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organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 66| Part 8| August 2010| Page o2071
https://doi.org/10.1107/S1600536810027947

Methyl 1-{4-[(S)-2-(meth­­oxy­carbon­yl)pyrrolidin-1-yl]-3,6-dioxo­cyclo­hexa-1,4-dien-1-yl}pyrrolidine-2-carboxyl­ate

Simon J. Garden,a Janet M. S. Skakle,b Edward R. T. Tiekinkc* and James L. Wardelld‡

aInstituto de Química, Departamento de Quimica Orgânica, Universidade, Federal do Rio de Janeiro, Ilha do Fundão, CT, Bloco A, Rio de Janeiro 21949-900, RJ, Brazil, bDepartment of Chemistry, University of Aberdeen, Old Aberdeen AB15 5NY, Scotland, cDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia, and dCentro de Desenvolvimento Tecnológico em Saúde (CDTS), Fundação Oswaldo Cruz (FIOCRUZ), Casa Amarela, Campus de Manguinhos, Av. Brasil 4365, 21040-900 Rio de Janeiro, RJ, Brazil
*Correspondence e-mail: edward.tiekink@gmail.com

(Received 11 July 2010; accepted 13 July 2010; online 21 July 2010)

The complete mol­ecule of the title diproline ester quinone, C18H22N2O6, is generated by a crystallographic twofold axis, which passes through the centre of the benzene ring. Both –CO2Me groups are orientated to the same side of the benzene ring, with the carbonyl groups pointing roughly towards each other. The conformation of the proline residue is an envelope. In the crystal, a three-dimensional network is sustained by C—H⋯O inter­actions involving both the quinone and carbonyl O atoms.

Related literature

For the oxidative nucleophilic addition of amines to quinones to form amino­quinones, see: Lyons & Thomson (1953[Lyons, J. M. & Thomson, R. H. (1953). J. Chem. Soc. pp. 2910-2915.]). For background to mitomycin anti­cancer drugs, see: Tomasz (1995[Tomasz, M. (1995). Chem. Biol. 2, 575-579.]). For additional geometric analysis, see: Cremer & Pople (1975[Cremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc. 97, 1354-1358.]).

[Scheme 1]

Experimental

Crystal data

  • C18H22N2O6

  • Mr = 362.38

  • Monoclinic, C 2

  • a = 11.4728 (5) Å

  • b = 7.1556 (4) Å

  • c = 11.7882 (7) Å

  • β = 111.230 (3)°

  • V = 902.07 (8) Å3

  • Z = 2

  • Mo Kα radiation

  • μ = 0.10 mm−1

  • T = 120 K

  • 0.24 × 0.12 × 0.08 mm
Data collection

  • Nonius KappaCCD area-detector diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2007[Sheldrick, G. M. (2007). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]) Tmin = 0.896, Tmax = 1.000

  • 6840 measured reflections

  • 1114 independent reflections

  • 1008 reflections with I > 2σ(I)

  • Rint = 0.034
Refinement

  • R[F2 > 2σ(F2)] = 0.038

  • wR(F2) = 0.136

  • S = 1.23

  • 1114 reflections

  • 119 parameters

  • 1 restraint

  • H-atom parameters constrained

  • Δρmax = 0.64 e Å−3

  • Δρmin = −0.63 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A D⋯A D—H⋯A
C3—H3⋯O2i 0.95 2.56 3.400 (3) 147
C5—H5b⋯O1ii 0.99 2.54 3.407 (3) 146
C9—H9b⋯O1iii 0.98 2.38 3.186 (4) 139
Symmetry codes: (i) [-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z]; (ii) [x+{\script{1\over 2}}, y-{\script{1\over 2}}, z]; (iii) [-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+1].

Data collection: COLLECT (Hooft, 1998[Hooft, R. W. W. (1998). COLLECT. Nonius BV, Delft, The Netherlands.]); cell refinement: DENZO (Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. New York: Academic Press.]) and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: ORTEP-3 (Farrugia, 1997[Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.]) and DIAMOND (Brandenburg, 2006[Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany.]); software used to prepare material for publication: publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536810027947/hb5550sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810027947/hb5550Isup2.hkl

checkCIF report


Comment top

Oxidative nucleophilic addition of amines to quinones results in the formation of aminoquinone products (Lyons & Thomson, 1953). As part of a study into concise methodology for the synthesis of heterocyclic systems, we envisaged that oxidative addition of α-amino acid derivatives to benzoquinone could yield a suitably functionalized precursor for cyclization to yield pyrroloindole quinones, a structural motif present in the mitomycin anticancer drugs (Tomasz, 1995). The title diproline ester quinone, (I), was synthesized in this context.

