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Acta Crystallogr Sect E Struct Rep Online. 2009 June 1; 65(Pt 6): o1328.
Published online 2009 May 20. doi:  10.1107/S1600536809018005
PMCID: PMC2969544

5-Benzyl-2-phenyl-6,8-dihydro-5H-1,2,4-triazolo[3,4-c][1,4]oxazin-2-ium hexa­fluoridophosphate

Abstract

The title compound, C18H18N3O+·PF6 , is a chiral bicyclic 1,2,4-triazolium salt which contains four rings, viz. a triazolium, a morpholine and two phenyl rings. Analysis of bond lengths shows that the N—CH—N group in the triazolium ring conforms to a typical three-center/four-electron bond (also known as the Pimentel–Rundle three-center model). The structure is completed by a disordered PF6 counter-ion [occupancies of F atoms 0.678 (8):0.322 (8)], which inter­acts with the main mol­ecule through weak inter­molecular P—F(...)π inter­actions.

Related literature

For details of different C—C bond-formation reactions, see: Fisher et al. (2006 [triangle]); Kerr et al. (2002 [triangle]); Knight & Leeper (1998 [triangle]); Readde Alaniz & Rovis (2005 [triangle]); Ma et al. (2008 [triangle]).

An external file that holds a picture, illustration, etc.
Object name is e-65-o1328-scheme1.jpg

Experimental

Crystal data

  • C18H18N3O+·PF6
  • M r = 437.32
  • Monoclinic, An external file that holds a picture, illustration, etc.
Object name is e-65-o1328-efi1.jpg
  • a = 11.4054 (13) Å
  • b = 8.1243 (9) Å
  • c = 11.8593 (14) Å
  • β = 118.678 (2)°
  • V = 964.09 (19) Å3
  • Z = 2
  • Mo Kα radiation
  • μ = 0.21 mm−1
  • T = 297 K
  • 0.53 × 0.42 × 0.32 mm

Data collection

  • Bruker SMART CCD area-detector diffractometer
  • Absorption correction: multi-scan (SADABS; Sheldrick, 1996 [triangle]) T min = 0.89, T max = 0.93
  • 5505 measured reflections
  • 3406 independent reflections
  • 2984 reflections with I > 2σ(I)
  • R int = 0.022

Refinement

  • R[F 2 > 2σ(F 2)] = 0.039
  • wR(F 2) = 0.114
  • S = 1.11
  • 3406 reflections
  • 318 parameters
  • 31 restraints
  • H-atom parameters constrained
  • Δρmax = 0.20 e Å−3
  • Δρmin = −0.20 e Å−3
  • Absolute structure: Flack (1983 [triangle]), 1368 Friedel pairs
  • Flack parameter: 0.01 (10)

Data collection: SMART (Siemens, 1996 [triangle]); cell refinement: SAINT (Siemens, 1996 [triangle]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 [triangle]); molecular graphics: SHELXTL (Sheldrick, 2008 [triangle]); software used to prepare material for publication: SHELXTL.

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809018005/bg2257sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809018005/bg2257Isup2.hkl

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

Acknowledgments

The authors are grateful to the National Natural Science Foundation of China (grant No. 20702035) for financial support.

supplementary crystallographic information

Comment

Triazolium salts which can be used as the precursors of carbenes are widely used in asymmetric catalysis for the C—C bond formation reactions, such as benzoin reactions (Knight & Leeper 1998; Ma et al. 2008), Stetter reactions (Kerr et al. 2002; Readde Alaniz & Rovis 2005) and Diels-Alder reactions (Fisher et al. 2006) because of their excellent catalytic performance in umpolung aldehyde chemistry. Most of the research performed shows that chiral bicyclic 1,2,4-triazole carbenes have excellent enanselectivity because they have many bulkier groups and show weaker nucleophility than thiazolium, imidazolium and imidazolinium salts. The crystal structure of the title compound shows that N1—C7—N3 is a typical 3-center-4-electron bond (well known as the Pimentel-Rundle three-center model), because both N1—C7 (1.312 (3) Å) and N3—C7 (1.325 (2) Å) bond lengths are longer than the N2=C8 (1.292 (3) Å) double bond but shorter than other N—C single bonds (1.365 (3)–1.486 (3) Å). The dihedral angle between the phenyl (C1—C6) and triazolium ring (N1/N2/C8/N3/C7) is 27.8 °. In the crystal packing, weak P—F···π (Cg 1) interactions interconnect adjacent molecules at the same time that it provides to the stability of the crystal structure.

