A ramsayite-type oxide, Ca₂Sn₂Al₂O₉

The title compound, dicalcium nonaoxidodistannate(IV)dialuminate, is the second example which crystallizes in the isotypic structure of a pyroxene silicate, Na₂Ti₂Si₂O₉ (ramsayite). _∞¹[Sn₂O₈] chains and pyroxene-type _∞¹[Al₂O₆] chains are formed along the b axis by sharing O atoms. The Ca atoms are situated in the resulting channels and exhibit a coordination number of 7.

Related literature

For the structure of ramsayite, Na₂Ti₂Si₂O₉, see: Sundberg et al. (1987). For the synthesis of Ca₈Sn₇Al₁₀O₃₇, see: Barbanyagre & Kotlyarov (2001). For the structure of a related stannate silicate, Ca₂SnSi₂O₉, see: Blasse et al. (1995). For bond-valence parameters, see: Brese & O'Keeffe (1991). For the CaO–Al₂O₃ system, see: Jerebtsov & Mikhailov (2001). For the Inorganic Crystal Structure Database, see: ICSD (2009).

Experimental

Crystal data

• Ca₂Sn₂Al₂O₉

• M_r = 515.50

• Orthorhombic, P b c n

• a = 8.9866 (6) Å

• b = 5.4894 (11) Å

• c = 14.9030 (18) Å

• V = 735.18 (18) ų

• Z = 4

• Mo Kα radiation

• μ = 8.46 mm⁻¹

• T = 293 K

• 0.17 × 0.15 × 0.07 mm

Data collection

• Rigaku R-AXIS RAPID diffractometer

• Absorption correction: numerical (NUMABS; Higashi, 1999) T_min = 0.427, T_max = 0.717

• 6534 measured reflections

• 845 independent reflections

• 788 reflections with I > 2σ(I)

• R_int = 0.051

Refinement

• R[F² > 2σ(F²)] = 0.018

• wR(F²) = 0.043

• S = 1.08

• 845 reflections

• 69 parameters

• Δρ_max = 0.72 e Å⁻³

• Δρ_min = −0.72 e Å⁻³

Table 1
Selected bond lengths (Å)

Ca1—O3^i	2.303 (2)
Ca1—O2	2.391 (2)
Ca1—O1^ii	2.404 (2)
Ca1—O4^i	2.412 (2)
Ca1—O2^i	2.463 (2)
Ca1—O5	2.486 (2)
Ca1—O3^iii	2.624 (2)
Al1—O2^i	1.735 (2)
Al1—O4	1.745 (2)
Al1—O2	1.763 (2)
Al1—O1^iv	1.777 (3)
Sn1—O4^v	2.002 (2)
Sn1—O3	2.032 (2)
Sn1—O3^i	2.053 (2)
Sn1—O5^vi	2.0682 (13)
Sn1—O1^i	2.106 (2)
Sn1—O1	2.207 (2)
Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .

Data collection: PROCESS-AUTO (Rigaku, 1998); cell refinement: PROCESS-AUTO; data reduction: CrystalStructure (Rigaku, 2005); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: VESTA (Momma & Izumi, 2008); software used to prepare material for publication: SHELXL97.

Supporting information

S1. Comment

Barbanyagre and Kotlyarov (2001) reported a quaternary oxide Ca₈Al₁₀Sn₇O₃₇ with a powder X-ray diffraction (PXRD) pattern, but they did not clarify the crystal structure. We have prepared single crystals of Ca₂Sn₂Al₂O₉ by slow cooling of a Ca—Al—Sn—O melt. The PXRD pattern of Ca₈Al₁₀Sn₇O₃₇ was similar to that calculated with the crystal structure parameters of Ca₂Sn₂Al₂O₉ analyzed by the present study.

Ca₂Sn₂Al₂O₉ is isostructural with ramsayite (lorenzenite) Na₂Ti₂Si₂O₉ (a = 8.7128 (10), b = 5.2327 (5), c = 14.487 (2) Å) (Sundberg, et al., 1987). Other compounds crystallizing in the isotypic structure were not found in the Inorganic Crystal Structure Database (ICSD, 2009).

