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Barium-deficient forms of celsian (barium aluminium silicate) with the formula Ba1-xAl2-2xSi2+2xO8 (x = 0.20 and 0.06) have been identified. In contrast with the celsian-orthoclase solid solutions which have been reported previously, these forms, refined in the space group C2/m, with Ba and one O atom in the 4i sites with m site symmetry, and a further O atom in a 4g site with twofold axial symmetry, suggest a slight solid solution with silica. The serendipitous preparation of the compounds represents a possible hazard associated with solid-state synthesis.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102023053/fg1678sup1.cif
Contains datablocks global, I, II

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102023053/fg1678Isup2.hkl
Contains datablock I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102023053/fg1678IIsup3.hkl
Contains datablock II

Comment top

The mineral celsian, with the ideal formula BaAl2Si2O8, is a barium feldspar. It is the only ternary phase within the BaO-Al2O3—SiO2 phase diagram (Drummond, 1990), and is of interest due to its resistance to oxidation and reduction and its low coefficient of thermal expansion, amongst other properties (Bošković et al., 1999). Originally, celsian was believed to have space group C2/m, with disorder of Al and Si over two sets of 8j sites (Taylor et al., 1934), and indeed this provides an adequate description of the structure (Newnham & Megaw, 1960). It was shown, however, that the structure is better described by an I2/c supercell with a doubled c axis, although the differences are very subtle (Newnham & Megaw, 1960; Ribbe & Griffen, 1976). Similarly, in the polymorph paracelsian, small differences in the Si/Al ordering lead to a slight monoclinic distortion, space group P21/a, with a strong orthorhombic (Pnam) subcell (Smith, 1953; Chiari et al., 1985). Finally, a hexagonal form, hexacelsian, is stable only at temperatures above 1863 K (Yoshiki & Matsumoto, 1951; Kakeuchi, 1958).

Celsian forms a continous solid solution of formula [K1 − xBax][Al1 + xSi3 − x]O8 with orthoclase, the ideal formula of which is KAlSi3O8 (Thomas, 1950). Thus in fact, previous reports on celsian are on the x = 0.84 and x = 0.95 members of this solid solution series (Newnham & Megaw, 1960; Ribbe & Griffen, 1976), whereas paracelsian has been consistently reported as the stoichiometric end-member (x = 1) (Smith, 1953; Balakin & Belov, 1960; Chiari et al., 1985).

The compounds studied here, (I) (with x = 0.06) and (II) (with x = 1/5), were by-products of melts of Ba-containing mixtures contained in platinum envelopes within aluminosilicate crucibles. The composition of (I) determined by EDXA Please define indicated that K was absent. However, the Ba:Al:Si ratio was non-stoichiometric and, apart from giving a range of overall compositions (Table 1), suggested either an excess of Si or a deficiency of Ba. The former is possible because of the open framework present in feldspars, and thus excess Si may be easily accommodated. Single-crystal X-ray diffraction was thus carried out, and the unit cell was determined to be comparable with the subcell of celsian (see Experimental). Further structure analysis was carried out in this subcell, as it adequately describes the structure and the emphasis here is primarily on the determination of the composition. \sch

The structure of (I) was solved without reference to the previously determined structure of (II) and was, along with (II), found to be consistent with that of orthoclase. No evidence was found for interstitial Si, but rather the overall scattering and refined displacement parameters tended to point to Ba deficiency. Indeed, refinement of the Ba and Al/Si site occupancies in the manner noted below gave improved refinement and a final composition of Ba0.80Al1.60Si2.40O8. A second crystal from a completely different synthesis, (II), was similarly refined to give the composition Ba0.94Al1.88Si2.12O8. Thus, rather than a solid solution with orthoclase, these indicate a slight solid solution with SiO2 and solid solution formula Ba1 − xAl2–2xSi2 + 2xO8, where the two refinements give x = 0.20 and x = 0.06, with respective refined values of 0.2024 (14) and 0.062 (5).

The atoms selected for inclusion in the asymmetric unit and the labelling scheme used in the refinement of (I) can be seen in Fig. 1, along with the M—O (M is Al or Si) connectivity. Figs. 2 and 3 display the connectivity of the aluminosilicate framework more extensively. Precisely the same selection of atoms and labelling scheme were used in the final refinement of (II). In (I) and (II), Ba—O (nine-coordinate Ba) and M—O (tetrahedral M) distances [those for (II) given in square brackets] are in the ranges 2.665 (2)–3.1212 (16) [2.645 (5)–3.120 (4)] and 1.6530 (17)–1.6830 (9) Å [1.675 (4)–1.694 (2) Å], respectively, and these are unexceptional (see also Table 2). The difference in each pair of ranges, although they overlap within the pair, is entirely consistent with the change in Ba and Al content between (I) and (II).