The molecule of (I), Fig. 1, exists about a crystallographic 2-fold axis of symmetry passing through the centre of the benzene ring. This has the result that the two –CO2Me groups are orientated to the same side of the benzene ring. The carbonyl groups are tucked in under the benzene ring. The conformation of the proline residue is an envelope with the C5 atom lying above the plane through the remaining atoms. The conformational descriptors (Cremer & Pople, 1975) are Q(2) = 0.348 (3) Å and φ(2) = 79.3 (4) °.

The crystal packing features C—H···O contacts, Table 1. The quinone-O1 atom accepts two such interactions, one from a methylene-H and the other from a methyl-H, whereas the carbonyl-O2 accepts a quinone-H. The C—H···O interactions combine to give a 3-D network, Fig. 2.

Related literature top

For the oxidative nucleophilic addition of amines to quinones to form aminoquinones, see: Lyons & Thomson (1953). For background to mitomycin anticancer drugs, see: Tomasz (1995). For additional geometric analysis, see: Cremer & Pople (1975).

Experimental top

Proline methyl ester hydrochloride (1.63 g, 9.8 mmol) and KOAc (1.07 g, 10.9 mmol) were mixed in MeOH (20 ml). Excess benzoquinone (1.00 g, 9.3 mmol) was added to the solution resulting in a deep-red coloured reaction. The reaction was stirred for an hour then all the volatiles were removed under reduced pressure. The crude product was solubilized in EtOAc and filtered through a plug of silica using EtOAc as eluent. The red coloured fraction was evaporated under reduced pressure and the product chromatographed on a column of silica eluting with CH2Cl2 (removed excess benzoquinone) followed by a CH2Cl2/EtOAc gradient (9:1 V/V to 4:1 V/V). Evaporation of the product containing fractions and recrystallization from MeOH gave 0.266 g of dark-red prisms of (I) (15% yield), m.pt. 463–465 K.

1H (CDCl3): δ 1.95 [2H, m]; 2.19 [2H, m]; 3.39 [1H, m]; 3.48 [1H, m]; 3.73 [3H, s]; 5.07 [1H, bs]; 5.37 [1H, bs] p.p.m. 13C (CDCl3): δ 22.0; 31.6; 51.3; 52.4; 62.9; 101.5; 148.7; 172.8; 181.2 p.p.m. IR (cm-1): 3066, 2982, 2955, 2927, 2881, 1744, 1625, 1555, 1432, 1349, 1274, 1207, 1166, 957, 833, 794. Mass (a.m.u.) abundance %: 362 (79), 331 (10), 303 (52), 276 (100), 261 (63), 243 (25), 235 (37), 217 (46), 176 (25), 122 (37).

Refinement top

The C-bound H atoms were geometrically placed (C–H = 0.95–1.00 Å) and refined as riding with Uiso(H) = 1.2–1.5Ueq(C). The maximum and minimum residual electron density peaks of 0.64 and 0.63 e Å-3, respectively, were located 1.59 Å and 0.85 Å from the H5b and C8 atoms, respectively. In the absence of significant anomalous scattering effects, 750 Friedel pairs were averaged in the final refinement. However, the absolute configuration was assigned on the basis of the chirality of the L-proline starting material.

Structure description top

Oxidative nucleophilic addition of amines to quinones results in the formation of aminoquinone products (Lyons & Thomson, 1953). As part of a study into concise methodology for the synthesis of heterocyclic systems, we envisaged that oxidative addition of α-amino acid derivatives to benzoquinone could yield a suitably functionalized precursor for cyclization to yield pyrroloindole quinones, a structural motif present in the mitomycin anticancer drugs (Tomasz, 1995). The title diproline ester quinone, (I), was synthesized in this context.

The molecule of (I), Fig. 1, exists about a crystallographic 2-fold axis of symmetry passing through the centre of the benzene ring. This has the result that the two –CO2Me groups are orientated to the same side of the benzene ring. The carbonyl groups are tucked in under the benzene ring. The conformation of the proline residue is an envelope with the C5 atom lying above the plane through the remaining atoms. The conformational descriptors (Cremer & Pople, 1975) are Q(2) = 0.348 (3) Å and φ(2) = 79.3 (4) °.