The selected bond distances in Ca₂Sn₂Al₂O₉ are summarized in Table 1. The coordination environments of Ca, Sn and Al are drawn with displacement ellipsoids in Fig. 1. The Sn site is in a distorted oxygen octhahedron with the Sn—O distances varying from 2.002 (2) to 2.207 (2) Å, (average 2.08 (8) Å). The bond valence sum (BVS) calculated for Sn atoms with the bond valence parameter of R (Sn—O) = 1.905 Å (Brese & O'Keeffe, 1991) was 3.815, a little smaller than the IV valence of Sn. These Sn—O bond lengths and the BVS are consistent with those reported for Ca₃SnSi₂O₉ (2.007–2.134 Å, avg. 2.08 (4) Å, BVS 3.803) (Blasse et al., 1995).

Each SnO₆ octahedron shares O1—O3 edges with both adjacent sides of SnO₆ octahedra and a one-dimensional chain _∞¹[Sn₂O₈] is formed along the b axis. Al atoms are tetrahedrally coordinated by O atoms and the AlO₄ tetrahedra form pyroxene-type _∞¹[Ali₂O₆] chains along the b axis by sharing O2. The Al—O bond lengths are from 1.735 to 1.777 (3) Å (avg. 1.755 (19) Å) and the BVS of 3.02 is consistent with trivalent of Al(III). The chains of _∞¹[Ali₂O₆] and _∞¹[Sn₂O₈] are bridged by sharing O4, and the _∞¹[Sn₂O₈] chains are linked each other by sharing O5 on a two-fold axis, forming rectangular channels along the b axis (Fig. 2). Ca sites are situated in the channels and surrounded by 7 oxygen atoms with the distances from 2.303 (2) to 2.624 (2) Å. The BVS of Ca atoms is 2.01 and well agrees with the valence number of Ca(II).

A permittivity of 48 and a tanδ of 0.02 were measured at room temperature with an impedance analyzer (Solartron 1260 and 1296) for the polycrystalline sample which was mainly composed of Ca₂Sn₂Al₂O₉ with a small amount of CaSnO₃ which crystallized at the initial stage of solid state reaction.

Related literature

For the structure of ramsayite, Na₂Ti₂Si₂O₉, see: Sundberg et al. (1987). For the synthesis of Ca₈Sn₇Al₁₀O₃₇, see: Barbanyagre & Kotlyarov (2001). For the structure of a related stanate silicate, Ca₂SnSi₂O₉, see: Blasse et al. (1995). Ffor bond-valence parameters, see: Brese & O'Keeffe (1991). For the CaO-Al₂O₃ system, see: Jerebtsov & Mikhailov (2001). For the Inorganic Crystal Structure Database, see: ICSD (2009).

S2. Experimental

The starting materials used were CaCO₃ (Rare Metallic, 99.99% purity), SnO₂ (Rare Metallic, 99.99% purity) and Al₂O₃ (Rare Metallic, 99.99% purity). The powders were weighed, mixed in an agate mortar with a pestle, and pressed into pellets, which were placed on a platinum plate and heated in an electric furnace in air. Single crystals of Ca₂Sn₂Al₂O₉ were prepared from a starting mixture with an atomic ratio Ca: Sn: Al ═ 5:1:4. The pellet of the mixture was heated to 1823 K at a heating rate of 200 K/h, and then cooled to 1773 K at a cooling rate of 5 K/h. The single crystals were probably grown in a flux with a composition close to a Ca₃Al₂O₆—CaAl₂O₄ mixture which has the eutectic point of 1644 K (Jerebtsov & Mikhailov, 2001). The samples were then cooled in the furnace by shutting off the electric power. The obtained sample was crushed into fragments and colorless transparent single crystals of about 0.06–0.14 mm were picked up under an optical microscope. A polycrystalline sample was prepared by heating the pellets of the starting mixtures with stoichiometric metal ratios Ca:Sn:Al ═ 1:1:1 at around 1600 K for 24 h.

S3. Refinement

The highest peak in the difference electron density map is 0.94 Å from Sn1 while the deepest hole is 1.08 Å from the same atom.

