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4-[(6-Chloro-2-pyrid­yl)meth­­oxy]-3-(2,4-di­chloro­phen­yl)-1-oxa­spiro­[4.5]dec-3-en-2-one

aCollege of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, People's Republic of China
*Correspondence e-mail: qknhs@yahoo.com.cn

(Received 3 March 2009; accepted 19 March 2009; online 25 March 2009)

In the title compound, C21H18Cl3NO3, the cyclo­hexane ring is in a chair conformation. The five-membered ring forms a dihedral angle of 69.89 (2)° with the benzene ring. The dihedral angle between the benzene and pyridine rings is 14.03 (7)°.

Related literature

For the biological activity of the title compound and a similar structure, see: Thomas et al. (2003[Thomas, B., Jordi, B. B., Reiner, F. & Ralf, N. (2003). Chimia, 57, 697-701.]). For its preparation, see: Lu et al. (2008[Lu, Y., Tao, J. Z. & Zhang, Z. R. (2008). Chem. Intermed. 10, 25-28.]); Sarcevic et al. (1973[Sarcevic, N., Zsindely, J. & Schmid, H. (1973). Helv. Chim. Acta, 56, 1457-1476.]). For puckering parameters, see: Cremer & Pople (1975[Cremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc. 97, 1354-1358.]).

[Scheme 1]

Experimental

Crystal data
  • C21H18Cl3NO3

  • Mr = 438.71

  • Monoclinic, P 21 /n

  • a = 7.2457 (14) Å

  • b = 13.108 (3) Å

  • c = 21.054 (4) Å

  • β = 95.77 (3)°

  • V = 1989.5 (7) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 0.48 mm−1

  • T = 113 K

  • 0.18 × 0.12 × 0.06 mm

Data collection
  • Rigaku Saturn diffractometer

  • Absorption correction: multi-scan (CrystalClear; Rigaku, 2005[Rigaku (2005). CrystalClear. Rigaku Corporation, Tokyo, Japan.]) Tmin = 0.918, Tmax = 0.972

  • 14740 measured reflections

  • 3519 independent reflections

  • 3191 reflections with I > 2σ(I)

  • Rint = 0.041

Refinement
  • R[F2 > 2σ(F2)] = 0.034

  • wR(F2) = 0.089

  • S = 1.08

  • 3519 reflections

  • 253 parameters

  • H-atom parameters constrained

  • Δρmax = 0.18 e Å−3

  • Δρmin = −0.31 e Å−3

Data collection: CrystalClear (Rigaku, 2005[Rigaku (2005). CrystalClear. Rigaku Corporation, Tokyo, Japan.]); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supporting information


Comment top

The goal of the synthesis of the title compound (I) is to obtain compounds with biological activity (Thomas et al., 2003). We report here the crystal structure of (I), Fig.1.The cyclohexane ring is a chair conformation [Puckering Amplitude (QT) = 0.5531 (18) Å, θ = 4.39 (19) °, ϕ = 142 (3) °] (Cremer & Pople, 1975).The five membered ring form a dihedral angle of 69.89 (2)° with the benzene ring. In the crystal structure, the molecular packing is stabilized by one intermolecular C—H···O hydrogen bond.

Related literature top

For the biological activity of the title compound, see: Thomas et al. (2003). For a similar structure, see: Thomas et al. (2003). For the preparation, see: Lu et al. (2008); Sarcevic et al. (1973). For puckering parameters, see: Cremer & Pople (1975).

Experimental top

3-(2,4-Dichlorophenyl)-2,4-dioxo-1-oxaspiro[4.5]decane (6.26 g ;20.0 mmol), was suspended in a solution of sodium carbonate (1.08 g ;10.2 mmol) in 40 ml of water in a flask equipped with stirrer, water separator and reflux condenser. Toluene (80 ml) was added after 0.5 h, the mixture was heated to dehydration. Then 2-chloro-6-(chloromethyl)pyridine 3.56 g (22.0 mmol) and N,N-dimethylformamide(DMF) (40 ml) were added while maintaining the temperature at 100° C for 4 h. Upon cooling at room temperature. Then water (40 ml) was added. The mixture was extracted with CH2Cl2 (35 ml) and the organic layer was washed with water and dried over sodium sulfate. The excess CH2Cl2 was removed on a water vacuum pump to obtain the oil product which was crystallized from methanol to afford the title compound 7.89 g (90% yield) (Lu et al., 2008; Sarcevic et al., 1973). Single crystals suitable for X-ray measurement were obtained by recrystallization from the mixture of acetone and methanol at room temperature.