The crystal packing features C—H···O contacts, Table 1. The quinone-O1 atom accepts two such interactions, one from a methylene-H and the other from a methyl-H, whereas the carbonyl-O2 accepts a quinone-H. The C—H···O interactions combine to give a 3-D network, Fig. 2.

For the oxidative nucleophilic addition of amines to quinones to form aminoquinones, see: Lyons & Thomson (1953). For background to mitomycin anticancer drugs, see: Tomasz (1995). For additional geometric analysis, see: Cremer & Pople (1975).

Computing details top

Data collection: COLLECT (Hooft, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); data reduction: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) showing displacement ellipsoids at the 50% probability level. Unlabelled atoms are generated by (–x, y, –z).
[Figure 2] Fig. 2. A view in projection down the b axis of the unit-cell contents (I) showing the C–H···O contacts as orange dashed lines.
Methyl 1-{4-[(S)-2-(methoxycarbonyl)pyrrolidin-1-yl]- 3,6-dioxocyclohexa-1,4-dien-1-yl}pyrrolidine-2-carboxylate top
Crystal data top
C18H22N2O6F(000) = 384
Mr = 362.38Dx = 1.334 Mg m−3
Monoclinic, C2Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C 2yCell parameters from 1107 reflections
a = 11.4728 (5) Åθ = 2.9–27.5°
b = 7.1556 (4) ŵ = 0.10 mm−1
c = 11.7882 (7) ÅT = 120 K
β = 111.230 (3)°Prism, dark-red
V = 902.07 (8) Å30.24 × 0.12 × 0.08 mm
Z = 2
Data collection top
Nonius KappaCCD area-detector
diffractometer		1114 independent reflections
Radiation source: Enraf Nonius FR591 rotating anode1008 reflections with I > 2σ(I)
10 cm confocal mirrors monochromatorRint = 0.034
Detector resolution: 9.091 pixels mm-1θmax = 27.5°, θmin = 3.4°
φ and ω scansh = −14→14
Absorption correction: multi-scan
(SADABS; Sheldrick, 2007)		k = −8→9
Tmin = 0.896, Tmax = 1.000l = −15→15
6840 measured reflections
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)] = 0.038Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.136H-atom parameters constrained
S = 1.23 w = 1/[σ2(Fo2) + (0.0929P)2]
where P = (Fo2 + 2Fc2)/3
1114 reflections(Δ/σ)max < 0.001
119 parametersΔρmax = 0.64 e Å−3
1 restraintΔρmin = −0.63 e Å−3
Crystal data top
C18H22N2O6V = 902.07 (8) Å3
Mr = 362.38Z = 2
Monoclinic, C2Mo Kα radiation
a = 11.4728 (5) ŵ = 0.10 mm−1
b = 7.1556 (4) ÅT = 120 K
c = 11.7882 (7) Å0.24 × 0.12 × 0.08 mm
β = 111.230 (3)°
Data collection top
Nonius KappaCCD area-detector
diffractometer		1114 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2007)		1008 reflections with I > 2σ(I)
Tmin = 0.896, Tmax = 1.000Rint = 0.034
6840 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0381 restraint
wR(F2) = 0.136H-atom parameters constrained
S = 1.23Δρmax = 0.64 e Å−3
1114 reflectionsΔρmin = −0.63 e Å−3
119 parameters
Special details top