Computing details

Data collection: PROCESS-AUTO (Rigaku, 1998); cell refinement: PROCESS-AUTO (Rigaku, 1998); data reduction: CrystalStructure (Rigaku, 2005); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: VESTA (Momma & Izumi, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. O-atom coordination around Ca, Al, and Sn atoms in the structure of Ca2Sn2Al2O9. Displacement ellipsoids are drawn at 99% probability level. [Symmetry codes as in Table 1.]
	Fig. 2. Crystal structure of Ca2Sn2Al2O9 illustrated with distorted Sn-centered oxygen octahedra and Al-centered oxygen tetrahedra.

dicalcium nonaoxydistanate(IV) dialuminate

Crystal data

Ca2Sn2Al2O9	F(000) = 952
Mr = 515.50	Dx = 4.657 Mg m^−3
Orthorhombic, Pbcn	Mo Kα radiation, λ = 0.71075 Å
Hall symbol: -P 2n 2ab	Cell parameters from 5414 reflections
a = 8.9866 (6) Å	θ = 3.6–27.8°
b = 5.4894 (11) Å	µ = 8.46 mm^−1
c = 14.9030 (18) Å	T = 293 K
V = 735.18 (18) Å^3	Platelet, colourless
Z = 4	0.17 × 0.15 × 0.07 mm

Data collection

Rigaku R-AXIS RAPID diffractometer	845 independent reflections
Radiation source: fine-focus sealed tube	788 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.051
Detector resolution: 10.00 pixels mm^-1	θmax = 27.5°, θmin = 3.6°
ω scans	h = −11→11
Absorption correction: numerical (NUMABS; Higashi, 1999)	k = −7→7
Tmin = 0.427, Tmax = 0.717	l = −19→19
6534 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.018	Secondary atom site location: difference Fourier map
wR(F^2) = 0.043	w = 1/[σ^2(Fo^2) + (0.002P)^2 + 2.2176P] where P = (Fo^2 + 2Fc^2)/3
S = 1.08	(Δ/σ)max = 0.001
845 reflections	Δρmax = 0.72 e Å^−3
69 parameters	Δρmin = −0.72 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Ca1	0.06714 (7)	0.36160 (11)	0.14603 (5)	0.00676 (14)
Al1	0.34369 (10)	0.31037 (18)	0.02817 (7)	0.0055 (2)
Sn1	0.34459 (2)	0.36611 (4)	0.333981 (15)	0.00525 (9)
O1	0.1618 (2)	0.1912 (4)	0.40897 (16)	0.0070 (5)
O2	0.2277 (2)	0.0795 (4)	0.07144 (15)	0.0071 (4)
O3	0.3314 (2)	0.0365 (4)	0.27250 (16)	0.0079 (5)
O4	0.5156 (2)	0.2310 (4)	0.07402 (16)	0.0078 (4)
O5	0.0000	0.0250 (6)	0.2500	0.0077 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ca1	0.0069 (3)	0.0071 (3)	0.0062 (3)	−0.0007 (2)	0.0006 (2)	−0.0003 (2)
Al1	0.0057 (5)	0.0058 (5)	0.0050 (5)	−0.0001 (3)	−0.0004 (3)	0.0001 (4)
Sn1	0.00529 (13)	0.00501 (14)	0.00544 (14)	0.00004 (7)	−0.00022 (7)	−0.00022 (8)
O1	0.0080 (11)	0.0067 (11)	0.0064 (12)	−0.0008 (8)	−0.0004 (8)	−0.0002 (9)
O2	0.0089 (11)	0.0054 (10)	0.0070 (11)	−0.0007 (8)	−0.0005 (9)	−0.0003 (9)
O3	0.0077 (11)	0.0064 (11)	0.0096 (13)	−0.0008 (8)	0.0026 (9)	−0.0019 (9)
O4	0.0059 (10)	0.0088 (11)	0.0087 (11)	−0.0003 (8)	−0.0024 (9)	−0.0011 (9)
O5	0.0086 (15)	0.0078 (15)	0.0066 (16)	0.000	−0.0014 (13)	0.000

Geometric parameters (Å, º)