Previous reports have cited similar compositions. Ba0.75Al1.5Si2.5O8 was found, though, to have the hollandite structure (Zhang & Burnham, 1994). This is, perhaps, not surprising, as it has been shown that certain feldspar materials can be transformed to hollandite under high pressure (Ringwood et al., 1967). KAlSi3O8 (sanidine) transforms to hollandite under 120 kbar s of pressure (1 bar = 10 5 Pa) at 1173 K (Ringwood et al., 1967) and celsian itself partially transforms under similar conditions (Reid & Ringwood, 1969). This is also consistent with the observation that the formation of celsian is more difficult in compositions with high SiO2 content (Thomas, 1950).

Bond-valence sums (BVS; Brown & Altermatt, 1985) calculated for each composition (Table 3) provide a check on the structure solution and the assumptions made. The composition Ba0.80Al1.60Si2.40O8 gives values of 3.60 for Al1/Si1 and 3.71 for Al2/Si2, which compare well with the expected value of 3.60 for Al:Si 0.40:0.60. The BVS for Ba is 1.65, compared with the expected value of 1.60. This is in reasonable agreement and provides further evidence for Ba deficiency. Similar results are obtained for the other composition. In both cases, slightly higher values are obtained for Al2/Si2, which might indicate more Si on this site. This, however, would have the effect of reducing the BVS on the Al1/Si1 site which, in both cases, is in very good agreement with the expected values. Therefore, the model used is perceived as giving an adequate representation of the structures.

Experimental top

Both compositions were by-products of melts containing barium. For composition (I) (x = 1/5), a powder sample of Ba2LaV3O11 was prepared by solid-state reaction; reagents used were BaCO3, La2O3 (both 99%; BDH Chemicals Ltd, Poole, England) and V2O5 (99.2%; Johnson Matthey, Royston, England). La2O3 was dried at 1173 K prior to use, and BaCO3 and V2O5 were both dried at 573 K. Single crystals were grown by the method of Huang et al. (1994). The powder was melted at 1573 K and held at this temperature for 30 min. The temperature was then decreased at a rate of 1 K min−1 to 1523 K, whereupon it was increased again to 1573 K in steps of 2 K min−1. This was repeated three times in order to obtain, after cooling to room temperature, crystals of (I) suitable for analysis. For composition (II) (x = 0.06), the single-crystal was accidentally grown during the study of the ternary phase diagram BaO-Li2O-TiO2 (Suckut, 1991). The target phase was in the range 10–18 mol% BaO, 12–16 mol% Li2O and 72–77 mol% TiO2, with an idealized formula of BaLi2Ti6O14. The starting reagents were BaCO3 (99.5%; May & Baker Ltd, Dagenham, England), TiO2 (99.9%; Aldrich, USA) and Li2CO3 (99%; FSA Laboratory Supplies, Loughborough, England). The composition 72 mol% TiO2, 16.5 mol% Li2O and 11.5 mol% BaO was used in an attempt to grow single crystals of the desired phase. The melting point of this composition was found to be 1533 K; the powder was heated to 10 K below the melting point and cooled at 0.5 K min−1 to 30 K below the melting point. It was then heated to 15 K below the melting point and finally cooled to room temperature. In both cases, the powder was placed in a platinum envelope in an aluminosilicate crucible. BaO is well known as a good fluxing agent in the growth of single crystals, and clearly has brought about escape of the Ba-containing melt from the envelope and reaction with the aluminosilicate crucible, to give the barium aluminosilicate phases described above. Thus, in addition to providing information on barium-deficient celsian phases, this constitutes a warning for solid-state chemists.

Refinement top

Anisotropic displacement parameters were refined for all atoms. Al/Si and Ba site occupancies were refined, but constrained so as to ensure charge balance, while assuming full occupancy but complete disorder of the Al/Si sites.

