organic compounds
Ethyl 2-(4-methoxyphenyl)-1-methyl-1H-benzimidazole-5-carboxylate
aInstitution of Excellence, University of Mysore, Manasagangotri, Mysuru 570 006, India, bPG Department of Chemistry, SDM College (Autonomous), Ujire 574 240, India, cDepartment of Chemistry, Mangalore University, Mangaluru 574 199, India, dDepartment of Chemistry, Science College, An-Najah National University, PO Box 7, Nablus, West Bank, Palestinian Territories, and eDepartment of Studies in Physics, University of Mysore, Manasagangotri, Mysuru 570 006, India
*Correspondence e-mail: lokanath@physics.uni-mysore.ac.in, khalil.i@najah.edu
In the title benzimidazole derivative, C18H18N2O3, the methoxyphenyl ring is twisted with respect to the benzimidazole ring system, making a dihedral angle of 28.81 (5)°. The pendant ethyl chain has an extended conformation. Within the imidazole ring, the C—N single bonds have a partial double-bond character. In the crystal, molecules are linked by weak C—H⋯π interactions and π–π stacking [the centroid-to-centroid distances being 3.6468 (7), 3.7279 (7) and 3.7481 (7) Å].
Keywords: crystal structure; benzimidazole; extended conformation.
CCDC reference: 1538919
Structure description
Benzimidazole and its derivatives are found to exhibit various biological activities such as antimicrobial (Göker et al., 2002), anti-inflammatory, antiallergic, antioxidant, antitubercular, anticancer, anthelmintic, antiviral and antimalarial. As part of ongoing research on benzimidazoles (Naveen et al., 2016a,b; Saberi et al., 2009), we report herein on the synthesis and of the title compound.
The title molecule, Fig. 1, is non-planar with the methoxyphenyl and the benzimidazole ring system inclined at an angle of 28.81 (5)°. The pendant ethyl chain has an extended conformation, as indicated by the C5—C16—O2—C17 torsion angle of −172.79 (10)°. The imidazole ring is planar, with a maximum deviation of 0.0163 (12) Å for the atom C7. The formal single bonds C1—N1 = 1.3839 (15) Å and C2—N1 = 1.3797 (15) Å have a partial double-bond character, and are significantly shorter than the Csp2—N bond distance. The methoxy group lies in the plane of the phenyl ring, as indicated by the C15—O1—C12—C13 torsion angle of −2.36 (18)°.
In the crystal, the molecules are linked by weak C—H⋯π (Table 1) and π–π stacking [centroid-to-centroid distances = 3.6468 (7), 3.7279 (7) and 3.7481 (7) Å] interactions.
Synthesis and crystallization
Sodium dithionite (3.0 eq) was added to a stirred solution of ethyl 3-nitro-4-(propylamino)benzoate (3.9 mmol) and 4-methoxy benzaldehyde (3.9 mmol) in DMSO (15 ml). The reaction mixture was stirred at 363 K for 3 h. After the completion of reaction [monitored by TLC hexane: ethyl acetate (7: 3, v/v)], it was poured onto crushed ice. The solid separated was filtered off, washed with water and dried. The product was recrystallized using dimethylformamide to get prismatic brown crystals. Yield 85%, m.p. 507 K.
Refinement
Crystal data, data collection and structure .