Experimental

The title compound was prepared according to literature methods (Knight & Leeper 1998). A solution of 3-benzyl-5-ethoxy-3,6-dihydro-2H-1,4-oxazine (prepared from (s)-2-amino-3-phenylpropan-1-ol) as a colorless liquid was added dropwise to phenylhydrazine hydrochloride (1.44 g, 10 mmol) in methanol (3 ml). The mixture was then stirred for 30 min, followed by addition of triethyl orthoformate (7.4 g, 50 mmol). After being heated at 353 K for 10 h, the reaction mixture was cooled to room temperature and concentrated in vacuo. The resulting residue was purified by column chromatography on silica gel with elution with methanol and followed with anion exchange with ammonium hexafluorophosphate to afford the pure triazolium salt (I) as a white solid in 63% overall yield. Colourless crystals suitable for X-ray structural analysis were grown by slow evaporation of actone solution. 1H NMR (400 MHz, DMSO): δ 3.17 (1 H, dd, J = 10.4 Hz, 4.8 Hz, 1H), 3.19 (dd, J = 10.0 Hz, 4.8 Hz, 1H), 3.95–4.01 (m, 2H), 4.87–4.93 (m, 1H), 5.22 (2 d, J = 16 Hz, 16 Hz, 2H), 7.47–7.68 (m, 8H), 7.69–7.91 (m, 2H), 11.20 (s, 1H).

Refinement

All H atoms were positioned geometrically and refined in the riding model approximation with C—H = 0.93, 0.97 or 0.98 Å, Uiso(H) = 1.2Ueq(C or N)

Figures

Fig. 1.
The molecular structure of (I), showing 30% probability displacement ellipsoids and the atomic numbering.

Crystal data

C18H18N3O+·F6PF(000) = 448
Mr = 437.32Dx = 1.506 Mg m3
Monoclinic, P21Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ybCell parameters from 3172 reflections
a = 11.4054 (13) Åθ = 3.1–26.0°
b = 8.1243 (9) ŵ = 0.21 mm1
c = 11.8593 (14) ÅT = 297 K
β = 118.678 (2)°Parallelepiped, colourless
V = 964.09 (19) Å30.53 × 0.42 × 0.32 mm
Z = 2

Data collection

Bruker SMART CCD area-detector diffractometer3406 independent reflections
Radiation source: fine-focus sealed tube2984 reflections with I > 2σ(I)
graphiteRint = 0.022
[var phi] and ω scansθmax = 26.0°, θmin = 2.0°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)h = −14→13
Tmin = 0.89, Tmax = 0.93k = −9→10
5505 measured reflectionsl = −12→14

Refinement

Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH-atom parameters constrained
R[F2 > 2σ(F2)] = 0.039w = 1/[σ2(Fo2) + (0.075P)2] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.114(Δ/σ)max = 0.009
S = 1.11Δρmax = 0.20 e Å3
3406 reflectionsΔρmin = −0.20 e Å3
318 parametersExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
31 restraintsExtinction coefficient: 0.019 (3)
Primary atom site location: structure-invariant direct methodsAbsolute structure: Flack (1983), 1368 Friedel pairs
Secondary atom site location: difference Fourier mapFlack parameter: 0.01 (10)

