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Logo of actae2this articlesearchopen accesssubmitActa Crystallographica Section E: Crystallographic CommunicationsActa Crystallographica Section E: Crystallographic Communications
 
Acta Crystallogr E Crystallogr Commun. 2017 October 1; 73(Pt 10): 1430–1433.
Published online 2017 September 8. doi:  10.1107/S2056989017012701
PMCID: PMC5730289

Crystal structures of 2-(benzene­carbo­thio­yloxy)ethyl benzene­carbo­thio­ate and 2-(benzene­carbo­thio­yloxy)ethyl benzoate

Abstract

The title compounds, C16H14O2S2 and C16H14O3S, which are monomeric models (models D and E) for a polythio­noester and a poly(ester-co-thio­noester), respectively, crystallize in the space group P21/c and are isostructural with each other. The mol­ecule in each crystal is located on an inversion centre and has an all-trans structure. The asymmetric unit comprises one half-mol­ecule. In the crystal, there are inter­molecular C(...)S contacts [3.391 (3) and 3.308 (3) Å for models D and E, respectively] and C—H(...)π inter­actions, which form a layer structure parallel to the bc plane. The carbonyl and thio­carbonyl groups of the model E compound are each disordered over two equivalent sites about the inversion centre with equal occupancies.

Keywords: crystal structure, thio­noester, all-trans structure, C(...)S close contact, C—H(...)π inter­action

Chemical context  

Compounds expressed as C6H5—C(=X)—Y—CH2—CH2Y—C(=X)—C6H5 (X, Y = O or S) can be considered to be monomeric models for polymers, [—C(=X)—C6H4—C(=X)—Y—CH2—CH2Y—]x, namely, X = Y = O, poly(ethyl­ene terephthalate) (designated herein as polymer A); X = O and Y = S, poly(ethyl­ene di­thio­terephthalate) (polymer B); X = Y = S, poly(ethyl­ene tetra­thio­terephthalate) (polymer C); X = S and Y = O, poly(ethyl­ene di­thio­noterephthalate) (polymer D). It is well established that the solution, mechanical and thermal properties of such aromatic polymers are essentially determined by the conformational characteristics of the Y—CH2—CH2Y unit (referred hereafter to as the spacer) and inter­molecular inter­actions between the benzene rings (Sasanuma, 2009  ; Sasanuma et al., 2013  ). In expectation that replacement of oxygen by sulfur at the X or Y site would affect the spacer conformation, and π–π and C—H(...)π inter­actions of the benzene rings, and thus lead to variations in the physical properties, we synthesized polymers B and C, and characterized them by X-ray diffraction, NMR spectroscopy, thermal analyses, mol­ecular orbital calculations and statistical mechanics of the chain mol­ecules (Abe & Sasanuma, 2012  ). Herein, the monomeric models for polymers AD are termed models AD, respectively.

By mol­ecular orbital calculations at the second-order Møller–Plesset perturbation (MP2) level with moderate-size basis sets, we have determined the most stable conformations of the Y—CH2—CH2Y parts of the models and evaluated their free energies relative to that of the all-trans form as follows: model A, tgt and −1.1 kcal mol−1 (Sasanuma, 2009  ); model B, g±tg[minus-or-plus sign] and −3.1 kcal mol−1 (Abe & Sasanuma, 2012  ); model C, g±tg[minus-or-plus sign] and −2.1 kcal mol−1 (Abe & Sasanuma, 2012  ); model D, tgt and −1.7 kcal mol−1 (this study). We have also predicted that an asymmetric model compound, C6H5—C(=O)—O—CH2—CH2—O—C(=S)—C6H5 (model E), would be most stabilized in the tg±g[minus-or-plus sign] conformation with a free energy of −1.8 kcal mol−1 (this study). However, not all the models and polymers crystallize in the lowest-energy conformations: model (polymer) A, ttt (ttt) (Pérez & Brisse, 1976  ; Daubeny et al., 1954  ); model (polymer) B, g±tg[minus-or-plus sign] (g±tg[minus-or-plus sign]) (Deguire & Brisse, 1988  ; Abe & Sasanuma, 2012  ); model (polymer) C, g±tg[minus-or-plus sign] (amorphous) (Abe et al., 2011  ; Abe & Sasanuma, 2012  ). In the crystals, the mol­ecules adopt conformations so as to form inter­molecular inter­actions effectively and minimize the total of intra­molecular and inter­molecular inter­action energies. Inter­estingly, however, models AC crystallize in the same spacer conformation as those of the corresponding polymers; therefore, the crystal structure of the model suggests the polymer conformation. This study has aimed to determine crystal structures of the title compounds (models D and E) to predict the crystal conformations of polymers D and E on the above hypothesis.

