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Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 70| Part 10| October 2014| Pages 192-195
doi:10.1107/S1600536814019874

Crystal structure of (±)-(3aR,5R,8bR)-5-hydroper­­oxy-2-phenyl-6-tosyl-4,5,6,8b-tetra­hydro­pyrrolo­[3,4-e]indole-1,3(2H,3aH)-dione

Wayland E. Noland,a* Glen C. Gullickson,a Rozalin R. Dickson,a Leah L. Groessa and Kenneth J. Tritcha

aDepartment of Chemistry, University of Minnesota, Minneapolis, MN 55455-0431, USA
*Correspondence e-mail: nolan001@umn.edu

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 19 July 2014; accepted 3 September 2014; online 13 September 2014)

The title compound, C23H20N2O6S, crystallizes as a racemate in the space group P-1, with an overall L- or J-shape to each mol­ecule. Centrosymmetric pairs of mol­ecules are tandem hydrogen bonded between the hydro­per­oxy H atom and carbonyl O atom. A different centrosymmetric pairing has stacked S-tolyl rings, and a third pairing is L,J-inter­locked by the short leg. Except for stacked tolyl pairs, neighboring π-systems are much closer to orthogonal than coaxial. The title compound is the first example of a hydro­peroxide obtained from the autoxidation of a Diels–Alder adduct of a 2-vinyl­pyrrole.

CCDC reference: 1022638

1. Chemical context

Diels–Alder reactions of vinyl­pyrroles with male­imides have been studied as a method to form substituted indole compounds (Noland et al., 2009[Noland, W. E., Lanzatella, N. P., Venkatraman, L., Anderson, N. F. & Gullickson, G. C. (2009). J. Heterocycl. Chem. 46, 1154-1176.]; Xiao & Ketcha, 1995[Xiao, D. & Ketcha, D. M. (1995). J. Heterocycl. Chem. 32, 499-503.]). Related reactions have been done with other heterocycles (Abarca et al., 1985[Abarca, B., Ballesteros, R., Enriquez, E. & Jones, G. (1985). Tetrahedron, 41, 2435-2440.]; Jones et al., 1984[Jones, A., Fresneda, T. A. & Arques, J. S. (1984). Tetrahedron, 40, 4837-4842.]; Noland et al., 1983[Noland, W. E., Lee, C. K., Bae, S. K., Chung, B. Y. & Hahn, C. S. (1983). J. Org. Chem. 48, 2488-2491.]). Diels–Alder reactions between vinyl­heterocycles and dienophiles are useful for forming fused ring systems that may have biological activity or versatility in natural product synthesis (Booth et al., 2005[Booth, R. J., Lee, H. H., Kraker, A., Ortwine, D. F., Palmer, B. D., Sheehan, D. J. & Toogood, P. L. (2005). US Patent 20050250836.]; Kanai et al. 2005[Kanai, F., Murakata, C., Tsujita, T., Yamashita, Y., Mizukami, T. & Akinaga, S. (2005). US Patent 20050070591 A1.]; Nagai et al. 1993[Nagai, T., Myokan, I., Takashi, F., Nomura, Y., Mizutani, M. & Hori, T. (1993). Jpn Patent 3178880.]; Noland & Pardi, 2005[Noland, W. E. & Pardi, G. (2005). J. Heterocycl. Chem. 42, 1149-1154.]).

[Scheme 1]

The hydro­peroxide title compound (I)[link] (Fig. 1[link]) was isolated after performing a Diels–Alder reaction between N-tosyl-2-vinyl­pyrrole (Settambolo et al., 1997[Settambolo, R., Caiazzo, A. & Lazzaroni, R. (1997). Synth. Commun. 23, 4111-4120.]) and N-phenyl­male­imide (commercially available). An analogous compound was proposed, though not isolated, as an inter­mediate for an alcohol product obtained from a similar reaction (Eitel & Pindur, 1988[Eitel, M. & Pindur, U. (1988). Heterocycles, 27, 2353-2362.]). No analogous hydro­peroxides have been claimed from reactions of 2-vinyl -pyrroles, -indoles, -thio­phenes, or -benzo­thio­phenes. There are a few examples of hydro­peroxides isolated from Diels–Alder reactions between 2-vinyl­furan or 2-vinyl­benzo­furan and dienophiles, but the products were not crystallographically categorized (Brewer & Elix, 1975[Brewer, J. D. & Elix, J. A. (1975). Aust. J. Chem. 28, 1059-1081.]; Kotsuki et al., 1981[Kotsuki, H., Kondo, A., Nishizawa, H., Ochi, M. & Matsuoka, K. (1981). J. Org. Chem. 46, 5454-5455.]; Skoric et al., 2001[Skoric, I., Basaric, N., Marinic, Z. & Sindler-Kulyk, M. (2001). Heterocycles, 55, 1889-1896.]).

[Figure 1]
Figure 1
The mol­ecular structure of (I)[link] with displacement ellipsoids drawn at the 50% probability level.

2. Structural commentary

The N-phenyl, S-phenyl, and pyrrolo rings are individually planar within 0.009, 0.011, and 0.010 Å, respectively. The N-phenyl ring (C7–C11) is twisted 58.3 (2)° out of plane from the imido moiety (C5, N2, C12, Figs. 2[link] and 4[link]). The cyclo­hexene ring has a half-chair conformation with C14 out of plane in the direction anti- to the S-tolyl group (Figs. 2[link] and 4[link]), which is bent 85.4 (2)° out of plane with the pyrrolo ring, giving the mol­ecule an overall L- or J- shape.

[Figure 2]
Figure 2
Two pairs of stacked tolyl groups, viewed along [1[\overline{1}]2]. The central two mol­ecules form an inter­locked pair. Twisting of the N-Phenyl group, and out-of-plane position of C14, are also depicted.
[Figure 4]
Figure 4
Hydrogen-bonded dimers, viewed along [100]. Hydrogen bonds (O2, O4) are shown in turquoise. Also apparent are the twisting of N-phenyl rings (C5, N2, C8, C9), and the half-chair conformation of the cyclo­hexene ring (C4, C14, lower mol­ecule).