Refinement top

All C-bound H atoms were placed in calculated positions, with C—H = 0.93 or 0.97 Å, and included in the final cycles of refinement using a riding model, with Uiso(H) = 1.2Ueq(C) for the aryl and methylene H atoms.

Computing details top

Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear (Rigaku, 2005); data reduction: CrystalClear (Rigaku, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. View of the title compound (I), with displacement ellipsoids drawn at the 40% probability level.
4-[(6-Chloro-2-pyridyl)methoxy]-3-(2,4-dichlorophenyl)-1-oxaspiro[4.5]dec-3-en-2-one top
Crystal data top
C21H18Cl3NO3F(000) = 904
Mr = 438.71Dx = 1.465 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 5265 reflections
a = 7.2457 (14) Åθ = 1.6–28.0°
b = 13.108 (3) ŵ = 0.48 mm1
c = 21.054 (4) ÅT = 113 K
β = 95.77 (3)°Platelet, colourless
V = 1989.5 (7) Å30.18 × 0.12 × 0.06 mm
Z = 4
Data collection top
Rigaku Saturn
diffractometer
3519 independent reflections
Radiation source: rotating anode3191 reflections with I > 2σ(I)
Confocal monochromatorRint = 0.041
ω scansθmax = 25.0°, θmin = 1.8°
Absorption correction: multi-scan
(CrystalClear; Rigaku, 2005)
h = 88
Tmin = 0.918, Tmax = 0.972k = 1515
14740 measured reflectionsl = 2525
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.034Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.089H-atom parameters constrained
S = 1.08 w = 1/[σ2(Fo2) + (0.053P)2]
where P = (Fo2 + 2Fc2)/3
3519 reflections(Δ/σ)max = 0.001
253 parametersΔρmax = 0.18 e Å3
0 restraintsΔρmin = 0.31 e Å3
Crystal data top
C21H18Cl3NO3V = 1989.5 (7) Å3
Mr = 438.71Z = 4
Monoclinic, P21/nMo Kα radiation
a = 7.2457 (14) ŵ = 0.48 mm1
b = 13.108 (3) ÅT = 113 K
c = 21.054 (4) Å0.18 × 0.12 × 0.06 mm
β = 95.77 (3)°
Data collection top
Rigaku Saturn
diffractometer
3519 independent reflections
Absorption correction: multi-scan
(CrystalClear; Rigaku, 2005)
3191 reflections with I > 2σ(I)
Tmin = 0.918, Tmax = 0.972Rint = 0.041
14740 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0340 restraints
wR(F2) = 0.089H-atom parameters constrained
S = 1.08Δρmax = 0.18 e Å3
3519 reflectionsΔρmin = 0.31 e Å3
253 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 > 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) top
xyzUiso*/Ueq
Cl10.28480 (7)0.08999 (4)0.06950 (2)0.03906 (15)
Cl20.06561 (6)0.21586 (3)0.228775 (19)0.02533 (13)
Cl30.36534 (7)0.22352 (4)0.06907 (2)0.03617 (15)
O10.00146 (14)0.14206 (8)0.42592 (5)0.0204 (3)
O20.26135 (15)0.13568 (9)0.35960 (5)0.0248 (3)
O30.35068 (14)0.00872 (8)0.35405 (5)0.0226 (3)
N10.4102 (2)0.18419 (11)0.19104 (7)0.0264 (3)
C10.1925 (2)0.10733 (12)0.42562 (7)0.0188 (3)
C20.3193 (2)0.20111 (12)0.42615 (8)0.0239 (4)
H2A0.44360.17950.41900.029*
H2B0.27450.24640.39150.029*
C30.3264 (2)0.25889 (13)0.48925 (8)0.0275 (4)
H3A0.20500.28700.49440.033*
H3B0.41350.31500.48890.033*
C40.3862 (3)0.18769 (13)0.54514 (8)0.0292 (4)
H4A0.51170.16410.54160.035*
H4B0.38620.22510.58490.035*
C50.2574 (2)0.09592 (13)0.54645 (8)0.0259 (4)
H5A0.13510.11880.55510.031*
H5B0.30420.05020.58060.031*
C60.2430 (2)0.03854 (12)0.48280 (7)0.0211 (4)
H6A0.36080.00580.47800.025*
H6B0.14980.01450.48350.025*
C70.1869 (2)0.05012 (11)0.36345 (7)0.0182 (3)
C80.3726 (2)0.04708 (12)0.29626 (8)0.0251 (4)
