Diethyl trans-2,5-bis­(4-methoxy­benzyl­sulfan­yl)-1,4-dimethyl-3,6-dioxopiperazine-2,5-carboxyl­ate

Polaske, N.W.; Nichol, G.S.; Olenyuk, B.

doi:10.1107/S1600536809022211

organic compounds

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ISSN: 2056-9890

Volume 65| Part 7| July 2009| Pages o1583-o1584

doi:10.1107/S1600536809022211

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Diethyl trans-2,5-bis(4-methoxybenzylsulfanyl)-1,4-dimethyl-3,6-dioxopiperazine-2,5-carboxylate

Nathan W. Polaske,^a Gary S. Nichol ^a ^* and Bogdan Olenyuk ^a ‡

^aDepartment of Chemistry and Biochemistry, The University of Arizona, 1306 E. University Boulevard, Tucson, AZ 85721, USA
^*Correspondence e-mail: gsnichol@email.arizona.edu

(Received 10 June 2009; accepted 11 June 2009; online 17 June 2009)

The title compound, C₂₈H₃₄N₂O₈S₂, was synthesized as part of a project to develop synthetic routes to analogues of sporidesmins, a class of secondary metabolite produced by the filamentous fungi Chaetomium and Pithomyces sp. The complete molecule is generated by crystallographic inversion symmetry: the methoxy group is essentially coplanar with the benzene ring to which it is bonded, a mean plane fitted through the non-H atoms of the aromatic ring and the methoxy group having an r.m.s. deviation of 0.0140 Å. Similarly, the ester group is also essentially planar (r.m.s. deviation of a plane fitted through all non-H atoms is 0.0101 Å). There is only one independent C—H⋯O interaction, which links together adjacent molecules into a two-dimensional sheet in the bc plane.

Related literature

For background information on the biological activity of sporidesmins, see: Fujimoto et al. (2004 ); Gardiner et al. (2005 ); Li et al. (2006 ); Saito et al. (1988 ); Waksman & Bugie (1944 ). For a discussion on the anti-cancer activity of these compounds, see: Brewer et al. (1978 ); Hauser et al. (1970 ); Kung et al. (2004 ); McInnes et al. (1976 ); Waksman & Bugie (1944). For related crystal structures, see: Isaka et al. (2005 ), Dubey et al. (2009 ); Polaske et al. (2009 ). For synthetic details, see: Hino & Sato (1974 ); Kawamura et al. (1975 ).

Experimental

Crystal data

C₂₈H₃₄N₂O₈S₂
M_r = 590.69
Monoclinic, P 2₁ /c
a = 11.290 (2) Å
b = 8.2259 (16) Å
c = 16.593 (3) Å
β = 109.704 (3)°
V = 1450.9 (5) Å³
Z = 2
Mo Kα radiation
μ = 0.24 mm⁻¹
T = 150 K
0.32 × 0.30 × 0.10 mm

Data collection

Bruker SMART 1000 CCD diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ) T_min = 0.919, T_max = 0.987
11556 measured reflections
3522 independent reflections
2778 reflections with I > 2σ(I)
R_int = 0.028

Refinement

R[F² > 2σ(F²)] = 0.036
wR(F²) = 0.092
S = 1.03
3522 reflections
184 parameters
H-atom parameters constrained
Δρ_max = 0.38 e Å⁻³
Δρ_min = −0.24 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C5—H5⋯O4ⁱ	0.95	2.43	3.2647 (19)	147
Symmetry code: (i) $[-x, y-{\script{1\over 2}}, -z-{\script{1\over 2}}]$ .