Special details

Experimental. Even if the Flack parameter coming out of refinement appears quite trustable, the fact that the heaviest atomic species in the structure is P could suggest that the absolute structure determination could be thought as dubious. However, because the stereogenic carbon does not directly participate in the cyclocondensation, there is little risk for the racemization of the stereogenic carbon in this reaction. (Knight, R. L. & Leeper, F. J. (1998) J. Chem. Soc., Perkin Trans. 1, 1891–1893.) From starting material (S)-2-amino-3-phenylpropan-1-ol, it give (S)-5-benzyl-2-phenyl-6,8-dihydro-5H- [1,2,4]triazolo[3,4-c][1,4]oxazin-2-ium hexafluorophosphate as product, whose absolute configuration (s) is consistent with the absolute structure characterized by X-ray structure analysis.
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)

xyzUiso*/UeqOcc. (<1)
P10.79225 (6)0.03833 (8)0.45453 (6)0.0488 (2)
O10.67186 (18)0.5581 (3)0.70365 (16)0.0669 (5)
N10.69585 (16)0.5547 (3)0.34299 (15)0.0428 (4)
N20.59091 (18)0.5715 (3)0.36766 (18)0.0514 (5)
N30.77918 (16)0.5257 (3)0.54549 (15)0.0422 (4)
C10.5666 (3)0.6481 (4)0.1230 (3)0.0637 (7)
H1A0.51310.70930.14690.076*
C20.5404 (3)0.6440 (5)−0.0031 (3)0.0788 (9)
H2B0.46750.7013−0.06540.095*
C30.6212 (3)0.5557 (5)−0.0376 (3)0.0707 (8)
H3A0.60230.5529−0.12310.085*
C40.7283 (3)0.4729 (5)0.0528 (3)0.0734 (9)
H4A0.78410.41620.02930.088*
C50.7556 (3)0.4719 (4)0.1800 (3)0.0636 (7)
H5A0.82790.41320.24180.076*
C60.6733 (2)0.5598 (3)0.2126 (2)0.0464 (5)
C70.8076 (2)0.5279 (4)0.44951 (19)0.0435 (5)
H7A0.89170.51320.45640.052*
C80.6451 (2)0.5535 (4)0.4908 (2)0.0486 (5)
C90.5763 (3)0.5573 (6)0.5721 (2)0.0713 (9)
H9A0.52090.65500.55190.086*
H9B0.51900.46160.55330.086*
C100.7696 (3)0.4335 (4)0.7317 (2)0.0579 (7)
H10A0.72610.33130.69080.069*
H10B0.81870.41520.82370.069*
C110.8654 (2)0.4849 (3)0.6834 (2)0.0447 (5)
H11A0.92290.39140.69040.054*
C120.9534 (3)0.6333 (3)0.7548 (2)0.0531 (6)
H12A1.00500.66670.71330.064*
H12B0.89710.72500.75100.064*
C131.0474 (2)0.5901 (3)0.8942 (2)0.0514 (6)
C141.1674 (3)0.5140 (4)0.9300 (3)0.0677 (8)
H14A1.19370.49040.86860.081*
C151.2500 (3)0.4720 (5)1.0580 (4)0.0796 (9)
H15A1.33210.42251.08190.095*
C161.2119 (3)0.5024 (4)1.1490 (3)0.0794 (10)
H16A1.26740.47261.23410.095*
C171.0925 (3)0.5766 (4)1.1146 (3)0.0710 (8)
H17A1.06620.59731.17640.085*
C181.0103 (3)0.6211 (4)0.9885 (3)0.0590 (7)
H18A0.92920.67260.96600.071*
F10.7113 (5)0.1769 (5)0.4784 (7)0.105 (2)0.678 (8)
F20.7470 (6)−0.0824 (7)0.5298 (6)0.115 (2)0.678 (8)
F30.8763 (5)−0.0945 (6)0.4304 (8)0.118 (3)0.678 (8)
F40.8458 (8)0.1611 (7)0.3921 (7)0.126 (3)0.678 (8)
F50.9187 (4)0.0816 (12)0.5876 (4)0.132 (3)0.678 (8)
F60.6692 (5)−0.0133 (10)0.3319 (4)0.128 (2)0.678 (8)
F1'0.767 (2)0.125 (3)0.5475 (17)0.214 (11)0.322 (8)
F2'0.6898 (13)−0.0908 (11)0.433 (2)0.142 (7)0.322 (8)
F3'0.811 (3)−0.036 (4)0.350 (2)0.280 (14)0.322 (8)
F4'0.8949 (12)0.1741 (13)0.476 (2)0.154 (9)0.322 (8)
F5'0.9061 (10)−0.069 (2)0.542 (2)0.174 (9)0.322 (8)
F6'0.6823 (13)0.138 (2)0.3481 (18)0.192 (8)0.322 (8)