details are summarized in Table 2Structural data
CCDC reference: 1538919
https://doi.org/10.1107/S2414314617004382/xu4025sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314617004382/xu4025Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2414314617004382/xu4025Isup3.cml
Data collection: APEX2 (Bruker, 2013); cell
SAINT (Bruker, 2013); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: Mercury (Macrae et al., 2008).C18H18N2O3 | F(000) = 1312 |
Mr = 310.34 | Dx = 1.345 Mg m−3 |
Orthorhombic, Pbcn | Cu Kα radiation, λ = 1.54178 Å |
Hall symbol: -P 2n 2ab | Cell parameters from 2422 reflections |
a = 13.5151 (3) Å | θ = 6.6–64.4° |
b = 7.3929 (2) Å | µ = 0.75 mm−1 |
c = 30.6704 (8) Å | T = 296 K |
V = 3064.46 (13) Å3 | Prism, brown |
Z = 8 | 0.27 × 0.24 × 0.22 mm |
Bruker X8 Proteum diffractometer | 2510 independent reflections |
Radiation source: Bruker MicroStar microfocus rotating anode | 2422 reflections with I > 2σ(I) |
Helios multilayer optics monochromator | Rint = 0.026 |
Detector resolution: 18.4 pixels mm-1 | θmax = 64.4°, θmin = 6.6° |
φ and ω scans | h = −15→14 |
Absorption correction: multi-scan (SADABS; Bruker, 2013) | k = −8→5 |
Tmin = 0.822, Tmax = 0.852 | l = −35→28 |
10668 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.034 | H-atom parameters constrained |
wR(F2) = 0.090 | w = 1/[σ2(Fo2) + (0.048P)2 + 1.1189P] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max = 0.001 |
2510 reflections | Δρmax = 0.16 e Å−3 |
212 parameters | Δρmin = −0.15 e Å−3 |
0 restraints | Extinction correction: SHELXL97 (Sheldrick, 2008), FC*=KFC[1+0.001XFC2Λ3/SIN(2Θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0031 (4) |
Experimental. M.p.: 234 °C; IR (KBr, γmax, cm-1): 3040 (=C-H), 2953 (C-H), 1713 (C=O), 1616 (C=N), 1538 (C=C), 1296 (C-O); 1H NMR (400 MHz, DMSO-d6, δ ppm): 8.53 (s,1H, benzimidazole-H4), 8.02-8.00 (dd, 1H, 8Hz and 2Hz, benzimidazole-H6), 7.65-7.63 (dd, 2H, J = 8 Hz and 2 Hz, 4-methoxyphenyl-H), 7.40 (d, 1H, J = 8 Hz, benzimidazole-H7), 7.04 (d, 2H, J = 8 Hz, 4-methoxyphenyl-H), 4.46-4.40 (q, 2H, J = 7.5 Hz, CH2), 4.03 (s, 3H, CH3), 3.84 (s, 3H, OCH3), 1.32 (t, 3H, J = 7.5 Hz, CH3); MS (m/z): 311.4 (M+1); Anal. calcd. For C18H18N2O3: C, 69.66; H, 5.85; N, 9.03; Found: C, 69.68; H, 5.87; N, 9.06. |
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles |
Refinement. Refinement on F2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The observed criterion of F2 > 2sigma(F2) is used only for calculating -R-factor-obs 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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.08135 (7) | 0.56378 (13) | 0.71043 (3) | 0.0312 (3) | |
O2 | 0.11642 (7) | 0.08394 (12) | 0.35399 (3) | 0.0268 (3) | |
O3 | 0.27489 (7) | 0.06640 (14) | 0.33238 (3) | 0.0355 (3) | |
N1 | 0.30071 (7) | 0.35550 (13) | 0.52717 (3) | 0.0216 (3) | |
N2 | 0.13886 (7) | 0.32053 (14) | 0.51133 (3) | 0.0223 (3) | |
C1 | 0.20388 (9) | 0.36488 (16) | 0.54167 (4) | 0.0209 (3) | |
C2 | 0.29650 (9) | 0.29805 (15) | 0.48441 (4) | 0.0212 (3) | |
C3 | 0.37076 (9) | 0.26025 (16) | 0.45417 (4) | 0.0238 (4) | |
C4 | 0.33989 (9) | 0.20238 (16) | 0.41371 (4) | 0.0237 (3) | |
C5 | 0.23893 (9) | 0.18021 (16) | 0.40344 (4) | 0.0223 (3) | |
C6 | 0.16582 (9) | 0.21861 (16) | 0.43400 (4) | 0.0220 (3) | |
C7 | 0.19542 (9) | 0.27813 (15) | 0.47489 (4) | 0.0205 (3) | |
C8 | 0.39114 (9) | 0.41890 (17) | 0.54821 (4) | 0.0257 (4) | |
C9 | 0.17570 (9) | 0.41237 (16) | 0.58652 (4) | 0.0212 (3) | |
C10 | 0.08255 (9) | 0.48988 (16) | 0.59397 (4) | 0.0215 (3) | |
C11 | 0.05289 (9) | 0.53785 (17) | 0.63549 (4) | 0.0233 (3) | |
C12 | 0.11594 (9) | 0.50725 (17) | 0.67093 (4) | 0.0231 (3) | |
C13 | 0.20661 (9) | 0.42354 (17) | 0.66442 (4) | 0.0244 (3) | |
C14 | 0.23554 (9) | 0.37614 (17) | 0.62252 (4) | 0.0240 (3) | |
C15 | 0.14151 (11) | 0.5281 (2) | 0.74794 (4) | 0.0339 (4) | |
C16 | 0.21437 (9) | 0.10645 (17) | 0.35984 (4) | 0.0244 (4) | |
C17 | 0.08742 (11) | −0.0079 (2) | 0.31430 (4) | 0.0318 (4) | |
C18 | −0.02236 (11) | −0.0354 (2) | 0.31644 (5) | 0.0375 (5) | |
H3 | 0.43740 | 0.27340 | 0.46090 | 0.0290* | |
H4 | 0.38710 | 0.17720 | 0.39250 | 0.0280* | |
H6 | 0.09920 | 0.20480 | 0.42720 | 0.0260* | |
H8A | 0.42190 | 0.32030 | 0.56340 | 0.0390* | |
H8B | 0.37530 | 0.51330 | 0.56850 | 0.0390* | |
H8C | 0.43570 | 0.46490 | 0.52650 | 0.0390* | |
H10 | 0.04010 | 0.50930 | 0.57060 | 0.0260* | |
H11 | −0.00880 | 0.59040 | 0.63990 | 0.0280* | |
H13 | 0.24780 | 0.39930 | 0.68800 | 0.0290* | |
H14 | 0.29610 | 0.31900 | 0.61840 | 0.0290* | |
H15A | 0.15260 | 0.40020 | 0.75040 | 0.0510* | |
H15B | 0.10840 | 0.57100 | 0.77360 | 0.0510* | |
H15C | 0.20380 | 0.58910 | 0.74490 | 0.0510* | |
H17A | 0.12100 | −0.12340 | 0.31200 | 0.0380* | |
H17B | 0.10460 | 0.06470 | 0.28910 | 0.0380* | |
H18A | −0.03870 | −0.10130 | 0.34240 | 0.0560* | |
H18B | −0.04380 | −0.10250 | 0.29140 | 0.0560* | |
