Sr₃(Al_3+xSi_13−x)(N_21−xO_2+x):Eu²⁺ (x ∼ 0): a monoclinic modification of Sr-sialon

The structure of the title compound, Sr-bearing oxonitrido­aluminosilicate (Sr-sialon), contains two types of channels running along the a axis, with the three unique Sr atoms (coordinatioon number seven) residing in the larger one. The channels cross a three-dimensional Si–Al–O–N network, in which the Si and Al atoms are in a tetra­hedral coordination with N and O atoms. The chemical composition of the crystal is close to Sr₃Al₃Si₁₃N₂₁O₂ (tris­trontium trialuminium trideca­silicon henicosa­nitride dioxide), which can be expressed as a mixture of SrSiN₂, Si₃N₄, AlN, and SiO₂ components in the molar ratio 3:3:3:1. The crystal studied was metrically orthorhombic, consisting of four twin components related by metric merohedry.

Related literature

For the isotypic Eu-bearing oxonitridoaluminosilicate (Eu-sialon) Eu₃Al_3+xSi_13-xN_21-xO_2+x (x = 1/3), see: Michiue et al. (2009). For the closely related Sr-bearing sialon structure Sr₅Al_5+xSi_21-xN_35-xO_2+x:Eu²⁺ (x ∼ 0), see: Oeckler et al. (2009). For the twin analysis, see: Coch (2004); Nespolo (2004). Ionic radii were taken from Shannon (1976).

Experimental

Crystal data

• Sr₃Al₃Si₁₃N₂₁O₂

• M_r = 2081.94

• Monoclinic, P 112₁

• a = 14.7557 (5) Å

• b = 7.4627 (2) Å

• c = 9.0348 (3) Å

• β = 90°

• V = 994.89 (5) ų

• Z = 1

• Mo Kα radiation

• μ = 9.05 mm⁻¹

• T = 296 K

• 0.08 × 0.08 × 0.01 mm

Data collection

• Bruker APEXII CCD diffractometer

• Absorption correction: numerical (de Meulenaer & Tompa, 1965) T_min = 0.532, T_max = 0.915

• 11854 measured reflections

• 4384 independent reflections

• 3672 reflections with I > 2σ(I)

• R_int = 0.036

Refinement

• R[F² > 2σ(F²)] = 0.045

• wR(F²) = 0.105

• S = 1.07

• 4384 reflections

• 162 parameters

• 1 restraint

• Δρ_max = 1.33 e Å⁻³

• Δρ_min = −1.25 e Å⁻³

• Absolute structure: Flack (1983), 1942 Friedel pairs

• Flack parameter: 0.00

Table 1
Selected bond lengths (Å)

Sr1—N9	2.618 (13)
Sr1—N8	2.682 (13)
Sr1—N22	2.690 (16)
Sr1—N21	2.745 (14)
Sr1—N7	2.773 (9)
Sr1—N16	2.955 (10)
Sr1—N3	3.032 (10)
Sr2—N23^i	2.557 (11)
Sr2—O17^ii	2.573 (13)
Sr2—N21^iii	2.702 (14)
Sr2—N4^i	2.764 (14)
Sr2—N12^iv	2.868 (7)
Sr2—N10	2.970 (8)
Sr2—N15	3.052 (10)
Sr3—O19^i	2.549 (12)
Sr3—N22^v	2.718 (16)
Sr3—N2	2.760 (7)
Sr3—N11^ii	2.783 (13)
Sr3—N23^i	2.851 (11)
Sr3—N6^iv	2.994 (13)
Sr3—N1	3.096 (10)
Symmetry codes: (i) x, y+1, z; (ii) x, y+1, z+1; (iii) ; (iv) x, y, z+1; (v) .

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).

Supporting information

S1. Comment

The connectivity diagram of the asymmetric unit of structure is shown in Fig. 1. The Si and Al atoms are in tetrahedral coordination with N and O atoms, forming 'dreier' and 'sechser' ring layers, as shown in Fig. 2. These names follow the paper of Oeckler et al. (2009) on the Sr₅Al_5+xSi_21-xN_35-xO_2+x:Eu²⁺ (x~0) structure. The Si(Al) tetrahedra are corner-shared in the dreier ring layer whereas an edge of each tetrahedron is shared with the other in the sechser ring layer. The alternating stacking of the dreier and sechser ring layers perpendicular to the b axis provides two channels with different sizes, running straight along the a axis. The crystals were usually grown in platelets developing {010} crystal faces, suggesting a slower growth rate along the stacking direction of the dreier and sechser ring layers.

