A cubic calcium oxynitrido-silicate, Ca2.89Si2N1.76O4.24

doi:10.1107/S1600536811042607

Acta Crystallogr Sect E Struct Rep Online. 2011 November 1; 67(Pt 11): i66.

Published online 2011 October 29. doi: 10.1107/S1600536811042607

PMCID: PMC3246911

A cubic calcium oxynitrido-silicate, Ca_2.89Si₂N_1.76O_4.24

Ali Sharafat,^a Pedro Berastegui,^b Saeid Esmaeilzadeh,^b Lars Eriksson,^b^* and Jekabs Grins^b

^aSchool of Engineering, Linné University, Växjö, S-351 95 Växjö, Sweden

^bDepartment of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden

Correspondence e-mail: lars.eriksson/at/mmk.su.se

Received September 21, 2011; Accepted October 14, 2011.

This is an open-access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

Abstract

The title compound, tricalcium oxynitride silicate, with composition Ca_3-xSi₂N_2-2xO_4+2x (x [similar, equals]

0.12), is a perovskite-related calcium oxynitrido silicate containing isolated oxynitrido silicate 12-rings. The N atoms are statistically disordered with O atoms (occupancy ratio N:O = 0.88:0.12) and occupy the bridging positions in the 12 ring oxynitrido silicate anion, while the remaining O atoms are located at the terminal positions of the Si(O,N)₄ tetrahedra. The majority of the Ca²⁺ cations fill the channels along [100] in the packing of the 12-ring anions. The rest of these cations are located at several positions, with partial occupancy, in channels along the body diagonals.

Related literature

For a closely related silicate, as well as a germanate, see: Fischer & Tillmanns (1984

) and for a more distantly related calcium aluminate, see: Mondal & Jeffery (1975

)

Experimental

Crystal data

Ca_2.89Si₂N_1.76O_4.24
M _r = 264.65
Cubic,
a = 15.0626 (1) Å
V = 3417.45 (4) Å³
Z = 24
Mo Kα radiation
μ = 3.18 mm⁻¹
T = 293 K
0.10 × 0.06 × 0.02 mm

Data collection

Oxford Diffraction XcaliburIII with Sapphire-3 CCD diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2008 ) T _min = 0.67, T _max = 0.94
30793 measured reflections
1982 independent reflections
1779 reflections with I > 2s(I)
R _int = 0.027

Refinement

R[F ² > 2σ(F ²)] = 0.032
wR(F ²) = 0.069
S = 1.22
1982 reflections
113 parameters
Δρ_max = 0.87 e Å⁻³
Δρ_min = −0.76 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2008

); cell refinement: CrysAlis RED (Oxford Diffraction, 2008

); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008

); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008

); molecular graphics: DIAMOND (Brandenburg, 2001

); software used to prepare material for publication: PLATON (Spek, 2009

) and SHELXL97.

Table 1

Selected bond lengths (Å)

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536811042607/fj2455sup1.cif

Click here to view.^{(14K, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811042607/fj2455Isup2.hkl

Click here to view.^{(98K, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

This work was supported by a grant from the Swedish Research Council and by the Faculty of Natural Sciences at Stockholm University.

supplementary crystallographic information

Comment

The title compound is a crystalline component formed in the melts of oxynitrido glasses, studied at our department. The title compound calcium oxynitrido-silicate contains isolated 12-ring anions with the ideal composition Ca_{3 -}_xSi₂N_2–2xO_{4 + 2x} where the title compound have x≈ 0.12. It should be emphasized that x=0 do not indicate an end member of a possible solid solution series of compounds. The nitrogen atoms in the anions occupies mainly the ring positions in the 12 ring while the oxygen atoms mainly occupy the apex positions. A figure of the oxynitrido-silicate anion is shown in Fig. 1. In Fig. 2 a simplified packing is shown where the arrangement of Ca atoims in channels along <100> as well as the disordered arrangement along the <111> directions. 56 Ca atoms in each unit cell fills channels along <100> in the packing of the 12-ring anions while the rest of the Ca positions are located in channels along <111> and show tendencies to be disordered. The split positions of the Ca cations along the <111> can be viewed as a consequence of the implied Pa-3 symmetry. Whether the space group should better be P2₁3 or even P2₁2₁2₁ with cubic twinning is unfortunately not possible to determine, neither from systematic reflection conditions nor from investigations of the s.u. of the cell parameters. No One can refine orthorhombic unit-cell parameters but if one should beleive the e.s.d.'s is more of an open question. We choose to describe the structure with highest possible symmetry but at the price of some disorder. Similar arrangements of cations and ring formed anions are found in the structurally related compounds K₄SrGe₃O₉ and Na₄CaSi₃O₉ (Fischer & Tillmanns, 1984).