3. Supra­molecular features

Inter­locking pairs are aligned such that the axis of the S-tolyl group (C21) points toward the face of the cyclo­hexene ring (C3, C14, C15, Fig. 3[link]). Hydrogen-bonded dimers form between H4O and O2 (Table 1[link], Figs. 4[link] and 6[link]). Hydrogen bonding acts approximately along [4[\overline{1}][\overline{1}]] and twists the hydro­per­oxy group to have a torsion angle of 95.0°. In different pairings than those that inter­lock, S-tolyl groups stack rotated 180° about an oblique axis, [0.803, −0.544, 0.244] (Figs. 2[link] and 5[link]). Each pair of S-tolyl pairs is sheared by approximately 3.7 Å from its neighbor. Similarly oriented N-phenyl rings are separated from each other by S-tolyl groups (C21, Fig. 6[link]), with an angle of 69.26° between the S-tolyl and N-phenyl planes. Pyrrolo groups (N1, C1, C2) each have their endo face toward an edge of an N-phenyl group (C10, C11, Fig. 7[link]), with an angle of 69.4 (2)° between the pyrrolo and N-phenyl planes.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A D⋯A D—H⋯A
O4—H4O⋯O2i 0.82 2.00 2.7929 (19) 163
Symmetry code: (i) -x+2, -y, -z.
[Figure 3]
Figure 3
The central inter­locked pair from Fig. 2[link], viewed along [221]. The C20,C21-axis is aligned with the face of the cyclo­hexene ring of its inter­locked partner.
[Figure 6]
Figure 6
Edge-to-face stacks of S-tolyl and N-phenyl rings, and hydrogen-bonded (turquoise) dimerization, viewed slightly off [001].
[Figure 5]
Figure 5
The two tolyl-stacked pairs from Fig. 2[link], viewed along [2[\overline{1}]0]. Neighboring pairs are sheared roughly 1.5 phenyl ring diameters.
[Figure 7]
Figure 7
The endo face of pyrrole rings (N1, C1, C2) neighboring the edge of an N-phenyl ring (C10, C11) of an adjacent mol­ecule of the same enanti­omer, viewed along [414].

4. Database survey

The structures shown in Fig. 8[link] represent the cores of most compounds that could be obtained by Diels–Alder reactions of the type that gave title compound (I)[link], using nitro­gen heterocyclic dienes and dienophiles. Searching these substructures found six entries in the current database (Cambridge Structural Database, Version 5.35, November 2013; Allen 2002[Allen, F. H. (2002). Acta Cryst. B58, 380-388.]). Only two of these were synthesized by cyclo­additions of this type [a combretastatin derivative (Ty et al., 2010[Ty, N., Dupeyre, G., Chabot, G. G., Seguin, J., Quentin, L., Chiaroni, A., Tillequin, F., Scherman, D., Michel, S. & Cachet, X. (2010). Eur. J. Med. Chem. 45, 3726-3739.]); carbazomycin B (Beccali et al., 1996[Beccali, E. M., Marchesini, A. & Pilati, T. (1996). Tetrahedron, 52, 3029-3036.])]. Upon expanding the search to include any combination of heteroatoms at nitro­gen and oxygen sites, seven additional entries were found, all within or closely related to the caesalmin family of furan­oditerpenoid anti­virals (i.e., Rodrigues et al., 2004[Rodrigues, L. P., Rubinger, M. M. M., Piló-Veloso, D., Malta, V. R. dosS. & Guilardi, S. (2004). Acta Cryst. E60, o1208-o1210.]; Jiang et al., 2002[Jiang, R.-W., Ma, S.-C., He, Z.-D., Huang, X.-S., But, P. P.-H., Wang, H., Chan, S.-P., Ooi, V. E.-C., Xu, H.-X. & Mak, T. C. W. (2002). Bioorg. Med. Chem. 10, 2161-2170.]). Of 13 total entries, none was found containing sulfur atoms. Ten exhibit inter­molecular hydrogen bonding, but only two of them are tandem-bonded dimers [pyrimidinone carbonyl to carb­oxy­lic acid (Obushak et al., 2011[Obushak, M. D., Horak, Y. I., Zaytsev, V. P., Motorygina, E. L., Zubkov, F. I. & Khrustalev, V. N. (2011). Acta Cryst. E67, o3031-o3032.]); succinimide dimerization between N-H and a carbonyl oxygen (Beccali et al., 1996[Beccali, E. M., Marchesini, A. & Pilati, T. (1996). Tetrahedron, 52, 3029-3036.])]. None of these structures resembles that of compound (I)[link].

[Figure 8]
Figure 8
Substructures used for the database survey.

5. Synthesis and crystallization

N-Tosyl-2-vinyl­pyrrole (458 mg) and N-phenyl­male­imide (272 mg) were dissolved in chloro­form (1.5 ml) and stirred for 72 h at room temperature in a vessel open to air. Column chromatography on silica gel (1:1 hexa­ne:ethyl acetate, Rf = 0.30), followed by recrystallization from di­chloro­methane–petroleum ether (b.p. 311–333 K) gave compound (I)[link] as colourless plates (17 mg, 2.4%, m.p. 425–426 K). 1H NMR (500 MHz, (CD3)2SO) δ 11.96 (s, 1H, H4O), 7.974 (d, J = 3.4 Hz, 2H, H18, H23), 7.483 (t, J = 8.0 Hz, 2H, H8, H10), 7.427 (m, 3H, H9, H19, H22), 7.283 (dd, J = 8.8, 1.0 Hz, 2H, H7, H11), 6.516 (d, J = 3.4 Hz, 1H, H2), 5.485 (dd, J = 2.9, 2.7 Hz, 1H, H15), 4.241 (d, J = 8.3 Hz, 1H, H4), 3.375 (ddd, J = 13.7, 8.3, 5.8 Hz, 1H, H13), 2.824 (ddd, J = 14.1, 5.8, 2.9 Hz, 1H, H14A), 2.384 (s, 3H, H21), 1.886 (ddd, J = 14.1, 13.7, 2.7 Hz, 1H, H14B); 13C NMR (126 MHz, (CD3)2SO) δ 178.09 (C12), 174.85 (C5), 145.49 (C20), 135.06 (C17), 132.36 (C6), 129.94 (C19, C22), 128.87 (C8, C10), 128.43 (C9), 127.57 (C18, C23), 127.26 (C7, C11), 125.32 (C16), 124.14 (C1), 121.63 (C3), 112.27 (C2), 70.77 (C15), 38.79 (C4), 35.32 (C13), 27.85 (C14), 21.10 (C21); IR (NaCl, cm−1) 3361 (O–H), 2917 (C–H), 1713 (C=O), 1595 (C=C), 1370 (S=O), 1177 (C–O), 808, 751, 672; MS (ESI, PEG, m/z) [M+Na]+ calculated for C23H20N2O6S 475.0934, found 475.0921.