An external file that holds a picture, illustration, etc.
Object name is e-73-01430-scheme1.jpg

Structural commentary  

The mol­ecule of model D lies on an inversion centre and the asymmetric unit contains one half-mol­ecule. The central O—CH2—CH2—O unit adopts an all-trans conformation (Fig. 1  ). The mol­ecule of model E is also located on an inversion centre and the O—CH2—CH2—O bond sequence is in an all-trans conformation. Since the mol­ecule has carbonyl and thio­carbonyl groups, the atoms S and O (S1 and O2) are each assumed to be disordered over two equivalent sites about the inversion centre with equal occupancies (Fig. 2  ). Consequently, it was proved that all the models (A, D and E) with the O—CH2—CH2—O spacer crystallize with all-trans structures, although models A, D and E in the free state are most stabilized in tgt, tgt, and tg±g[minus-or-plus sign] conformations, respectively.

Figure 1
The mol­ecular structure of model D, showing atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. The unlabelled atoms are related to the labelled atoms by inversion symmetry (symmetry code: 2 −  ...
Figure 2
The mol­ecular structure of model E, showing atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. The unlabelled atoms are related to the labelled atoms by inversion symmetry (symmetry code: 2 −  ...

Supra­molecular features  

The compounds of models D and E are isotypic and crystallize in the space group P21/c. There are no classical hydrogen bonds but inter­molecular close contacts between atoms C and S [C1—S1i = 3.391 (3) and 3.308 (3) Å for models D and E, respectively; symmetry code: (i) x, –y + An external file that holds a picture, illustration, etc.
Object name is e-73-01430-efi1.jpg, z – An external file that holds a picture, illustration, etc.
Object name is e-73-01430-efi1.jpg]. Both compounds also have C—H(...)π inter­actions (Tables 1  and 2  ) and form layer structures parallel to the bc plane via these inter­molecular inter­actions (Figs. 3  and 4  ).

Figure 3
A packing diagram of model D, showing inter­molecular C(...)S contacts (red dotted lines) and C—H(...)π inter­actions (blue dotted lines).
Figure 4
A packing diagram of model E, showing inter­molecular C(...)S contacts (red dotted lines) and C—H(...)π inter­actions (blue dotted lines).
Table 1
C—H(...)π inter­action geometry (Å, °) for model D
Table 2
C—H(...)π inter­action geometry (Å, °) for model E

Synthesis and crystallization  

Benzoyl chloride (10.0 ml, 87 mmol) was added dropwise under a nitro­gen atmosphere to ethyl­ene glycol (2.4 ml, 43 mmol) and pyridine (7.0 ml, 87 mmol) placed in a four-necked flask connected to a drying tube filled with calcium chloride, and the mixture was stirred at room temperature overnight. Water was added to the reaction mixture to yield a precipitate, which was collected by filtration, dissolved in chloro­form, washed thrice with 5% aqueous solution of sodium bicarbonate, and dried over anhydrous magnesium sulfate overnight. The liquid phase was separated by filtration and condensed on a rotary evaporator, and the residue was recrystallized from ethanol (15 ml). The white crystallites thus obtained were dried under reduced pressure at room temperature overnight to yield ethane-1,2-diyl dibenzoate (8.3 g, 71%). The synthesized ethane-1,2-diyl dibenzoate (0.10 g, 0.37 mmol) was ground in a mortar and mixed thoroughly with Lawesson’s reagent (0.24 g, 0.59 mmol), and the powder mixture was moved to a 15 ml vial container and placed in a Yuasa PRE-7017R microwave oven. The powder was heated under the following microwave irradiation at 500 W: on for 2.0 min – off for several seconds – on for 1.0 min. The above handling was repeated ten times to obtain the product sufficiently.