Computing details top

Data collection: SMART (Bruker, 1998) for (I); P3 software (Nicolet, 1980) for (II). Cell refinement: SAINT (Bruker, 2000) for (I); P3 software for (II). Data reduction: SAINT for (I); RDNIC (Howie, 1980) for (II). For both compounds, program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997). Molecular graphics: ORTEX in OSCAIL (McArdle, 1994, 2000) and ATOMS (Dowty, 1999) for (I). For both compounds, software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The cell of (I). Atoms are shown as 50% probability displacement ellipsoids. Ba—O contacts have been omitted for clarity. Atoms labelled with a hash (#) or dollar sign (add) are at the symmetry positions (1/2 − x, 1/2 − y, 1 − z) and (x − 1/2, 1/2 − y, z), respectively.
[Figure 2] Fig. 2. A portion of the structure of (I) projected on (001), with the z coordinates of the atoms confined to the range −1/4 to 5/4. A l1/Si1 and Al2/S12 tetrahedra are hatched and open, respectively, and Ba are shown as spheres of arbitrary radius. Ba—O contacts have been omitted for clarity.
[Figure 3] Fig. 3. A more extensive view of the structure of (I), viewed along c (up out of the page). The representation is otherwise the same as that in Fig. 2.
(I) Barium aluminium silicate top
Crystal data top
Al1.60Ba0.80O8Si2.40F(000) = 652
Mr = 348.12Dx = 3.159 Mg m3
Monoclinic, C2/mMo Kα radiation, λ = 0.71073 Å
a = 8.6090 (8) ÅCell parameters from 2197 reflections
b = 13.0658 (12) Åθ = 4.8–32.4°
c = 7.2047 (7) ŵ = 4.96 mm1
β = 115.418 (2)°T = 292 K
V = 731.96 (12) Å3Block, colourless
Z = 40.20 × 0.18 × 0.14 mm
Data collection top
Bruker SMART 1000 CCD area-detector
diffractometer
1366 independent reflections
Radiation source: fine-focus sealed tube1223 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.022
ϕ/ω scansθmax = 32.5°, θmin = 3.1°
Absorption correction: multi-scan
(SADABS; Bruker, 2000)
h = 1213
Tmin = 0.349, Tmax = 0.500k = 1619
3542 measured reflectionsl = 107
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: heavy-atom method
R[F2 > 2σ(F2)] = 0.022Secondary atom site location: difference Fourier map
wR(F2) = 0.056 w = 1/[σ2(Fo2) + (0.0302P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.07(Δ/σ)max < 0.001
1366 reflectionsΔρmax = 0.73 e Å3
64 parametersΔρmin = 0.82 e Å3
Crystal data top
Al1.60Ba0.80O8Si2.40V = 731.96 (12) Å3
Mr = 348.12Z = 4
Monoclinic, C2/mMo Kα radiation
a = 8.6090 (8) ŵ = 4.96 mm1
b = 13.0658 (12) ÅT = 292 K
c = 7.2047 (7) Å0.20 × 0.18 × 0.14 mm
β = 115.418 (2)°
Data collection top
Bruker SMART 1000 CCD area-detector
diffractometer
1366 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2000)
1223 reflections with I > 2σ(I)
Tmin = 0.349, Tmax = 0.500Rint = 0.022
3542 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02264 parameters
wR(F2) = 0.0560 restraints
S = 1.07Δρmax = 0.73 e Å3
1366 reflectionsΔρmin = 0.82 e Å3
Special details top

Experimental. Intensity data, in terms of the reflections allowed by C-centring, are in fact 99.0% complete.

