Ethyl 3,5-dimethyl-1H-pyrrole-2-carboxyl­ate

Arranja, C.T.; Ramos Silva, M.; Matos Beja, A.; Ferreira, A.F.P.V.; Sobral, A.J.F.N.

doi:10.1107/S1600536808029929

organic compounds

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ISSN: 2056-9890

Volume 64| Part 10| October 2008| Page o1989

doi:10.1107/S1600536808029929

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Ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate

Cláudia T. Arranja,^a Manuela Ramos Silva,^b ^* Ana Matos Beja,^b Ana F. P. V. Ferreira ^a and Abílio J. F. N. Sobral ^a

^aChemistry Department, University of Coimbra, P-3004-535 Coimbra, Portugal, and ^bCEMDRX, Physics Department, University of Coimbra, P-3004-516 Coimbra, Portugal
^*Correspondence e-mail: manuela@pollux.fis.uc.pt

(Received 15 September 2008; accepted 17 September 2008; online 24 September 2008)

In the title compound, C₉H₁₃NO₂, there are two independent molecules per asymmetric unit. The molecules are very similar and almost planar, with the ethoxycarbonyl group anti to the pyrrole N atom. The two independent molecules are joined into dimeric units by strong hydrogen bonds between NH groups and carbonyl O atoms.

Related literature

For general background, see: Bonnett (1995 , 2000 ). For related structures, see: Paixão et al. (2002 ), Ramos Silva et al. (2002 ); Sobral & Rocha Gonsalves (2001 ).

Experimental

Crystal data

C₉H₁₃NO₂
M_r = 167.20
Triclinic, $[P \overline 1]$
a = 8.1357 (2) Å
b = 10.5568 (2) Å
c = 12.1428 (2) Å
α = 101.5451 (13)°
β = 97.8791 (14)°
γ = 110.4821 (14)°
V = 932.52 (4) Å³
Z = 4
Mo Kα radiation
μ = 0.08 mm⁻¹
T = 293 (2) K
0.25 × 0.20 × 0.15 mm

Data collection

Bruker APEX CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2000 ) T_min = 0.899, T_max = 0.987
20370 measured reflections
4456 independent reflections
2368 reflections with I > 2σ(I)
R_int = 0.028

Refinement

R[F² > 2σ(F²)] = 0.052
wR(F²) = 0.182
S = 1.03
4456 reflections
223 parameters
H-atom parameters constrained
Δρ_max = 0.20 e Å⁻³
Δρ_min = −0.21 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O4	0.86	2.02	2.857 (2)	166
N2—H2⋯O2	0.86	2.00	2.834 (2)	163

Data collection: SMART (Bruker, 2003 ); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPII (Johnson, 1976 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808029929/bt2791sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536808029929/bt2791Isup2.hkl

checkCIF report

Comment top

Photodynamic therapy (PDT) is a developing method for the treatment of carcinomas and sarcomas. It consists in a selective absorption of a photosensitizer in a tumor, followed by irradiation with light of a selected wavelength, originating tumor necrosis. The fewer side effects of this therapeutic method when compared to chemotherapy and radiotherapy have prompted the search for new and more efficient photosensitizers, namely porphyrins (Bonnett, 1995, 2000). Pyrroles are building blocks for the synthesis of porphyrins and following our previous structural studies on pyrrole chemistry (Sobral & Rocha Gonsalves, 2001; Ramos Silva et al., 2002; Paixão et al., 2002) we present here the title compound ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate, (I), Fig. 1. There are two independent molecules per asymmetric unit. The two molecules are very similar and almost planar with the angle between molecular planes being 3.87 (5)°. The molecules show an eclipsed conformation, when viewed along the C1—C7 direction, with the ethoxycarbonylgroup anti to the pyrrole N atom. The molecules are grouped in dimers by strong hydrogen bonds between N—H groups and carbonyl O atoms (Fig.1, Table 1). The dimers stack in planes approximately 5 Å apart (Fig.2).

Related literature top

For related literature, see: Paixão et al. (2002), Ramos Silva et al. (2002); Sobral & Rocha Gonsalves (2001); Bonnett (1995, 2000).

Experimental top

The ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate was prepared by a Knorr-type reaction from the condensation of acetylacetone and ethyl oximinoacetoacetate.

Computing details top

Data collection: SMART (Bruker, 2003); 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: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

	Fig. 1. ORTEPII (Johnson, 1976) plot of the title compound. Displacement ellipsoids are drawn at the 50% level. The H-bonds are represented as dashed lines.
	Fig. 2. Packing diagram of the title compound.

Ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate top

Crystal data top

C₉H₁₃NO₂	Z = 4
M_r = 167.20	F(000) = 360
Triclinic, P1	D_x = 1.191 Mg m⁻³
a = 8.1357 (2) Å	Mo Kα radiation, λ = 0.71073 Å
b = 10.5568 (2) Å	Cell parameters from 3873 reflections
c = 12.1428 (2) Å	θ = 2.4–23.9°
α = 101.5451 (13)°	µ = 0.08 mm⁻¹
β = 97.8791 (14)°	T = 293 K
γ = 110.4821 (14)°	Prism, colourless
V = 932.52 (4) Å³	0.25 × 0.20 × 0.15 mm

Data collection top

Bruker APEX CCD area-detector diffractometer	4456 independent reflections
Radiation source: fine-focus sealed tube	2368 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.028
ϕ and ω scans	θ_max = 28.0°, θ_min = 1.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 2000)	h = −10→10
T_min = 0.899, T_max = 0.987	k = −13→13
20370 measured reflections	l = −15→15

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)] = 0.052	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.182	H-atom parameters constrained
S = 1.03	w = 1/[σ²(F_o²) + (0.0939P)² + 0.0508P] where P = (F_o² + 2F_c²)/3
4456 reflections	(Δ/σ)_max < 0.001
223 parameters	Δρ_max = 0.20 e Å⁻³
0 restraints	Δρ_min = −0.21 e Å⁻³

Crystal data top

C₉H₁₃NO₂	γ = 110.4821 (14)°
M_r = 167.20	V = 932.52 (4) Å³
Triclinic, P1	Z = 4
a = 8.1357 (2) Å	Mo Kα radiation
b = 10.5568 (2) Å	µ = 0.08 mm⁻¹
c = 12.1428 (2) Å	T = 293 K
α = 101.5451 (13)°	0.25 × 0.20 × 0.15 mm
β = 97.8791 (14)°

