organic compounds
Ethyl {[5-acetyl-3-cyano-4-(4-methoxyphenyl)-6-methylpyridin-2-yl]sulfanyl}acetate
aDepartment of Chemistry, Faculty of Science, Sana'a University, Sana'a, Yemen, bDepartment of Chemistry, Keene State College, 229 Main Street, Keene, NH 03435-2001, USA, cChemistry and Environmental Division, Manchester Metropolitan University, Manchester M1 5GD, England, dChemistry Department, Faculty of Science, Mini University, 61519 El-Minia, Egypt, and eDepartment of Physics, Faculty of Sciences, Erciyes University, 38039 Kayseri, Turkey
*Correspondence e-mail: shaabankamel@yahoo.com
In the title molecule, C20H20N2O4S, the dihedral angle between the benzene and pyridine rings is 60.97 (7)°. In the crystal, molecules are linked by C—H⋯O hydrogen bonds and C—H⋯π interactions, forming a three-dimensional network.
Keywords: crystal structure; pyridine ring; cyano group; hydrogen bonding; ethyl acetate derivative.
CCDC reference: 1511438
Structure description
Pyridine scaffold compounds continue to attract great interest due to their wide variety of interesting biological activities. They exhibit anticancer, analgesic, antimicrobial and antidepressant activities (Kumar et al., 2011). In addition, pyridines are used in the pharmaceutical industry as raw materials for various drugs, vitamins and fungicides (Kumar et al., 2011). These facts promoted us to synthesize and determine the of the title compound.
The dihedral angle between the benzene and pyridine rings of the title molecule (Fig. 1) is 60.97 (7)°. The torsion C10—C11—O4—C20, C5—C6—C15—C16, C5—C6—C15—O3, N1—C3—S1—C2, C3—S1—C2—C1, C2—C1—O2—C18 and C1—O2—C18—C19 are 3.6 (2), 73.37 (19), −109.33 (17), −20.05 (13), −73.89 (12), −174.92 (13) and 75.85 (18), respectively. All bonds and bond angles in the title molecule are within the normal range.
In the via C—H⋯O hydrogen bonds and C—H⋯π interactions with each to other, forming a three-dimensional network (Fig. 2 and Table 1).
adjacent molecules are connectedSynthesis and crystallization
To a mixture of 5-acetyl-3-cyano-4-(4-methoxyphenyl)-6-methylpyridine-2(1H)-thione (10 mmol) and ethyl chloroacetate (10 mmol) in ethanol (20 ml), sodium acetate trihydrate (11 mmol) was added. The resulting mixture was heated under reflux for 2 h and then allowed to cool. The precipitated solid was collected and recrystallized from ethanol (yield 98%; m.p. 409–410 K). IR: 2200 (CN), 1730 (C=O, ester), 1690 (C=O, acetyl) cm-1. 1H NMR (CDCl3): 6.9–7.4 (dd, 4H, ArH); 4.1–4.3 (q, 2H, OCH2); 3.9 (s, 2H, SCH2); 3.7 (s, 3H, OCH3); 2.4 (s, 3H, COCH3); 1.8 (s, 3H, CH3 at C-6); 1.1–1.3 (t, 3H, CH3 of ester).
Refinement
Crystal data, data collection and structure .