The crude product was extracted with chloro­form and condensed under reduced pressure. The residue was dissolved in a mixed solvent of ethyl acetate and n-hexane (1:9 v/v) and subjected to column chromatography. The yellowish fraction (R f = 0.5) was collected and condensed, and the residue underwent column chromatography again with a mixed solvent of toluene and n-hexane (1:5 v/v). Two yellow fractions [(1) R f = 0.1 and (2) 0.3 − 0.5] were stratified and collected separately. The layer (1) was condensed and recrystallized from ethanol to yield a yellow solid, which was identified as 2-(benzene­carbo­thio­yloxy)ethyl benzoate (model E, yield 23%) by 1H and 13C NMR, and the layer (2) was condensed and dried at room temperature overnight to yield a red solid, which was identified as 2-(benzene­carbo­thio­yloxy)ethyl benzene­carbo­thio­ate (model D, yield 0.9%). A small qu­antity of model D was dissolved in chloro­form in a thin vial container. The vessel was placed in a larger vial containing a small amount of n-hexane, and the outer container was capped. After a week, single crystals were found to be formed in the inner vessel. Single crystals of model E were prepared similarly.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 3  . All H atoms were geometrically positioned with C—H = 0.95 and 0.99 Å for the aromatic and methyl­ene groups, respectively, and were refined as riding with U iso(H) = 1.2 U eq(C).

Table 3
Experimental details

Supplementary Material

Crystal structure: contains datablock(s) General, model_D, model_E. DOI: 10.1107/S2056989017012701/is5479sup1.cif

Structure factors: contains datablock(s) model_D. DOI: 10.1107/S2056989017012701/is5479model_Dsup4.hkl

Structure factors: contains datablock(s) model_E. DOI: 10.1107/S2056989017012701/is5479model_Esup5.hkl

CCDC references: 1572676, 1572675

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

2-(Benzenecarbothioyloxy)ethyl benzenecarbothioate (model_D)   Crystal data

C16H14O2S2F(000) = 316
Mr = 302.39Dx = 1.374 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 8.829 (5) ÅCell parameters from 2339 reflections
b = 11.680 (7) Åθ = 2.5–27.6°
c = 7.727 (5) ŵ = 0.36 mm1
β = 113.475 (10)°T = 173 K
V = 730.9 (8) Å3Prismatic, yellow
Z = 20.40 × 0.40 × 0.20 mm

2-(Benzenecarbothioyloxy)ethyl benzenecarbothioate (model_D)   Data collection

Bruker APEXII CCD area detector diffractometer1617 independent reflections
Radiation source: fine-focus sealed tube1487 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.014
Detector resolution: 8.3333 pixels mm-1θmax = 27.4°, θmin = 2.5°
[var phi] and ω scansh = −10→11
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)k = −13→15
Tmin = 0.88, Tmax = 0.93l = −9→5
4017 measured reflections

2-(Benzenecarbothioyloxy)ethyl benzenecarbothioate (model_D)   Refinement

Refinement on F20 restraints
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.029H-atom parameters constrained
wR(F2) = 0.080w = 1/[σ2(Fo2) + (0.0425P)2 + 0.2706P] where P = (Fo2 + 2Fc2)/3
S = 1.03(Δ/σ)max = 0.001
1617 reflectionsΔρmax = 0.39 e Å3
91 parametersΔρmin = −0.20 e Å3

2-(Benzenecarbothioyloxy)ethyl benzenecarbothioate (model_D)   Special details

Experimental. SADABS (Sheldrick 1996)
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.