Ca1—O3^i	2.303 (2)	Sn1—O1^i	2.106 (2)
Ca1—O2	2.391 (2)	Sn1—O1	2.207 (2)
Ca1—O1^ii	2.404 (2)	O1—Al1^vii	1.777 (3)
Ca1—O4^i	2.412 (2)	O1—Sn1^viii	2.106 (2)
Ca1—O2^i	2.463 (2)	O1—Ca1^ii	2.404 (2)
Ca1—O5	2.486 (2)	O2—Al1^viii	1.735 (2)
Ca1—O3^iii	2.624 (2)	O2—Ca1^viii	2.463 (2)
Al1—O2^i	1.735 (2)	O3—Sn1^viii	2.053 (2)
Al1—O4	1.745 (2)	O3—Ca1^viii	2.303 (2)
Al1—O2	1.763 (2)	O3—Ca1^ix	2.624 (2)
Al1—O1^iv	1.777 (3)	O4—Sn1^v	2.002 (2)
Sn1—O4^v	2.002 (2)	O4—Ca1^viii	2.412 (2)
Sn1—O3	2.032 (2)	O5—Sn1^x	2.0682 (13)
Sn1—O3^i	2.053 (2)	O5—Sn1^viii	2.0682 (13)
Sn1—O5^vi	2.0682 (13)	O5—Ca1^ii	2.486 (2)
O3^i—Ca1—O2	114.30 (8)	O3^i—Sn1—O1^i	80.21 (9)
O3^i—Ca1—O1^ii	141.26 (8)	O5^vi—Sn1—O1^i	88.98 (9)
O2—Ca1—O1^ii	96.08 (8)	O4^v—Sn1—O1	87.66 (9)
O3^i—Ca1—O4^i	97.80 (8)	O3—Sn1—O1	78.32 (9)
O2—Ca1—O4^i	121.59 (8)	O3^i—Sn1—O1	81.41 (9)
O1^ii—Ca1—O4^i	84.93 (8)	O5^vi—Sn1—O1	173.05 (6)
O3^i—Ca1—O2^i	82.57 (8)	O1^i—Sn1—O1	94.57 (9)
O2—Ca1—O2^i	69.69 (4)	Al1^vii—O1—Sn1^viii	121.70 (13)
O1^ii—Ca1—O2^i	132.50 (8)	Al1^vii—O1—Sn1	121.93 (11)
O4^i—Ca1—O2^i	67.76 (7)	Sn1^viii—O1—Sn1	96.90 (9)
O3^i—Ca1—O5	84.02 (7)	Al1^vii—O1—Ca1^ii	108.61 (10)
O2—Ca1—O5	87.41 (7)	Sn1^viii—O1—Ca1^ii	97.21 (9)
O1^ii—Ca1—O5	73.48 (6)	Sn1—O1—Ca1^ii	107.17 (10)
O4^i—Ca1—O5	145.85 (7)	Al1^viii—O2—Al1	134.02 (15)
O2^i—Ca1—O5	145.50 (6)	Al1^viii—O2—Ca1	120.07 (11)
O3^i—Ca1—O3^iii	77.78 (9)	Al1—O2—Ca1	93.51 (9)
O2—Ca1—O3^iii	159.97 (8)	Al1^viii—O2—Ca1^viii	91.78 (9)
O1^ii—Ca1—O3^iii	67.00 (8)	Al1—O2—Ca1^viii	94.11 (10)
O4^i—Ca1—O3^iii	69.47 (7)	Ca1—O2—Ca1^viii	123.82 (10)
O2^i—Ca1—O3^iii	129.46 (7)	Sn1—O3—Sn1^viii	104.43 (10)
O5—Ca1—O3^iii	77.73 (6)	Sn1—O3—Ca1^viii	135.82 (11)
O2^i—Al1—O4	113.24 (12)	Sn1^viii—O3—Ca1^viii	118.71 (10)
O2^i—Al1—O2	104.92 (9)	Sn1—O3—Ca1^ix	94.02 (9)
O4—Al1—O2	101.59 (11)	Sn1^viii—O3—Ca1^ix	104.41 (10)
O2^i—Al1—O1^iv	111.43 (12)	Ca1^viii—O3—Ca1^ix	84.64 (7)
O4—Al1—O1^iv	114.50 (11)	Al1—O4—Sn1^v	137.01 (13)
O2—Al1—O1^iv	110.23 (11)	Al1—O4—Ca1^viii	96.38 (10)
O4^v—Sn1—O3	90.89 (9)	Sn1^v—O4—Ca1^viii	101.55 (9)
O4^v—Sn1—O3^i	163.28 (9)	Sn1^x—O5—Sn1^viii	130.13 (15)
O3—Sn1—O3^i	99.18 (9)	Sn1^x—O5—Ca1^ii	121.78 (5)
O4^v—Sn1—O5^vi	98.44 (7)	Sn1^viii—O5—Ca1^ii	95.75 (4)
O3—Sn1—O5^vi	98.16 (9)	Sn1^x—O5—Ca1	95.75 (4)
O3^i—Sn1—O5^vi	93.33 (8)	Sn1^viii—O5—Ca1	121.78 (5)
O4^v—Sn1—O1^i	88.14 (9)	Ca1^ii—O5—Ca1	83.96 (10)
O3—Sn1—O1^i	172.86 (9)

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