The Si(Al)1-10 sites and N(O)1-16 sites in the dreier ring layer are almost exclusively occupied by Si and N, respectively, within the experimental error. The mean bond distance of the Si tetrahedra in the dreier ring layer is 1.76 (2) Å which is close to 1.72 Å as expected from the sum of ionic radii of Si⁴⁺ adn N^3- (Shannon, 1976). The N(O)17-20 sites are located at the boundary of the dreier and sechser ring layers and occupied equally by N and O atoms. The Si(Al)11-14 sites in the sechser ring layers contain Si and Al atoms. The Si(Al)15 -16 and Si(Al)17 -18 split pair sites in the sechser ring layers are half filled with Si or Al. The N(O)21-23 sites are located in the sechser ring layer and occupied by N almost exclusively within the experimental error. All the Si(Al) tetrahedra in sechser ring layer have at least one long bond of circa 1.80 Å, suggesting a statistical presence of Al—N bonds of ca. 1.85 Å (Shannon, 1976). This geometrical feature supports the result of population analysis for the structure containing two different atoms with similar scattering powers for X-rays at the same site.

The geometry around the Si(Al)15-16 and Si(Al)17-18 split pairs in the sechser ring layer is shown in Fig. 3. The configuration varies depending upon the real location of Si(Al) atom at either site of the split pair. The N23 site bridges two Si(Al) atoms in tetrahedral coordination.

The Sr atoms reside in the larger channel coordinating to 7 N(O) atoms at distances less than 3.1 Å. The Eu atoms displace 4-6% Sr atoms at Sr(Eu)2-3 sites, whereas none at Sr(Eu)1 within the experimental error. Since Sr(Eu)2-3 sites enriches O around themselves, a possible coupling of the Eu and O distributions in the structure can be pointed out.

Oeckler et al. (2009) reported that the composition of their Sr-bearing sialon Sr₅Al_5+xSi_21-xN_35-xO_2+x:Eu²⁺ (x~0) can be expressed as '5551' , i.e., 5SrSiN₂+5AlN+5Si₃N₄+1SiO₂, when x=0. In this context, the composition of the present crystal, Sr₃(Al_3+xSi_13-x) (N_21-xO_2+x) :Eu²⁺ (x~0), corresponds to '6662'(='3331'), i. e., 6SrSiN₂+6Si₃N₄+6AlN+2SiO₂. The Eu analogue, Eu₃(Al_3+xSi_13-x) (N_21-xO_2+x) (x=1/3) (Michiue et al., 2009), is also close to 3331 where SrSiN₂ should read EuSiN₂.

The 5551 Sr-sialon has a commensurately modulated structure approximated by the orthorhombic Pmn2₁ symmetry (Oeckler et al., 2009). The unit cells of 5551 and 3331 Sr-sialons have similar b and c dimensions (~ 7.47 and ~9.04 Å, respectively), while they differ in a (~ 23.614 and ~14.756 Å, respectively). The two structures are considered as 8 and 5 times superstructure regarding the underlying parent structure with a_o =2.954 Å (Oeckler et al. 2009), respectively. Actually, the ratio in a-length is 23.614/14.756 ~1.600 (=8/5), and the ratio in cell volume is 1602/995 ~1.610 (~ 8/5). If we apply this 8/5 rule to the composition, the 3331 compound can be expressed as Sr_4.8(Al,Si)_25.6(N,O)_36.8 with respect to Sr₅(Al,Si)₂₆(N,O)₃₇ of 5551. The ca. 4 at% relative deficiency of Sr in 3331 expressed as such is conspicuous compared with those of the other constituent atoms, providing an insight into a possible modulation mechanism in these structures.

The relative Sr-deficiency is a measure of Sr concentration per unit volume. Since the b and c lengths are approximately the same in 3331 and 5551, the Sr concentration per volume is reduced to that per length along the channel in which the Sr atoms reside. The mean Sr—Sr distances in 3331 and 5551 are 4.919 Å (=a₃₃₃₁/3=5a_o/3) and 4.723 Å (=a₅₅₅₁/5=8a_o/5) along the channel, respectively. The superimposed figure, as shown in Fig. 4, indicates that the Sr atoms faintly slip out of position as they depart further from a reference point on one of the two-fold screw axes. In another point of view, compounds 3331 and 5551 have 24 and 25 Sr atoms, respectively, in a single channel spanning 40a_o. This one Sr-atom difference in number for every ~118 Å span along the Sr channel is an essential point that characterizes the structural difference between 3331 and 5551.

