Crystal structure of bis­(azido-κN)bis­[2,5-bis­(pyridin-2-yl)-1,3,4-thia­diazole-κ2N2,N3]nickel(II)

Laachir, A.; Bentiss, F.; Guesmi, S.; Saadi, M.; El Ammari, L.

doi:10.1107/S2056989015000201

metal-organic compounds

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ISSN: 2056-9890

Volume 71| Part 2| February 2015| Pages m24-m25

doi:10.1107/S2056989015000201

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Crystal structure of bis(azido-κN)bis[2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole-κ²N²,N³]nickel(II)

Abdelhakim Laachir,^a Fouad Bentiss,^b ^* Salaheddine Guesmi,^a Mohamed Saadi ^c and Lahcen El Ammari ^c

^aLaboratoire de Chimie de Coordination et d'Analytique (LCCA), Faculté des Sciences, Université Chouaib Doukkali, BP 20, M-24000 El Jadida, Morocco, ^bLaboratoire de Catalyse et de Corrosion de Matériaux (LCCM), Faculté des Sciences, Université Chouaib Doukkali, BP 20, M-24000 El Jadida, Morocco, and ^cLaboratoire de Chimie du Solide Appliquée, Faculté des Sciences, Université Mohammed V, Avenue Ibn Battouta, BP 1014, Rabat, Morocco
^*Correspondence e-mail: f_bentiss@yahoo.fr

Edited by M. Weil, Vienna University of Technology, Austria (Received 18 December 2014; accepted 6 January 2015; online 14 January 2015)

Reaction of 2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole and sodium azide with nickel(II) triflate yielded the mononuclear title complex, [Ni(N₃)₂(C₁₂H₈N₄S)₂]. The Ni^II ion is located on a centre of symmetry and is octahedrally coordinated by four N atoms of the two bidentate heterocyclic ligands in the equatorial plane. The axial positions are occupied by the N atoms of two almost linear azide ions [N—N—N = 178.8 (2)°]. The thiadiazole and pyridine rings of the heterocyclic ligand are almost coplanar, with a maximum deviation from the mean plane of 0.0802 (9) Å. The cohesion of the crystal structure is ensured by π–π interactions between parallel pyridine rings of neighbouring molecules [centroid-to-centroid distance = 3.6413 (14) Å], leading to a layered arrangement of the molecules parallel to (001).

Keywords: crystal structure; mononuclear nickel(II) complex; 1,3,4-thiadiazole; azide ligand; π–π interactions.

CCDC reference: 1042351

1. Related literature

2,5-Bis(pyridin-2-yl)-1,3,4-thiadiazole has been used as a bidentate or tetradentate ligand forming mononuclear (Bentiss et al., 2004 , 2011a , 2012 ; Zheng et al., 2006 ) or dinuclear complexes (Laachir et al., 2013 ). Coordination of the azide ion to transition metals results in compounds with interesting magnetic properties (Machura et al., 2011 ; Świtlicka-Olszewska et al., 2014 ). The iron salt with the same heterocyclic ligand and thiocyanate as the pseudohalide was reported by Klingele et al. (2010 ). For the crystal structure of the related tetrafluoridoborate salt of [Ni(C₁₂H₈N₄S)₂(H₂O)₂], see: Bentiss et al. (2011b ). For the synthesis of the heterocyclic ligand, see: Lebrini et al. (2005 ).

2. Experimental

2.1. Crystal data

[Ni(N₃)₂(C₁₂H₈N₄S)₂]
M_r = 623.34
Monoclinic, P 2₁ /c
a = 7.7981 (3) Å
b = 8.2410 (3) Å
c = 20.1555 (7) Å
β = 93.141 (2)°
V = 1293.33 (8) Å³
Z = 2
Mo Kα radiation
μ = 0.96 mm⁻¹
T = 296 K
0.39 × 0.31 × 0.18 mm

2.2. Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ) T_min = 0.640, T_max = 0.747
15710 measured reflections
3077 independent reflections
2643 reflections with I > 2σ(I)
R_int = 0.033

2.3. Refinement

R[F² > 2σ(F²)] = 0.036
wR(F²) = 0.100
S = 1.04
3077 reflections
187 parameters
H-atom parameters constrained
Δρ_max = 1.25 e Å⁻³
Δρ_min = −0.35 e Å⁻³

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012 ); software used to prepare material for publication: WinGX (Farrugia, 2012).