details are summarized in Table 2
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Structural data
CCDC reference: 1511438
https://doi.org/10.1107/S2414314616017156/bv4005sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314616017156/bv4005Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2414314616017156/bv4005Isup3.cml
Data collection: CrysAlis PRO (Agilent, 2014); cell
CrysAlis PRO (Agilent, 2014); data reduction: CrysAlis PRO (Agilent, 2014); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).C20H20N2O4S | F(000) = 808 |
Mr = 384.44 | Dx = 1.364 Mg m−3 |
Monoclinic, P21/c | Cu Kα radiation, λ = 1.54184 Å |
a = 13.4883 (2) Å | Cell parameters from 3634 reflections |
b = 8.23273 (16) Å | θ = 4.1–71.5° |
c = 16.8923 (3) Å | µ = 1.78 mm−1 |
β = 93.8000 (17)° | T = 173 K |
V = 1871.69 (6) Å3 | Irregular, colourless |
Z = 4 | 0.49 × 0.46 × 0.22 mm |
Rigaku Oxford Diffraction diffractometer | 3553 independent reflections |
Radiation source: Enhance (Cu) X-ray Source | 3278 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.026 |
Detector resolution: 16.0416 pixels mm-1 | θmax = 71.2°, θmin = 3.3° |
ω scans | h = −16→15 |
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2014) | k = −9→6 |
Tmin = 0.600, Tmax = 1.000 | l = −20→20 |
6913 measured reflections |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.040 | w = 1/[σ2(Fo2) + (0.0702P)2 + 0.4141P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.112 | (Δ/σ)max = 0.001 |
S = 1.05 | Δρmax = 0.29 e Å−3 |
3553 reflections | Δρmin = −0.29 e Å−3 |
249 parameters | Extinction correction: SHELXL2014 (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.0045 (4) |
Primary atom site location: structure-invariant direct methods |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
x | y | z | Uiso*/Ueq | ||
S1 | 0.62202 (3) | 1.02799 (5) | 0.73252 (2) | 0.02850 (15) | |
O1 | 0.41273 (8) | 0.94698 (14) | 0.79041 (6) | 0.0281 (3) | |
O2 | 0.45128 (8) | 1.05466 (14) | 0.91107 (6) | 0.0282 (3) | |
O3 | 0.75861 (9) | 0.29044 (14) | 0.87453 (8) | 0.0367 (3) | |
O4 | 1.05277 (9) | 0.32068 (14) | 0.56752 (7) | 0.0331 (3) | |
N1 | 0.63715 (9) | 0.78612 (15) | 0.83887 (7) | 0.0222 (3) | |
N2 | 0.80930 (12) | 0.90691 (19) | 0.60820 (9) | 0.0378 (4) | |
C1 | 0.46752 (11) | 1.02342 (17) | 0.83507 (9) | 0.0222 (3) | |
C2 | 0.56182 (11) | 1.10919 (18) | 0.81526 (9) | 0.0248 (3) | |
H2A | 0.6093 | 1.1056 | 0.8625 | 0.030* | |
H2B | 0.5460 | 1.2247 | 0.8043 | 0.030* | |