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*/UeqOcc. (<1)
Ba10.28318 (3)0.00000.13152 (4)0.01796 (8)0.7976 (14)
Al10.00846 (7)0.18359 (4)0.22433 (8)0.01116 (13)0.3988 (7)
Si10.00846 (7)0.18359 (4)0.22433 (8)0.01116 (13)0.6012 (7)
Al20.20494 (7)0.38160 (4)0.34646 (8)0.01057 (13)0.3988 (7)
Si20.20494 (7)0.38160 (4)0.34646 (8)0.01057 (13)0.6012 (7)
O10.00000.14056 (16)0.00000.0175 (4)
O20.1254 (3)0.50000.2877 (4)0.0193 (4)
O30.3272 (2)0.36019 (13)0.2256 (3)0.0233 (3)
O40.0273 (2)0.31038 (12)0.2538 (3)0.0203 (3)
O50.1850 (2)0.12649 (13)0.4000 (2)0.0212 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ba10.01254 (11)0.02096 (12)0.01868 (12)0.0000.00509 (8)0.000
Al10.0109 (2)0.0127 (2)0.0102 (3)0.00217 (18)0.0049 (2)0.00089 (19)
Si10.0109 (2)0.0127 (2)0.0102 (3)0.00217 (18)0.0049 (2)0.00089 (19)
Al20.0103 (2)0.0106 (2)0.0108 (3)0.00013 (17)0.0046 (2)0.00002 (18)
Si20.0103 (2)0.0106 (2)0.0108 (3)0.00013 (17)0.0046 (2)0.00002 (18)
O10.0206 (10)0.0215 (10)0.0124 (10)0.0000.0090 (8)0.000
O20.0145 (9)0.0120 (9)0.0280 (12)0.0000.0057 (9)0.000
O30.0205 (8)0.0279 (8)0.0237 (9)0.0037 (6)0.0117 (7)0.0002 (7)
O40.0189 (7)0.0188 (7)0.0234 (8)0.0027 (5)0.0092 (6)0.0008 (6)
O50.0201 (7)0.0249 (8)0.0165 (7)0.0010 (6)0.0058 (6)0.0004 (6)
Geometric parameters (Å, º) top
Ba1—O2i2.665 (2)Al1—O3viii1.6653 (17)
Ba1—O1ii2.8689 (14)Al1—O41.6692 (16)
Ba1—O12.8689 (14)Al1—O51.6784 (16)
Ba1—O52.9307 (17)Al1—O11.6830 (9)
Ba1—O5iii2.9307 (17)Al1—Ba1ii3.6201 (6)
Ba1—O3iv2.9599 (17)Al2—O31.6530 (17)
Ba1—O3v2.9599 (17)Al2—O5ix1.6615 (16)
Ba1—O4vi3.1212 (16)Al2—O41.6656 (16)
Ba1—O4i3.1212 (16)Al2—O21.6710 (10)
Ba1—Si1ii3.6201 (6)Al2—Ba1x3.6261 (6)
Ba1—Al1ii3.6201 (6)Al2—Ba1v3.8164 (7)
Ba1—Al1vii3.6201 (6)
O2i—Ba1—O1ii140.20 (3)Si1ii—Ba1—Al1vii82.999 (19)
O2i—Ba1—O1140.20 (3)Al1ii—Ba1—Al1vii82.999 (19)
O1ii—Ba1—O179.60 (7)O3viii—Al1—O4112.34 (9)
O2i—Ba1—O5107.51 (5)O3viii—Al1—O5112.99 (9)
O1ii—Ba1—O597.71 (4)O4—Al1—O5109.76 (9)
O1—Ba1—O554.00 (3)O3viii—Al1—O1103.65 (7)
O2i—Ba1—O5iii107.51 (5)O4—Al1—O1114.57 (9)
O1ii—Ba1—O5iii54.00 (3)O5—Al1—O1103.15 (7)
O1—Ba1—O5iii97.71 (4)O3viii—Al1—Ba1ii53.82 (6)
O5—Ba1—O5iii68.66 (6)O4—Al1—Ba1ii138.40 (6)
O2i—Ba1—O3iv104.57 (5)O5—Al1—Ba1ii111.58 (6)
O1ii—Ba1—O3iv53.66 (3)O1—Al1—Ba1ii50.77 (4)
O1—Ba1—O3iv101.40 (4)O3viii—Al1—Ba1117.42 (6)
O5—Ba1—O3iv147.75 (4)O4—Al1—Ba1130.14 (6)
O5iii—Ba1—O3iv98.60 (4)O5—Al1—Ba152.68 (6)
O2i—Ba1—O3v104.57 (5)O1—Al1—Ba150.57 (4)
O1ii—Ba1—O3v101.40 (4)Ba1ii—Al1—Ba174.935 (13)
O1—Ba1—O3v53.66 (3)O3—Al2—O5ix112.15 (8)
O5—Ba1—O3v98.60 (4)O3—Al2—O4112.17 (9)
O5iii—Ba1—O3v147.75 (4)O5ix—Al2—O4113.39 (9)
O3iv—Ba1—O3v76.22 (7)O3—Al2—O2107.93 (10)
O2i—Ba1—O4vi52.58 (3)O5ix—Al2—O2108.40 (10)
O1ii—Ba1—O4vi167.19 (4)O4—Al2—O2102.11 (9)
O1—Ba1—O4vi87.64 (4)O3—Al2—Ba1x126.50 (6)
O5—Ba1—O4vi73.50 (4)O5ix—Al2—Ba1x119.38 (6)
O5iii—Ba1—O4vi127.68 (4)O4—Al2—Ba1x59.22 (6)
O3iv—Ba1—O4vi131.41 (4)O2—Al2—Ba1x43.15 (7)
O3v—Ba1—O4vi71.44 (4)O3—Al2—Ba1v47.42 (6)
O2i—Ba1—O4i52.58 (3)O5ix—Al2—Ba1v142.61 (6)
O1ii—Ba1—O4i87.64 (4)O4—Al2—Ba1v103.92 (6)
O1—Ba1—O4i167.19 (4)O2—Al2—Ba1v64.10 (9)
O5—Ba1—O4i127.68 (4)Ba1x—Al2—Ba1v81.459 (12)
O5iii—Ba1—O4i73.50 (4)Si1vii—O1—Al1vii0.00 (6)
O3iv—Ba1—O4i71.44 (4)Si1vii—O1—Al1140.97 (14)
O3v—Ba1—O4i131.41 (4)Al1vii—O1—Al1140.97 (14)
O4vi—Ba1—O4i105.08 (6)Si1vii—O1—Ba1ii102.49 (4)
