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BaY2Si3O10, barium diyttrium trisilicate, is a new silicate grown from a molybdate-based flux. The structure is based on zigzag chains, parallel to [010], of edge-sharing distorted YO6 octa­hedra, linked by horseshoe-shaped trisilicate groups and Ba atoms in irregular eight-coordination. The layered character of the structure is caused by a succession of zigzag chains and trisilicate groups in planes parallel to (\overline{1}01). The Ba atoms occupy narrow channels extending parallel to [100]. The mean Y-O, Si-O and Ba-O bond lengths are 2.268, 1.626 and 1.633, and 2.872 Å, respectively. The two symmetry-equivalent terminal SiO4 tetra­hedra in the Si3O10 unit adopt an eclipsed conformation with respect to the central SiO4 tetra­hedron; the Si-O-Si and Si-Si-Si angles are 136.35 (9) and 96.12 (4)°, respectively. One Ba, one Si and two O atoms are located on mirror planes; all remaining atoms are in general positions. The geometry of isolated trisilicate groups in inorganic compounds is briefly discussed.

Supporting information


Crystallographic Information File (CIF)
Contains datablocks global, I


Structure factor file (CIF format)
Contains datablock I

Comment top

As part of a comprehensive study of the synthesis (by hydrothermal and flux growth methods), crystal chemistry and topologies of MI–(MII–)MIII silicates (MI = Na, K, Rb and Cs; MII = Sr and Ba; MIII = Sc, V, Cr, Fe, In, Y and Yb) with mixed octahedral–tetrahedral frameworks (Wierzbicka et al., 2005), the title compound, (I), was prepared from a molybdate-based flux. Further new Ba–Y and Sr–Y silicates prepared by the flux method include BaKYSi2O7 (Kolitsch et al., 2006a), BaY4Si5O17 (Kolitsch et al., 2006b) and SrY2Si3O10 (Kolitsch et al., 2006c; Wierzbicka et al., 2006). The latter trisilicate is not isostructural with (I).

The asymmetric unit of (I) contains one Ba, one Y, two Si and six O atoms. The Ba, Si1, O1 and O2 atoms are located on mirror planes (y = 1/4); all remaining atoms are in general positions. The building units in the crystal structure of (I) are YO6 octahedra, SiO4 tetrahedra and eight-coordinated Ba atoms. The structure is based on zigzag chains parallel to [010] of edge-sharing distorted YO6 octahedra, linked by horseshoe-shaped trisilicate (Si3O10) groups and Ba in irregular eight-coordination (Figs. 1 and 2); two further O neighbours (O6) of the Ba atom, each located 3.462 (2) Å away, are too remote to be considered as ligands.

A succession of octahedral zigzag chains and trisilicate groups in planes parallel to (101) results in the octahedral–tetrahedral layered character of (I) (Fig. 1). The strong linkage of these two different polyhedral units along [100] results in a heteropolyhedral slab parallel to (001) that is linked to adjacent slabs only via atoms O5 and Ba; the latter occupy narrow channels extending parallel to [100] (Fig. 1a). The mean Y—O, Si—O and Ba—O bond lengths are 2.268, 1.626 and 1.633, and 2.872 Å, respectively. The horseshoe-shaped geometry of the trisilicate unit is noteworthy. The two symmetry-equivalent terminal Si2O4 tetrahedra in this unit show an eclipsed conformation with respect to the central Si1O4 tetrahedron; the Si1—O—Si2 and Si2—Si1—Si2 angles are 136.35 (9) and 96.12 (4)°, respectively.

Bond-valence sums for all atoms were calculated using the bond-valence parameters of Brese & O'Keeffe (1991). The bond-valence sums are 1.76 (Ba1), 3.05 (Y1), 3.98 (Si1), 3.91 (Si2), 2.14 (O1), 2.02 (O2), 1.96 (O3), 1.88 (O4), 1.99 (O5) and 1.92 valence units (O6), and thus are all reasonably close to ideal valencies. Although the sum calculated for Ba may appear somewhat low, it is well known that Ba compounds in general tend to give poor bond-valence sums (Brown & Wu, 1976).

Trisilicates such as (I) are uncommon representatives of the silicate family. In a first overview on natural and synthetic trisilicate compounds, Povarennykh et al. (1976) characterize only 17 compounds, and state `The scarcity of the minerals is due to the difficulty in forming stoichiometric compounds with such a large silicate anion and the instability of the Si3O10 group relative to Si2O7 and Si3O9 during mineral formation.' Few further examples of trisilicates have been described since then.