Data collection top

Bruker APEX CCD area-detector diffractometer	4456 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2000)	2368 reflections with I > 2σ(I)
T_min = 0.899, T_max = 0.987	R_int = 0.028
20370 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.052	0 restraints
wR(F²) = 0.182	H-atom parameters constrained
S = 1.03	Δρ_max = 0.20 e Å⁻³
4456 reflections	Δρ_min = −0.21 e Å⁻³
223 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
N1	0.2122 (2)	0.18401 (15)	0.96119 (12)	0.0526 (4)
H1	0.1472	0.1689	0.8941	0.063*
C1	0.2894 (2)	0.31179 (18)	1.04326 (14)	0.0483 (4)
C2	0.3837 (3)	0.29357 (19)	1.13867 (15)	0.0535 (5)
C3	0.3587 (3)	0.1515 (2)	1.11083 (17)	0.0620 (5)
H3	0.4060	0.1083	1.1589	0.074*
C4	0.2537 (3)	0.08658 (19)	1.00165 (17)	0.0561 (5)
C5	0.1877 (3)	−0.0621 (2)	0.92988 (19)	0.0745 (6)
H5A	0.0653	−0.0912	0.8891	0.112*
H5B	0.1938	−0.1218	0.9790	0.112*
H5C	0.2617	−0.0684	0.8756	0.112*
C6	0.4927 (3)	0.4029 (2)	1.24868 (16)	0.0700 (6)
H6A	0.5941	0.4716	1.2331	0.105*
H6B	0.5346	0.3594	1.3024	0.105*
H6C	0.4193	0.4476	1.2810	0.105*
C7	0.2626 (2)	0.43124 (19)	1.01696 (15)	0.0497 (4)
C8	0.3246 (3)	0.67311 (19)	1.08651 (16)	0.0598 (5)
H8A	0.1987	0.6598	1.0744	0.072*
H8B	0.3685	0.6956	1.0196	0.072*
C9	0.4325 (3)	0.7891 (2)	1.19379 (19)	0.0736 (6)
H9A	0.3901	0.7642	1.2595	0.110*
H9B	0.4191	0.8742	1.1869	0.110*
H9C	0.5573	0.8030	1.2035	0.110*
O1	0.34589 (17)	0.54785 (12)	1.10374 (10)	0.0571 (4)
O2	0.1739 (2)	0.42886 (14)	0.92727 (11)	0.0697 (4)
N2	−0.03335 (19)	0.33131 (15)	0.69754 (12)	0.0514 (4)
H2	0.0341	0.3455	0.7635	0.062*
C10	−0.0692 (3)	0.43124 (19)	0.65748 (16)	0.0532 (5)
C11	−0.1793 (3)	0.3672 (2)	0.54923 (17)	0.0581 (5)
H11	−0.2237	0.4120	0.5012	0.070*
C12	−0.2140 (2)	0.22325 (19)	0.52282 (15)	0.0511 (5)
C13	−0.1210 (2)	0.20295 (18)	0.61697 (14)	0.0470 (4)
C14	−0.3308 (3)	0.1161 (2)	0.41335 (16)	0.0666 (6)
H14A	−0.2676	0.0606	0.3829	0.100*
H14B	−0.3600	0.1628	0.3580	0.100*
H14C	−0.4397	0.0564	0.4290	0.100*
C15	0.0049 (3)	0.58075 (19)	0.72855 (18)	0.0681 (6)
H15A	−0.0667	0.5910	0.7837	0.102*
H15B	0.0018	0.6407	0.6791	0.102*
H15C	0.1270	0.6063	0.7684	0.102*
C16	−0.1000 (3)	0.08222 (19)	0.64427 (15)	0.0525 (5)
C17	−0.1825 (3)	−0.16323 (19)	0.58381 (18)	0.0635 (5)
H17A	−0.2223	−0.1772	0.6538	0.076*
H17B	−0.0591	−0.1565	0.5933	0.076*
C18	−0.3012 (3)	−0.2831 (2)	0.4826 (2)	0.0777 (7)
H18A	−0.4226	−0.2880	0.4734	0.116*
H18B	−0.2979	−0.3691	0.4953	0.116*
H18C	−0.2593	−0.2690	0.4141	0.116*
O3	−0.19388 (17)	−0.03673 (13)	0.56183 (10)	0.0574 (4)
O4	−0.0063 (2)	0.08520 (14)	0.73228 (12)	0.0806 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
N1	0.0640 (10)	0.0477 (9)	0.0397 (8)	0.0212 (8)	0.0025 (7)	0.0053 (7)
C1	0.0532 (10)	0.0434 (10)	0.0407 (9)	0.0155 (8)	0.0037 (8)	0.0055 (8)
C2	0.0575 (11)	0.0533 (11)	0.0445 (10)	0.0198 (9)	0.0041 (8)	0.0099 (8)
C3	0.0759 (14)	0.0568 (12)	0.0565 (12)	0.0307 (11)	0.0067 (10)	0.0189 (10)
C4	0.0674 (12)	0.0478 (11)	0.0552 (11)	0.0256 (9)	0.0123 (9)	0.0133 (9)
C5	0.0935 (16)	0.0467 (12)	0.0772 (15)	0.0282 (11)	0.0119 (12)	0.0069 (10)
C6	0.0797 (15)	0.0690 (14)	0.0472 (11)	0.0236 (11)	−0.0088 (10)	0.0103 (10)
C7	0.0534 (11)	0.0470 (11)	0.0408 (10)	0.0160 (8)	0.0037 (8)	0.0059 (8)
C8	0.0741 (13)	0.0482 (11)	0.0566 (12)	0.0256 (10)	0.0108 (10)	0.0124 (9)
C9	0.0911 (16)	0.0509 (12)	0.0669 (14)	0.0229 (11)	0.0142 (12)	0.0014 (10)
O1	0.0726 (9)	0.0436 (7)	0.0455 (7)	0.0207 (6)	−0.0015 (6)	0.0050 (6)
O2	0.0918 (11)	0.0559 (8)	0.0498 (8)	0.0314 (8)	−0.0130 (7)	0.0039 (6)
N2	0.0561 (9)	0.0459 (9)	0.0428 (8)	0.0157 (7)	0.0011 (7)	0.0061 (7)
C10	0.0583 (11)	0.0456 (11)	0.0535 (11)	0.0191 (9)	0.0097 (9)	0.0126 (9)
C11	0.0639 (12)	0.0531 (12)	0.0538 (11)	0.0222 (9)	0.0002 (9)	0.0166 (9)
C12	0.0511 (10)	0.0515 (11)	0.0439 (10)	0.0166 (9)	0.0035 (8)	0.0089 (8)
C13	0.0496 (10)	0.0423 (10)	0.0403 (9)	0.0133 (8)	0.0035 (8)	0.0050 (7)
C14	0.0691 (13)	0.0649 (13)	0.0491 (11)	0.0186 (11)	−0.0086 (10)	0.0081 (10)
C15	0.0796 (15)	0.0451 (12)	0.0702 (13)	0.0218 (10)	0.0066 (11)	0.0068 (10)
C16	0.0580 (11)	0.0476 (11)	0.0426 (10)	0.0169 (9)	0.0017 (9)	0.0050 (8)
C17	0.0701 (13)	0.0484 (12)	0.0643 (13)	0.0226 (10)	0.0037 (10)	0.0073 (10)
C18	0.0850 (16)	0.0475 (12)	0.0825 (16)	0.0204 (11)	0.0047 (12)	−0.0019 (11)
O3	0.0664 (8)	0.0428 (7)	0.0508 (8)	0.0179 (6)	−0.0027 (6)	0.0029 (6)
O4	0.1088 (12)	0.0548 (9)	0.0572 (9)	0.0290 (8)	−0.0237 (8)	0.0037 (7)