H8A0.27600.09840.29010.030*
H8B0.49110.08220.30100.030*
C90.3640 (2)0.01985 (12)0.23785 (8)0.0221 (4)
C100.3138 (2)0.02018 (13)0.17760 (8)0.0285 (4)
H100.28100.08860.17300.034*
C110.3125 (2)0.04149 (14)0.12452 (8)0.0293 (4)
H110.27990.01620.08370.035*
C120.3619 (2)0.14262 (13)0.13470 (8)0.0254 (4)
C130.4111 (2)0.12222 (13)0.24178 (8)0.0247 (4)
H130.44530.14960.28200.030*
C140.0183 (2)0.05485 (11)0.33042 (7)0.0185 (3)
C150.0991 (2)0.11385 (12)0.37036 (7)0.0199 (4)
C160.0574 (2)0.01791 (12)0.26666 (7)0.0190 (3)
C170.0880 (2)0.08572 (12)0.25352 (8)0.0233 (4)
H170.06180.13320.28600.028*
C180.1565 (2)0.11919 (13)0.19334 (8)0.0263 (4)
H180.17360.18850.18530.032*
C190.1993 (2)0.04852 (13)0.14529 (8)0.0253 (4)
C200.1746 (2)0.05474 (12)0.15634 (8)0.0229 (4)
H200.20480.10200.12400.027*
C210.1040 (2)0.08598 (11)0.21652 (8)0.0185 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cl10.0450 (3)0.0442 (3)0.0269 (3)0.0021 (2)0.0017 (2)0.0110 (2)
Cl20.0338 (3)0.0155 (2)0.0269 (2)0.00057 (16)0.00361 (19)0.00429 (15)
Cl30.0350 (3)0.0439 (3)0.0300 (3)0.0021 (2)0.0051 (2)0.00633 (19)
O10.0162 (6)0.0236 (6)0.0215 (6)0.0040 (5)0.0021 (5)0.0022 (5)
O20.0166 (6)0.0297 (6)0.0280 (6)0.0052 (5)0.0021 (5)0.0069 (5)
O30.0187 (6)0.0257 (6)0.0233 (6)0.0067 (5)0.0016 (5)0.0029 (5)
N10.0241 (8)0.0266 (8)0.0287 (8)0.0017 (6)0.0034 (6)0.0031 (6)
C10.0152 (8)0.0185 (8)0.0226 (8)0.0032 (6)0.0020 (7)0.0025 (6)
C20.0237 (9)0.0211 (8)0.0276 (9)0.0004 (7)0.0062 (7)0.0020 (7)
C30.0257 (10)0.0208 (9)0.0361 (10)0.0019 (7)0.0043 (8)0.0039 (7)
C40.0313 (10)0.0279 (9)0.0277 (10)0.0004 (8)0.0006 (8)0.0068 (8)
C50.0262 (9)0.0291 (9)0.0221 (9)0.0026 (7)0.0002 (7)0.0017 (7)
C60.0186 (8)0.0201 (8)0.0242 (9)0.0013 (7)0.0005 (7)0.0018 (7)
C70.0181 (8)0.0148 (8)0.0220 (8)0.0015 (6)0.0034 (7)0.0037 (6)
C80.0233 (9)0.0229 (9)0.0292 (9)0.0074 (7)0.0027 (7)0.0058 (7)
C90.0156 (8)0.0231 (9)0.0279 (9)0.0034 (7)0.0038 (7)0.0053 (7)
C100.0291 (10)0.0248 (9)0.0326 (10)0.0035 (7)0.0083 (8)0.0096 (8)
C110.0289 (10)0.0354 (10)0.0240 (9)0.0051 (8)0.0050 (7)0.0105 (8)
C120.0168 (9)0.0346 (10)0.0255 (9)0.0004 (7)0.0051 (7)0.0024 (7)
C130.0210 (9)0.0291 (9)0.0237 (9)0.0018 (7)0.0009 (7)0.0071 (7)
C140.0182 (8)0.0152 (8)0.0221 (8)0.0000 (6)0.0020 (7)0.0047 (6)
C150.0219 (9)0.0170 (8)0.0207 (8)0.0012 (7)0.0019 (7)0.0071 (6)
C160.0158 (8)0.0186 (8)0.0226 (8)0.0003 (6)0.0022 (7)0.0024 (6)
C170.0223 (9)0.0184 (8)0.0290 (9)0.0011 (7)0.0019 (7)0.0048 (7)
C180.0257 (10)0.0199 (9)0.0332 (10)0.0032 (7)0.0031 (8)0.0023 (7)
C190.0220 (9)0.0300 (9)0.0237 (9)0.0023 (7)0.0015 (7)0.0054 (7)
C200.0202 (9)0.0267 (9)0.0218 (8)0.0022 (7)0.0030 (7)0.0039 (7)
C210.0175 (8)0.0150 (8)0.0234 (9)0.0009 (6)0.0041 (7)0.0003 (6)
Geometric parameters (Å, º) top
Cl1—C191.7398 (17)C6—H6A0.9700
Cl2—C211.7400 (16)C6—H6B0.9700
Cl3—C121.7440 (17)C7—C141.345 (2)
O1—C151.366 (2)C8—C91.507 (2)
O1—C11.4577 (18)C8—H8A0.9700
O2—C151.2090 (19)C8—H8B0.9700
O3—C71.3375 (18)C9—C131.385 (2)
O3—C81.4421 (18)C9—C101.387 (2)
N1—C121.320 (2)C10—C111.378 (2)
N1—C131.342 (2)C10—H100.9300
C1—C71.505 (2)C11—C121.384 (2)
C1—C61.519 (2)C11—H110.9300
C1—C21.534 (2)C13—H130.9300
C2—C31.526 (2)C14—C151.474 (2)
C2—H2A0.9700C14—C161.480 (2)
C2—H2B0.9700C16—C211.398 (2)
C3—C41.530 (2)C16—C171.400 (2)
C3—H3A0.9700C17—C181.385 (2)