The 3331 and 5551 Sr-sialons have a structural similarity in the skeleton surrounding the Sr channels. The ADP ellipsoids of Sr in 3331 and 5551 compounds show a very large component along a, with the ratio of the largest/ smallest principal ADP components being close to 10, as shown in Figs. 1, 3 and 4. This extraordinary large anisotropy may suggest a possible occurrence of displacive modulation of the slippery Sr atoms along the channel. In the 5551 compound, this modulation has been evidenced in the diffuse scattering of commensurately modulated satellites along a (Oeckler et al., 2009). On the other hand, many small crystal fragments picked up from the 3331 batch in the present study did not show any such diffuse nature. This could partly owe to the higher firing temperature of 2173 K to which the present 3331 batch was subjected.

The present analysis on the 3331 Sr-sialon was carried out independently and in a different approach against the study on the 3331 Eu-sialon by Michiue et al., (2009). Although these 3331 sialons were finally found to have similar structures, a complicated microstructure like twins in crystals of Sr-sialon should be noted, as given in Refinement. This may suggest a presence of microstress in channels, which can be introduced by the replacement of Eu with Sr having a slightly larger ionic radius.

Related literature

For the isotypic Eu-bearing oxonitridoaluminosilicate (Eu-sialon) Eu₃Al_3+xSi_13-xN_21-xO_2+x (x = 1/3), see: Michiue et al. (2009). For the closely related Sr-bearing sialon structure Sr₅Al_5+xSi_21-xN_35-xO_2+x:Eu²⁺ (x ~0), see: Oeckler et al. (2009). For the twin analysis, see: Coch (2004); Nespolo (2004). Ionic radii were taken from Shannon (1976).

S2. Experimental

The powder sample with a starting composition of Sr₆Si₂₇Al₆O₆N₄₂ was prepared from α-Si₃N₄ (SN—E10, Ube Industries Ltd.), SrO (Kojyundo Chemical Laboratory Co., Ltd.), and AlN (Type F, Tokuyama Co., Ltd.). The mixture was ground in the Si₃N₄ mortar and pestle. The powder sample was filled in h-BN crucible and fired in a graphite resistance furnace at 2173 K for 24 hours under 1 MPa nitrogen atmosphere. The chemical composition was not analyzed on this batch, but done on another Eu-doped (3.0 at%) batch using EPMA, resulting in Sr_5.82Eu_0.18Al_6.67Si_26.77N_41.50O_4.11. This composition can be rewritten as (Sr,Eu)₃(Al_3+xSi_13-x)(N_21-xO_2+x) (x~0.06±0.32). A small amount of Eu was also detected from the X-ray diffraction analysis for the crystals sampled from the batch in which no Eu was included as starting components. This probably came from a contamination from the furnace or the crucible.

S3. Refinement

The reciprocal sections synthesized from the frame data indicated no significant diffuse scattering for any reflections. Several very weak reflections were found not coincident at the lattice points expected for the present structure. They were neglected because their locations differed from sample to sample. No significant departure from the metrical orthrhombicity was detected from the laboratory source and the synchrotron X-ray experiments. The Laue symmetry was well approximated by mmm. However, all trials of structure solution assuming the orthorhombic space groups were unsuccessful or only revealed that almost all the atom sites except for Sr should assume the split atom model. The best R1 factor was 0.11 for P2₁22₁.

The possibility of orthorhombic-mimicking monoclinic structure was then examined. From the systematic absence of reflections, possible space groups were limited to the noncentrosymmetric P112₁ and centrosymmetric P112₁/m. The latter was discarded in the course of solving structures. The refinement of the P112₁ model assuming a single component in the crystal gave R1=0.0635 for 4384 reflections. A possible existence of twin components was suspected from a high K factor, defined as Mean[F_o²]/Mean[F_c²], of 2.6 in the region F_c/F_c(max) <0.033.