H18C | −0.05490 | 0.08010 | 0.31690 | 0.0560* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0268 (5) | 0.0484 (6) | 0.0183 (5) | 0.0074 (4) | 0.0001 (4) | −0.0012 (4) |
O2 | 0.0244 (5) | 0.0332 (5) | 0.0229 (5) | 0.0015 (4) | −0.0008 (4) | −0.0036 (4) |
O3 | 0.0303 (5) | 0.0497 (6) | 0.0266 (5) | −0.0012 (4) | 0.0074 (4) | −0.0084 (4) |
N1 | 0.0196 (5) | 0.0229 (5) | 0.0223 (5) | −0.0013 (4) | 0.0006 (4) | 0.0002 (4) |
N2 | 0.0204 (5) | 0.0251 (5) | 0.0215 (5) | 0.0004 (4) | 0.0020 (4) | 0.0002 (4) |
C1 | 0.0198 (6) | 0.0193 (6) | 0.0236 (6) | 0.0005 (5) | 0.0012 (5) | 0.0019 (5) |
C2 | 0.0221 (6) | 0.0187 (6) | 0.0227 (6) | −0.0004 (5) | 0.0012 (5) | 0.0017 (5) |
C3 | 0.0178 (6) | 0.0248 (6) | 0.0288 (7) | −0.0002 (5) | 0.0025 (5) | 0.0006 (5) |
C4 | 0.0212 (6) | 0.0238 (6) | 0.0261 (6) | 0.0015 (5) | 0.0058 (5) | 0.0006 (5) |
C5 | 0.0226 (6) | 0.0213 (6) | 0.0230 (6) | 0.0014 (5) | 0.0025 (5) | 0.0017 (5) |
C6 | 0.0184 (6) | 0.0231 (6) | 0.0244 (6) | 0.0008 (5) | 0.0010 (5) | 0.0020 (5) |
C7 | 0.0191 (6) | 0.0202 (6) | 0.0222 (6) | 0.0010 (5) | 0.0032 (5) | 0.0018 (5) |
C8 | 0.0207 (6) | 0.0275 (7) | 0.0290 (7) | −0.0036 (5) | −0.0024 (5) | 0.0022 (5) |
C9 | 0.0220 (6) | 0.0191 (6) | 0.0224 (6) | −0.0027 (5) | 0.0010 (5) | 0.0014 (5) |
C10 | 0.0205 (6) | 0.0224 (6) | 0.0217 (6) | −0.0022 (5) | −0.0020 (5) | 0.0012 (5) |
C11 | 0.0189 (6) | 0.0261 (6) | 0.0250 (6) | 0.0006 (5) | 0.0013 (5) | 0.0006 (5) |
C12 | 0.0229 (6) | 0.0264 (6) | 0.0201 (6) | −0.0028 (5) | 0.0019 (5) | 0.0010 (5) |
C13 | 0.0226 (6) | 0.0281 (6) | 0.0225 (6) | 0.0007 (5) | −0.0021 (5) | 0.0044 (5) |
C14 | 0.0210 (6) | 0.0254 (6) | 0.0256 (6) | 0.0024 (5) | 0.0013 (5) | 0.0029 (5) |
C15 | 0.0308 (7) | 0.0510 (8) | 0.0200 (6) | 0.0031 (7) | −0.0026 (5) | −0.0003 (6) |
C16 | 0.0247 (7) | 0.0254 (6) | 0.0231 (6) | 0.0013 (5) | 0.0035 (5) | 0.0022 (5) |
C17 | 0.0354 (8) | 0.0367 (7) | 0.0233 (7) | −0.0006 (6) | −0.0031 (6) | −0.0048 (6) |
C18 | 0.0356 (8) | 0.0425 (8) | 0.0344 (8) | −0.0056 (6) | −0.0051 (6) | −0.0054 (6) |
O1—C12 | 1.3641 (15) | C12—C13 | 1.3873 (17) |
O1—C15 | 1.4332 (16) | C13—C14 | 1.3882 (17) |
O2—C16 | 1.3462 (15) | C17—C18 | 1.499 (2) |
O2—C17 | 1.4479 (16) | C3—H3 | 0.9300 |
O3—C16 | 1.2108 (15) | C4—H4 | 0.9300 |
N1—C1 | 1.3839 (15) | C6—H6 | 0.9300 |
N1—C2 | 1.3797 (15) | C8—H8A | 0.9600 |
N1—C8 | 1.4594 (15) | C8—H8B | 0.9600 |
N2—C1 | 1.3212 (15) | C8—H8C | 0.9600 |
N2—C7 | 1.3899 (15) | C10—H10 | 0.9300 |