Safety Note: Hydro­peroxides, particularly those bearing an α-proton (e.g., H15, Fig. 1[link]), can be shock- or heat-sensitive and detonate violently (Francisco, 1993[Francisco, M. A. (1993). Chem. Eng. News, 71, 4-5.]). Although sensitivity tests on our batch of title compound (I)[link] were negative, appropriate precautions should be taken when reproducing or extending our work with (I)[link] or similar compounds. Metal tools, glass or metal storage vessels, high oxygen- or nitro­gen-to-carbon ratios, and large scales should all be avoided. The bulk of product should be kept in solution, with small aliquots being allowed to dry only as necessary.

6. Refinement

A direct-methods solution was calculated which provided most non-hydrogen atoms from the E-map. Full-matrix least-squares/difference Fourier cycles were performed, which located the remaining non-hydrogen atoms. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms except for H4O were placed in ideal positions and refined as constrained atoms with Uiso(Hn) = 1.2Ueq(Cn), except for the methyl group, where Uiso(H21i) = 1.5Ueq(C21). The bond lengths (Å) specified for C–H hydrogens were 0.93 (ar­yl), 0.96 (meth­yl), 0.97 (methyl­ene), and 0.98 (methine). H4O was found from the difference Fourier map and refined with Uiso(H4O) = 1.2Ueq(O4) and an O—H bond length of 0.82 Å. The final full-matrix least-squares refinement converged to R1 = 0.0364 and wR2 = 0.1161 (F2, all data). Crystal data, data collection and structure refinement details are summarized in Table 2[link].

Table 2
Experimental details

Crystal data
Chemical formula C23H20N2O6S
Mr 452.48
Crystal system, space group Triclinic, P[\overline{1}]
Temperature (K) 293
a, b, c (Å) 8.6563 (13), 9.8819 (15), 13.533 (2)
α, β, γ (°) 102.068 (3), 107.786 (2), 96.364 (2)
V (Å3) 1058.8 (3)
Z 2
Radiation type Mo Kα
μ (mm−1) 0.20
Crystal size (mm) 0.60 × 0.50 × 0.20
 
Data collection
Diffractometer Bruker SMART Platform CCD
Absorption correction Multi-scan (SADABS; Blessing, 1995[Blessing, R. H. (1995). Acta Cryst. A51, 33-38.])
Tmin, Tmax 0.891, 0.962
No. of measured, independent and observed [I > 2σ(I)] reflections 10544, 3751, 3194
Rint 0.021
(sin θ/λ)max (Å−1) 0.596
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.036, 0.116, 1.06
No. of reflections 3751
No. of parameters 290
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 0.27, −0.28
Computer programs: SMART (Bruker, 2001[Bruker (2001). SMART. Bruker AXS Inc., Madison, Wisconsin, USA.]), SAINT (Bruker, 2003[Bruker (2003). SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXS97 and SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]), Mercury (Macrae et al., 2008[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.]), enCIFer (Allen et al., 2004[Allen, F. H., Johnson, O., Shields, G. P., Smith, B. R. & Towler, M. (2004). J. Appl. Cryst. 37, 335-338.]), and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information

CCDC reference: 1022638

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536814019874/hb7256sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536814019874/hb7256Isup2.hkl

Supporting information file. DOI: 10.1107/S1600536814019874/hb7256Isup3.cml

checkCIF report


Chemical context top

Diels–Alder reactions of vinyl­pyrroles with male­imides have been studied as a method to form substituted indole compounds (Noland et al., 2009; Xiao & Ketcha, 1995). Related reactions have been done with other heterocycles (Abarca et al., 1985; Jones et al., 1984; Noland et al., 1983). Diels–Alder reactions between vinyl­heterocycles and dienophiles are useful for forming fused ring systems that may have biological activity or versatility in natural product synthesis (Booth et al., 2005; Kanai et al. 2005; Nagai et al. 1993; Noland & Pardi, 2005).

The hydro­peroxide title compound (I) (Fig. 1) was isolated after performing a Diels–Alder reaction between N-tosyl-2-vinyl­pyrrole (Settambolo et al., 1997) and N-phenyl­male­imide (commercially available). An analogous compound was proposed, though not isolated, as an inter­mediate for an alcohol product obtained from a similar reaction (Eitel & Pindur, 1988). No analogous hydro­peroxides have been claimed from reactions of 2-vinyl -pyrroles, -indoles, -thio­phenes, or -benzo­thio­phenes. There are a few examples of hydro­peroxides isolated from Diels–Alder reactions between 2-vinyl­furan or 2-vinyl­benzo­furan and dienophiles, but the products were not crystallographically categorized (Brewer & Elix, 1975; Kotsuki et al., 1981; Skoric et al., 2001).