Data collection: SMART (Bruker, 2007 ); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ); program(s) used to refine structure: SHELXTL; molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ) and Mercury (Macrae et al., 2008 ); software used to prepare material for publication: SHELXTL, publCIF (Westrip, 2009 ) and local programs.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536809022211/fj2226sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536809022211/fj2226Isup2.hkl

checkCIF report

Comment top

Sporidesmins are an interesting class of secondary metabolites produced by the filamentous fungi Chaetomium and Pithomyces sp. This diverse class of natural products contains molecules with one or two epidithiodioxopiperazine rings that display a wide variety of biological activities (Waksman & Bugie, 1944; Saito et al., 1988; Fujimoto et al., 2004; Gardiner et al., 2005; Li et al., 2006). While toxic to mammalian cells, recent studies have suggested that certain sporidesmins may possess anticancer activity due to their ability to suppress neovascularization (Waksman & Bugie, 1944; Hauser et al., 1970; McInnes et al., 1976; Brewer et al., 1978; Kung et al., 2004). In the process of developing synthetic methodologies towards the synthesis of sporidesmin natural products, we came across a number of sulfenylated 2,5-piperazinediones whose structures could not be determined with confidence by NMR spectroscopy. Single crystal X-ray diffraction was found to be the only method available capable of unambiguously identifying the structures of these molecules. Herein we report the structure of the title compound (I).

The stucture of (I) is shown in Figure 1. Molecular dimensions are unexceptional and the compound crystallizes with crystallographic inversion symmetry in an extended conformation composed of essentially planar components. The methoxy group is essentially coplanar with the benzene ring to which it is bonded and a mean plane fitted through the non-hydrogen atoms of the aromatic ring and the methoxy group has an r.m.s. deviation of 0.0140 Å. Similarly the ester moiety is also essentially planar (r.m.s. deviation of a plane fitted through all non-hydrogen atoms is 0.0101 Å). The crystal packing has few notable intermolecular interactions; there is only one C–H···O interaction (plus an equivalent related by inversion symmetry) which links together adjacent molecules into a thick two-dimensional sheet in the bc plane.

Related literature top

For background information on the biological activity of sporidesmins, see: Fujimoto et al. (2004); Gardiner et al. (2005); Li et al. (2006); Saito et al. (1988); Waksman & Bugie (1944). For a discussion on the anti-cancer activity of these compounds, see: Brewer et al. (1978); Hauser et al. (1970); Kung et al. (2004); McInnes et al. (1976); Waksman & Bugie (1944). For related crystal structures, see: Isaka et al. (2005), Dubey et al. (2009); Polaske et al. (2009). For synthetic details, see: Hino & Sato (1974); Kawamura et al. (1975).

Experimental top

To a dry flask equipped with a stir bar was added 1,4-dimethyl-3,6-diethoxycarbonyl-2,5-piperazinedione (Hino & Sato, 1974) (144 mg, 0.50 mmol), (DHQD)₂PYR (88 mg, 0.10 mmol) and N-(4-methoxybenzylthio)succinimide (Kawamura et al., 1975) (504 mg, 2.0 mmol). The compounds were then dried under vacuum for 15 minutes, followed by the addition of CH₂Cl₂ (2.25 ml). The mixture was allowed to stir at room temperature for 5 days. Once complete, the reaction was quenched with 1M KHSO₄ (3 ml) and extracted with CH₂Cl₂ (3 x 15 ml). The organic extracts were combined, dried over anhydrous MgSO₄, filtered, and concentrated under reduced pressure. Purification by column chromatography (silica gel, hexane:CH₂Cl₂:EtOAc (5:4:1)) followed by recrystallization from ethanol yielded colorless prisms (236 mg, 80% yield). LRMS (FAB, [M+H]+) found 591.36, C₂₈H₃₅N₂O₈S₂ requires 591.18.

Computing details top

Data collection: SMART (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008), publCIF (Westrip, 2009) and local programs.

Figures top

	Fig. 1. The molecular structure of (I). Displacement ellipsoids are at the 50% probability level and hydrogen atoms are omitted. Labelled atoms denote the asymmetric unit; unlabelled atoms are related by inversion symmetry (symmetry operator -x, -y + 1, -z).
	Fig. 2. An a axis projection of the crystal packing of (I). Hydrogen bonding is indicated by dotted blue lines (dotted red lines indicate continuation of hydrogen bonding).