Experimental

The title compound was obtained by slow cooling of a melt with the nominal composition Ca_1.71Si₂O_1.71N_2.67 from 1700° C by 1° C / min in a graphite furnace.

Figures

Fig. 1.

The oxynitrido-silicate anion of the title compound (I) with the unique atoms of the oxynitrido-silicate anion labelled. Displacement ellipsoids drawn at 50% probability.

Fig. 2.

Stereoview of the unitcell viewed approximately along [100] with the oxynitrido-silicate anions marked with red colour and the Ca atoms ffwith blue colour. The disordered arrays of Ca atoms along the <111> shown by a solid rod.

Crystal data

Ca_2.89Si₂N_1.76O_4.24	D_x = 3.087 Mg m⁻³
M_r = 264.65	Mo Kα radiation, λ = 0.71073 Å
Cubic, Pa3	Cell parameters from 19622 reflections
Hall symbol: -P 2ac 2ab 3	θ = 3.8–32.2°
a = 15.0626 (1) Å	µ = 3.18 mm⁻¹
V = 3417.45 (4) Å³	T = 293 K
Z = 24	Block, colourless
F(000) = 3158	0.10 × 0.06 × 0.02 mm

Data collection

Oxford Diffraction XcaliburIII with Sapphire-3 CCD diffractometer	1982 independent reflections
Radiation source: fine-focus sealed tube	1779 reflections with I > 2s(I)
graphite	R_int = 0.027
Detector resolution: 16.5467 pixels mm^-1	θ_max = 32.3°, θ_min = 3.8°
ω scans at different	h = −22→18
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2008)	k = −18→21
T_min = 0.67, T_max = 0.94	l = −22→21
30793 measured reflections

Refinement

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.032	w = 1/[σ²(F_o²) + (0.026P)² + 5.7834P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.069	(Δ/σ)_max = 0.001
S = 1.22	Δρ_max = 0.87 e Å⁻³
1982 reflections	Δρ_min = −0.76 e Å⁻³
113 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00048 (5)

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 (Å²)

	x	y	z	U_iso*/U_eq	Occ. (<1)
Si1	0.00530 (3)	0.27221 (3)	0.76315 (3)	0.00633 (9)
Si2	0.01658 (3)	0.24358 (3)	0.98439 (3)	0.00567 (9)
N1	0.01861 (12)	0.37791 (11)	0.72676 (13)	0.0176 (3)	0.88
O1	0.01861 (12)	0.37791 (11)	0.72676 (13)	0.0176 (3)	0.12
N2	0.00891 (13)	0.26556 (13)	0.87435 (11)	0.0193 (4)	0.88
O2	0.00891 (13)	0.26556 (13)	0.87435 (11)	0.0193 (4)	0.12
O3	0.09048 (10)	0.21494 (9)	0.72534 (9)	0.0131 (3)
O4	−0.09065 (10)	0.23612 (10)	0.72964 (10)	0.0160 (3)
O5	−0.01845 (10)	0.33802 (10)	1.02719 (10)	0.0147 (3)
O6	−0.04423 (10)	0.15759 (10)	1.01040 (10)	0.0153 (3)
Ca1	−0.12893 (2)	0.37107 (2)	1.12893 (2)	0.01028 (12)
Ca2	−0.11371 (3)	0.38333 (3)	0.90382 (3)	0.01162 (8)
Ca3	0.13964 (3)	0.13071 (3)	0.85405 (3)	0.01601 (9)
Ca4	0.24330 (14)	0.25670 (14)	0.74330 (14)	0.0094 (6)*	0.1715 (6)
Ca5	0.1757 (2)	0.3243 (2)	0.6757 (2)	0.0094 (2)*	0.140 (2)
Ca6	0.15523 (5)	0.34477 (5)	0.65523 (5)	0.0094 (2)*	0.670 (3)
Ca7	0.1254 (9)	0.3746 (9)	0.6254 (9)	0.0094 (2)*	0.043 (3)
Ca8	0.1031 (7)	0.3969 (7)	0.6031 (7)	0.0094 (2)*	0.076 (2)
Ca9	0.0819 (5)	0.4181 (5)	0.5819 (5)	0.0094 (2)*	0.086 (3)
Ca10	0.0572 (3)	0.4428 (3)	0.5572 (3)	0.0094 (2)*	0.099 (2)
Ca11	0.0166 (4)	0.4834 (4)	0.5166 (4)	0.0094 (2)*	0.095 (3)
Ca12	0.0000	0.5000	0.5000	0.0094 (2)*	0.603 (6)