C3 | 0.67375 (10) | 0.84809 (18) | 0.77408 (8) | 0.0212 (3) | |
C4 | 0.75159 (10) | 0.77387 (18) | 0.73602 (8) | 0.0208 (3) | |
C5 | 0.79313 (10) | 0.62958 (18) | 0.76679 (8) | 0.0204 (3) | |
C6 | 0.75585 (10) | 0.56783 (18) | 0.83602 (8) | 0.0207 (3) | |
C7 | 0.67650 (10) | 0.64734 (18) | 0.86890 (8) | 0.0217 (3) | |
C8 | 0.86906 (11) | 0.54322 (18) | 0.72251 (8) | 0.0208 (3) | |
C9 | 0.95693 (11) | 0.61926 (19) | 0.70468 (9) | 0.0254 (3) | |
H9 | 0.9722 | 0.7235 | 0.7262 | 0.030* | |
C10 | 1.02267 (11) | 0.54571 (19) | 0.65599 (9) | 0.0243 (3) | |
H10 | 1.0839 | 0.5966 | 0.6463 | 0.029* | |
C11 | 0.99780 (11) | 0.39687 (18) | 0.62161 (9) | 0.0231 (3) | |
C12 | 0.91130 (11) | 0.31666 (18) | 0.64035 (9) | 0.0245 (3) | |
H12 | 0.8958 | 0.2131 | 0.6180 | 0.029* | |
C13 | 0.84814 (10) | 0.38804 (18) | 0.69154 (9) | 0.0221 (3) | |
H13 | 0.7905 | 0.3317 | 0.7057 | 0.027* | |
C14 | 0.78475 (11) | 0.84630 (19) | 0.66472 (9) | 0.0254 (3) | |
C15 | 0.80209 (11) | 0.41777 (18) | 0.87574 (8) | 0.0221 (3) | |
C16 | 0.90163 (13) | 0.4406 (2) | 0.91893 (11) | 0.0347 (4) | |
H16A | 0.8959 | 0.5187 | 0.9622 | 0.052* | |
H16B | 0.9488 | 0.4817 | 0.8821 | 0.052* | |
H16C | 0.9253 | 0.3363 | 0.9408 | 0.052* | |
C17 | 0.62897 (13) | 0.5812 (2) | 0.94013 (10) | 0.0302 (4) | |
H17A | 0.5897 | 0.6668 | 0.9635 | 0.045* | |
H17B | 0.6807 | 0.5437 | 0.9794 | 0.045* | |
H17C | 0.5855 | 0.4901 | 0.9240 | 0.045* | |
C18 | 0.35925 (12) | 0.9943 (2) | 0.94011 (10) | 0.0300 (4) | |
H18A | 0.3038 | 1.0188 | 0.9006 | 0.036* | |
H18B | 0.3462 | 1.0517 | 0.9899 | 0.036* | |
C19 | 0.36222 (13) | 0.8147 (2) | 0.95549 (10) | 0.0340 (4) | |
H19A | 0.3677 | 0.7566 | 0.9053 | 0.051* | |
H19B | 0.3012 | 0.7813 | 0.9794 | 0.051* | |
H19C | 0.4197 | 0.7888 | 0.9918 | 0.051* | |
C20 | 1.13748 (12) | 0.4044 (2) | 0.54211 (10) | 0.0327 (4) | |
H20A | 1.1696 | 0.3381 | 0.5030 | 0.049* | |
H20B | 1.1845 | 0.4244 | 0.5878 | 0.049* | |
H20C | 1.1166 | 0.5083 | 0.5180 | 0.049* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.0316 (2) | 0.0278 (2) | 0.0272 (2) | 0.00865 (15) | 0.01043 (16) | 0.00996 (14) |
O1 | 0.0252 (5) | 0.0322 (6) | 0.0262 (6) | −0.0021 (5) | −0.0026 (4) | −0.0026 (4) |
O2 | 0.0259 (5) | 0.0345 (6) | 0.0248 (6) | −0.0081 (5) | 0.0054 (4) | −0.0048 (4) |
O3 | 0.0307 (6) | 0.0269 (6) | 0.0525 (7) | −0.0050 (5) | 0.0021 (5) | 0.0100 (5) |
O4 | 0.0322 (6) | 0.0278 (6) | 0.0413 (6) | 0.0027 (5) | 0.0161 (5) | −0.0049 (5) |