Geometric parameters (Å, º) top

N1—C4	1.346 (2)	N2—C10	1.348 (2)
N1—C1	1.380 (2)	N2—C13	1.380 (2)
N1—H1	0.8600	N2—H2	0.8600
C1—C2	1.384 (2)	C10—C11	1.373 (3)
C1—C7	1.440 (2)	C10—C15	1.498 (2)
C2—C3	1.404 (3)	C11—C12	1.405 (2)
C2—C6	1.498 (3)	C11—H11	0.9300
C3—C4	1.369 (3)	C12—C13	1.378 (2)
C3—H3	0.9300	C12—C14	1.500 (2)
C4—C5	1.498 (3)	C13—C16	1.438 (3)
C5—H5A	0.9600	C14—H14A	0.9600
C5—H5B	0.9600	C14—H14B	0.9600
C5—H5C	0.9600	C14—H14C	0.9600
C6—H6A	0.9600	C15—H15A	0.9600
C6—H6B	0.9600	C15—H15B	0.9600
C6—H6C	0.9600	C15—H15C	0.9600
C7—O2	1.212 (2)	C16—O4	1.213 (2)
C7—O1	1.336 (2)	C16—O3	1.333 (2)
C8—O1	1.443 (2)	C17—O3	1.444 (2)
C8—C9	1.504 (3)	C17—C18	1.497 (3)
C8—H8A	0.9700	C17—H17A	0.9700
C8—H8B	0.9700	C17—H17B	0.9700
C9—H9A	0.9600	C18—H18A	0.9600
C9—H9B	0.9600	C18—H18B	0.9600
C9—H9C	0.9600	C18—H18C	0.9600

C4—N1—C1	109.98 (15)	C10—N2—C13	109.89 (15)
C4—N1—H1	125.0	C10—N2—H2	125.1
C1—N1—H1	125.0	C13—N2—H2	125.1
N1—C1—C2	107.62 (15)	N2—C10—C11	107.26 (16)
N1—C1—C7	119.00 (15)	N2—C10—C15	121.47 (17)
C2—C1—C7	133.38 (16)	C11—C10—C15	131.26 (18)
C1—C2—C3	105.90 (16)	C10—C11—C12	108.90 (17)
C1—C2—C6	127.36 (17)	C10—C11—H11	125.6
C3—C2—C6	126.73 (17)	C12—C11—H11	125.6
C4—C3—C2	109.18 (17)	C13—C12—C11	106.15 (16)
C4—C3—H3	125.4	C13—C12—C14	128.26 (17)
C2—C3—H3	125.4	C11—C12—C14	125.59 (17)
N1—C4—C3	107.32 (16)	C12—C13—N2	107.79 (15)
N1—C4—C5	121.31 (18)	C12—C13—C16	133.95 (16)
C3—C4—C5	131.37 (19)	N2—C13—C16	118.26 (15)
C4—C5—H5A	109.5	C12—C14—H14A	109.5
C4—C5—H5B	109.5	C12—C14—H14B	109.5
H5A—C5—H5B	109.5	H14A—C14—H14B	109.5
C4—C5—H5C	109.5	C12—C14—H14C	109.5
H5A—C5—H5C	109.5	H14A—C14—H14C	109.5
H5B—C5—H5C	109.5	H14B—C14—H14C	109.5
C2—C6—H6A	109.5	C10—C15—H15A	109.5
C2—C6—H6B	109.5	C10—C15—H15B	109.5
H6A—C6—H6B	109.5	H15A—C15—H15B	109.5
C2—C6—H6C	109.5	C10—C15—H15C	109.5
H6A—C6—H6C	109.5	H15A—C15—H15C	109.5
H6B—C6—H6C	109.5	H15B—C15—H15C	109.5
O2—C7—O1	122.56 (16)	O4—C16—O3	121.97 (17)
O2—C7—C1	124.92 (16)	O4—C16—C13	124.71 (16)
O1—C7—C1	112.52 (15)	O3—C16—C13	113.32 (15)
O1—C8—C9	106.73 (15)	O3—C17—C18	107.56 (16)
O1—C8—H8A	110.4	O3—C17—H17A	110.2
C9—C8—H8A	110.4	C18—C17—H17A	110.2
O1—C8—H8B	110.4	O3—C17—H17B	110.2
C9—C8—H8B	110.4	C18—C17—H17B	110.2
H8A—C8—H8B	108.6	H17A—C17—H17B	108.5
C8—C9—H9A	109.5	C17—C18—H18A	109.5
C8—C9—H9B	109.5	C17—C18—H18B	109.5
H9A—C9—H9B	109.5	H18A—C18—H18B	109.5
C8—C9—H9C	109.5	C17—C18—H18C	109.5
H9A—C9—H9C	109.5	H18A—C18—H18C	109.5
H9B—C9—H9C	109.5	H18B—C18—H18C	109.5
C7—O1—C8	116.76 (13)	C16—O3—C17	116.64 (14)