Structural commentary top

The N-phenyl, S-phenyl, and pyrrolo rings are individually planar within 0.009, 0.011, and 0.010 Å, respectively. The N-phenyl ring (C7–C11) is twisted 58.3 (2)° out of plane from the imido moiety (C5, N2, C12, Figs. 2 and 4). The cyclo­hexene ring has half-chair geometry with C14 out of plane in the direction anti- to the S-tolyl group (Figs. 2 and 4), which is bent 85.4 (2)° out of plane with the pyrrolo ring, giving the molecule an overall L- or J- shape.

Supra­molecular features top

Inter­locking pairs are aligned such that the axis of the S-tolyl group (C21) points toward the face of the cyclo­hexene ring (C3, C14, C15, Fig. 3). Hydrogen-bonded dimers form between H4O and O2 (Table 1, Figs. 4 and 6). Hydrogen bonding acts approximately along [411] and twists the hydro­per­oxy group to have a torsion angle of 95.0°. In different pairings than those that inter­lock, S-tolyl groups stack rotated 180° about an oblique axis, [0.803, -0.544, 0.244] (Figs. 2 and 5). Each pair of S-tolyl pairs is sheared by approximately 3.7 Å from its neighbor. Similarly oriented N-phenyl rings are separated from each other by S-tolyl groups (C21, Fig. 6), with an angle of 69.26° between the S-tolyl and N-phenyl planes. Pyrrolo groups (N1, C1, C2) each have their endo face toward an edge of an N-phenyl group (C10, C11, Fig. 7), with an angle of 69.4 (2)° between the pyrrolo and N-phenyl planes.

Database survey top

The structures shown in Figure 8 represent the cores of most compounds that could be obtained by Diels–Alder reactions of the type that gave title compound (I), using nitro­gen heterocyclic dienes and dienophiles. Searching these substructures found six entries in the current database (Cambridge Structural Database, Version 5.35, November 2013; Allen 2002). Only two of these were synthesized by cyclo­additions of this type [a combretastatin derivative (Ty et al., 2010); carbazomycin B (Beccali et al., 1996)]. Upon expanding the search to include any combination of heteroatoms at nitro­gen and oxygen sites, seven additional entries were found, all within or closely related to the caesalmin family of furan­oditerpenoid anti­virals (i.e., Rodrigues et al., 2004; Jiang et al., 2002). Of 13 total entries, none was found containing sulfur atoms anywhere. Ten exhibit inter­molecular hydrogen bonding, but only two of them are tandem-bonded dimers [pyrimidinone carbonyl to carb­oxy­lic acid (Obushak et al., 2011); succinimide dimerization between N—H and a carbonyl oxygen (Beccali et al., 1996)]. None of these structures resembles that of compound (I).

Synthesis and crystallization top

N-Tosyl-2-vinyl­pyrrole (458 mg) and N-phenyl­male­imide (272 mg) were dissolved in chloro­form (1.5 ml) and stirred for 72 hours at room temperature in a vessel open to air. Column chromatography on silica gel (1:1 hexane:ethyl acetate, Rf = 0.30), followed by recrystallization from di­chloro­methane–petroleum ether (b.p. 311–333 K) gave compound (I) as colourless plates (17 mg, 2.4%, m.p. 425–426 K). 1H NMR (500 MHz, (CD3)2SO) δ 11.96 (s, 1H, H4O), 7.974 (d, J = 3.4 Hz, 2H, H18, H23), 7.483 (t, J = 8.0 Hz, 2H, H8, H10), 7.427 (m, 3H, H9, H19, H22), 7.283 (dd, J = 8.8, 1.0 Hz, 2H, H7, H11), 6.516 (d, J = 3.4 Hz, 1H, H2), 5.485 (dd, J = 2.9, 2.7 Hz, 1H, H15), 4.241 (d, J = 8.3 Hz, 1H, H4), 3.375 (ddd, J = 13.7, 8.3, 5.8 Hz, 1H, H13), 2.824 (ddd, J = 14.1, 5.8, 2.9 Hz, 1H, H14A), 2.384 (s, 3H, H21), 1.886 (ddd, J = 14.1, 13.7, 2.7 Hz, 1H, H14B); 13C NMR (126 MHz, (CD3)2SO) δ 178.09 (C12), 174.85 (C5), 145.49 (C20), 135.06 (C17), 132.36 (C6), 129.94 (C19, C22), 128.87 (C8, C10), 128.43 (C9), 127.57 (C18, C23), 127.26 (C7, C11), 125.32 (C16), 124.14 (C1), 121.63 (C3), 112.27 (C2), 70.77 (C15), 38.79 (C4), 35.32 (C13), 27.85 (C14), 21.10 (C21); IR (NaCl, cm-1) 3361 (O–H), 2917 (C–H), 1713 (C=O), 1595 (C=C), 1370 (S=O), 1177 (C–O), 808, 751, 672; MS (ESI, PEG, m/z) [M+Na]+ calculated for C23H20N2O6S 475.0934, found 475.0921.

Safety Note: Hydro­peroxides, particularly those bearing an α-proton (e.g., H15, Fig. 1), can be shock- or heat-sensitive and detonate violently (Francisco, 1993). Although sensitivity tests on our batch of title compound (I) were negative, appropriate precautions should be taken when reproducing or extending our work with (I) or similar compounds. Metal tools, glass or metal storage vessels, high oxygen- or nitro­gen-to-carbon ratios, and large scales should all be avoided. The bulk of product should be kept in solution, with small aliquots being allowed to dry only as necessary.

Refinement top

A direct-methods solution was calculated which provided most non-hydrogen atoms from the E-map. Full-matrix least squares / difference Fourier cycles were performed which located the remaining non-hydrogen atoms. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms except for H4O were placed in ideal positions and refined as constrained atoms with Uiso(Hn) = 1.2Ueq(Cn), except for the methyl group, where Uiso(H21i) = 1.5Ueq(C21) . The bond lengths (Å) specified for C–H hydrogens were 0.93 (aryl), 0.96 (methyl), 0.97 (methyl­ene), and 0.98 (methine). H4O was found from the difference map and refined with Uiso(H4O) = 1.2Ueq(O4) and an O—H bond length of 0.82 Å. The final full-matrix least-squares refinement converged to R1 = 0.0364 and wR2 = 0.1161 (F2, all data). Crystal data, data collection and structure refinement details are summarized in Table 2.