In the following we provide a brief overview of silicate compounds containing isolated Si3O10 units, including the protonated derivative Si3O8(OH)2, where the two terminal SiO4 groups are protonated. Trisilicate units show an notably variable geometry: They can appear nearly linear to slightly curved, with Si—Si—Si angles between about 160 and 150° {e.g. Na2Ca3[Si3O10] (Treushnikov et al., 1971) and isotypic Na2Cd3[Si3O10] (Simonov et al., 1977); ardennite, Mn2(Mn,Ca)2(Al,Mg)6(OH)6 [(As,V,Si)O4][SiO4]2[Si3O10] (Donnay & Allmann, 1968, Pasero et al., 1994); high-pressure L-type REE2Si2O7, where REE is a rare earth element (Fleet & Liu, 2004); B-type REE4[Si3O10][SiO4] (Felsche, 1972, Fleet & Liu, 2003, Hartenbach et al., 2003)].

More or less strongly curved units, with Si—Si—Si angles between about 134 and 103° occur in SrY2[Si3O10] (Kolitsch et al., 2006c; Wierzbicka et al., 2006), in rosenhahnite, Ca3[Si3O8(OH)2] (Jeffery & Lindley, 1973; Wan et al., 1977), in Na4Cd2[Si3O10] (Simonov et al., 1968, 1978), and in the microporous compound MCV-2, Ba2Na[Na0.5,(H2O)0.5]2Zr2Si6O19·3H2O (Si—Si—Si = 103.4°, Ferdov et al., 2005).

Finally, Si3O10 units with horseshoe-shaped geometries and Si—Si—Si angles ranging between 98.1 and 76.2° are encountered in kilchoanite, Ca6[SiO4][Si3O10] (Taylor, 1971), in the title compound, in kinoite, Ca2Cu2(H2O)2[Si3O10] (Laughon, 1971), in fluorthalenite-(Y)-type M3F[Si3O10], where M = Y, Dy, Ho and Er (Yakubovich et al., 1988 or 1998; Schleid & Müller-Bunz, 1998; Müller-Bunz & Schleid, 2000), in K3Y[Si3O8(OH)2] (Maksimov et al., 1968), and in isotypic K3Ho[Si3O8(OH)2] (Ponomarev et al., 1988) and K3Yb[Si3O8(OH)2] (Filipenko et al., 1999).

It is conspicuous that the narrowest Si—Si—Si angles are predominantly shown by silicates containing either F atoms or OH groups (not bonded to Si) or [Si3O8(OH)2]- groups. Preliminary studies of the several possible influences on the unusually variable geometry of Si3O10 groups in the mentioned compounds indicate that very narrow Si—Si—Si angles preferentially occur in structures where larger metal cations are octahedrally coordinated. A more detailed discussion, including a comparison with compounds containing Ge3O10 and Al3O10 groups, will be presented as part of the description of the crystal structure of SrY2Si3O10 (Wierzbicka et al., 2006).

Experimental top

The title compound was grown from a BaO–Rb2O–MoO3 flux containing dissolved precursor compounds of Ba, Rb, Y and Si (experimental parameters: 1 g BaCO3, 0.6 g Rb2CO3, 1 g MoO3, 0.1614 g Y2O3, 0.1718 g SiO2; Pt crucible covered with lid, Tmax = 1423 K, holding time 3 h, cooling rate 2 K h−1, Tmin = 1173 K, slow cooling to room temperature after switching off furnace). The reaction products were recovered by dissolving the flux in distilled water. BaY2Si3O10 formed small (up to about 0.10 mm) pseudohexagonal plates, accompanied by rectangular plates to thick tabular crystals of a silicate with the tentative chemical formula Rb3YSi8O19, which, according to preliminary results, appears to be a superstructure variant of Cs3ScSi8O19 (MCV-1; Kolitsch & Tillmanns, 2004) and isotypic Cs3YSi8O19 (Kolitsch et al., 2006a). Preliminary results from single-crystal X-ray diffraction studies prove that an isotypic Yb analogue of the title compound can also be synthesized; this analogue has the following unit-cell parameters: a = 5.377 (1) Å, b = 12.117 (2) Å, c = 6.790 (1) Å, β = 106.50 (3)°) and V = 424.17 (12) Å3.

Refinement top

The highest electron-density peak in (I) is at a distance of 0.98 Å from the O5 site. The deepest hole in the difference map is at a distance of 0.99 Å from the Ba1 site.