Atomic displacement parameters (Å2)

U11U22U33U12U13U23
P10.0462 (3)0.0449 (3)0.0583 (4)−0.0032 (3)0.0276 (3)−0.0032 (3)
O10.0668 (10)0.0884 (15)0.0578 (10)0.0000 (12)0.0398 (9)−0.0050 (11)
N10.0398 (8)0.0493 (11)0.0410 (9)−0.0007 (10)0.0207 (7)0.0010 (9)
N20.0407 (9)0.0657 (16)0.0500 (11)0.0068 (10)0.0234 (8)0.0035 (10)
N30.0418 (8)0.0444 (11)0.0410 (9)0.0000 (10)0.0203 (7)0.0004 (9)
C10.0640 (16)0.0757 (19)0.0531 (15)0.0131 (15)0.0296 (14)0.0078 (13)
C20.0738 (19)0.104 (3)0.0513 (16)0.015 (2)0.0243 (15)0.0201 (17)
C30.0831 (18)0.085 (2)0.0498 (14)−0.002 (2)0.0368 (14)0.0091 (16)
C40.092 (2)0.083 (2)0.0690 (18)0.0091 (18)0.0574 (18)0.0011 (16)
C50.0673 (16)0.0746 (18)0.0560 (15)0.0157 (15)0.0353 (13)0.0103 (13)
C60.0459 (10)0.0514 (15)0.0429 (11)−0.0081 (12)0.0220 (9)0.0001 (11)
C70.0395 (10)0.0474 (13)0.0451 (11)−0.0023 (11)0.0216 (9)−0.0006 (10)
C80.0448 (11)0.0535 (14)0.0520 (12)0.0022 (12)0.0269 (10)−0.0003 (12)
C90.0583 (13)0.110 (3)0.0584 (15)0.012 (2)0.0380 (13)0.0084 (19)
C100.0607 (15)0.0610 (17)0.0487 (14)−0.0096 (13)0.0237 (12)0.0041 (12)
C110.0463 (12)0.0444 (13)0.0402 (11)0.0020 (9)0.0182 (10)0.0008 (9)
C120.0546 (14)0.0538 (15)0.0494 (13)−0.0061 (12)0.0237 (12)0.0018 (11)
C130.0511 (13)0.0465 (14)0.0512 (13)−0.0076 (10)0.0201 (11)−0.0039 (10)
C140.0515 (13)0.071 (2)0.0762 (18)−0.0059 (14)0.0270 (13)−0.0082 (15)
C150.0495 (15)0.072 (2)0.091 (2)−0.0005 (15)0.0126 (15)0.0044 (17)
C160.079 (2)0.064 (2)0.0590 (17)−0.0103 (16)0.0041 (16)0.0011 (14)
C170.092 (2)0.064 (2)0.0467 (14)−0.0145 (16)0.0250 (14)−0.0090 (13)
C180.0632 (15)0.0567 (16)0.0523 (14)−0.0026 (13)0.0240 (13)−0.0087 (12)
F10.084 (3)0.054 (2)0.219 (7)−0.0148 (17)0.107 (4)−0.037 (3)
F20.125 (4)0.104 (4)0.137 (4)−0.005 (3)0.081 (3)0.047 (3)
F30.079 (3)0.072 (3)0.216 (7)0.009 (2)0.083 (4)−0.037 (4)
F40.190 (7)0.091 (4)0.167 (5)−0.017 (4)0.143 (5)0.023 (4)
F50.076 (2)0.214 (8)0.081 (2)−0.029 (4)0.0164 (18)−0.037 (3)
F60.098 (3)0.163 (6)0.073 (2)−0.015 (3)0.002 (2)−0.033 (3)
F1'0.30 (2)0.26 (2)0.156 (13)−0.078 (17)0.172 (16)−0.120 (13)
F2'0.100 (8)0.052 (5)0.33 (2)−0.035 (5)0.145 (12)−0.062 (10)
F3'0.34 (3)0.40 (4)0.237 (19)−0.08 (2)0.24 (2)−0.16 (2)
F4'0.072 (6)0.075 (6)0.34 (3)−0.024 (5)0.120 (12)−0.059 (12)
F5'0.085 (6)0.148 (13)0.218 (16)0.027 (8)0.015 (9)0.130 (13)
F6'0.119 (9)0.163 (14)0.181 (14)0.025 (10)−0.017 (9)0.086 (12)