The point group of the crystal is 112 which is a merohedry in monoclinic crystal system. The symmetry element for the inversion twin is m' of the monoclinic holohedry, 112'/m'. In addition, since the crystal lattice is metrically orthorhombic, 'double twinning' can take place in which 'twin by merohedry' and 'twin by metric merohedry' occur at the same time (Coch, 2004; Nespolo, 2004). In the twin by metric merohedry, the twin element can be chosen from the symmetry elements of the orthorhombic holohedry, 2"/m"2"/m"2"/m". Possible combinations are categorized into five groups, (1) 112 (no twin), (2) 112/m' (inversion twin by merohedry), (3) m"12, 1m"2, and m"m"2 (reflection twin by metric merohedry), (4) 2"12, 12"2, and 2"2"2 (rotation twin by metric merohedry), and (5) m"2"2, 2"/m"12, 2"/m"2"/m"2, 2"12/m', 1m"2/m', and 2"/m"2"/m"2/m' (twin by double merohedry), each of which contains the same set of equivalent points. All these groups were examined through the least-squares procedure. The R1 factors are 0.0635 for group 1, 0.595 for group 2, 0.0481 for group 3, 0.475 for group 4, and 0.0447 for group 5. The double merohedry model (group 5) was finally adopted from comparing R1 factors, residual electrons, and K factors. The K factor improved significantly to 0.98 which is close to the ideal value of 1. The refined volume fractions of the individual twin components assuming 2"12/m' in the crystal are 28 (1)%, 22 (1)%, 21 (1)%, and 29 (1)%, where the second individual is related to the first by the two–fold rotation about a, and the third and forth are the inversions of the first and second, respectively.

Anisotropic ADPs for Sr(Eu) and isotropic ones for the other atoms were employed in the refinement. It was difficult to refine ADPs of all crystallographically independent Al(Si) and N(O) atom sites simultaneously, mainly due to insufficient high-angle diffraction data. As mentioned in Comment, the structure is composed of the dreier and sechser ring layers. The dreier ring layer is mainly composed of Si and N, while the sechser ring layers enriches Al and O at Si(Al) and N(O) sites, respectively, presenting more ionic bonding nature. It is also noted that the sechser ring layer contains Si(Al)15-16 and Si(Al)17-18 split atom pair sites with 50% population. Therefore the Al and Si atoms were classified into three groups each of which has similar circumstance in view of the structural-chemistry: (a) Si(Al)1 through Si(Al)10 in the dreier ring layer, having a tetrahedral coordination to N(O), (b) Si(Al)11 thorough Si(Al)14 in the sechser ring layer, and (c) Si(Al)15 through Si(Al)18 split pairs in the sechser ring layer. In a similar way, the N and O atoms are classified into (d) N(O)1 through N(O)16 with distorted planer 3-fold coordination in the dreier ring layer, (e) N(O)17 through N(O)20 with distorted planer 3-fold coordination in the sechser ring layer, and (f) N(O)21 through N(O)23 with distorted linear coordination with Si(Al) in the sechser ring layer and additional coordination to two Sr(Eu) atoms in the channel. The same ADP and the same population were assumed for Si(Al) atom sites belonging to the same group. Similar constraints were assumed for the N(O) atom sites. Preliminary population analysis suggested no Al in group (a), and no O in groups (d) and (f) within experimental errors. The other sites in groups (b), (c) and (e) were supposed to be almost equally occupied by the two atoms. To reduce ambiguities, fixed population numbers were assumed in the final stage of refinements except for Sr(Eu)2 and Sr(Eu)3. These constraints led the composition of the crystal to (Sr,Eu)₃(Al_3+xSi_13-x)(N_21-xO_2+x) with x=0, which agreed with the EPMA analysis on a compound synthesized in similar conditions as mentioned in Experimental.

Computing details

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS (Dowty, 2008); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. The asymmetric unit of the structure ; the displacement ellipsoids are plotted at the 80% probability level.
	Fig. 2. Drawings of the structure featuring alternate stacking of the dreier and sechser ring layers. The Si1—Si10 tetrahedra in the dreier ring layer are colored in dark blue, while the edge-sharing Si(Al)11-14 and Si(Al)l15-18 tetrahedra in the sechser ring layer are colored in pale blue and green, respectively. Sr (red) are located in the larger channels formed in the Si—Al—O—N skeleton.
	Fig. 3. Local structure around the Si(Al)15-16 and Si(Al)17-18 split pairs in the sechser ring layer (top), and one of the possible conformations (bottom). The shared edge of tetrahedra is shown in dashed line in the bottom figure.
	Fig. 4. Comparison between the '3331' P1121 (top) and '5551' Pmn21 (bottom) structures projected along the b axis. Superposition of 3331 (blue) onto 5551 is shown in the middle where the screw axis at x=0 in 3331 overlaps with that at x=0.25 in 5551.