C1—C9 | 1.4699 (17) | C11—H11 | 0.9300 |
C2—C3 | 1.3948 (17) | C13—H13 | 0.9300 |
C2—C7 | 1.4047 (17) | C14—H14 | 0.9300 |
C3—C4 | 1.3773 (17) | C15—H15A | 0.9600 |
C4—C5 | 1.4099 (17) | C15—H15B | 0.9600 |
C5—C6 | 1.3912 (17) | C15—H15C | 0.9600 |
C5—C16 | 1.4818 (17) | C17—H17A | 0.9700 |
C6—C7 | 1.3880 (17) | C17—H17B | 0.9700 |
C9—C10 | 1.4020 (17) | C18—H18A | 0.9600 |
C9—C14 | 1.3946 (17) | C18—H18B | 0.9600 |
C10—C11 | 1.3813 (17) | C18—H18C | 0.9600 |
C11—C12 | 1.3996 (17) | ||
C12—O1—C15 | 117.52 (10) | C4—C3—H3 | 122.00 |
C16—O2—C17 | 115.86 (10) | C3—C4—H4 | 119.00 |
C1—N1—C2 | 106.37 (9) | C5—C4—H4 | 119.00 |
C1—N1—C8 | 129.33 (10) | C5—C6—H6 | 121.00 |
C2—N1—C8 | 123.62 (10) | C7—C6—H6 | 121.00 |
C1—N2—C7 | 104.86 (10) | N1—C8—H8A | 109.00 |
N1—C1—N2 | 112.97 (10) | N1—C8—H8B | 109.00 |
N1—C1—C9 | 123.90 (11) | N1—C8—H8C | 109.00 |
N2—C1—C9 | 123.10 (11) | H8A—C8—H8B | 110.00 |
N1—C2—C3 | 131.61 (11) | H8A—C8—H8C | 110.00 |
N1—C2—C7 | 105.66 (10) | H8B—C8—H8C | 109.00 |
C3—C2—C7 | 122.72 (11) | C9—C10—H10 | 119.00 |
C2—C3—C4 | 116.32 (11) | C11—C10—H10 | 119.00 |
C3—C4—C5 | 122.04 (11) | C10—C11—H11 | 120.00 |
C4—C5—C6 | 120.87 (11) | C12—C11—H11 | 120.00 |
C4—C5—C16 | 117.46 (11) | C12—C13—H13 | 120.00 |
C6—C5—C16 | 121.60 (11) | C14—C13—H13 | 120.00 |
C5—C6—C7 | 117.95 (11) | C9—C14—H14 | 119.00 |
N2—C7—C2 | 110.13 (10) | C13—C14—H14 | 119.00 |
N2—C7—C6 | 129.76 (11) | O1—C15—H15A | 109.00 |
C2—C7—C6 | 120.09 (11) | O1—C15—H15B | 109.00 |
C1—C9—C10 | 118.87 (11) | O1—C15—H15C | 109.00 |
C1—C9—C14 | 123.01 (11) | H15A—C15—H15B | 110.00 |
C10—C9—C14 | 118.05 (11) | H15A—C15—H15C | 109.00 |
C9—C10—C11 | 121.05 (11) | H15B—C15—H15C | 109.00 |
C10—C11—C12 | 119.85 (11) | O2—C17—H17A | 110.00 |
O1—C12—C11 | 115.57 (11) | O2—C17—H17B | 110.00 |
O1—C12—C13 | 124.56 (11) | C18—C17—H17A | 110.00 |
C11—C12—C13 | 119.88 (11) | C18—C17—H17B | 110.00 |
C12—C13—C14 | 119.65 (11) | H17A—C17—H17B | 109.00 |
C9—C14—C13 | 121.41 (11) | C17—C18—H18A | 109.00 |
O2—C16—O3 | 122.78 (11) | C17—C18—H18B | 110.00 |
O2—C16—C5 | 112.71 (10) | C17—C18—H18C | 109.00 |
O3—C16—C5 | 124.50 (11) | H18A—C18—H18B | 109.00 |
O2—C17—C18 | 107.14 (11) | H18A—C18—H18C | 110.00 |
C2—C3—H3 | 122.00 | H18B—C18—H18C | 109.00 |
C15—O1—C12—C11 | 177.32 (11) | N1—C2—C7—C6 | −179.07 (10) |
C15—O1—C12—C13 | −2.36 (18) | C3—C2—C7—N2 | 178.38 (11) |
C17—O2—C16—O3 | 5.78 (18) | C3—C2—C7—C6 | 0.00 (18) |