C3—H3B0.9700C17—H170.9300
C4—C51.524 (2)C18—C191.384 (2)
C4—H4A0.9700C18—H180.9300
C4—H4B0.9700C19—C201.382 (2)
C5—C61.531 (2)C20—C211.380 (2)
C5—H5A0.9700C20—H200.9300
C5—H5B0.9700
C15—O1—C1109.69 (12)C9—C8—H8A108.9
C7—O3—C8120.36 (13)O3—C8—H8B108.9
C12—N1—C13116.43 (15)C9—C8—H8B108.9
O1—C1—C7102.52 (12)H8A—C8—H8B107.7
O1—C1—C6109.58 (12)C13—C9—C10117.49 (15)
C7—C1—C6112.12 (13)C13—C9—C8121.71 (15)
O1—C1—C2108.54 (12)C10—C9—C8120.77 (15)
C7—C1—C2111.66 (12)C11—C10—C9119.95 (16)
C6—C1—C2111.93 (14)C11—C10—H10120.0
C3—C2—C1111.83 (13)C9—C10—H10120.0
C3—C2—H2A109.2C10—C11—C12117.11 (16)
C1—C2—H2A109.2C10—C11—H11121.4
C3—C2—H2B109.2C12—C11—H11121.4
C1—C2—H2B109.2N1—C12—C11125.13 (16)
H2A—C2—H2B107.9N1—C12—Cl3115.93 (13)
C2—C3—C4110.44 (14)C11—C12—Cl3118.94 (13)
C2—C3—H3A109.6N1—C13—C9123.89 (15)
C4—C3—H3A109.6N1—C13—H13118.1
C2—C3—H3B109.6C9—C13—H13118.1
C4—C3—H3B109.6C7—C14—C15105.99 (14)
H3A—C3—H3B108.1C7—C14—C16133.52 (14)
C5—C4—C3111.65 (14)C15—C14—C16120.44 (14)
C5—C4—H4A109.3O2—C15—O1121.42 (14)
C3—C4—H4A109.3O2—C15—C14128.58 (15)
C5—C4—H4B109.3O1—C15—C14109.99 (13)
C3—C4—H4B109.3C21—C16—C17116.66 (15)
H4A—C4—H4B108.0C21—C16—C14121.05 (14)
C4—C5—C6111.10 (14)C17—C16—C14122.28 (14)
C4—C5—H5A109.4C18—C17—C16121.58 (15)
C6—C5—H5A109.4C18—C17—H17119.2
C4—C5—H5B109.4C16—C17—H17119.2
C6—C5—H5B109.4C19—C18—C17119.35 (15)
H5A—C5—H5B108.0C19—C18—H18120.3
C1—C6—C5113.06 (13)C17—C18—H18120.3
C1—C6—H6A109.0C20—C19—C18121.13 (16)
C5—C6—H6A109.0C20—C19—Cl1119.24 (13)
C1—C6—H6B109.0C18—C19—Cl1119.63 (13)
C5—C6—H6B109.0C21—C20—C19118.36 (15)
H6A—C6—H6B107.8C21—C20—H20120.8
O3—C7—C14135.67 (15)C19—C20—H20120.8
O3—C7—C1112.59 (13)C20—C21—C16122.90 (14)
C14—C7—C1111.73 (13)C20—C21—Cl2117.74 (12)
O3—C8—C9113.22 (12)C16—C21—Cl2119.32 (12)
O3—C8—H8A108.9
C15—O1—C1—C72.79 (15)C12—N1—C13—C90.3 (2)
C15—O1—C1—C6122.03 (13)C10—C9—C13—N10.2 (2)
C15—O1—C1—C2115.46 (13)C8—C9—C13—N1178.20 (15)
O1—C1—C2—C368.12 (17)O3—C7—C14—C15179.93 (16)
C7—C1—C2—C3179.60 (13)C1—C7—C14—C151.50 (17)
C6—C1—C2—C352.96 (18)O3—C7—C14—C162.6 (3)
C1—C2—C3—C455.70 (18)C1—C7—C14—C16175.99 (15)
C2—C3—C4—C557.18 (19)C1—O1—C15—O2179.05 (13)
C3—C4—C5—C655.15 (19)C1—O1—C15—C142.09 (16)
O1—C1—C6—C569.25 (17)C7—C14—C15—O2179.10 (15)
C7—C1—C6—C5177.61 (13)C16—C14—C15—O23.0 (2)
C2—C1—C6—C551.22 (18)C7—C14—C15—O10.35 (16)
C4—C5—C6—C152.32 (18)C16—C14—C15—O1178.24 (13)
C8—O3—C7—C140.0 (3)C7—C14—C16—C21109.1 (2)
C8—O3—C7—C1178.59 (12)C15—C14—C16—C2168.14 (19)
O1—C1—C7—O3178.43 (12)C7—C14—C16—C1771.7 (2)
C6—C1—C7—O360.99 (17)C15—C14—C16—C17111.08 (17)
C2—C1—C7—O365.55 (16)C21—C16—C17—C181.7 (2)
O1—C1—C7—C142.66 (16)C14—C16—C17—C18179.07 (15)
C6—C1—C7—C14120.10 (15)C16—C17—C18—C191.3 (2)
C2—C1—C7—C14113.36 (15)C17—C18—C19—C200.1 (3)
C7—O3—C8—C969.36 (18)C17—C18—C19—Cl1179.83 (12)
O3—C8—C9—C1326.2 (2)C18—C19—C20—C210.7 (2)
O3—C8—C9—C10155.88 (14)Cl1—C19—C20—C21179.05 (12)
C13—C9—C10—C110.1 (2)C19—C20—C21—C160.3 (2)
C8—C9—C10—C11177.88 (16)C19—C20—C21—Cl2177.62 (12)
C9—C10—C11—C120.3 (2)C17—C16—C21—C200.9 (2)
C13—N1—C12—C110.2 (2)C14—C16—C21—C20179.87 (14)
C13—N1—C12—Cl3178.92 (12)C17—C16—C21—Cl2178.75 (12)
C10—C11—C12—N10.2 (3)C14—C16—C21—Cl22.0 (2)
C10—C11—C12—Cl3179.21 (13)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C13—H13···O30.932.532.864 (2)102