tristrontium trialuminium tridecasilicon henicosanitride dioxide

Crystal data

Sr3Al3Si13N21O2	F(000) = 1001.0
Mr = 2081.94	Dx = 3.475 Mg m^−3
Monoclinic, P1121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c	Cell parameters from 3169 reflections
a = 14.7557 (5) Å	θ = 4.5–35.7°
b = 7.4627 (2) Å	µ = 9.05 mm^−1
c = 9.0348 (3) Å	T = 296 K
β = 90°	Plate, light yellow
V = 994.89 (5) Å^3	0.08 × 0.08 × 0.01 mm
Z = 1

Data collection

Bruker APEXII CCD diffractometer	4384 independent reflections
Radiation source: fine-focus sealed tube	3672 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.036
φ and ω scans	θmax = 27.5°, θmin = 1.4°
Absorption correction: numerical (Meulenaer & Tompa, 1965)	h = −18→19
Tmin = 0.532, Tmax = 0.915	k = −9→9
11854 measured reflections	l = −11→11

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.045	w = 1/[σ^2(Fo^2) + (0.0316P)^2 + 7.9067P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.105	(Δ/σ)max < 0.001
S = 1.07	Δρmax = 1.33 e Å^−3
4384 reflections	Δρmin = −1.25 e Å^−3
162 parameters	Absolute structure: Flack (1983), 1942 Friedel pairs
1 restraint	Absolute structure parameter: 0.00