O2i—Ba1—Si1ii127.17 (3)Al1vii—O1—Ba1ii102.49 (4)
O1ii—Ba1—Si1ii27.026 (13)Al1—O1—Ba1ii102.21 (4)
O1—Ba1—Si1ii87.57 (3)Si1vii—O1—Ba1102.21 (4)
O5—Ba1—Si1ii122.16 (3)Al1vii—O1—Ba1102.21 (4)
O5iii—Ba1—Si1ii77.58 (3)Al1—O1—Ba1102.49 (4)
O3iv—Ba1—Si1ii27.01 (3)Ba1ii—O1—Ba1100.40 (7)
O3v—Ba1—Si1ii85.81 (4)Al2—O2—Si2xi135.57 (14)
O4vi—Ba1—Si1ii154.72 (3)Al2—O2—Al2xi135.57 (14)
O4i—Ba1—Si1ii81.50 (3)Si2xi—O2—Al2xi0.00 (7)
O2i—Ba1—Al1ii127.17 (3)Al2—O2—Ba1x111.45 (7)
O1ii—Ba1—Al1ii27.026 (13)Si2xi—O2—Ba1x111.45 (7)
O1—Ba1—Al1ii87.57 (3)Al2xi—O2—Ba1x111.45 (7)
O5—Ba1—Al1ii122.16 (3)Al2—O3—Si1vi150.59 (12)
O5iii—Ba1—Al1ii77.58 (3)Al2—O3—Al1vi150.59 (12)
O3iv—Ba1—Al1ii27.01 (3)Si1vi—O3—Al1vi0.00 (6)
O3v—Ba1—Al1ii85.81 (4)Al2—O3—Ba1v108.30 (7)
O4vi—Ba1—Al1ii154.72 (3)Si1vi—O3—Ba1v99.16 (7)
O4i—Ba1—Al1ii81.50 (3)Al1vi—O3—Ba1v99.16 (7)
Si1ii—Ba1—Al1ii0.00 (3)Al2—O4—Al1128.89 (10)
O2i—Ba1—Al1vii127.17 (3)Al2—O4—Ba1x93.49 (7)
O1ii—Ba1—Al1vii87.57 (3)Al1—O4—Ba1x137.31 (8)
O1—Ba1—Al1vii27.026 (13)Si2ix—O5—Al2ix0.00 (6)
O5—Ba1—Al1vii77.58 (3)Si2ix—O5—Al1139.61 (11)
O5iii—Ba1—Al1vii122.16 (3)Al2ix—O5—Al1139.61 (11)
O3iv—Ba1—Al1vii85.81 (4)Si2ix—O5—Ba1120.00 (8)
O3v—Ba1—Al1vii27.01 (3)Al2ix—O5—Ba1120.00 (8)
O4vi—Ba1—Al1vii81.50 (3)Al1—O5—Ba1100.22 (7)
O4i—Ba1—Al1vii154.72 (3)
Symmetry codes: (i) x+1/2, y1/2, z; (ii) x, y, z; (iii) x, y, z; (iv) x+1/2, y1/2, z; (v) x+1/2, y+1/2, z; (vi) x+1/2, y+1/2, z; (vii) x, y, z; (viii) x1/2, y+1/2, z; (ix) x+1/2, y+1/2, z+1; (x) x1/2, y+1/2, z; (xi) x, y+1, z.
(II) Barium aluminium silicate top
Crystal data top
Al1.88Ba0.94O8Si2.12F(000) = 682
Mr = 367.03Dx = 3.311 Mg m3
Monoclinic, C2/mMo Kα radiation, λ = 0.71073 Å
a = 8.633 (6) ÅCell parameters from 14 reflections
b = 13.063 (8) Åθ = 12.3–14.2°
c = 7.214 (5) ŵ = 5.65 mm1
β = 115.17 (5)°T = 298 K
V = 736.3 (9) Å3Block, colourless
Z = 40.6 × 0.6 × 0.3 mm
Data collection top
Nicolet P3
diffractometer
1111 reflections with I > 2σ(I)
Radiation source: normal-focus sealed tubeRint = 0.049
Graphite monochromatorθmax = 30.0°, θmin = 3.0°
ω scansh = 012
Absorption correction: ψ scan
(North et al., 1968)
k = 018
Tmin = 0.127, Tmax = 0.551l = 109
1169 measured reflections2 standard reflections every 50 reflections
1112 independent reflections intensity decay: none
Refinement top
Refinement on F2Primary atom site location: heavy-atom method
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.032 w = 1/[σ2(Fo2) + (0.0373P)2 + 6.7094P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.095(Δ/σ)max < 0.001
S = 1.36Δρmax = 1.31 e Å3
1112 reflectionsΔρmin = 1.03 e Å3
65 parametersExtinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0261 (16)
Crystal data top
Al1.88Ba0.94O8Si2.12V = 736.3 (9) Å3
Mr = 367.03Z = 4
Monoclinic, C2/mMo Kα radiation
a = 8.633 (6) ŵ = 5.65 mm1
b = 13.063 (8) ÅT = 298 K
c = 7.214 (5) Å0.6 × 0.6 × 0.3 mm
β = 115.17 (5)°
Data collection top
Nicolet P3
diffractometer
1111 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.049
Tmin = 0.127, Tmax = 0.5512 standard reflections every 50 reflections
1169 measured reflections intensity decay: none
1112 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.03265 parameters
wR(F2) = 0.0950 restraints
S = 1.36Δρmax = 1.31 e Å3
1112 reflectionsΔρmin = 1.03 e Å3
Special details top