Diethyl trans-2,5-bis(4-methoxybenzylsulfanyl)-1,4-dimethyl- 3,6-dioxopiperazine-2,5-carboxylate top

Crystal data top

C₂₈H₃₄N₂O₈S₂	F(000) = 624
M_r = 590.69	D_x = 1.352 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 5275 reflections
a = 11.290 (2) Å	θ = 2.3–28.3°
b = 8.2259 (16) Å	µ = 0.24 mm⁻¹
c = 16.593 (3) Å	T = 150 K
β = 109.704 (3)°	Plate, colourless
V = 1450.9 (5) Å³	0.32 × 0.30 × 0.10 mm
Z = 2

Data collection top

Bruker SMART 1000 CCD diffractometer	3522 independent reflections
Radiation source: sealed tube	2778 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.028
Thin–slice ω scans	θ_max = 28.3°, θ_min = 1.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −14→14
T_min = 0.919, T_max = 0.987	k = −10→10
11556 measured reflections	l = −21→22

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.036	Hydrogen site location: difference Fourier map
wR(F²) = 0.092	H-atom parameters constrained
S = 1.03	w = 1/[σ²(F_o²) + (0.0397P)² + 0.678P] where P = (F_o² + 2F_c²)/3
3522 reflections	(Δ/σ)_max < 0.001
184 parameters	Δρ_max = 0.38 e Å⁻³
0 restraints	Δρ_min = −0.24 e Å⁻³

Crystal data top

C₂₈H₃₄N₂O₈S₂	V = 1450.9 (5) Å³
M_r = 590.69	Z = 2
Monoclinic, P2₁/c	Mo Kα radiation
a = 11.290 (2) Å	µ = 0.24 mm⁻¹
b = 8.2259 (16) Å	T = 150 K
c = 16.593 (3) Å	0.32 × 0.30 × 0.10 mm
β = 109.704 (3)°

Data collection top

Bruker SMART 1000 CCD diffractometer	3522 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	2778 reflections with I > 2σ(I)
T_min = 0.919, T_max = 0.987	R_int = 0.028
11556 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.036	0 restraints
wR(F²) = 0.092	H-atom parameters constrained
S = 1.03	Δρ_max = 0.38 e Å⁻³
3522 reflections	Δρ_min = −0.24 e Å⁻³
184 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