Special details

Geometry. Atom labels of Al and O are used for the Si(Al) and N(O) mixed sites, respectively, to distinguish them from the pure Si and N sites in Geometric parameters. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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	Occ. (<1)
Sr1	0.7496 (2)	0.7488 (2)	0.5178 (4)	0.0275 (3)
Sr2	0.91735 (19)	1.2554 (2)	1.00147 (13)	0.0361 (8)	0.943 (11)
Eu2	0.91735 (19)	1.2554 (2)	1.00147 (13)	0.0361 (8)	0.057 (11)
Sr3	0.58236 (18)	1.2652 (2)	1.03237 (15)	0.0390 (8)	0.963 (11)
Eu3	0.58236 (18)	1.2652 (2)	1.03237 (15)	0.0390 (8)	0.037 (11)
Si1	0.9992 (3)	0.1230 (6)	0.6686 (5)	0.00785 (14)*
Si2	0.8011 (3)	1.1316 (6)	0.6707 (4)	0.00785 (14)*
Si3	0.5002 (3)	0.8635 (5)	0.8784 (5)	0.00785 (14)*
Si4	0.6000 (3)	1.1307 (4)	0.6782 (4)	0.00785 (14)*
Si5	0.6989 (3)	0.8634 (6)	0.8770 (4)	0.00785 (14)*
Si6	0.8019 (3)	0.8726 (6)	0.1733 (5)	0.00785 (14)*
Si7	0.6983 (3)	1.1443 (5)	0.3783 (4)	0.00785 (14)*
Si8	0.6021 (3)	0.8640 (4)	1.1774 (3)	0.00785 (14)*
Si9	0.8979 (3)	1.1420 (4)	0.3693 (4)	0.00785 (14)*
Si10	0.8997 (3)	0.8467 (4)	0.8744 (3)	0.00785 (14)*
Si11	0.9081 (4)	0.4859 (5)	0.6769 (4)	0.0089 (2)*	0.50
Al11	0.9081 (4)	0.4859 (5)	0.6769 (4)	0.0089 (2)*	0.50
Si12	0.9111 (3)	0.5575 (5)	0.3255 (4)	0.0089 (2)*	0.50
Al12	0.9111 (3)	0.5575 (5)	0.3255 (4)	0.0089 (2)*	0.50
Si13	0.5914 (3)	0.4893 (5)	0.3518 (4)	0.0089 (2)*	0.50
Al13	0.5914 (3)	0.4893 (5)	0.3518 (4)	0.0089 (2)*	0.50
Si14	0.5930 (4)	0.5559 (5)	0.7048 (4)	0.0089 (2)*	0.50
Al14	0.5930 (4)	0.5559 (5)	0.7048 (4)	0.0089 (2)*	0.50
Si15	0.7794 (5)	0.5102 (12)	0.8496 (9)	0.0031 (4)*	0.25
Al15	0.7794 (5)	0.5102 (12)	0.8496 (9)	0.0031 (4)*	0.25
Si16	0.7174 (5)	0.4400 (10)	0.8280 (8)	0.0031 (4)*	0.25
Al16	0.7174 (5)	0.4400 (10)	0.8280 (8)	0.0031 (4)*	0.25
Si17	0.7759 (5)	0.4455 (10)	0.1969 (8)	0.0031 (4)*	0.25
Al17	0.7759 (5)	0.4455 (10)	0.1969 (8)	0.0031 (4)*	0.25
Si18	0.7234 (5)	0.5127 (11)	0.1785 (9)	0.0031 (4)*	0.25
Al18	0.7234 (5)	0.5127 (11)	0.1785 (9)	0.0031 (4)*	0.25
N1	0.5017 (7)	0.9760 (14)	1.2397 (11)	0.0108 (3)*
N2	0.6002 (7)	0.9021 (10)	0.9819 (9)	0.0108 (3)*
N3	0.7020 (7)	0.9704 (14)	0.2475 (11)	0.0108 (3)*
N4	1.0012 (10)	0.3442 (18)	0.7379 (15)	0.0108 (3)*
N5	0.8092 (8)	1.3587 (16)	0.7131 (11)	0.0108 (3)*
N6	0.6873 (9)	1.3573 (19)	0.3056 (15)	0.0108 (3)*
N7	0.7989 (7)	1.1040 (13)	0.4784 (12)	0.0108 (3)*
N8	0.8076 (9)	0.6538 (19)	0.2477 (15)	0.0108 (3)*
N9	0.6904 (9)	0.6535 (18)	0.7795 (13)	0.0108 (3)*
N10	0.9000 (8)	1.0199 (10)	0.7380 (8)	0.0108 (3)*
N11	0.5017 (9)	0.3505 (18)	0.3017 (15)	0.0108 (3)*
N12	0.9011 (8)	0.9851 (10)	0.2255 (8)	0.0108 (3)*
N13	0.7984 (7)	0.8789 (13)	0.9806 (12)	0.0108 (3)*
N14	0.5986 (8)	1.1229 (10)	0.4854 (8)	0.0108 (3)*
N15	1.0006 (7)	0.8822 (13)	0.9770 (12)	0.0108 (3)*
N16	0.7037 (7)	1.0287 (13)	0.7367 (11)	0.0108 (3)*
N17	0.8937 (9)	0.3424 (17)	0.2743 (14)	0.0198 (8)*	0.50
O17	0.8937 (9)	0.3424 (17)	0.2743 (14)	0.0198 (8)*	0.50
N18	0.6009 (8)	0.6407 (13)	0.2163 (12)	0.0198 (8)*	0.50
O18	0.6009 (8)	0.6407 (13)	0.2163 (12)	0.0198 (8)*	0.50
N19	0.6054 (9)	0.3427 (16)	0.7602 (14)	0.0198 (8)*	0.50
O19	0.6054 (9)	0.3427 (16)	0.7602 (14)	0.0198 (8)*	0.50
N20	0.8832 (7)	0.6333 (16)	0.8160 (15)	0.0198 (8)*	0.50
O20	0.8832 (7)	0.6333 (16)	0.8160 (15)	0.0198 (8)*	0.50
N21	0.9172 (10)	0.5896 (13)	0.5118 (15)	0.0170 (7)*
N22	0.5862 (11)	0.5887 (12)	0.5222 (15)	0.0170 (7)*
N23	0.7617 (8)	0.4054 (11)	1.0138 (16)	0.0170 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sr1	0.0449 (6)	0.0107 (4)	0.0270 (6)	−0.0073 (12)	0.0216 (5)	−0.0071 (9)
Sr2	0.0732 (18)	0.0225 (7)	0.0126 (7)	−0.0157 (15)	0.0099 (9)	−0.0044 (5)
Eu2	0.0732 (18)	0.0225 (7)	0.0126 (7)	−0.0157 (15)	0.0099 (9)	−0.0044 (5)
Sr3	0.0664 (17)	0.0363 (11)	0.0143 (8)	0.0289 (14)	0.0104 (9)	−0.0003 (6)
Eu3	0.0664 (17)	0.0363 (11)	0.0143 (8)	0.0289 (14)	0.0104 (9)	−0.0003 (6)

Geometric parameters (Å, º)