Supporting information

CCDC reference: 1042351

Crystal structure: contains datablock I. DOI: 10.1107/S2056989015000201/wm5108sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S2056989015000201/wm5108Isup2.hkl

checkCIF report

Related literature top

2,5-Bis(pyridin-2-yl)-1,3,4-thiadiazole has been used as a bidentate or tetradentate ligand forming mononuclear (Bentiss et al., 2004, 2011a, 2012; Zheng et al., 2006) or dinuclear complexes (Laachir et al., 2013). Coordination of the azide ion to transition metals results in compounds with interesting magnetic properties (Machura et al., 2011; Świtlicka-Olszewska et al., 2014). The iron salt with the same heterocyclic ligand and thiocyanate as the pseudohalide was reported by Klingele et al. (2010). For the crystal structure of the related tetrafluoridoborate salt of [Ni(C₁₂H₈N₄S)₂(H₂O)₂], see: Bentiss et al. (2011b). For the synthesis of the heterocyclic ligand, see: Lebrini et al. (2005).

Experimental top

The 2,5-bis(2-pyridyl)-1,3,4-thiadiazole ligand (noted L) was synthesized as described previously by Lebrini et al. (2005). Ni₂L₂(N₃)₂ was obtained in bulk quantity by dropwise addition of an aqueous solution of NaN₃ (0.4 mmol, 26 mg) to an ethanol/water solution of L (0.1 mmol, 24 mg) and Ni(O₃SCF₃)₂ (0.1 mmol, 36 mg) under constant stirring at room temperature. An orange coloured solid was precipitated, filtered and washed with cold ethanol. Single crystals of Ni₂L₂(N₃)₂ were grown by slow interdiffusion of a solution of Ni(O₃SCF₃)₂ and L in acetonitrile into NaN₃ dissolved in water. Orange block-shaped single crystals appeared after one month. The crystals were washed with water and dried under vacuum (yield 50%).

CAUTION. Azide compounds are potentially explosive. Only a small amount of material should be prepared and handled with care.

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

Figures top

	Fig. 1. The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented as spheres of arbitrary radius. [Symmetry code: (i) -x + 2, -y + 1, -z + 2.]
	Fig. 2. The crystal packing of the title compound, showing intermolecular π–π interactions between pyridyl rings (dashed green lines).

Bis(azido-κN)bis[2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole-κ²N²,N³]nickel(II) top

Crystal data top

[Ni(N₃)₂(C₁₂H₈N₄S)₂]	F(000) = 636
M_r = 623.34	D_x = 1.601 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3077 reflections
a = 7.7981 (3) Å	θ = 2.6–27.9°
b = 8.2410 (3) Å	µ = 0.96 mm⁻¹
c = 20.1555 (7) Å	T = 296 K
β = 93.141 (2)°	Block, orange
V = 1293.33 (8) Å³	0.39 × 0.31 × 0.18 mm
Z = 2

Data collection top

Bruker APEXII CCD diffractometer	3077 independent reflections
Radiation source: fine-focus sealed tube	2643 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.033
ϕ and ω scans	θ_max = 27.9°, θ_min = 2.6°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −10→9
T_min = 0.640, T_max = 0.747	k = −10→10
15710 measured reflections	l = −26→26

Refinement top

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)] = 0.036	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.100	H-atom parameters constrained
S = 1.04	w = 1/[σ²(F_o²) + (0.0522P)² + 0.8063P] where P = (F_o² + 2F_c²)/3
3077 reflections	(Δ/σ)_max < 0.001
187 parameters	Δρ_max = 1.25 e Å⁻³
0 restraints	Δρ_min = −0.35 e Å⁻³

Crystal data top

[Ni(N₃)₂(C₁₂H₈N₄S)₂]	V = 1293.33 (8) Å³
M_r = 623.34	Z = 2
Monoclinic, P2₁/c	Mo Kα radiation
a = 7.7981 (3) Å	µ = 0.96 mm⁻¹
b = 8.2410 (3) Å	T = 296 K
c = 20.1555 (7) Å	0.39 × 0.31 × 0.18 mm
β = 93.141 (2)°