C4—N1—C1—C2	0.3 (2)	C13—N2—C10—C11	−0.8 (2)
C4—N1—C1—C7	179.58 (15)	C13—N2—C10—C15	178.44 (16)
N1—C1—C2—C3	−0.4 (2)	N2—C10—C11—C12	0.8 (2)
C7—C1—C2—C3	−179.57 (19)	C15—C10—C11—C12	−178.28 (19)
N1—C1—C2—C6	178.72 (18)	C10—C11—C12—C13	−0.6 (2)
C7—C1—C2—C6	−0.4 (3)	C10—C11—C12—C14	179.03 (18)
C1—C2—C3—C4	0.4 (2)	C11—C12—C13—N2	0.1 (2)
C6—C2—C3—C4	−178.74 (19)	C14—C12—C13—N2	−179.49 (17)
C1—N1—C4—C3	0.0 (2)	C11—C12—C13—C16	−179.8 (2)
C1—N1—C4—C5	−179.76 (16)	C14—C12—C13—C16	0.6 (3)
C2—C3—C4—N1	−0.3 (2)	C10—N2—C13—C12	0.4 (2)
C2—C3—C4—C5	179.4 (2)	C10—N2—C13—C16	−179.68 (15)
N1—C1—C7—O2	1.0 (3)	C12—C13—C16—O4	177.7 (2)
C2—C1—C7—O2	−179.9 (2)	N2—C13—C16—O4	−2.2 (3)
N1—C1—C7—O1	−179.56 (14)	C12—C13—C16—O3	−1.7 (3)
C2—C1—C7—O1	−0.5 (3)	N2—C13—C16—O3	178.41 (15)
O2—C7—O1—C8	0.4 (3)	O4—C16—O3—C17	1.7 (3)
C1—C7—O1—C8	−178.98 (15)	C13—C16—O3—C17	−178.86 (15)
C9—C8—O1—C7	−178.86 (15)	C18—C17—O3—C16	178.37 (16)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O4	0.86	2.02	2.857 (2)	166
N2—H2···O2	0.86	2.00	2.834 (2)	163

Experimental details

Crystal data
Chemical formula	C₉H₁₃NO₂
M_r	167.20
Crystal system, space group	Triclinic, P1
Temperature (K)	293
a, b, c (Å)	8.1357 (2), 10.5568 (2), 12.1428 (2)
α, β, γ (°)	101.5451 (13), 97.8791 (14), 110.4821 (14)
V (Å³)	932.52 (4)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.08
Crystal size (mm)	0.25 × 0.20 × 0.15

Data collection
Diffractometer	Bruker APEX CCD area-detector diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 2000)
T_min, T_max	0.899, 0.987
No. of measured, independent and observed [I > 2σ(I)] reflections	20370, 4456, 2368
R_int	0.028
(sin θ/λ)_max (Å⁻¹)	0.660

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.052, 0.182, 1.03
No. of reflections	4456
No. of parameters	223
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.20, −0.21

Computer programs: SMART (Bruker, 2003), SAINT (Bruker, 2003), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEPII (Johnson, 1976).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O4	0.8600	2.0200	2.857 (2)	166.00
N2—H2···O2	0.8600	2.0000	2.834 (2)	163.00

Acknowledgements

This work was supported by Fundação para a Ciência e a Tecnologia (FCT) under project POCI/AMB/55281/2004.

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