Computing details top

Data collection: COLLECT (Nonius, 2005); cell refinement: SCALEPACK (Otwinowski et al., 2003); data reduction: DENZO (Otwinowski et al., 2003) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Shape Software, 1999); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The crystal structure of BaY2Si3O10, (a) projected along [100] and (b) projected along [001]. Zigzag chains parallel to [010] of edge-sharing distorted YO6 octahedra are linked by horseshoe-shaped trisilicate groups and Ba atoms (shown as spheres).
[Figure 2] Fig. 2. Connectivity in the structure of BaY2Si3O10, shown with displacement ellipsoids at the 50% probability level. [Symmetry codes: (i) x, −y + 1/2, z; (ii) x, y, z + 1; (iii) −x + 1, −y, −z + 1; (iv) −x, −y, −z + 1; (v) x − 1, y, z.]
barium diyttrium triscilicate top
Crystal data top
BaY2Si3O10F(000) = 512
Mr = 559.43Dx = 4.298 Mg m3
Monoclinic, P21/mMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybCell parameters from 1640 reflections
a = 5.399 (1) Åθ = 2.0–32.6°
b = 12.179 (2) ŵ = 18.28 mm1
c = 6.852 (1) ÅT = 293 K
β = 106.37 (3)°Fragment, colourless
V = 432.28 (14) Å30.11 × 0.10 × 0.02 mm
Z = 2
Data collection top
Nonius KappaCCD
1636 independent reflections
Radiation source: fine-focus sealed tube1578 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.013
ϕ and ω scansθmax = 32.6°, θmin = 3.1°
Absorption correction: multi-scan
(SCALEPACK; Otwinowski et al., 2003)
h = 88
Tmin = 0.238, Tmax = 0.711k = 1818
3139 measured reflectionsl = 1010
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)] = 0.016 w = 1/[σ2(Fo2) + (0.02P)2 + 0.43P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.040(Δ/σ)max = 0.001
S = 1.10Δρmax = 0.97 e Å3
1636 reflectionsΔρmin = 1.29 e Å3
80 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0116 (5)
Crystal data top
BaY2Si3O10V = 432.28 (14) Å3
Mr = 559.43Z = 2
Monoclinic, P21/mMo Kα radiation
a = 5.399 (1) ŵ = 18.28 mm1
b = 12.179 (2) ÅT = 293 K
c = 6.852 (1) Å0.11 × 0.10 × 0.02 mm
β = 106.37 (3)°
Data collection top
Nonius KappaCCD
1636 independent reflections
Absorption correction: multi-scan
(SCALEPACK; Otwinowski et al., 2003)
1578 reflections with I > 2σ(I)
Tmin = 0.238, Tmax = 0.711Rint = 0.013
3139 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.01680 parameters
wR(F2) = 0.0400 restraints
S = 1.10Δρmax = 0.97 e Å3
1636 reflectionsΔρmin = 1.29 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
Ba10.76082 (3)0.25000.01992 (2)0.00954 (5)
Y10.15801 (3)0.098858 (14)0.68431 (2)0.00637 (5)
Si10.58242 (13)0.25000.48917 (10)0.00570 (12)
Si20.30379 (9)0.06205 (4)0.21344 (7)0.00579 (9)
O10.3723 (4)0.25000.6158 (3)0.0078 (3)
O20.8766 (3)0.25000.6344 (3)0.0069 (3)
O30.5483 (3)0.14287 (12)0.3397 (2)0.0105 (2)
O40.4308 (3)0.05455 (11)0.1907 (2)0.0105 (2)
O50.1652 (3)0.12347 (12)0.0030 (2)0.0107 (2)
O60.1002 (3)0.05192 (12)0.3511 (2)0.0088 (2)
Atomic displacement parameters (Å2) top
Ba10.01005 (8)0.01136 (8)0.00778 (8)0.0000.00344 (5)0.000
Y10.00760 (9)0.00671 (9)0.00475 (9)0.00103 (5)0.00167 (6)0.00053 (5)
Si10.0050 (3)0.0074 (3)0.0048 (3)0.0000.0015 (2)0.000
Si20.0062 (2)0.0067 (2)0.0046 (2)0.00039 (16)0.00165 (16)0.00015 (15)
O10.0075 (8)0.0071 (8)0.0104 (8)0.0000.0050 (6)0.000
O20.0058 (7)0.0069 (8)0.0068 (8)0.0000.0004 (6)0.000
O30.0087 (6)0.0129 (6)0.0105 (6)0.0034 (5)0.0036 (5)0.0051 (5)
O40.0102 (6)0.0090 (6)0.0115 (6)0.0020 (5)0.0015 (5)0.0007 (5)
O50.0138 (6)0.0127 (6)0.0050 (6)0.0047 (5)0.0016 (5)0.0015 (5)
O60.0094 (6)0.0112 (6)0.0070 (6)0.0038 (5)0.0042 (4)0.0023 (4)
Geometric parameters (Å, º) top
Si1—O11.611 (2)Y1—O62.2883 (14)
Si1—O21.619 (2)Y1—O12.2920 (11)
Si1—O31.6368 (14)Y1—O2v2.3497 (12)
Si1—O3i1.6368 (14)Ba1—O5vi2.7013 (14)
Si2—O41.6037 (15)Ba1—O5vii2.7013 (14)
Si2—O51.6096 (15)Ba1—O4viii2.8245 (14)
Si2—O61.6421 (14)Ba1—O4ix2.8245 (14)
Si2—O31.6781 (15)Ba1—O2x2.881 (2)
Y1—O5ii2.1935 (14)Ba1—O1x2.965 (2)
Y1—O4iii2.2092 (15)Ba1—O3i3.0392 (15)
Y1—O6iv2.2769 (14)Ba1—O33.0392 (15)
O5ii—Y1—O4iii85.04 (6)O1—Si1—O2112.73 (10)
O5ii—Y1—O6iv93.14 (5)O1—Si1—O3111.41 (7)
O4iii—Y1—O6iv111.25 (5)O2—Si1—O3107.61 (7)
O5ii—Y1—O6170.62 (5)O1—Si1—O3i111.41 (7)
O4iii—Y1—O699.51 (6)O2—Si1—O3i107.61 (7)
O6iv—Y1—O677.59 (5)O3—Si1—O3i105.72 (11)
O5ii—Y1—O1103.05 (6)O4—Si2—O5115.34 (8)
O4iii—Y1—O176.43 (6)O4—Si2—O6111.29 (8)
O6iv—Y1—O1162.79 (6)O5—Si2—O6109.39 (8)
O6—Y1—O186.05 (6)O4—Si2—O3105.88 (7)
O5ii—Y1—O2v82.36 (6)O5—Si2—O3106.79 (8)
O4iii—Y1—O2v141.78 (5)O6—Si2—O3107.73 (7)
O6iv—Y1—O2v105.36 (5)Si1—O3—Si2136.35 (9)
O6—Y1—O2v98.62 (6)Si2—Si1—Si2i96.12 (4)
O1—Y1—O2v71.59 (5)
Symmetry codes: (i) x, y+1/2, z; (ii) x, y, z+1; (iii) x+1, y, z+1; (iv) x, y, z+1; (v) x1, y, z; (vi) x+1, y+1/2, z; (vii) x+1, y, z; (viii) x+1, y, z; (ix) x+1, y+1/2, z; (x) x, y, z1.