N1 | 0.0195 (6) | 0.0241 (6) | 0.0234 (6) | 0.0019 (5) | 0.0037 (5) | 0.0025 (5) |
N2 | 0.0459 (9) | 0.0391 (8) | 0.0298 (7) | 0.0026 (7) | 0.0132 (6) | 0.0077 (6) |
C1 | 0.0222 (7) | 0.0207 (7) | 0.0235 (7) | 0.0042 (6) | 0.0010 (6) | 0.0022 (6) |
C2 | 0.0251 (7) | 0.0211 (7) | 0.0288 (7) | 0.0009 (6) | 0.0075 (6) | 0.0008 (6) |
C3 | 0.0189 (7) | 0.0226 (7) | 0.0221 (7) | −0.0005 (5) | 0.0012 (5) | 0.0018 (5) |
C4 | 0.0202 (6) | 0.0230 (7) | 0.0195 (6) | −0.0021 (5) | 0.0029 (5) | 0.0005 (5) |
C5 | 0.0172 (6) | 0.0230 (7) | 0.0208 (6) | −0.0024 (5) | 0.0008 (5) | −0.0020 (6) |
C6 | 0.0186 (7) | 0.0214 (7) | 0.0219 (7) | −0.0016 (5) | 0.0000 (5) | 0.0001 (6) |
C7 | 0.0206 (7) | 0.0237 (7) | 0.0207 (7) | −0.0020 (6) | 0.0016 (5) | 0.0011 (6) |
C8 | 0.0186 (7) | 0.0236 (7) | 0.0201 (7) | 0.0016 (5) | 0.0004 (5) | 0.0010 (5) |
C9 | 0.0233 (7) | 0.0258 (8) | 0.0270 (7) | −0.0044 (6) | 0.0018 (6) | −0.0041 (6) |
C10 | 0.0189 (7) | 0.0262 (8) | 0.0279 (7) | −0.0019 (6) | 0.0030 (6) | 0.0001 (6) |
C11 | 0.0228 (7) | 0.0228 (7) | 0.0240 (7) | 0.0053 (6) | 0.0035 (6) | 0.0026 (6) |
C12 | 0.0250 (7) | 0.0200 (7) | 0.0285 (7) | 0.0001 (6) | 0.0019 (6) | 0.0000 (6) |
C13 | 0.0188 (7) | 0.0225 (7) | 0.0250 (7) | −0.0003 (5) | 0.0014 (5) | 0.0029 (6) |
C14 | 0.0252 (7) | 0.0260 (8) | 0.0254 (8) | 0.0011 (6) | 0.0051 (6) | 0.0003 (6) |
C15 | 0.0236 (7) | 0.0219 (7) | 0.0214 (7) | 0.0020 (6) | 0.0058 (5) | 0.0010 (6) |
C16 | 0.0357 (9) | 0.0247 (8) | 0.0416 (10) | 0.0044 (7) | −0.0126 (7) | −0.0005 (7) |
C17 | 0.0317 (8) | 0.0309 (8) | 0.0291 (8) | 0.0052 (7) | 0.0115 (6) | 0.0082 (7) |
C18 | 0.0246 (8) | 0.0367 (9) | 0.0294 (8) | −0.0035 (7) | 0.0077 (6) | −0.0032 (7) |
C19 | 0.0348 (8) | 0.0386 (9) | 0.0292 (8) | −0.0068 (7) | 0.0055 (7) | 0.0022 (7) |
C20 | 0.0278 (8) | 0.0364 (9) | 0.0352 (8) | 0.0043 (7) | 0.0127 (7) | 0.0006 (7) |
S1—C2 | 1.7917 (15) | C9—H9 | 0.9500 |
S1—C3 | 1.7630 (15) | C9—C10 | 1.388 (2) |
O1—C1 | 1.1988 (19) | C10—H10 | 0.9500 |
O2—C1 | 1.3415 (18) | C10—C11 | 1.388 (2) |
O2—C18 | 1.4522 (19) | C11—C12 | 1.395 (2) |
O3—C15 | 1.201 (2) | C12—H12 | 0.9500 |
O4—C11 | 1.3666 (18) | C12—C13 | 1.384 (2) |
O4—C20 | 1.425 (2) | C13—H13 | 0.9500 |
N1—C3 | 1.3318 (18) | C15—C16 | 1.497 (2) |
N1—C7 | 1.345 (2) | C16—H16A | 0.9800 |
N2—C14 | 1.145 (2) | C16—H16B | 0.9800 |
C1—C2 | 1.512 (2) | C16—H16C | 0.9800 |
C2—H2A | 0.9900 | C17—H17A | 0.9800 |
C2—H2B | 0.9900 | C17—H17B | 0.9800 |