Related literature top

For related literature, see: Abarca et al. (1985); Allen (2002); Beccali et al. (1996); Booth et al. (2005); Brewer & Elix (1975); Eitel & Pindur (1988); Francisco (1993); Jiang et al. (2002); Jones et al. (1984); Kanai et al. (2005); Kotsuki et al. (1981); Nagai et al. (1993); Noland & Pardi (2005); Noland et al. (1983, 2009); Obushak et al. (2011); Rodrigues et al. (2004); Settambolo et al. (1997); Skoric et al. (2001); Ty et al. (2010); Xiao & Ketcha (1995).

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003); 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: SHELXL97 (Sheldrick, 2008), enCIFer (Allen et al., 2004), and publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) with displacement ellipsoids drawn at the 50% probability level.
[Figure 2] Fig. 2. Two pairs of stacked tolyl groups, viewed along [112]. The central two molecules form an interlocked pair. Twisting of the N-Phenyl group, and out-of-plane position of C14, are also depicted.
[Figure 3] Fig. 3. The central interlocked pair from Figure 2, viewed along [221]. The C20,C21-axis is aligned with the face of the cyclohexene ring of its interlocked partner.
[Figure 4] Fig. 4. Hydrogen-bonded dimers, viewed along [100]. Hydrogen bonds (O2, O4) are shown in turquoise. Also apparent are the twisting of N-phenyl rings (C5, N2, C8, C9), and the half-chair conformation of the cyclohexene ring (C4, C14, lower molecule).
[Figure 5] Fig. 5. The two tolyl-stacked pairs from Figure 2, viewed along [210]. Neighboring pairs are sheared roughly 1.5 phenyl ring diameters.
[Figure 6] Fig. 6. Edge-to-face stacks of S-tolyl and N-phenyl rings, and hydrogen-bonded (turquoise) dimerization, viewed slightly off [001].
[Figure 7] Fig. 7. The endo face of pyrrole rings (N1, C1, C2) neighboring the edge of an N-phenyl ring (C10, C11) of an adjacent molecule of the same enantiomer, viewed along [414].
[Figure 8] Fig. 8. Substructures used for the database survey.
(±)-(3aR,5R,8bR)-5-Hydroperoxy-2-phenyl-6-tosyl-4,5,6,8b-tetrahydropyrrolo[3,4-e]indole-1,3(2H,3aH)-dione top
Crystal data top
C23H20N2O6SF(000) = 472
Mr = 452.48Dx = 1.419 Mg m−3
Triclinic, P1Melting point: 425 K
a = 8.6563 (13) ÅMo Kα radiation, λ = 0.71073 Å
b = 9.8819 (15) ÅCell parameters from 2698 reflections
c = 13.533 (2) Åθ = 2.5–25.1°
α = 102.068 (3)°µ = 0.20 mm−1
β = 107.786 (2)°T = 293 K
γ = 96.364 (2)°Block, colourless
V = 1058.8 (3) Å30.60 × 0.50 × 0.20 mm
Z = 2
Data collection top
Bruker SMART Platform CCD
diffractometer		3751 independent reflections
Radiation source: normal-focus sealed tube3194 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.021
area detector, ω scans per phiθmax = 25.1°, θmin = 1.6°
Absorption correction: multi-scan
(SADABS; Blessing, 1995)		h = −10→10
Tmin = 0.891, Tmax = 0.962k = −11→11
10544 measured reflectionsl = −16→16
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)] = 0.036Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.116H-atom parameters constrained
S = 1.06 w = 1/[σ2(Fo2) + (0.0678P)2 + 0.2551P]
where P = (Fo2 + 2Fc2)/3
3751 reflections(Δ/σ)max < 0.001
290 parametersΔρmax = 0.27 e Å−3
0 restraintsΔρmin = −0.28 e Å−3
Crystal data top
C23H20N2O6Sγ = 96.364 (2)°
Mr = 452.48V = 1058.8 (3) Å3
Triclinic, P1Z = 2
a = 8.6563 (13) ÅMo Kα radiation
b = 9.8819 (15) ŵ = 0.20 mm−1
c = 13.533 (2) ÅT = 293 K
α = 102.068 (3)°0.60 × 0.50 × 0.20 mm
β = 107.786 (2)°
Data collection top
Bruker SMART Platform CCD
diffractometer		3751 independent reflections
Absorption correction: multi-scan
(SADABS; Blessing, 1995)		3194 reflections with I > 2σ(I)
Tmin = 0.891, Tmax = 0.962Rint = 0.021
10544 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0360 restraints
wR(F2) = 0.116H-atom parameters constrained
S = 1.06Δρmax = 0.27 e Å−3
3751 reflectionsΔρmin = −0.28 e Å−3
290 parameters
Special details top

Experimental. The space group P-1 was determined based on systematic absences and intensity statistics.