2-(Benzenecarbothioyloxy)ethyl benzenecarbothioate (model_D)   Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/Ueq
C10.70662 (15)0.86862 (11)0.98706 (17)0.0209 (3)
C20.52641 (15)0.87852 (10)0.86705 (17)0.0205 (3)
C30.41444 (16)0.80285 (12)0.89460 (19)0.0271 (3)
H30.45320.74680.99160.033*
C40.24591 (17)0.80973 (13)0.7796 (2)0.0312 (3)
H40.17050.75860.79910.037*
C50.18837 (16)0.89124 (13)0.6367 (2)0.0309 (3)
H50.07410.89470.55720.037*
C60.29824 (17)0.96779 (13)0.6101 (2)0.0316 (3)
H60.25851.0240.51360.038*
C70.46690 (16)0.96209 (11)0.72503 (19)0.0259 (3)
H70.54131.01480.7070.031*
C80.97120 (15)0.94978 (12)1.04144 (19)0.0267 (3)
H8A1.01840.87711.01940.032*
H8B1.00410.95991.17880.032*
O10.79324 (11)0.95006 (8)0.94319 (13)0.0252 (2)
S10.79118 (4)0.77062 (3)1.15081 (5)0.02945 (13)

2-(Benzenecarbothioyloxy)ethyl benzenecarbothioate (model_D)   Atomic displacement parameters (Å2)

U11U22U33U12U13U23
C10.0204 (6)0.0227 (6)0.0205 (6)−0.0032 (5)0.0091 (5)−0.0036 (5)
C20.0189 (6)0.0224 (6)0.0205 (6)−0.0013 (5)0.0080 (5)−0.0036 (5)
C30.0232 (6)0.0300 (7)0.0265 (7)−0.0040 (5)0.0081 (5)0.0023 (5)
C40.0221 (6)0.0373 (8)0.0334 (7)−0.0072 (6)0.0103 (6)−0.0024 (6)
C50.0191 (6)0.0376 (8)0.0318 (7)0.0020 (5)0.0057 (5)−0.0050 (6)
C60.0274 (7)0.0315 (7)0.0314 (7)0.0051 (6)0.0068 (6)0.0049 (6)
C70.0244 (7)0.0244 (6)0.0283 (7)−0.0010 (5)0.0099 (5)0.0014 (5)
C80.0170 (6)0.0314 (7)0.0281 (6)−0.0041 (5)0.0051 (5)0.0030 (5)
O10.0174 (4)0.0269 (5)0.0282 (5)−0.0042 (3)0.0057 (4)0.0037 (4)
S10.02236 (19)0.0332 (2)0.0302 (2)−0.00007 (13)0.00763 (14)0.00936 (13)

2-(Benzenecarbothioyloxy)ethyl benzenecarbothioate (model_D)   Geometric parameters (Å, º)

C1—O11.3458 (16)C5—C61.393 (2)
C1—C21.4931 (18)C5—H50.95
C1—S11.6481 (14)C6—C71.399 (2)
C2—C31.4042 (19)C6—H60.95
C2—C71.4049 (19)C7—H70.95
C3—C41.399 (2)C8—O11.4474 (17)
C3—H30.95C8—C8i1.518 (3)
C4—C51.392 (2)C8—H8A0.99
C4—H40.95C8—H8B0.99
O1—C1—C2111.15 (11)C6—C5—H5120.0
O1—C1—S1123.72 (10)C5—C6—C7120.22 (13)
C2—C1—S1125.13 (9)C5—C6—H6119.9
C3—C2—C7119.27 (12)C7—C6—H6119.9
C3—C2—C1119.84 (12)C6—C7—C2120.09 (12)
C7—C2—C1120.89 (11)C6—C7—H7120.0
C4—C3—C2120.17 (13)C2—C7—H7120.0
C4—C3—H3119.9O1—C8—C8i104.66 (13)
C2—C3—H3119.9O1—C8—H8A110.8
C5—C4—C3120.21 (13)C8i—C8—H8A110.8
C5—C4—H4119.9O1—C8—H8B110.8
C3—C4—H4119.9C8i—C8—H8B110.8
C4—C5—C6120.02 (13)H8A—C8—H8B108.9
C4—C5—H5120.0C1—O1—C8118.26 (10)

Symmetry code: (i) −x+2, −y+2, −z+2.