Data collection top

Bruker APEXII CCD diffractometer	3077 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2009)	2643 reflections with I > 2σ(I)
T_min = 0.640, T_max = 0.747	R_int = 0.033
15710 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.036	0 restraints
wR(F²) = 0.100	H-atom parameters constrained
S = 1.04	Δρ_max = 1.25 e Å⁻³
3077 reflections	Δρ_min = −0.35 e Å⁻³
187 parameters

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 > 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 (Å²) top

	x	y	z	U_iso*/U_eq
C1	1.3016 (3)	0.4676 (3)	0.90640 (11)	0.0356 (5)
H1	1.3538	0.4022	0.9392	0.043*
C2	1.3853 (3)	0.4935 (3)	0.84813 (12)	0.0397 (5)
H2	1.4916	0.4460	0.8423	0.048*
C3	1.3091 (3)	0.5902 (3)	0.79925 (10)	0.0380 (5)
H3	1.3630	0.6089	0.7599	0.046*
C4	1.1511 (3)	0.6589 (3)	0.80960 (10)	0.0350 (4)
H4	1.0966	0.7246	0.7774	0.042*
C5	1.0759 (2)	0.6281 (2)	0.86873 (9)	0.0292 (4)
C6	0.9114 (3)	0.6956 (3)	0.88563 (9)	0.0304 (4)
C7	0.6422 (2)	0.8193 (2)	0.90011 (10)	0.0313 (4)
C8	0.4793 (3)	0.9088 (3)	0.89219 (11)	0.0336 (4)
C9	0.3101 (4)	1.0642 (4)	0.82288 (15)	0.0575 (7)
H9	0.2915	1.1167	0.7823	0.069*
C10	0.1844 (3)	1.0747 (3)	0.86751 (15)	0.0536 (7)
H10	0.0843	1.1332	0.8575	0.064*
C11	0.2099 (3)	0.9966 (3)	0.92746 (14)	0.0498 (6)
H11	0.1274	1.0021	0.9590	0.060*
C12	0.3601 (3)	0.9095 (3)	0.94026 (11)	0.0401 (5)
H12	0.3799	0.8534	0.9800	0.048*
N1	1.1488 (2)	0.5333 (2)	0.91692 (8)	0.0298 (4)
N2	0.8473 (2)	0.6603 (2)	0.94235 (8)	0.0313 (4)
N3	0.6911 (2)	0.7303 (2)	0.95059 (8)	0.0320 (4)
N4	0.4563 (3)	0.9844 (2)	0.83359 (11)	0.0463 (5)
N5	0.8723 (3)	0.3030 (2)	0.95247 (9)	0.0427 (4)
N6	0.8332 (2)	0.3118 (2)	0.89483 (9)	0.0385 (4)
N7	0.7973 (3)	0.3188 (3)	0.83827 (11)	0.0645 (7)
S1	0.78523 (7)	0.82456 (7)	0.83744 (3)	0.03745 (15)
Ni1	1.0000	0.5000	1.0000	0.02650 (12)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0333 (11)	0.0420 (11)	0.0319 (10)	0.0063 (9)	0.0056 (8)	0.0008 (9)
C2	0.0340 (11)	0.0477 (13)	0.0387 (12)	0.0036 (9)	0.0120 (9)	−0.0044 (9)
C3	0.0386 (11)	0.0478 (13)	0.0288 (10)	−0.0037 (10)	0.0128 (8)	−0.0036 (9)
C4	0.0374 (11)	0.0451 (12)	0.0228 (9)	0.0007 (9)	0.0050 (8)	0.0023 (8)
C5	0.0301 (9)	0.0351 (10)	0.0226 (9)	0.0005 (8)	0.0046 (7)	−0.0011 (7)
C6	0.0309 (9)	0.0385 (11)	0.0219 (9)	0.0017 (8)	0.0008 (7)	0.0026 (8)
C7	0.0290 (9)	0.0367 (10)	0.0283 (9)	0.0022 (8)	0.0027 (7)	0.0006 (8)
C8	0.0291 (10)	0.0329 (10)	0.0385 (11)	0.0033 (8)	0.0006 (8)	−0.0013 (8)
C9	0.0508 (15)	0.0563 (16)	0.0656 (17)	0.0155 (13)	0.0046 (13)	0.0247 (14)
C10	0.0362 (12)	0.0439 (14)	0.081 (2)	0.0158 (11)	0.0015 (12)	−0.0001 (13)
C11	0.0355 (12)	0.0543 (15)	0.0608 (16)	−0.0010 (10)	0.0129 (11)	−0.0183 (12)
C12	0.0398 (12)	0.0451 (13)	0.0354 (11)	−0.0025 (10)	0.0021 (9)	−0.0026 (9)
N1	0.0312 (8)	0.0357 (9)	0.0229 (8)	0.0022 (7)	0.0045 (6)	0.0003 (6)
N2	0.0298 (8)	0.0410 (9)	0.0235 (8)	0.0063 (7)	0.0045 (6)	0.0019 (7)
N3	0.0283 (8)	0.0407 (9)	0.0271 (8)	0.0072 (7)	0.0029 (6)	0.0014 (7)
N4	0.0380 (10)	0.0508 (12)	0.0507 (12)	0.0098 (9)	0.0090 (9)	0.0182 (9)
N5	0.0501 (11)	0.0467 (11)	0.0315 (9)	−0.0058 (9)	0.0040 (8)	−0.0017 (8)
N6	0.0304 (9)	0.0464 (11)	0.0387 (10)	0.0060 (8)	0.0015 (7)	−0.0129 (8)
N7	0.0631 (15)	0.0907 (19)	0.0379 (12)	0.0154 (13)	−0.0121 (10)	−0.0185 (12)
S1	0.0343 (3)	0.0496 (3)	0.0289 (3)	0.0091 (2)	0.00513 (19)	0.0117 (2)
Ni1	0.02602 (19)	0.0358 (2)	0.01789 (17)	0.00586 (14)	0.00320 (12)	0.00259 (13)