Experimental. Scan rates, dependent on pre-scan intensity Ip, were variable in the range 1.0 (Ip<150) to 29.3 (Ip>2500)° ω min−1. The scan width was fixed at 0.6° ω. Stationary crystal background counts were made at 1° in ω on either side of the Bragg angle each for 25% of the total (peak plus background) count time.

Intensity data, in terms of the reflections allowed by C-centring, are in fact 99.4% complete.

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*/UeqOcc. (<1)
Ba10.28270 (5)0.00000.13057 (6)0.0203 (2)0.938 (5)
Al10.00832 (15)0.18272 (9)0.22450 (18)0.0167 (4)0.469 (2)
Si10.00832 (15)0.18272 (9)0.22450 (18)0.0167 (4)0.531 (2)
Al20.20313 (15)0.38148 (10)0.34697 (18)0.0165 (3)0.469 (2)
Si20.20313 (15)0.38148 (10)0.34697 (18)0.0165 (3)0.531 (2)
O10.00000.1381 (3)0.00000.0192 (8)
O20.1209 (6)0.50000.2878 (8)0.0220 (9)
O30.3266 (5)0.3626 (3)0.2241 (5)0.0259 (7)
O40.0251 (4)0.3101 (3)0.2520 (6)0.0250 (7)
O50.1865 (4)0.1264 (3)0.3970 (5)0.0245 (7)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ba10.0171 (3)0.0182 (3)0.0232 (3)0.0000.00635 (16)0.000
Al10.0166 (6)0.0131 (6)0.0185 (6)0.0017 (4)0.0056 (4)0.0002 (4)
Si10.0166 (6)0.0131 (6)0.0185 (6)0.0017 (4)0.0056 (4)0.0002 (4)
Al20.0170 (6)0.0140 (6)0.0166 (6)0.0013 (4)0.0054 (4)0.0003 (4)
Si20.0170 (6)0.0140 (6)0.0166 (6)0.0013 (4)0.0054 (4)0.0003 (4)
O10.023 (2)0.0156 (19)0.0177 (18)0.0000.0076 (16)0.000
O20.020 (2)0.0100 (18)0.032 (2)0.0000.0071 (18)0.000
O30.0267 (16)0.0248 (17)0.0249 (16)0.0031 (13)0.0096 (13)0.0016 (13)
O40.0231 (15)0.0182 (15)0.0337 (17)0.0008 (12)0.0120 (13)0.0031 (13)
O50.0232 (15)0.0255 (16)0.0221 (15)0.0004 (13)0.0072 (12)0.0030 (13)
Geometric parameters (Å, º) top
Ba1—O2i2.645 (5)Al2—O41.675 (4)
Ba1—O12.853 (3)Al2—O21.681 (2)
Ba1—O1ii2.853 (3)Al2—O5ix1.683 (4)
Ba1—O5iii2.910 (4)Al2—Ba1x3.632 (3)
Ba1—O52.910 (4)Al2—Ba1v3.826 (3)
Ba1—O3iv2.933 (4)O1—Si1vii1.694 (2)
Ba1—O3v2.933 (4)O1—Al1vii1.694 (2)
Ba1—O4vi3.120 (4)O1—Ba1ii2.853 (3)
Ba1—O4i3.120 (4)O2—Si2xi1.681 (2)
Ba1—Si1ii3.619 (2)O2—Al2xi1.681 (2)
Ba1—Al1ii3.619 (2)O2—Ba1x2.645 (5)
Ba1—Al1vii3.619 (2)O3—Si1vi1.676 (4)
Al1—O41.675 (4)O3—Al1vi1.676 (4)
Al1—O3viii1.676 (4)O3—Ba1v2.933 (4)
Al1—O51.682 (4)O4—Ba1x3.120 (4)
Al1—O11.694 (2)O5—Si2ix1.683 (4)
Al1—Ba1ii3.619 (2)O5—Al2ix1.683 (4)
Al2—O31.669 (4)
O2i—Ba1—O1140.79 (8)Si1ii—Ba1—Al1vii82.53 (7)
O2i—Ba1—O1ii140.79 (8)Al1ii—Ba1—Al1vii82.53 (7)
O1—Ba1—O1ii78.42 (15)O4—Al1—O3viii112.64 (19)
O2i—Ba1—O5iii106.85 (12)O4—Al1—O5109.97 (19)
O1—Ba1—O5iii97.61 (9)O3viii—Al1—O5114.1 (2)
O1ii—Ba1—O5iii54.21 (8)O4—Al1—O1114.9 (2)
O2i—Ba1—O5106.85 (12)O3viii—Al1—O1102.58 (16)
O1—Ba1—O554.21 (8)O5—Al1—O1102.13 (17)
O1ii—Ba1—O597.61 (9)O4—Al1—Ba1ii137.57 (14)