Experimental details

Crystal data
Chemical formulaBaY2Si3O10
Crystal system, space groupMonoclinic, P21/m
Temperature (K)293
a, b, c (Å)5.399 (1), 12.179 (2), 6.852 (1)
β (°) 106.37 (3)
V3)432.28 (14)
Radiation typeMo Kα
µ (mm1)18.28
Crystal size (mm)0.11 × 0.10 × 0.02
Data collection
DiffractometerNonius KappaCCD
Absorption correctionMulti-scan
(SCALEPACK; Otwinowski et al., 2003)
Tmin, Tmax0.238, 0.711
No. of measured, independent and
observed [I > 2σ(I)] reflections
3139, 1636, 1578
(sin θ/λ)max1)0.757
R[F2 > 2σ(F2)], wR(F2), S 0.016, 0.040, 1.10
No. of reflections1636
No. of parameters80
Δρmax, Δρmin (e Å3)0.97, 1.29

Computer programs: COLLECT (Nonius, 2005), SCALEPACK (Otwinowski et al., 2003), DENZO (Otwinowski et al., 2003) and SCALEPACK, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ATOMS (Shape Software, 1999), SHELXL97.

Selected geometric parameters (Å, º) top
Si1—O11.611 (2)Y1—O6iii2.2769 (14)
Si1—O21.619 (2)Y1—O62.2883 (14)
Si1—O31.6368 (14)Y1—O12.2920 (11)
Si2—O41.6037 (15)Y1—O2iv2.3497 (12)
Si2—O51.6096 (15)Ba1—O5v2.7013 (14)
Si2—O61.6421 (14)Ba1—O4vi2.8245 (14)
Si2—O31.6781 (15)Ba1—O2vii2.881 (2)
Y1—O5i2.1935 (14)Ba1—O1vii2.965 (2)
Y1—O4ii2.2092 (15)Ba1—O3viii3.0392 (15)
Si1—O3—Si2136.35 (9)Si2—Si1—Si2viii96.12 (4)
Symmetry codes: (i) x, y, z+1; (ii) x+1, y, z+1; (iii) x, y, z+1; (iv) x1, y, z; (v) x+1, y+1/2, z; (vi) x+1, y, z; (vii) x, y, z1; (viii) x, y+1/2, z.

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