Experimental details

Crystal data
Chemical formulaC21H18Cl3NO3
Mr438.71
Crystal system, space groupMonoclinic, P21/n
Temperature (K)113
a, b, c (Å)7.2457 (14), 13.108 (3), 21.054 (4)
β (°) 95.77 (3)
V3)1989.5 (7)
Z4
Radiation typeMo Kα
µ (mm1)0.48
Crystal size (mm)0.18 × 0.12 × 0.06
Data collection
DiffractometerRigaku Saturn
diffractometer
Absorption correctionMulti-scan
(CrystalClear; Rigaku, 2005)
Tmin, Tmax0.918, 0.972
No. of measured, independent and
observed [I > 2σ(I)] reflections
14740, 3519, 3191
Rint0.041
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.034, 0.089, 1.08
No. of reflections3519
No. of parameters253
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.18, 0.31

Computer programs: CrystalClear (Rigaku, 2005), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C13—H13···O30.932.532.864 (2)102
 

References

First citationCremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc. 97, 1354–1358.  CrossRef CAS Web of Science Google Scholar
First citationLu, Y., Tao, J. Z. & Zhang, Z. R. (2008). Chem. Intermed. 10, 25–28.  Google Scholar
First citationRigaku (2005). CrystalClear. Rigaku Corporation, Tokyo, Japan.  Google Scholar
First citationSarcevic, N., Zsindely, J. & Schmid, H. (1973). Helv. Chim. Acta, 56, 1457–1476.  CAS Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationThomas, B., Jordi, B. B., Reiner, F. & Ralf, N. (2003). Chimia, 57, 697–701.  Google Scholar

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