C17—O2—C16—C5 | −172.79 (10) | C2—C3—C4—C5 | −0.76 (17) |
C16—O2—C17—C18 | 174.33 (11) | C3—C4—C5—C6 | 0.82 (18) |
C2—N1—C1—N2 | −0.92 (13) | C3—C4—C5—C16 | −176.30 (11) |
C2—N1—C1—C9 | 176.89 (11) | C4—C5—C6—C7 | −0.41 (17) |
C8—N1—C1—N2 | 169.74 (11) | C16—C5—C6—C7 | 176.59 (11) |
C8—N1—C1—C9 | −12.44 (19) | C4—C5—C16—O2 | 177.52 (10) |
C1—N1—C2—C3 | −178.03 (12) | C4—C5—C16—O3 | −1.02 (19) |
C1—N1—C2—C7 | 0.94 (12) | C6—C5—C16—O2 | 0.42 (17) |
C8—N1—C2—C3 | 10.64 (19) | C6—C5—C16—O3 | −178.11 (12) |
C8—N1—C2—C7 | −170.39 (10) | C5—C6—C7—N2 | −178.00 (11) |
C7—N2—C1—N1 | 0.47 (13) | C5—C6—C7—C2 | 0.00 (17) |
C7—N2—C1—C9 | −177.36 (11) | C1—C9—C10—C11 | −179.61 (11) |
C1—N2—C7—C2 | 0.16 (13) | C14—C9—C10—C11 | 3.36 (18) |
C1—N2—C7—C6 | 178.32 (12) | C1—C9—C14—C13 | 179.78 (12) |
N1—C1—C9—C10 | 153.90 (11) | C10—C9—C14—C13 | −3.32 (18) |
N1—C1—C9—C14 | −29.23 (18) | C9—C10—C11—C12 | −0.71 (19) |
N2—C1—C9—C10 | −28.51 (18) | C10—C11—C12—O1 | 178.21 (11) |
N2—C1—C9—C14 | 148.37 (12) | C10—C11—C12—C13 | −2.09 (19) |
N1—C2—C3—C4 | 179.18 (12) | O1—C12—C13—C14 | −178.19 (12) |
C7—C2—C3—C4 | 0.36 (17) | C11—C12—C13—C14 | 2.14 (19) |
N1—C2—C7—N2 | −0.70 (13) | C12—C13—C14—C9 | 0.61 (19) |
Cg3 is the centroid of the C9–C14 ring. |
D—H···A | D—H | H···A | D···A | D—H···A |
C14—H14···Cg3i | 0.93 | 2.81 | 3.4950 (13) | 132 |
Symmetry code: (i) −x+1/2, y−1/2, z. |
Acknowledgements
The authors are grateful to the Institution of Excellence, Vijnana Bhavana, University of Mysore, India, for providing the single-crystal X-ray diffractometer facility.
References
Bruker (2013). APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Göker, H., Kuş, C., Boykin, D. W., Yildiz, S. & Altanlar, N. (2002). Bioorg. Med. Chem. 10, 2589–2596. Web of Science CrossRef PubMed CAS Google Scholar
Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466–470. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Naveen, S., Kumar, V., Poojary, B., Shivarama Holla, B., Lokanath, N. K. & Abdoh, M. M. M. (2016a). IUCrData, 1, x161759. Google Scholar
Naveen, S., Kumar, V., Poojary, B., Vishwanatha, P., Lokanath, N. K. & Abdoh, M. M. M. (2016b). IUCrData, 1, x161744. Google Scholar
Saberi, A., Manjunath, H. R., Naveen, S., Prasad, T. N. M., Rangappa, K. S., Sridhar, M. A. & Prasad, J. S. (2009). Mol. Cryst. Liq. Cryst. 515, 199–206. Web of Science CSD CrossRef CAS Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
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