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
S10.46933 (5)0.12220 (5)0.31067 (4)0.04468 (16)
O11.0118 (2)−0.3093 (2)0.31048 (15)0.0865 (6)
O21.09502 (19)−0.14706 (14)0.03647 (12)0.0582 (4)
O30.74791 (17)0.17137 (13)0.16243 (10)0.0499 (3)
O40.6719 (2)0.20863 (16)0.06212 (12)0.0649 (4)
H4O0.73390.20330.02680.078*
O50.40641 (16)0.13010 (15)0.20262 (10)0.0566 (4)
O60.36195 (16)0.06483 (15)0.35954 (12)0.0601 (4)
N10.60788 (18)0.01608 (15)0.31539 (12)0.0418 (3)
N21.08339 (19)−0.24962 (16)0.17207 (12)0.0474 (4)
C10.6732 (2)−0.0313 (2)0.40679 (15)0.0480 (4)
H10.6284−0.03010.46120.058*
C20.8110 (2)−0.0788 (2)0.40345 (15)0.0502 (5)
H20.8770−0.11820.45390.060*
C30.8381 (2)−0.05797 (19)0.30826 (13)0.0420 (4)
C40.9808 (2)−0.0811 (2)0.27117 (14)0.0457 (4)
H41.0786−0.01650.32470.055*
C51.0216 (2)−0.2278 (2)0.25780 (16)0.0539 (5)
C61.1781 (2)−0.35732 (19)0.15237 (15)0.0486 (4)
C71.1125 (3)−0.4973 (2)0.13290 (17)0.0610 (5)
H71.0042−0.52520.12910.073*
C81.2118 (4)−0.5966 (2)0.11898 (18)0.0739 (7)
H81.1700−0.69160.10760.089*
C91.3694 (4)−0.5565 (3)0.1218 (2)0.0801 (8)
H91.4336−0.62390.11120.096*
C101.4322 (4)−0.4178 (3)0.1400 (2)0.0857 (8)
H101.5393−0.39040.14130.103*
C111.3370 (3)−0.3167 (2)0.1568 (2)0.0669 (6)
H111.3811−0.22170.17100.080*
C121.0551 (2)−0.14946 (18)0.11427 (15)0.0443 (4)
C130.9635 (2)−0.04746 (18)0.16302 (14)0.0429 (4)
H131.01880.04960.17520.051*
C140.7826 (2)−0.06872 (18)0.09075 (14)0.0427 (4)
H14A0.7783−0.04550.02390.051*
H14B0.7310−0.16680.07390.051*
C150.6877 (2)0.02411 (18)0.14624 (13)0.0415 (4)
H150.56970.00010.10390.050*
C160.7143 (2)0.00040 (17)0.25498 (13)0.0378 (4)
C170.5829 (2)0.28523 (19)0.39512 (14)0.0435 (4)
C180.6708 (3)0.3751 (2)0.35718 (17)0.0550 (5)
H180.66560.35210.28580.066*
C190.7667 (3)0.5001 (2)0.42738 (19)0.0618 (6)
H190.82530.56160.40240.074*
C200.7770 (3)0.5351 (2)0.53416 (18)0.0592 (5)
C210.8857 (3)0.6697 (3)0.6109 (2)0.0849 (8)
H21A0.95010.64980.67600.127*
H21B0.81800.73590.62700.127*
H21C0.95820.70910.57850.127*
C220.6853 (3)0.4442 (2)0.56897 (17)0.0623 (6)
H220.68860.46820.63990.075*
C230.5893 (3)0.3192 (2)0.50137 (16)0.0561 (5)
H230.52970.25850.52640.067*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.0331 (2)0.0524 (3)0.0469 (3)0.00619 (19)0.01535 (19)0.0075 (2)
O10.1099 (14)0.1116 (14)0.0929 (12)0.0657 (12)0.0665 (11)0.0702 (12)
O20.0736 (9)0.0576 (8)0.0673 (9)0.0237 (7)0.0473 (8)0.0254 (7)
O30.0635 (8)0.0467 (7)0.0459 (7)0.0136 (6)0.0247 (6)0.0140 (6)
O40.0787 (10)0.0795 (10)0.0667 (9)0.0402 (8)0.0424 (8)0.0423 (8)
O50.0447 (7)0.0696 (9)0.0483 (8)0.0146 (6)0.0084 (6)0.0091 (6)
O60.0425 (7)0.0688 (9)0.0723 (9)0.0034 (6)0.0314 (7)0.0108 (7)
N10.0391 (8)0.0465 (8)0.0433 (8)0.0059 (6)0.0196 (6)0.0115 (6)
N20.0507 (9)0.0484 (9)0.0504 (9)0.0150 (7)0.0236 (7)0.0157 (7)
C10.0546 (11)0.0550 (11)0.0443 (10)0.0098 (9)0.0266 (9)0.0189 (8)
C20.0535 (11)0.0612 (12)0.0418 (10)0.0152 (9)0.0183 (9)0.0200 (9)
C30.0367 (9)0.0502 (10)0.0377 (9)0.0062 (7)0.0133 (7)0.0079 (7)
C40.0361 (9)0.0583 (11)0.0408 (9)0.0088 (8)0.0130 (7)0.0088 (8)
C50.0495 (11)0.0702 (13)0.0537 (11)0.0214 (10)0.0238 (9)0.0255 (10)
C60.0549 (11)0.0473 (10)0.0450 (10)0.0172 (8)0.0162 (8)0.0120 (8)
C70.0657 (13)0.0542 (12)0.0545 (12)0.0097 (10)0.0096 (10)0.0126 (9)
C80.106 (2)0.0464 (12)0.0550 (13)0.0230 (13)0.0084 (13)0.0055 (10)
C90.093 (2)0.0737 (17)0.0715 (16)0.0450 (15)0.0204 (14)0.0114 (13)
C100.0717 (16)0.0843 (19)0.108 (2)0.0351 (14)0.0369 (15)0.0195 (16)
C110.0604 (13)0.0548 (12)0.0870 (16)0.0165 (10)0.0291 (12)0.0117 (11)
C120.0451 (10)0.0424 (9)0.0510 (10)0.0071 (8)0.0240 (8)0.0127 (8)
C130.0429 (9)0.0414 (9)0.0484 (10)0.0062 (7)0.0227 (8)0.0101 (8)
C140.0502 (10)0.0423 (9)0.0373 (9)0.0078 (8)0.0185 (8)0.0086 (7)
C150.0393 (9)0.0458 (9)0.0382 (9)0.0061 (7)0.0136 (7)0.0087 (7)
C160.0339 (8)0.0419 (9)0.0367 (8)0.0019 (7)0.0148 (7)0.0065 (7)
C170.0371 (9)0.0475 (10)0.0458 (10)0.0115 (8)0.0136 (8)0.0105 (8)
C180.0590 (12)0.0555 (11)0.0552 (11)0.0105 (9)0.0291 (10)0.0096 (9)
C190.0603 (13)0.0477 (11)0.0815 (15)0.0054 (9)0.0356 (11)0.0105 (10)
C200.0478 (11)0.0485 (11)0.0684 (14)0.0165 (9)0.0076 (10)0.0023 (10)
C210.0708 (16)0.0581 (14)0.100 (2)0.0107 (12)0.0115 (14)−0.0084 (13)
C220.0750 (15)0.0585 (12)0.0453 (11)0.0179 (11)0.0106 (10)0.0079 (9)
C230.0663 (13)0.0558 (12)0.0466 (11)0.0108 (10)0.0192 (10)0.0142 (9)
Geometric parameters (Å, º) top
S1—O51.4182 (14)C8—H80.9300
S1—O61.4278 (14)C9—C101.359 (4)
S1—N11.6740 (15)C9—H90.9300
S1—C171.7494 (19)C10—C111.389 (3)
O1—C51.194 (2)C10—H100.9300
O2—C121.208 (2)C11—H110.9300
O3—C151.437 (2)C12—C131.516 (2)