	x	y	z	U_iso*/U_eq
S	0.18848 (3)	0.24066 (4)	0.04288 (2)	0.02157 (10)
O1	0.59043 (11)	0.03836 (16)	−0.14348 (8)	0.0357 (3)
O2	−0.08416 (10)	0.32864 (14)	0.13178 (7)	0.0271 (3)
O3	0.07865 (11)	0.15503 (14)	0.16459 (7)	0.0301 (3)
O4	−0.16577 (11)	0.45732 (14)	−0.15608 (7)	0.0283 (3)
N	−0.05515 (11)	0.34842 (14)	−0.02822 (7)	0.0168 (2)
C1	0.32030 (15)	0.27272 (19)	−0.06556 (10)	0.0251 (3)
C2	0.44789 (16)	0.2787 (2)	−0.01800 (11)	0.0336 (4)
H2	0.4754	0.3387	0.0339	0.040*
C3	0.53537 (16)	0.1986 (2)	−0.04519 (12)	0.0363 (4)
H3	0.6222	0.2038	−0.0118	0.044*
C4	0.49678 (14)	0.1106 (2)	−0.12108 (10)	0.0247 (3)
C5	0.37024 (14)	0.1019 (2)	−0.16888 (10)	0.0256 (3)
H5	0.3426	0.0411	−0.2206	0.031*
C6	0.28382 (15)	0.1832 (2)	−0.14039 (11)	0.0283 (4)
H6	0.1970	0.1770	−0.1734	0.034*
C7	0.22463 (17)	0.3623 (2)	−0.03733 (12)	0.0313 (4)
H7A	0.1472	0.3810	−0.0870	0.038*
H7B	0.2587	0.4692	−0.0129	0.038*
C8	0.55425 (18)	−0.0657 (2)	−0.21608 (12)	0.0361 (4)
H8A	0.5000	−0.1524	−0.2077	0.054*
H8B	0.6295	−0.1137	−0.2233	0.054*
H8C	0.5084	−0.0029	−0.2673	0.054*
C9	0.05188 (13)	0.35374 (17)	0.05104 (9)	0.0167 (3)
C10	0.01900 (14)	0.26530 (18)	0.12339 (9)	0.0201 (3)
C11	−0.12546 (17)	0.2576 (2)	0.19906 (11)	0.0353 (4)
H11A	−0.0596	0.2720	0.2557	0.042*
H11B	−0.1417	0.1399	0.1887	0.042*
C12	−0.24275 (16)	0.3430 (2)	0.19672 (11)	0.0304 (4)
H12A	−0.2258	0.4595	0.2063	0.046*
H12B	−0.2721	0.2993	0.2416	0.046*
H12C	−0.3077	0.3263	0.1407	0.046*
C13	−0.10631 (15)	0.18707 (19)	−0.05932 (10)	0.0258 (3)
H13A	−0.1961	0.1967	−0.0923	0.039*
H13B	−0.0950	0.1145	−0.0104	0.039*
H13C	−0.0619	0.1424	−0.0959	0.039*
C14	−0.09368 (13)	0.47399 (17)	−0.08292 (9)	0.0178 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S	0.02166 (18)	0.01810 (18)	0.02652 (19)	0.00695 (14)	0.01018 (14)	0.00412 (15)
O1	0.0249 (6)	0.0441 (7)	0.0408 (7)	0.0008 (5)	0.0145 (5)	−0.0176 (6)
O2	0.0304 (6)	0.0287 (6)	0.0284 (6)	0.0097 (5)	0.0184 (5)	0.0123 (5)
O3	0.0366 (6)	0.0273 (6)	0.0291 (6)	0.0119 (5)	0.0147 (5)	0.0126 (5)
O4	0.0332 (6)	0.0242 (6)	0.0189 (5)	0.0013 (5)	−0.0027 (5)	−0.0015 (4)
N	0.0183 (6)	0.0145 (6)	0.0161 (6)	0.0000 (4)	0.0037 (5)	−0.0009 (5)
C1	0.0254 (8)	0.0225 (8)	0.0316 (8)	0.0054 (6)	0.0152 (7)	0.0069 (6)
C2	0.0301 (9)	0.0408 (10)	0.0309 (9)	0.0015 (7)	0.0117 (7)	−0.0124 (8)
C3	0.0183 (8)	0.0505 (11)	0.0367 (10)	0.0005 (7)	0.0047 (7)	−0.0152 (8)
C4	0.0211 (7)	0.0271 (8)	0.0283 (8)	0.0015 (6)	0.0116 (6)	−0.0024 (7)
C5	0.0237 (8)	0.0287 (8)	0.0237 (8)	−0.0021 (6)	0.0069 (6)	−0.0034 (6)
C6	0.0178 (7)	0.0342 (9)	0.0311 (8)	0.0026 (6)	0.0059 (6)	0.0052 (7)
C7	0.0341 (9)	0.0250 (8)	0.0439 (10)	0.0109 (7)	0.0252 (8)	0.0104 (7)
C8	0.0418 (10)	0.0350 (10)	0.0387 (10)	−0.0007 (8)	0.0228 (8)	−0.0108 (8)
C9	0.0173 (7)	0.0161 (7)	0.0158 (6)	0.0028 (5)	0.0046 (5)	0.0013 (5)
C10	0.0237 (7)	0.0191 (7)	0.0175 (7)	0.0013 (6)	0.0070 (6)	0.0006 (6)
C11	0.0384 (10)	0.0417 (10)	0.0341 (9)	0.0085 (8)	0.0233 (8)	0.0183 (8)
C12	0.0295 (8)	0.0381 (10)	0.0272 (8)	0.0022 (7)	0.0141 (7)	0.0070 (7)
C13	0.0292 (8)	0.0166 (7)	0.0273 (8)	−0.0032 (6)	0.0038 (7)	−0.0009 (6)
C14	0.0180 (7)	0.0178 (7)	0.0180 (7)	0.0024 (5)	0.0066 (6)	−0.0017 (5)