C3—C4 | 1.407 (2) | C17—H17C | 0.9800 |
C4—C5 | 1.399 (2) | C18—H18A | 0.9900 |
C4—C14 | 1.441 (2) | C18—H18B | 0.9900 |
C5—C6 | 1.399 (2) | C18—C19 | 1.502 (2) |
C5—C8 | 1.489 (2) | C19—H19A | 0.9800 |
C6—C7 | 1.400 (2) | C19—H19B | 0.9800 |
C6—C15 | 1.520 (2) | C19—H19C | 0.9800 |
C7—C17 | 1.502 (2) | C20—H20A | 0.9800 |
C8—C9 | 1.391 (2) | C20—H20B | 0.9800 |
C8—C13 | 1.402 (2) | C20—H20C | 0.9800 |
C3—S1—C2 | 100.99 (7) | C11—C12—H12 | 120.0 |
C1—O2—C18 | 117.07 (12) | C13—C12—C11 | 119.96 (14) |
C11—O4—C20 | 117.44 (13) | C13—C12—H12 | 120.0 |
C3—N1—C7 | 118.48 (12) | C8—C13—H13 | 119.9 |
O1—C1—O2 | 124.74 (14) | C12—C13—C8 | 120.19 (13) |
O1—C1—C2 | 126.77 (14) | C12—C13—H13 | 119.9 |
O2—C1—C2 | 108.39 (12) | N2—C14—C4 | 178.24 (17) |
S1—C2—H2A | 108.4 | O3—C15—C6 | 121.09 (13) |
S1—C2—H2B | 108.4 | O3—C15—C16 | 122.63 (14) |
C1—C2—S1 | 115.46 (11) | C16—C15—C6 | 116.22 (13) |
C1—C2—H2A | 108.4 | C15—C16—H16A | 109.5 |
C1—C2—H2B | 108.4 | C15—C16—H16B | 109.5 |
H2A—C2—H2B | 107.5 | C15—C16—H16C | 109.5 |
N1—C3—S1 | 119.38 (11) | H16A—C16—H16B | 109.5 |
N1—C3—C4 | 122.54 (13) | H16A—C16—H16C | 109.5 |
C4—C3—S1 | 118.07 (11) | H16B—C16—H16C | 109.5 |
C3—C4—C14 | 118.99 (13) | C7—C17—H17A | 109.5 |
C5—C4—C3 | 119.46 (13) | C7—C17—H17B | 109.5 |
C5—C4—C14 | 121.53 (13) | C7—C17—H17C | 109.5 |
C4—C5—C6 | 117.52 (13) | H17A—C17—H17B | 109.5 |
C4—C5—C8 | 119.40 (12) | H17A—C17—H17C | 109.5 |
C6—C5—C8 | 122.95 (13) | H17B—C17—H17C | 109.5 |
C5—C6—C7 | 119.22 (13) | O2—C18—H18A | 109.1 |
C5—C6—C15 | 120.31 (13) | O2—C18—H18B | 109.1 |
C7—C6—C15 | 120.46 (13) | O2—C18—C19 | 112.44 (14) |
N1—C7—C6 | 122.72 (13) | H18A—C18—H18B | 107.8 |
N1—C7—C17 | 115.53 (13) | C19—C18—H18A | 109.1 |
C6—C7—C17 | 121.75 (13) | C19—C18—H18B | 109.1 |
C9—C8—C5 | 121.23 (13) | C18—C19—H19A | 109.5 |
C9—C8—C13 | 118.85 (13) | C18—C19—H19B | 109.5 |
C13—C8—C5 | 119.64 (13) | C18—C19—H19C | 109.5 |
C8—C9—H9 | 119.4 | H19A—C19—H19B | 109.5 |
C10—C9—C8 | 121.27 (14) | H19A—C19—H19C | 109.5 |
C10—C9—H9 | 119.4 | H19B—C19—H19C | 109.5 |
C9—C10—H10 | 120.4 | O4—C20—H20A | 109.5 |
C11—C10—C9 | 119.14 (14) | O4—C20—H20B | 109.5 |
C11—C10—H10 | 120.4 | O4—C20—H20C | 109.5 |
O4—C11—C10 | 123.93 (13) | H20A—C20—H20B | 109.5 |
O4—C11—C12 | 115.68 (14) | H20A—C20—H20C | 109.5 |
C10—C11—C12 | 120.37 (14) | H20B—C20—H20C | 109.5 |
S1—C3—C4—C5 | −178.97 (11) | C5—C8—C13—C12 | 170.24 (13) |
S1—C3—C4—C14 | −0.71 (19) | C6—C5—C8—C9 | −125.95 (16) |