O3—O41.4590 (18)C13—C141.536 (3)
O4—H4O0.8200C13—H130.9800
N1—C11.393 (2)C14—C151.528 (2)
N1—C161.407 (2)C14—H14A0.9700
N2—C121.383 (2)C14—H14B0.9700
N2—C51.407 (2)C15—C161.491 (2)
N2—C61.443 (2)C15—H150.9800
C1—C21.340 (3)C17—C181.382 (3)
C1—H10.9300C17—C231.389 (3)
C2—C31.429 (2)C18—C191.384 (3)
C2—H20.9300C18—H180.9300
C3—C161.356 (2)C19—C201.386 (3)
C3—C41.492 (2)C19—H190.9300
C4—C51.517 (3)C20—C221.381 (3)
C4—C131.535 (2)C20—C211.510 (3)
C4—H40.9800C21—H21A0.9600
C6—C111.369 (3)C21—H21B0.9600
C6—C71.373 (3)C21—H21C0.9600
C7—C81.396 (3)C22—C231.374 (3)
C7—H70.9300C22—H220.9300
C8—C91.364 (4)C23—H230.9300
O5—S1—O6120.26 (9)C10—C11—H11120.1
O5—S1—N1106.58 (8)O2—C12—N2124.70 (16)
O6—S1—N1104.10 (8)O2—C12—C13126.41 (16)
O5—S1—C17110.99 (9)N2—C12—C13108.87 (15)
O6—S1—C17108.79 (9)C12—C13—C4103.09 (14)
N1—S1—C17104.77 (8)C12—C13—C14111.55 (14)
C15—O3—O4107.67 (12)C4—C13—C14112.69 (14)
O3—O4—H4O109.5C12—C13—H13109.8
C1—N1—C16108.04 (14)C4—C13—H13109.8
C1—N1—S1120.64 (12)C14—C13—H13109.8
C16—N1—S1127.91 (12)C15—C14—C13110.81 (14)
C12—N2—C5112.50 (15)C15—C14—H14A109.5
C12—N2—C6123.69 (15)C13—C14—H14A109.5
C5—N2—C6123.61 (15)C15—C14—H14B109.5
C2—C1—N1108.87 (15)C13—C14—H14B109.5
C2—C1—H1125.6H14A—C14—H14B108.1
N1—C1—H1125.6O3—C15—C16106.51 (13)
C1—C2—C3107.45 (17)O3—C15—C14111.80 (14)
C1—C2—H2126.3C16—C15—C14108.60 (14)
C3—C2—H2126.3O3—C15—H15110.0
C16—C3—C2108.74 (16)C16—C15—H15110.0
C16—C3—C4121.81 (16)C14—C15—H15110.0
C2—C3—C4129.26 (17)C3—C16—N1106.87 (15)
C3—C4—C5117.02 (16)C3—C16—C15125.22 (15)
C3—C4—C13113.64 (15)N1—C16—C15127.44 (15)
C5—C4—C13104.65 (14)C18—C17—C23120.96 (18)
C3—C4—H4107.0C18—C17—S1119.98 (14)
C5—C4—H4107.0C23—C17—S1118.99 (15)
C13—C4—H4107.0C17—C18—C19118.74 (19)
O1—C5—N2124.96 (19)C17—C18—H18120.6
O1—C5—C4128.61 (19)C19—C18—H18120.6
N2—C5—C4106.36 (16)C18—C19—C20121.3 (2)
C11—C6—C7120.53 (19)C18—C19—H19119.3
C11—C6—N2118.49 (18)C20—C19—H19119.3
C7—C6—N2120.95 (18)C22—C20—C19118.47 (19)
C6—C7—C8118.6 (2)C22—C20—C21120.6 (2)
C6—C7—H7120.7C19—C20—C21121.0 (2)
C8—C7—H7120.7C20—C21—H21A109.5
C9—C8—C7120.9 (2)C20—C21—H21B109.5
C9—C8—H8119.5H21A—C21—H21B109.5
C7—C8—H8119.5C20—C21—H21C109.5
C10—C9—C8119.9 (2)H21A—C21—H21C109.5
C10—C9—H9120.1H21B—C21—H21C109.5
C8—C9—H9120.1C23—C22—C20121.6 (2)
C9—C10—C11120.2 (3)C23—C22—H22119.2
C9—C10—H10119.9C20—C22—H22119.2
C11—C10—H10119.9C22—C23—C17118.9 (2)
C6—C11—C10119.8 (2)C22—C23—H23120.5
C6—C11—H11120.1C17—C23—H23120.5
O5—S1—N1—C1−169.75 (14)O2—C12—C13—C1470.7 (2)
O6—S1—N1—C1−41.65 (15)N2—C12—C13—C14−107.92 (17)
C17—S1—N1—C172.53 (15)C3—C4—C13—C12−148.89 (15)
O5—S1—N1—C1633.70 (17)C5—C4—C13—C12−20.06 (18)
O6—S1—N1—C16161.79 (14)C3—C4—C13—C14−28.5 (2)
C17—S1—N1—C16−84.02 (16)C5—C4—C13—C14100.34 (17)
C16—N1—C1—C2−1.8 (2)C12—C13—C14—C15174.11 (14)
S1—N1—C1—C2−162.56 (14)C4—C13—C14—C1558.70 (19)
N1—C1—C2—C31.6 (2)O4—O3—C15—C16−159.65 (12)
C1—C2—C3—C16−0.8 (2)O4—O3—C15—C1481.87 (16)
C1—C2—C3—C4174.24 (19)H4O—O4—O3—C15−95.0
C16—C3—C4—C5−128.24 (19)C13—C14—C15—O365.49 (18)
C2—C3—C4—C557.3 (3)C13—C14—C15—C16−51.74 (18)
C16—C3—C4—C13−6.0 (2)C2—C3—C16—N1−0.4 (2)
C2—C3—C4—C13179.55 (18)C4—C3—C16—N1−175.81 (15)
C12—N2—C5—O1169.9 (2)C2—C3—C16—C15−173.01 (16)
C6—N2—C5—O1−15.1 (3)C4—C3—C16—C1511.5 (3)
C12—N2—C5—C4−12.9 (2)C1—N1—C16—C31.32 (19)
C6—N2—C5—C4162.11 (16)S1—N1—C16—C3160.22 (13)
C3—C4—C5—O1−35.7 (3)C1—N1—C16—C15173.76 (16)
C13—C4—C5—O1−162.4 (2)S1—N1—C16—C15−27.3 (2)
C3—C4—C5—N2147.29 (16)O3—C15—C16—C3−102.19 (19)
C13—C4—C5—N220.51 (19)C14—C15—C16—C318.4 (2)
C12—N2—C6—C1156.6 (3)O3—C15—C16—N186.68 (19)
C5—N2—C6—C11−117.8 (2)C14—C15—C16—N1−152.76 (16)
C12—N2—C6—C7−125.4 (2)O5—S1—C17—C18−32.44 (18)
C5—N2—C6—C760.2 (3)O6—S1—C17—C18−166.93 (15)
C11—C6—C7—C80.7 (3)N1—S1—C17—C1882.23 (16)
N2—C6—C7—C8−177.25 (18)O5—S1—C17—C23150.62 (15)
C6—C7—C8—C9−1.7 (3)O6—S1—C17—C2316.13 (18)
C7—C8—C9—C101.1 (4)N1—S1—C17—C23−94.71 (16)
C8—C9—C10—C110.5 (4)C23—C17—C18—C190.3 (3)
C7—C6—C11—C100.9 (4)S1—C17—C18—C19−176.53 (16)
N2—C6—C11—C10178.9 (2)C17—C18—C19—C200.7 (3)
C9—C10—C11—C6−1.5 (4)C18—C19—C20—C22−1.8 (3)
C5—N2—C12—O2−179.12 (19)C18—C19—C20—C21178.3 (2)
C6—N2—C12—O25.9 (3)C19—C20—C22—C232.0 (3)
C5—N2—C12—C13−0.4 (2)C21—C20—C22—C23−178.1 (2)
C6—N2—C12—C13−175.46 (16)C20—C22—C23—C17−1.0 (3)
O2—C12—C13—C4−168.10 (19)C18—C17—C23—C22−0.2 (3)
N2—C12—C13—C413.25 (18)S1—C17—C23—C22176.73 (15)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O4—H4O···O2i0.822.002.7929 (19)163
Symmetry code: (i) −x+2, −y, −z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O4—H4O···O2i0.822.002.7929 (19)163
Symmetry code: (i) −x+2, −y, −z.