Geometric parameters (Å, º) top

S—C7	1.8181 (17)	C5—C6	1.391 (2)
S—C9	1.8447 (14)	C6—H6	0.9500
O1—C4	1.3689 (19)	C7—H7A	0.9900
O1—C8	1.421 (2)	C7—H7B	0.9900
O2—C10	1.3255 (18)	C8—H8A	0.9800
O2—C11	1.4682 (19)	C8—H8B	0.9800
O3—C10	1.1972 (18)	C8—H8C	0.9800
O4—C14	1.2201 (17)	C9—C10	1.552 (2)
N—C9	1.4560 (17)	C9—C14ⁱ	1.531 (2)
N—C13	1.4698 (19)	C11—H11A	0.9900
N—C14	1.3469 (18)	C11—H11B	0.9900
C1—C2	1.391 (2)	C11—C12	1.488 (2)
C1—C6	1.382 (2)	C12—H12A	0.9800
C1—C7	1.507 (2)	C12—H12B	0.9800
C2—H2	0.9500	C12—H12C	0.9800
C2—C3	1.383 (2)	C13—H13A	0.9800
C3—H3	0.9500	C13—H13B	0.9800
C3—C4	1.389 (2)	C13—H13C	0.9800
C4—C5	1.382 (2)	C14—C9ⁱ	1.531 (2)
C5—H5	0.9500

C7—S—C9	100.12 (7)	H8A—C8—H8B	109.5
C4—O1—C8	117.65 (13)	H8A—C8—H8C	109.5
C10—O2—C11	116.04 (12)	H8B—C8—H8C	109.5
C9—N—C13	116.90 (11)	S—C9—N	112.23 (9)
C9—N—C14	124.53 (12)	S—C9—C10	104.14 (9)
C13—N—C14	117.16 (12)	S—C9—C14ⁱ	108.92 (9)
C2—C1—C6	117.82 (15)	N—C9—C10	110.02 (11)
C2—C1—C7	121.36 (16)	N—C9—C14ⁱ	113.91 (11)
C6—C1—C7	120.82 (15)	C10—C9—C14ⁱ	107.03 (11)
C1—C2—H2	119.5	O2—C10—O3	125.65 (14)
C1—C2—C3	121.00 (16)	O2—C10—C9	110.17 (12)
H2—C2—C3	119.5	O3—C10—C9	124.17 (13)
C2—C3—H3	119.9	O2—C11—H11A	110.2
C2—C3—C4	120.24 (15)	O2—C11—H11B	110.2
H3—C3—C4	119.9	O2—C11—C12	107.49 (13)
O1—C4—C3	115.94 (14)	H11A—C11—H11B	108.5
O1—C4—C5	124.42 (14)	H11A—C11—C12	110.2
C3—C4—C5	119.64 (15)	H11B—C11—C12	110.2
C4—C5—H5	120.4	C11—C12—H12A	109.5
C4—C5—C6	119.20 (15)	C11—C12—H12B	109.5
H5—C5—C6	120.4	C11—C12—H12C	109.5
C1—C6—C5	122.08 (14)	H12A—C12—H12B	109.5
C1—C6—H6	119.0	H12A—C12—H12C	109.5
C5—C6—H6	119.0	H12B—C12—H12C	109.5
S—C7—C1	108.65 (11)	N—C13—H13A	109.5
S—C7—H7A	110.0	N—C13—H13B	109.5
S—C7—H7B	110.0	N—C13—H13C	109.5
C1—C7—H7A	110.0	H13A—C13—H13B	109.5
C1—C7—H7B	110.0	H13A—C13—H13C	109.5
H7A—C7—H7B	108.3	H13B—C13—H13C	109.5
O1—C8—H8A	109.5	O4—C14—N	122.68 (13)
O1—C8—H8B	109.5	O4—C14—C9ⁱ	118.20 (13)
O1—C8—H8C	109.5	N—C14—C9ⁱ	119.02 (12)