Geometric parameters (Å, °)

P1—F1'1.446 (10)C4—C51.386 (4)
P1—F2'1.498 (7)C4—H4A0.9300
P1—F5'1.495 (7)C5—C61.375 (4)
P1—F3'1.480 (10)C5—H5A0.9300
P1—F6'1.516 (8)C7—H7A0.9300
P1—F61.517 (4)C8—C91.508 (3)
P1—F41.533 (4)C9—H9A0.9700
P1—F4'1.539 (9)C9—H9B0.9700
P1—F11.565 (3)C10—C111.515 (3)
P1—F31.559 (4)C10—H10A0.9700
P1—F21.570 (4)C10—H10B0.9700
P1—F51.584 (4)C11—C121.537 (3)
O1—C91.410 (3)C11—H11A0.9800
O1—C101.422 (4)C12—C131.518 (3)
N1—C71.312 (3)C12—H12A0.9700
N1—N21.369 (2)C12—H12B0.9700
N1—C61.442 (3)C13—C141.371 (4)
N2—C81.292 (3)C13—C181.395 (4)
N3—C71.325 (2)C14—C151.391 (4)
N3—C81.364 (3)C14—H14A0.9300
N3—C111.486 (3)C15—C161.365 (5)
C1—C61.373 (4)C15—H15A0.9300
C1—C21.377 (4)C16—C171.361 (5)
C1—H1A0.9300C16—H16A0.9300
C2—C31.376 (5)C17—C181.379 (4)
C2—H2B0.9300C17—H17A0.9300
C3—C41.356 (5)C18—H18A0.9300
C3—H3A0.9300
F1'—P1—F2'92.7 (10)C4—C5—H5A120.8
F1'—P1—F5'100.2 (14)C1—C6—C5121.7 (2)
F2'—P1—F5'93.2 (9)C1—C6—N1118.7 (2)
F1'—P1—F3'174.1 (17)C5—C6—N1119.5 (2)
F2'—P1—F3'89.3 (11)N1—C7—N3107.70 (17)
F5'—P1—F3'85.2 (12)N1—C7—H7A126.2
F1'—P1—F6'89.4 (11)N3—C7—H7A126.2
F2'—P1—F6'88.0 (9)N2—C8—N3112.03 (18)
F5'—P1—F6'170.3 (13)N2—C8—C9127.4 (2)
F3'—P1—F6'85.1 (15)N3—C8—C9120.6 (2)
F1'—P1—F4'86.6 (10)O1—C9—C8110.13 (19)
F2'—P1—F4'178.6 (6)O1—C9—H9A109.6
F5'—P1—F4'88.1 (7)C8—C9—H9A109.6
F3'—P1—F4'91.3 (11)O1—C9—H9B109.6
F6'—P1—F4'90.9 (9)C8—C9—H9B109.6
F6—P1—F191.0 (3)H9A—C9—H9B108.1
F4—P1—F191.5 (3)O1—C10—C11110.0 (2)
F6—P1—F191.0 (3)O1—C10—H10A109.7
F4—P1—F191.5 (3)C11—C10—H10A109.7
F6—P1—F390.0 (3)O1—C10—H10B109.7
F4—P1—F386.5 (4)C11—C10—H10B109.7
F1—P1—F3177.8 (3)H10A—C10—H10B108.2
F6—P1—F288.1 (3)N3—C11—C10105.10 (19)
F4—P1—F2175.1 (4)N3—C11—C12110.14 (19)
F1—P1—F287.9 (3)C10—C11—C12114.0 (2)
F3—P1—F294.1 (4)N3—C11—H11A109.2
F6—P1—F5175.9 (5)C10—C11—H11A109.2
F4—P1—F587.3 (3)C12—C11—H11A109.2
F1—P1—F589.7 (3)C13—C12—C11110.6 (2)
F3—P1—F589.5 (3)C13—C12—H12A109.5
F2—P1—F587.8 (4)C11—C12—H12A109.5
C9—O1—C10111.0 (2)C13—C12—H12B109.5
C7—N1—N2110.85 (16)C11—C12—H12B109.5
C7—N1—C6128.92 (17)H12A—C12—H12B108.1
N2—N1—C6120.16 (17)C14—C13—C18118.4 (3)
C8—N2—N1103.74 (17)C14—C13—C12121.3 (2)
C7—N3—C8105.68 (17)C18—C13—C12120.3 (2)
C7—N3—C11130.00 (18)C13—C14—C15120.0 (3)
C8—N3—C11124.03 (17)C13—C14—H14A120.0
C6—C1—C2118.5 (3)C15—C14—H14A120.0
C6—C1—H1A120.7C16—C15—C14120.9 (3)
C2—C1—H1A120.7C16—C15—H15A119.6
C3—C2—C1120.6 (3)C14—C15—H15A119.6
C3—C2—H2B119.7C17—C16—C15119.7 (3)
C1—C2—H2B119.7C17—C16—H16A120.1
C4—C3—C2120.1 (2)C15—C16—H16A120.1
C4—C3—H3A120.0C16—C17—C18120.2 (3)
C2—C3—H3A120.0C16—C17—H17A119.9
C3—C4—C5120.7 (3)C18—C17—H17A119.9
C3—C4—H4A119.7C17—C18—C13120.8 (3)
C5—C4—H4A119.7C17—C18—H18A119.6
C6—C5—C4118.4 (3)C13—C18—H18A119.6
C6—C5—H5A120.8