O1—C1—C2—S1 | −25.7 (2) | C6—C5—C8—C13 | 60.16 (19) |
O2—C1—C2—S1 | 157.87 (10) | C7—N1—C3—S1 | 178.89 (10) |
O4—C11—C12—C13 | −176.80 (13) | C7—N1—C3—C4 | 0.1 (2) |
N1—C3—C4—C5 | −0.2 (2) | C7—C6—C15—O3 | 71.7 (2) |
N1—C3—C4—C14 | 178.08 (13) | C7—C6—C15—C16 | −105.64 (17) |
C1—O2—C18—C19 | 75.85 (18) | C8—C5—C6—C7 | −172.72 (13) |
C2—S1—C3—N1 | 20.05 (13) | C8—C5—C6—C15 | 8.3 (2) |
C2—S1—C3—C4 | −161.11 (12) | C8—C9—C10—C11 | 3.0 (2) |
C3—S1—C2—C1 | −73.89 (12) | C9—C8—C13—C12 | −3.8 (2) |
C3—N1—C7—C6 | 1.6 (2) | C9—C10—C11—O4 | 174.13 (14) |
C3—N1—C7—C17 | −177.76 (13) | C9—C10—C11—C12 | −4.7 (2) |
C3—C4—C5—C6 | −1.4 (2) | C10—C11—C12—C13 | 2.1 (2) |
C3—C4—C5—C8 | 174.50 (13) | C11—C12—C13—C8 | 2.2 (2) |
C4—C5—C6—C7 | 3.1 (2) | C13—C8—C9—C10 | 1.2 (2) |
C4—C5—C6—C15 | −175.95 (12) | C14—C4—C5—C6 | −179.65 (13) |
C4—C5—C8—C9 | 58.34 (19) | C14—C4—C5—C8 | −3.7 (2) |
C4—C5—C8—C13 | −115.55 (16) | C15—C6—C7—N1 | 175.72 (13) |
C5—C6—C7—N1 | −3.3 (2) | C15—C6—C7—C17 | −4.9 (2) |
C5—C6—C7—C17 | 176.07 (14) | C18—O2—C1—O1 | −1.6 (2) |
C5—C6—C15—O3 | −109.33 (17) | C18—O2—C1—C2 | 174.92 (13) |
C5—C6—C15—C16 | 73.37 (19) | C20—O4—C11—C10 | −3.6 (2) |
C5—C8—C9—C10 | −172.76 (14) | C20—O4—C11—C12 | 175.24 (13) |
Cg1 and Cg2 are the centroids of the pyridine (N1/C3–C7) and benzene (C8–C13) rings, respectively. |
D—H···A | D—H | H···A | D···A | D—H···A |
C2—H2A···O3i | 0.99 | 2.52 | 3.150 (2) | 121 |
C2—H2B···O1ii | 0.99 | 2.52 | 3.3345 (19) | 140 |
C19—H19C···O2iii | 0.98 | 2.65 | 3.437 (2) | 138 |
C9—H9···Cg2iv | 0.95 | 2.88 | 3.7803 (17) | 159 |
C20—H20B···Cg1v | 0.98 | 2.84 | 3.5619 (18) | 131 |
Symmetry codes: (i) x, y+1, z; (ii) −x+1, y+1/2, −z+3/2; (iii) −x+1, −y+2, −z+2; (iv) −x+2, y+1/2, −z+3/2; (v) −x+2, y−1/2, −z+3/2. |
Acknowledgements
JPJ would like to acknowledge the NSF–MRI program (grant No. CHE-1039027) for funds to purchase the X ray diffractometer.
References
Agilent (2014). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, Oxfordshire, England. Google Scholar
Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339–341. Web of Science CrossRef CAS IUCr Journals Google Scholar
Kumar, S., Sharma, P. K., Dudhe, R. & Kumar, N. (2011). J. Chronother. Drug Deliv, 2, 71–78. CAS Google Scholar
Sheldrick, G. M. (2015a). Acta Cryst. A71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Sheldrick, G. M. (2015b). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
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