Geometric parameters (Å, º) top

C1—N1	1.336 (3)	C9—N4	1.324 (3)
C1—C2	1.391 (3)	C9—C10	1.369 (4)
C1—H1	0.9300	C9—H9	0.9300
C2—C3	1.376 (3)	C10—C11	1.374 (4)
C2—H2	0.9300	C10—H10	0.9300
C3—C4	1.382 (3)	C11—C12	1.386 (3)
C3—H3	0.9300	C11—H11	0.9300
C4—C5	1.380 (3)	C12—H12	0.9300
C4—H4	0.9300	N1—Ni1	2.1069 (17)
C5—N1	1.348 (2)	N2—N3	1.366 (2)
C5—C6	1.456 (3)	N2—Ni1	2.0885 (16)
C6—N2	1.305 (3)	N5—N6	1.187 (3)
C6—S1	1.714 (2)	N5—Ni1	2.1075 (19)
C7—N3	1.295 (2)	N6—N7	1.160 (3)
C7—C8	1.470 (3)	Ni1—N2ⁱ	2.0885 (16)
C7—S1	1.731 (2)	Ni1—N1ⁱ	2.1069 (17)
C8—N4	1.339 (3)	Ni1—N5ⁱ	2.108 (2)
C8—C12	1.379 (3)

N1—C1—C2	122.4 (2)	C10—C11—H11	120.5
N1—C1—H1	118.8	C12—C11—H11	120.5
C2—C1—H1	118.8	C8—C12—C11	117.8 (2)
C3—C2—C1	119.3 (2)	C8—C12—H12	121.1
C3—C2—H2	120.4	C11—C12—H12	121.1
C1—C2—H2	120.4	C1—N1—C5	117.71 (18)
C2—C3—C4	118.9 (2)	C1—N1—Ni1	127.46 (15)
C2—C3—H3	120.6	C5—N1—Ni1	114.79 (13)
C4—C3—H3	120.6	C6—N2—N3	113.55 (16)
C5—C4—C3	118.63 (19)	C6—N2—Ni1	113.19 (13)
C5—C4—H4	120.7	N3—N2—Ni1	133.19 (13)
C3—C4—H4	120.7	C7—N3—N2	111.69 (16)
N1—C5—C4	123.14 (19)	C9—N4—C8	116.6 (2)
N1—C5—C6	113.27 (17)	N6—N5—Ni1	119.16 (16)
C4—C5—C6	123.58 (18)	N7—N6—N5	178.8 (2)
N2—C6—C5	120.32 (18)	C6—S1—C7	86.77 (9)
N2—C6—S1	113.49 (15)	N2—Ni1—N2ⁱ	180.00 (7)
C5—C6—S1	126.18 (15)	N2—Ni1—N1	78.32 (6)
N3—C7—C8	125.80 (19)	N2ⁱ—Ni1—N1	101.68 (6)
N3—C7—S1	114.47 (15)	N2—Ni1—N1ⁱ	101.68 (6)
C8—C7—S1	119.72 (15)	N2ⁱ—Ni1—N1ⁱ	78.32 (6)
N4—C8—C12	123.7 (2)	N1—Ni1—N1ⁱ	180.000 (1)
N4—C8—C7	113.74 (19)	N2—Ni1—N5	89.63 (8)
C12—C8—C7	122.5 (2)	N2ⁱ—Ni1—N5	90.37 (8)
N4—C9—C10	124.4 (3)	N1—Ni1—N5	90.35 (7)
N4—C9—H9	117.8	N1ⁱ—Ni1—N5	89.65 (7)
C10—C9—H9	117.8	N2—Ni1—N5ⁱ	90.37 (8)
C9—C10—C11	118.3 (2)	N2ⁱ—Ni1—N5ⁱ	89.63 (8)
C9—C10—H10	120.8	N1—Ni1—N5ⁱ	89.65 (7)
C11—C10—H10	120.8	N1ⁱ—Ni1—N5ⁱ	90.35 (7)
C10—C11—C12	119.1 (2)	N5—Ni1—N5ⁱ	179.998 (1)