2-(Benzenecarbothioyloxy)ethyl benzoate (model_E)   Crystal data

C16H14O3SF(000) = 300
Mr = 286.33Dx = 1.380 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 8.800 (5) ÅCell parameters from 1991 reflections
b = 11.403 (6) Åθ = 2.5–27.6°
c = 7.506 (4) ŵ = 0.24 mm1
β = 113.831 (6)°T = 173 K
V = 689.0 (6) Å3Prismatic, yellow
Z = 20.40 × 0.40 × 0.10 mm

2-(Benzenecarbothioyloxy)ethyl benzoate (model_E)   Data collection

Bruker APEXII CCD area detector diffractometer1523 independent reflections
Radiation source: fine-focus sealed tube1335 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.015
Detector resolution: 8.3333 pixels mm-1θmax = 27.7°, θmin = 2.5°
[var phi] and ω scansh = −11→11
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)k = −6→14
Tmin = 0.84, Tmax = 0.98l = −8→9
3265 measured reflections

2-(Benzenecarbothioyloxy)ethyl benzoate (model_E)   Refinement

Refinement on F20 restraints
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.038H-atom parameters constrained
wR(F2) = 0.090w = 1/[σ2(Fo2) + (0.0288P)2 + 0.2342P] where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max = 0.002
1523 reflectionsΔρmax = 0.19 e Å3
100 parametersΔρmin = −0.16 e Å3

2-(Benzenecarbothioyloxy)ethyl benzoate (model_E)   Special details

Experimental. SADABS (Sheldrick 1996)
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.

2-(Benzenecarbothioyloxy)ethyl benzoate (model_E)   Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

xyzUiso*/UeqOcc. (<1)
S10.78695 (19)0.76827 (18)1.1323 (3)0.0410 (3)0.5
O20.7837 (8)0.7828 (6)1.0959 (10)0.087 (3)0.5
O10.79258 (12)0.94978 (9)0.93503 (15)0.0404 (3)
C10.70747 (18)0.86474 (13)0.9769 (2)0.0372 (3)
C20.52662 (17)0.87657 (12)0.86227 (19)0.0338 (3)
C30.4186 (2)0.79742 (14)0.8908 (2)0.0428 (4)
H30.4610.73720.98570.051*
C40.2497 (2)0.80604 (15)0.7815 (2)0.0486 (4)
H40.17620.75160.80140.058*
C50.1873 (2)0.89288 (16)0.6442 (3)0.0492 (4)
H50.07110.89780.56810.059*
C60.2934 (2)0.97304 (15)0.6168 (2)0.0470 (4)
H60.24981.03360.52290.056*
C70.46254 (18)0.96570 (12)0.7252 (2)0.0381 (3)
H70.53511.02130.70640.046*
C80.97020 (18)0.94635 (14)1.0342 (2)0.0440 (4)
H8A1.01530.87440.99990.053*
H8B1.00470.94851.17710.053*

2-(Benzenecarbothioyloxy)ethyl benzoate (model_E)   Atomic displacement parameters (Å2)