Atomic displacement parameters (Å²)

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Si1	0.0077 (2)	0.0061 (2)	0.0052 (2)	−0.00013 (16)	−0.00028 (15)	−0.00047 (15)
Si2	0.00564 (19)	0.0064 (2)	0.0049 (2)	0.00030 (16)	0.00068 (15)	−0.00020 (16)
N1	0.0206 (8)	0.0063 (7)	0.0260 (9)	0.0011 (6)	0.0043 (7)	0.0004 (6)
O1	0.0206 (8)	0.0063 (7)	0.0260 (9)	0.0011 (6)	0.0043 (7)	0.0004 (6)
N2	0.0240 (9)	0.0274 (9)	0.0066 (7)	−0.0007 (7)	0.0010 (6)	−0.0004 (6)
O2	0.0240 (9)	0.0274 (9)	0.0066 (7)	−0.0007 (7)	0.0010 (6)	−0.0004 (6)
O3	0.0149 (6)	0.0105 (6)	0.0140 (6)	0.0035 (5)	0.0042 (5)	−0.0008 (5)
O4	0.0150 (6)	0.0162 (7)	0.0169 (7)	−0.0055 (5)	−0.0065 (5)	0.0014 (5)
O5	0.0174 (7)	0.0124 (6)	0.0144 (6)	0.0057 (5)	−0.0035 (5)	−0.0062 (5)
O6	0.0157 (7)	0.0132 (6)	0.0170 (7)	−0.0063 (5)	0.0040 (5)	0.0008 (5)
Ca1	0.01028 (12)	0.01028 (12)	0.01028 (12)	−0.00048 (12)	0.00048 (12)	0.00048 (12)
Ca2	0.01262 (17)	0.00917 (16)	0.01306 (17)	0.00006 (12)	−0.00140 (13)	0.00004 (12)
Ca3	0.01781 (19)	0.01586 (19)	0.01435 (18)	0.00563 (14)	−0.00307 (14)	−0.00105 (14)

Geometric parameters (Å, °)

Si1—O4	1.6245 (15)	Si2—O6	1.6341 (15)
Si1—O3	1.6476 (14)	Si2—O5	1.6485 (15)
Si1—N2	1.6788 (18)	Si2—N1ⁱ	1.6899 (17)
Si1—N1	1.6958 (17)	Si2—N2	1.6942 (18)

O4—Si1—O3	114.22 (8)	O6—Si2—N1ⁱ	109.58 (9)
O4—Si1—N2	108.60 (9)	O5—Si2—N1ⁱ	108.13 (9)
O3—Si1—N2	106.76 (9)	O6—Si2—N2	110.56 (9)
O4—Si1—N1	108.59 (9)	O5—Si2—N2	101.08 (9)
O3—Si1—N1	106.72 (8)	O1ⁱ—Si2—N2	113.07 (9)
N2—Si1—N1	112.00 (10)	N1ⁱ—Si2—N2	113.07 (9)
O6—Si2—O5	114.26 (8)	Si2ⁱⁱ—N1—Si1	142.98 (12)
O6—Si2—O1ⁱ	109.58 (9)	Si1—N2—Si2	171.87 (14)
O5—Si2—O1ⁱ	108.13 (9)

N2—Si1—N1—Si2ⁱⁱ	−46.7 (2)

Symmetry codes: (i) −y+1/2, z−1/2, x+1; (ii) z−1, −x+1/2, y+1/2.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FJ2455).

References

Brandenburg, K. (2001). DIAMOND Crystal Impact GbR, Bonn, Germany.
Fischer, R. X. & Tillmanns, E. (1984). Z. Kristallogr. 166, 245–256.
Mondal, P. & Jeffery, J. W. (1975). Acta Cryst. B31, 689–697.
Oxford Diffraction. (2008). CrysAlis CCD and CrysAlis RED Oxford Diffraction Ltd, Abingdon, England.
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
Spek, A. L. (2009). Acta Cryst. D65, 148–155. [PMC free article] [PubMed]

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