C6—C1—C2—C3	0.5 (3)	C14—N—C9—C10	138.48 (13)
C7—C1—C2—C3	−178.77 (17)	C14—N—C9—C14ⁱ	18.3 (2)
C1—C2—C3—C4	0.1 (3)	C7—S—C9—N	64.78 (12)
C8—O1—C4—C3	173.97 (17)	C7—S—C9—C10	−176.24 (10)
C8—O1—C4—C5	−6.6 (2)	C7—S—C9—C14ⁱ	−62.31 (11)
C2—C3—C4—O1	178.72 (17)	C11—O2—C10—O3	1.3 (2)
C2—C3—C4—C5	−0.7 (3)	C11—O2—C10—C9	−179.23 (13)
O1—C4—C5—C6	−178.71 (16)	S—C9—C10—O2	−175.74 (10)
C3—C4—C5—C6	0.7 (3)	S—C9—C10—O3	3.69 (18)
C2—C1—C6—C5	−0.5 (2)	N—C9—C10—O2	−55.27 (15)
C7—C1—C6—C5	178.73 (15)	N—C9—C10—O3	124.16 (15)
C4—C5—C6—C1	0.0 (3)	C14ⁱ—C9—C10—O2	68.99 (14)
C2—C1—C7—S	−81.68 (18)	C14ⁱ—C9—C10—O3	−111.58 (16)
C6—C1—C7—S	99.06 (17)	C10—O2—C11—C12	−178.98 (14)
C9—S—C7—C1	−169.77 (12)	C9—N—C14—O4	164.45 (14)
C13—N—C9—S	59.98 (15)	C9—N—C14—C9ⁱ	−19.2 (2)
C13—N—C9—C10	−55.48 (16)	C13—N—C14—O4	−1.6 (2)
C13—N—C9—C14ⁱ	−175.65 (12)	C13—N—C14—C9ⁱ	174.82 (12)
C14—N—C9—S	−106.05 (13)

Symmetry code: (i) −x, −y+1, −z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5···O4ⁱⁱ	0.95	2.43	3.2647 (19)	147

Symmetry code: (ii) −x, y−1/2, −z−1/2.

Experimental details

Crystal data
Chemical formula	C₂₈H₃₄N₂O₈S₂
M_r	590.69
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	150
a, b, c (Å)	11.290 (2), 8.2259 (16), 16.593 (3)
β (°)	109.704 (3)
V (Å³)	1450.9 (5)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	0.24
Crystal size (mm)	0.32 × 0.30 × 0.10

Data collection
Diffractometer	Bruker SMART 1000 CCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996)
T_min, T_max	0.919, 0.987
No. of measured, independent and observed [I > 2σ(I)] reflections	11556, 3522, 2778
R_int	0.028
(sin θ/λ)_max (Å⁻¹)	0.667

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.036, 0.092, 1.03
No. of reflections	3522
No. of parameters	184
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.38, −0.24

Computer programs: SMART (Bruker, 2007), SAINT (Bruker, 2007), ORTEP-3 for Windows (Farrugia, 1997) and Mercury (Macrae et al., 2008), SHELXTL (Sheldrick, 2008), publCIF (Westrip, 2009) and local programs.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5···O4ⁱ	0.95	2.43	3.2647 (19)	147

Symmetry code: (i) −x, y−1/2, −z−1/2.

Footnotes

‡Additional correspondence author, e-mail olenyuk@email.arizona.edu.

Acknowledgements

We thank the US National Science Foundation (CHE-0748838 & CHE-9610347) for support.

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