Symmetry code: (i) −x+2, −y+1, −z+2.

Experimental details

Crystal data
Chemical formula	[Ni(N₃)₂(C₁₂H₈N₄S)₂]
M_r	623.34
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	296
a, b, c (Å)	7.7981 (3), 8.2410 (3), 20.1555 (7)
β (°)	93.141 (2)
V (Å³)	1293.33 (8)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.96
Crystal size (mm)	0.39 × 0.31 × 0.18

Data collection
Diffractometer	Bruker APEXII CCD diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2009)
T_min, T_max	0.640, 0.747
No. of measured, independent and observed [I > 2σ(I)] reflections	15710, 3077, 2643
R_int	0.033
(sin θ/λ)_max (Å⁻¹)	0.658

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.036, 0.100, 1.04
No. of reflections	3077
No. of parameters	187
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	1.25, −0.35

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 2012), WinGX (Farrugia, 2012).

Acknowledgements

The authors thank the Unit of Support for Technical and Scientific Research (UATRS, CNRST) for the X-ray measurements.

References

Bentiss, F., Capet, F., Lagrenée, M., Saadi, M. & El Ammari, L. (2011a). Acta Cryst. E67, m1052–m1053. Web of Science CSD CrossRef IUCr Journals Google Scholar
Bentiss, F., Capet, F., Lagrenée, M., Saadi, M. & El Ammari, L. (2011b). Acta Cryst. E67, m834–m835. Web of Science CSD CrossRef IUCr Journals Google Scholar
Bentiss, F., Lagrenée, M., Vezin, H., Wignacourt, J. P. & Holt, E. M. (2004). Polyhedron, 23, 1903–1907. Web of Science CSD CrossRef CAS Google Scholar
Bentiss, F., Outirite, M., Lagrenée, M., Saadi, M. & El Ammari, L. (2012). Acta Cryst. E68, m360–m361. CSD CrossRef CAS IUCr Journals Google Scholar
Bruker (2009). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854. Web of Science CrossRef CAS IUCr Journals Google Scholar
Klingele, J., Kaase, D., Klingele, M. H., Lach, J. & Demeshko, S. (2010). Dalton Trans. 39, 1689–1691. Web of Science CrossRef CAS PubMed Google Scholar
Laachir, A., Bentiss, F., Guesmi, S., Saadi, M. & El Ammari, L. (2013). Acta Cryst. E69, m351–m352. CSD CrossRef IUCr Journals Google Scholar
Lebrini, M., Bentiss, F. & Lagrenée, M. (2005). J. Heterocycl. Chem. 42, 991–994. CrossRef CAS Google Scholar
Machura, B., Świtlicka, A., Nawrot, I., Mroziński, J. & Michalik, K. (2011). Polyhedron, 30, 2815–2823. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Świtlicka-Olszewska, A., Machura, B. & Mroziński, J. (2014). Inorg. Chem. Commun. 43, 86–89. Google Scholar
Zheng, X.-F., Wan, X.-S., Liu, W., Niu, C.-Y. & Kou, C.-H. (2006). Z. Kristallogr., 221, 543–544. Google Scholar

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