Hydrogen-bond geometry (Å, °)

D—H···AD—HH···AD···AD—H···A
P1—F1···Cg1i1.57 (1)3.034.235 (11)132
P1—F2···Cg11.57 (1)3.194.102 (11)115
P1—F2'···Cg11.50 (1)2.934.102 (11)133

Symmetry codes: (i) x, y+1, z.

Footnotes

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BG2257).

References

  • Fisher, C., Smith, S. W., Powell, D. A. & Fu, G. C. (2006). J. Am. Chem. Soc.128, 1472–1473. [PMC free article] [PubMed]
  • Flack, H. D. (1983). Acta Cryst. A39, 876–881.
  • Kerr, M. S., Alaniz, J. & Rovis, T. (2002). J. Am. Chem. Soc.124, 10298–10299. [PubMed]
  • Knight, R. L. & Leeper, F. J. (1998). J. Chem. Soc. Perkin Trans. 1, pp. 1891–1893.
  • Ma, Y., Wei, S., Wu, J., Yang, F., Liu, B., Lan, J., Yang, S. & You, J. (2008). Adv. Synth. Catal.350, 2645–2651.
  • Readde Alaniz, J. & Rovis, T. (2005). J. Am. Chem. Soc.127, 6284–6289. [PubMed]
  • Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
  • Siemens (1996). SMART and SAINT. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA.

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