U11U22U33U12U13U23
S10.0345 (5)0.0398 (5)0.0452 (6)0.0040 (4)0.0125 (4)0.0086 (5)
O20.094 (4)0.073 (4)0.086 (5)−0.007 (3)0.028 (3)0.007 (3)
O10.0368 (5)0.0394 (6)0.0392 (6)−0.0059 (4)0.0093 (4)0.0043 (4)
C10.0457 (8)0.0330 (7)0.0324 (8)−0.0042 (6)0.0153 (6)−0.0013 (6)
C20.0419 (8)0.0332 (7)0.0270 (7)−0.0048 (6)0.0144 (6)−0.0058 (5)
C30.0536 (9)0.0417 (8)0.0333 (8)−0.0113 (7)0.0176 (7)−0.0028 (6)
C40.0475 (9)0.0563 (10)0.0462 (10)−0.0191 (8)0.0233 (7)−0.0124 (8)
C50.0380 (8)0.0592 (10)0.0489 (10)−0.0037 (7)0.0159 (7)−0.0100 (8)
C60.0445 (8)0.0470 (9)0.0464 (10)0.0036 (7)0.0151 (7)0.0021 (7)
C70.0427 (8)0.0343 (7)0.0380 (8)−0.0027 (6)0.0171 (6)−0.0010 (6)
C80.0365 (8)0.0462 (9)0.0437 (9)−0.0044 (7)0.0103 (6)0.0033 (7)

2-(Benzenecarbothioyloxy)ethyl benzoate (model_E)   Geometric parameters (Å, º)

S1—C11.549 (3)C4—H40.95
O2—C11.279 (6)C5—C61.380 (2)
O1—C11.3381 (18)C5—H50.95
O1—C81.4349 (19)C6—C71.380 (2)
C1—C21.478 (2)C6—H60.95
C2—C31.389 (2)C7—H70.95
C2—C71.393 (2)C8—C8i1.501 (3)
C3—C41.381 (2)C8—H8A0.99
C3—H30.95C8—H8B0.99
C4—C51.374 (3)
C1—O1—C8117.01 (12)C4—C5—C6119.98 (15)
O2—C1—O1120.5 (3)C4—C5—H5120.0
O2—C1—C2127.6 (3)C6—C5—H5120.0
O1—C1—C2111.73 (13)C5—C6—C7120.36 (16)
O1—C1—S1124.48 (13)C5—C6—H6119.8
C2—C1—S1123.75 (13)C7—C6—H6119.8
C3—C2—C7119.33 (14)C6—C7—C2119.85 (14)
C3—C2—C1119.61 (14)C6—C7—H7120.1
C7—C2—C1121.06 (13)C2—C7—H7120.1
C4—C3—C2120.12 (15)O1—C8—C8i104.96 (15)
C4—C3—H3119.9O1—C8—H8A110.8
C2—C3—H3119.9C8i—C8—H8A110.8
C5—C4—C3120.33 (15)O1—C8—H8B110.8
C5—C4—H4119.8C8i—C8—H8B110.8
C3—C4—H4119.8H8A—C8—H8B108.8

Symmetry code: (i) −x+2, −y+2, −z+2.

Funding Statement

This work was funded by Japan Society for the Promotion of Science grant 16K05906.

This paper was supported by the following grant(s):

Japan Society for the Promotion of Science 16K05906.

References

  • Daubeny, R. de P., Bunn, C. W. & Brown, C. J. (1954). Proc. R. Soc. London Ser. A, 226, 531–542.
  • Abe, D. & Sasanuma, Y. (2012). Polym. Chem. 3, 1576–1587.
  • Abe, D., Sasanuma, Y. & Sato, H. (2011). Acta Cryst. E67, o961. [PMC free article] [PubMed]
  • Bruker (2012). APEX2, SAINT, XCIF and XSHEL. Bruker AXS Inc., Madison, Wisconsin, USA.
  • Deguire, S. & Brisse, F. (1988). Can. J. Chem. 66, 341–347.
  • Pérez, S. & Brisse, F. (1976). Acta Cryst. B32, 470–474.
  • Sasanuma, Y. (2009). Macromolecules, 42, 2854–2862.
  • Sasanuma, Y., Wagai, Y., Suzuki, N. & Abe, D. (2013). Polymer, 54, 3904–3913.
  • Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.
  • Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. [PubMed]
  • Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. [PMC free article] [PubMed]

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