.

Mihajlović, T., Kolitsch, U. & Effenberger, H. (2004). J. Alloys Compd, 379, 103–109.

Murashova, E. V., Velikodnyi, Yu. A. & Trunov, V. K. (1991). Russ. J. Inorg. Chem. 36, 479–481.

Nonius (2002). COLLECT. Nonius BV, Delft, The Netherlands.

Nord, A. G., Kierkegaard, P., Stefanidis, T. & Baran, J. (1988). Chem. Commun. Univ. Stockholm, 5, 841–848.

Otwinowski, Z., Borek, D., Majewski, W. & Minor, W. (2003). Acta Cryst. A59, 228–234.

Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press.

Pertlik, F. (1986). Monatsh. Chem. 117, 1343–1348.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Staack, M. & Müller-Buschbaum, H. (1998). Z. Anorg. Allg. Chem. 624, 1796–1800.

Wardojo, T. A. & Hwu, S. J. (1995). J. Solid State Chem. 118, 280–284.

Westrip, S. P. (2008). publCIF. In preparation.