O5iii—Ba1—O569.13 (16)O3viii—Al1—Ba1ii53.00 (13)
O2i—Ba1—O3iv105.13 (12)O5—Al1—Ba1ii112.10 (15)
O1—Ba1—O3iv100.73 (10)O1—Al1—Ba1ii50.34 (10)
O1ii—Ba1—O3iv54.03 (8)O4—Al1—Ba1130.25 (14)
O5iii—Ba1—O3iv98.79 (11)O3viii—Al1—Ba1116.93 (14)
O5—Ba1—O3iv147.89 (10)O5—Al1—Ba152.06 (13)
O2i—Ba1—O3v105.13 (12)O1—Al1—Ba150.19 (10)
O1—Ba1—O3v54.03 (8)Ba1ii—Al1—Ba175.25 (6)
O1ii—Ba1—O3v100.73 (10)O3—Al2—O4112.5 (2)
O5iii—Ba1—O3v147.89 (10)O3—Al2—O2107.3 (2)
O5—Ba1—O3v98.79 (11)O4—Al2—O2101.2 (2)
O3iv—Ba1—O3v75.44 (15)O3—Al2—O5ix112.49 (19)
O2i—Ba1—O4vi52.66 (7)O4—Al2—O5ix114.1 (2)
O1—Ba1—O4vi88.14 (11)O2—Al2—O5ix108.4 (2)
O1ii—Ba1—O4vi166.50 (10)O3—Al2—Ba1x125.59 (14)
O5iii—Ba1—O4vi127.67 (11)O4—Al2—Ba1x59.05 (13)
O5—Ba1—O4vi73.10 (11)O2—Al2—Ba1x42.37 (15)
O3iv—Ba1—O4vi131.27 (10)O5ix—Al2—Ba1x119.56 (14)
O3v—Ba1—O4vi71.77 (11)O3—Al2—Ba1v46.33 (13)
O2i—Ba1—O4i52.66 (7)O4—Al2—Ba1v103.42 (14)
O1—Ba1—O4i166.50 (10)O2—Al2—Ba1v64.55 (18)
O1ii—Ba1—O4i88.14 (11)O5ix—Al2—Ba1v142.45 (14)
O5iii—Ba1—O4i73.10 (11)Ba1x—Al2—Ba1v81.33 (5)
O5—Ba1—O4i127.67 (11)Al1—O1—Si1vii139.7 (3)
O3iv—Ba1—O4i71.77 (11)Al1—O1—Al1vii139.7 (3)
O3v—Ba1—O4i131.27 (10)Si1vii—O1—Al1vii0.00 (13)
O4vi—Ba1—O4i105.28 (14)Al1—O1—Ba1ii102.46 (9)
O2i—Ba1—Si1ii127.66 (7)Si1vii—O1—Ba1ii102.68 (9)
O1—Ba1—Si1ii86.81 (9)Al1vii—O1—Ba1ii102.68 (9)
O1ii—Ba1—Si1ii27.20 (3)Al1—O1—Ba1102.68 (9)
O5iii—Ba1—Si1ii77.65 (9)Si1vii—O1—Ba1102.46 (9)
O5—Ba1—Si1ii122.31 (8)Al1vii—O1—Ba1102.46 (9)
O3iv—Ba1—Si1ii27.14 (8)Ba1ii—O1—Ba1101.58 (15)
O3v—Ba1—Si1ii85.25 (9)Al2—O2—Si2xi134.2 (3)
O4vi—Ba1—Si1ii154.64 (8)Al2—O2—Al2xi134.2 (3)
O4i—Ba1—Si1ii81.68 (9)Si2xi—O2—Al2xi0.00 (15)
O2i—Ba1—Al1ii127.66 (7)Al2—O2—Ba1x112.27 (15)
O1—Ba1—Al1ii86.81 (9)Si2xi—O2—Ba1x112.27 (15)
O1ii—Ba1—Al1ii27.20 (3)Al2xi—O2—Ba1x112.27 (15)
O5iii—Ba1—Al1ii77.65 (9)Al2—O3—Si1vi149.3 (2)
O5—Ba1—Al1ii122.31 (8)Al2—O3—Al1vi149.3 (2)
O3iv—Ba1—Al1ii27.14 (8)Si1vi—O3—Al1vi0.00 (13)
O3v—Ba1—Al1ii85.25 (9)Al2—O3—Ba1v109.37 (17)
O4vi—Ba1—Al1ii154.64 (8)Si1vi—O3—Ba1v99.85 (16)
O4i—Ba1—Al1ii81.68 (9)Al1vi—O3—Ba1v99.85 (16)
Si1ii—Ba1—Al1ii0.00 (7)Al2—O4—Al1128.3 (2)
O2i—Ba1—Al1vii127.66 (7)Al2—O4—Ba1x93.54 (16)
O1—Ba1—Al1vii27.20 (3)Al1—O4—Ba1x137.96 (18)
O1ii—Ba1—Al1vii86.82 (9)Al1—O5—Si2ix138.7 (2)
O5iii—Ba1—Al1vii122.31 (8)Al1—O5—Al2ix138.7 (2)
O5—Ba1—Al1vii77.65 (9)Si2ix—O5—Al2ix0.00 (14)
O3iv—Ba1—Al1vii85.25 (9)Al1—O5—Ba1100.82 (16)
O3v—Ba1—Al1vii27.14 (8)Si2ix—O5—Ba1120.20 (18)
O4vi—Ba1—Al1vii81.68 (9)Al2ix—O5—Ba1120.20 (18)
O4i—Ba1—Al1vii154.64 (8)
Symmetry codes: (i) x+1/2, y1/2, z; (ii) x, y, z; (iii) x, y, z; (iv) x+1/2, y1/2, z; (v) x+1/2, y+1/2, z; (vi) x+1/2, y+1/2, z; (vii) x, y, z; (viii) x1/2, y+1/2, z; (ix) x+1/2, y+1/2, z+1; (x) x1/2, y+1/2, z; (xi) x, y+1, z.