Experimental details

Crystal data
Chemical formulaC23H20N2O6S
Mr452.48
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)8.6563 (13), 9.8819 (15), 13.533 (2)
α, β, γ (°)102.068 (3), 107.786 (2), 96.364 (2)
V (Å3)1058.8 (3)
Z2
Radiation typeMo Kα
µ (mm−1)0.20
Crystal size (mm)0.60 × 0.50 × 0.20
Data collection
DiffractometerBruker SMART Platform CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Blessing, 1995)
Tmin, Tmax0.891, 0.962
No. of measured, independent and
observed [I > 2σ(I)] reflections		10544, 3751, 3194
Rint0.021
(sin θ/λ)max (Å−1)0.596
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.036, 0.116, 1.06
No. of reflections3751
No. of parameters290
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å−3)0.27, −0.28

Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2003), SHELXS97 (Sheldrick, 2008), Mercury (Macrae et al., 2008), SHELXL97 (Sheldrick, 2008), enCIFer (Allen et al., 2004), and publCIF (Westrip, 2010).

 

Acknowledgements

The authors thank Victor G. Young Jr (X-Ray Crystallographic Laboratory, University of Minnesota) and Dr Matthew J. Bruzek for assistance with the crystal structure analysis, and the Wayland E. Noland Research Fellowship Fund at the University of Minnesota Foundation for generous financial support of this project.

References

First citationAbarca, B., Ballesteros, R., Enriquez, E. & Jones, G. (1985). Tetrahedron, 41, 2435–2440.  CrossRef CAS Web of Science Google Scholar
 First citationAllen, F. H. (2002). Acta Cryst. B58, 380–388.  Web of Science CrossRef CAS IUCr Journals Google Scholar
 First citationAllen, F. H., Johnson, O., Shields, G. P., Smith, B. R. & Towler, M. (2004). J. Appl. Cryst. 37, 335–338.  Web of Science CrossRef CAS IUCr Journals Google Scholar
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ISSN: 2056-9890
Volume 70| Part 10| October 2014| Pages 192-195
doi:10.1107/S1600536814019874
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