Sr1—N9	2.618 (13)	Si7—N7	1.764 (11)
Sr1—N8	2.682 (13)	Si7—N14	1.769 (11)
Sr1—N22	2.690 (16)	Si8—O18^iv	1.703 (10)
Sr1—N21	2.745 (14)	Si8—N3^iv	1.789 (11)
Sr1—N7	2.773 (9)	Si8—N2	1.789 (8)
Sr1—N16	2.955 (10)	Si8—N1	1.792 (11)
Sr1—N3	3.032 (10)	Si9—O17^i	1.725 (13)
Sr2—N23^i	2.557 (11)	Si9—N12	1.749 (8)
Sr2—O17^ii	2.573 (13)	Si9—N7	1.784 (11)
Sr2—N21^iii	2.702 (14)	Si9—N15^xii	1.795 (11)
Sr2—N4^i	2.764 (14)	Si10—O20	1.696 (13)
Sr2—N12^iv	2.868 (7)	Si10—N15	1.775 (11)
Sr2—N10	2.970 (8)	Si10—N10	1.786 (8)
Sr2—N15	3.052 (10)	Si10—N13	1.792 (11)
Sr3—O19^i	2.549 (12)	Al11—N21	1.687 (13)
Sr3—N22^v	2.718 (16)	Al11—O20	1.710 (14)
Sr3—N2	2.760 (7)	Al11—N5^viii	1.771 (12)
Sr3—N11^ii	2.783 (13)	Al11—N4	1.819 (14)
Sr3—N23^i	2.851 (11)	Al12—N4^vi	1.685 (15)
Sr3—N6^iv	2.994 (13)	Al12—O17	1.690 (13)
Sr3—N1	3.096 (10)	Al12—N21	1.702 (14)
Si1—N15^vi	1.732 (12)	Al12—N8	1.829 (14)
Si1—N12^vii	1.755 (12)	Al13—O18	1.672 (11)
Si1—N4	1.765 (14)	Al13—N22	1.711 (13)
Si1—N10^viii	1.769 (11)	Al13—N11	1.740 (14)
Si2—N16	1.734 (11)	Al13—N6^viii	1.773 (14)
Si2—N5	1.742 (13)	Al14—N22	1.671 (14)
Si2—N7	1.750 (12)	Al14—O19	1.678 (12)
Si2—N10	1.787 (11)	Al14—N9	1.747 (14)
Si3—N1^ix	1.734 (11)	Al14—N11^x	1.791 (15)
Si3—N11^x	1.741 (15)	Al15—N23	1.697 (15)
Si3—N14^v	1.752 (11)	Al15—N5^viii	1.730 (14)
Si3—N2	1.770 (11)	Al15—N9	1.807 (16)
Si4—N14	1.743 (8)	Al15—O20	1.811 (13)
Si4—O19^i	1.749 (13)	Al16—N9	1.700 (15)
Si4—N1^ix	1.788 (12)	Al16—N5^viii	1.811 (14)
Si4—N16	1.789 (12)	Al16—N23	1.820 (15)
Si5—N13	1.745 (11)	Al16—O19	1.906 (15)
Si5—N2	1.762 (11)	Al17—N8	1.687 (16)
Si5—N16	1.770 (11)	Al17—N23^xi	1.694 (16)
Si5—N9	1.802 (14)	Al17—N6^viii	1.762 (15)
Si6—N13^xi	1.742 (12)	Al17—O17	2.026 (15)
Si6—N12	1.752 (12)	Al18—N6^viii	1.716 (16)
Si6—N8	1.768 (15)	Al18—N8	1.745 (16)
Si6—N3	1.777 (11)	Al18—N23^xi	1.783 (15)
Si7—N6	1.728 (15)	Al18—O18	2.072 (14)
Si7—N3	1.756 (11)
N15^vi—Si1—N12^vii	106.4 (5)	O20—Si10—N15	115.0 (5)
N15^vi—Si1—N4	112.0 (6)	O20—Si10—N10	117.7 (6)
N12^vii—Si1—N4	108.2 (6)	N15—Si10—N10	104.5 (5)
N15^vi—Si1—N10^viii	110.2 (5)	O20—Si10—N13	100.0 (6)
N12^vii—Si1—N10^viii	113.0 (4)	N15—Si10—N13	113.6 (4)
N4—Si1—N10^viii	107.1 (6)	N10—Si10—N13	106.0 (5)
N16—Si2—N5	114.3 (6)	N21—Al11—O20	111.8 (6)
N16—Si2—N7	105.9 (5)	N21—Al11—N5^viii	118.4 (6)