Experimental details

(I)(II)
Crystal data
Chemical formulaAl1.60Ba0.80O8Si2.40Al1.88Ba0.94O8Si2.12
Mr348.12367.03
Crystal system, space groupMonoclinic, C2/mMonoclinic, C2/m
Temperature (K)292298
a, b, c (Å)8.6090 (8), 13.0658 (12), 7.2047 (7)8.633 (6), 13.063 (8), 7.214 (5)
β (°) 115.418 (2) 115.17 (5)
V3)731.96 (12)736.3 (9)
Z44
Radiation typeMo KαMo Kα
µ (mm1)4.965.65
Crystal size (mm)0.20 × 0.18 × 0.140.6 × 0.6 × 0.3
Data collection
DiffractometerBruker SMART 1000 CCD area-detector
diffractometer
Nicolet P3
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2000)
ψ scan
(North et al., 1968)
Tmin, Tmax0.349, 0.5000.127, 0.551
No. of measured, independent and
observed [I > 2σ(I)] reflections
3542, 1366, 1223 1169, 1112, 1111
Rint0.0220.049
(sin θ/λ)max1)0.7560.703
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.022, 0.056, 1.07 0.032, 0.095, 1.36
No. of reflections13661112
No. of parameters6465
Δρmax, Δρmin (e Å3)0.73, 0.821.31, 1.03

Computer programs: SMART (Bruker, 1998), P3 software (Nicolet, 1980), SAINT (Bruker, 2000), P3 software, SAINT, RDNIC (Howie, 1980), SHELXS86 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ORTEX in OSCAIL (McArdle, 1994, 2000) and ATOMS (Dowty, 1999), SHELXL97.

Results of EDXA analysis of a range of crystals from preparation (I) (atom %) top
AlSiBa
135.6 (5)48.5 (6)15.9 (2)
234.9 (6)49.5 (7)15.6 (2)
333.5 (6)51.8 (7)14.7 (2)
434.4 (4)49.6 (5)16.09 (13)
535.6 (5)48.4 (6)16.01 (16)
635.9 (6)47.6 (7)16.57 (20)
734.3 (9)49.3 (10)16.3 (3)
Mean34.949.215.9
σn-10.91.30.6
Selected bond lengths and angles (Å, °) for compositions (I) and (II) top
(I) (x = 1/5)(II) (x = 0.06)
Ba1-O2i2.665 (2)2.645 (2)
Ba1-O12.8689 (14)2.853 (3)
Ba1-O52.9307 (17)2.910 (4)
Ba1-O3ii2.9599 (17)2.933 (4)
Ba1-O4i3.1212 (16)3.120 (4)
M1-O3iii1.6653 (17)1.676 (4)
M1-O41.6692 (16)1.675 (4)
M1-O51.6784 (16)1.682 (4)
M1-O11.6830 (9)1.694 (2)
M2-O31.6530 (17)1.669 (4)
M2-O5iv1.6615 (16)1.683 (4)
M2-O41.6656 (16)1.675 (4)
M2-O21.6710 (10)1.681 (2)
O4-M1-O3iii112.34 (9)112.64 (19)
O5-M1-O3iii112.99 (9)114.1 (2)
O1-M1-O3iii103.65 (7)102.58 (16)
O5-M1-O4109.76 (9)109.97 (19)
O1-M1-O4114.57 (9)114.9 (2)
O1-M1-O5103.15 (7)102.13 (17)
O3-M2-O5iv112.15 (8)112.49 (19)
O4-M2-O5iv113.39 (9)114.1 (2)
O2-M2-O5iv108.40 (10)108.4 (2)
O4-M2-O3112.17 (9)112.5 (2)
O2-M2-O3107.93 (10)107.3 (2)
O2-M2-O4102.11 (9)101.2 (2)
M1-O1-M1v140.97 (14)139.7 (3)
M2-O2-M2vi135.57 (14)134.2 (3)
M2-O3-M1vii150.59 (12)149.3 (2)
M1-O4-M2128.89 (10)128.3 (2)
M1-O5-M2iv139.61 (11)138.7 (2)
M1 and M2 represent the Al1/Si1 and Al2/Si2 sites, respectively. Symmetry codes: (i) 1/2 + x, y − 1/2, z; (ii) 1/2 − x, y − 1/2, −z; (iii) x − 1/2, 1/2 − y, z; (iv) 1/2 − x, 1/2 − y, 1 − z; (v) −x, y, −z; (vi) x, 1 − y, z; (vii) 1/2 + x, 1/2 − y, z.
Bond-valence sums for Ba1 − xAl2–2xSi2 + 2xO8 top
Composition (I) (x = 1/5)Composition (II) (x = 0.06)
ExpectedCalculatedExpectedCalculated
Ba11.601.651.881.74
Al1/Si13.603.603.533.55
Al2/Si23.603.713.533.59
 

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