N5—Si2—N7	109.5 (5)	O20—Al11—N5^viii	91.8 (6)
N16—Si2—N10	110.7 (5)	N21—Al11—N4	118.3 (7)
N5—Si2—N10	108.8 (5)	O20—Al11—N4	108.3 (6)
N7—Si2—N10	107.3 (5)	N5^viii—Al11—N4	104.8 (6)
N1^ix—Si3—N11^x	110.2 (6)	N4^vi—Al12—O17	113.7 (7)
N1^ix—Si3—N14^v	110.2 (5)	N4^vi—Al12—N21	111.3 (7)
N11^x—Si3—N14^v	105.0 (6)	O17—Al12—N21	114.4 (6)
N1^ix—Si3—N2	106.4 (5)	N4^vi—Al12—N8	106.8 (6)
N11^x—Si3—N2	112.0 (6)	O17—Al12—N8	98.1 (7)
N14^v—Si3—N2	113.1 (4)	N21—Al12—N8	111.7 (6)
N14—Si4—O19^i	117.0 (5)	O18—Al13—N22	111.7 (5)
N14—Si4—N1^ix	106.6 (5)	O18—Al13—N11	106.0 (6)
O19^i—Si4—N1^ix	108.0 (6)	N22—Al13—N11	117.3 (7)
N14—Si4—N16	107.0 (5)	O18—Al13—N6^viii	97.8 (7)
O19^i—Si4—N16	102.8 (6)	N22—Al13—N6^viii	119.2 (7)
N1^ix—Si4—N16	115.9 (4)	N11—Al13—N6^viii	102.4 (5)
N13—Si5—N2	113.3 (5)	N22—Al14—O19	116.1 (6)
N13—Si5—N16	107.7 (5)	N22—Al14—N9	111.7 (7)
N2—Si5—N16	107.7 (5)	O19—Al14—N9	101.0 (7)
N13—Si5—N9	112.2 (6)	N22—Al14—N11^x	112.3 (7)
N2—Si5—N9	110.4 (6)	O19—Al14—N11^x	108.0 (7)
N16—Si5—N9	105.0 (5)	N9—Al14—N11^x	106.9 (6)
N13^xi—Si6—N12	106.4 (5)	N23—Al15—N5^viii	111.2 (7)
N13^xi—Si6—N8	114.0 (6)	N23—Al15—N9	117.9 (7)
N12—Si6—N8	107.5 (6)	N5^viii—Al15—N9	108.8 (7)
N13^xi—Si6—N3	109.9 (5)	N23—Al15—O20	120.7 (7)
N12—Si6—N3	113.3 (5)	N5^viii—Al15—O20	89.8 (7)
N8—Si6—N3	106.0 (6)	N9—Al15—O20	104.8 (7)
N6—Si7—N3	115.2 (6)	N9—Al16—N5^viii	109.9 (7)
N6—Si7—N7	115.5 (6)	N9—Al16—N23	117.1 (6)
N3—Si7—N7	101.2 (5)	N5^viii—Al16—N23	102.3 (6)
N6—Si7—N14	102.3 (5)	N9—Al16—O19	94.1 (6)
N3—Si7—N14	109.1 (4)	N5^viii—Al16—O19	109.7 (6)
N7—Si7—N14	113.9 (5)	N23—Al16—O19	123.7 (6)
O18^iv—Si8—N3^iv	111.7 (6)	N8—Al17—N23^xi	117.6 (7)
O18^iv—Si8—N2	111.1 (5)	N8—Al17—N6^viii	113.5 (8)
N3^iv—Si8—N2	107.0 (5)	N23^xi—Al17—N6^viii	112.7 (7)
O18^iv—Si8—N1	112.5 (6)	N8—Al17—O17	91.0 (7)
N3^iv—Si8—N1	111.3 (4)	N23^xi—Al17—O17	112.1 (7)
N2—Si8—N1	102.8 (5)	N6^viii—Al17—O17	107.6 (7)
O17^i—Si9—N12	102.2 (5)	N6^viii—Al18—N8	112.9 (8)
O17^i—Si9—N7	112.5 (6)	N6^viii—Al18—N23^xi	110.7 (7)
N12—Si9—N7	109.0 (5)	N8—Al18—N23^xi	110.1 (7)
O17^i—Si9—N15^xii	112.8 (6)	N6^viii—Al18—O18	86.0 (6)
N12—Si9—N15^xii	108.2 (5)	N8—Al18—O18	106.5 (7)
N7—Si9—N15^xii	111.6 (4)	N23^xi—Al18—O18	128.4 (7)

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