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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
O10.08333 (15)0.9788 (3)0.24336 (14)0.0259 (4)
O20.27854 (17)1.2823 (3)0.25151 (17)0.0334 (5)
O30.34432 (18)1.1322 (4)0.43176 (16)0.0417 (6)
N10.25815 (18)0.9487 (3)0.12794 (16)0.0218 (5)
C10.0437 (2)0.9680 (4)0.1309 (2)0.0201 (5)
C20.1346 (2)0.9582 (4)0.06419 (19)0.0195 (5)
C30.0870 (2)0.9607 (4)−0.06108 (19)0.0211 (5)
H30.14380.9574−0.10290.025*
C40.3199 (2)0.9490 (4)0.2607 (2)0.0251 (5)
H40.28090.85340.29770.030*
C50.4542 (2)0.8929 (4)0.2793 (2)0.0297 (6)
H5A0.51390.94580.35590.036*
H5B0.46350.75520.28150.036*
C60.4758 (2)0.9750 (5)0.1691 (2)0.0291 (6)
H6A0.54110.90440.15080.035*
H6B0.50131.10780.18300.035*
C70.3489 (2)0.9556 (4)0.0660 (2)0.0236 (5)
H7A0.33241.06380.01010.028*
H7B0.34540.83970.01900.028*
C80.3099 (2)1.1413 (4)0.3104 (2)0.0261 (6)
C90.3358 (4)1.3085 (7)0.4894 (3)0.0656 (12)
H9A0.37671.40690.45950.098*
H9B0.37721.29660.57780.098*
H9C0.24761.34090.46980.098*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0265 (8)0.0356 (11)0.0146 (7)−0.0001 (8)0.0063 (6)0.0006 (8)
O20.0369 (10)0.0308 (11)0.0359 (10)−0.0014 (9)0.0174 (8)−0.0048 (9)
O30.0396 (11)0.0594 (14)0.0204 (9)0.0108 (11)0.0040 (8)−0.0119 (10)
N10.0203 (9)0.0265 (11)0.0177 (9)0.0016 (9)0.0057 (7)−0.0024 (9)
C10.0233 (10)0.0196 (11)0.0180 (9)0.0033 (10)0.0082 (8)0.0030 (10)
C20.0225 (10)0.0185 (11)0.0174 (10)0.0002 (11)0.0071 (8)−0.0006 (10)
C30.0232 (10)0.0234 (11)0.0186 (10)−0.0013 (10)0.0097 (8)−0.0033 (10)
C40.0224 (11)0.0328 (14)0.0175 (10)0.0019 (12)0.0041 (8)−0.0005 (11)
C50.0265 (12)0.0330 (14)0.0256 (12)0.0064 (11)0.0046 (9)−0.0003 (11)
C60.0219 (11)0.0326 (14)0.0309 (12)−0.0004 (11)0.0072 (9)−0.0011 (12)
C70.0219 (11)0.0255 (12)0.0247 (10)0.0023 (11)0.0100 (8)−0.0003 (11)
C80.0175 (11)0.0380 (15)0.0215 (11)0.0021 (11)0.0055 (8)−0.0045 (11)
C90.064 (2)0.088 (3)0.0364 (16)0.017 (2)0.0078 (15)−0.034 (2)
Geometric parameters (Å, º) top
O1—C11.238 (3)C4—C51.530 (3)
O2—C81.203 (4)C4—H41.0000
O3—C81.341 (3)C5—C61.525 (4)
O3—C91.453 (5)C5—H5A0.9900
N1—C21.345 (3)C5—H5B0.9900
N1—C41.466 (3)C6—C71.528 (3)
N1—C71.473 (3)C6—H6A0.9900
C1—C3i1.426 (3)C6—H6B0.9900
C1—C21.518 (3)C7—H7A0.9900
C2—C31.377 (3)C7—H7B0.9900
C3—C1i1.426 (3)C9—H9A0.9800
C3—H30.9500C9—H9B0.9800
C4—C81.516 (4)C9—H9C0.9800
C8—O3—C9114.4 (3)C4—C5—H5B110.9
C2—N1—C4126.92 (18)H5A—C5—H5B109.0
C2—N1—C7120.87 (18)C5—C6—C7103.91 (19)
C4—N1—C7111.96 (18)C5—C6—H6A111.0
O1—C1—C3i121.5 (2)C7—C6—H6A111.0
O1—C1—C2120.2 (2)C5—C6—H6B111.0
C3i—C1—C2118.3 (2)C7—C6—H6B111.0
N1—C2—C3121.90 (19)H6A—C6—H6B109.0
N1—C2—C1119.72 (19)N1—C7—C6104.46 (19)
C3—C2—C1118.4 (2)N1—C7—H7A110.9
C2—C3—C1i123.07 (19)C6—C7—H7A110.9
C2—C3—H3118.5N1—C7—H7B110.9
C1i—C3—H3118.5C6—C7—H7B110.9
N1—C4—C8109.8 (2)H7A—C7—H7B108.9
N1—C4—C5102.97 (18)O2—C8—O3124.5 (3)
C8—C4—C5113.3 (2)O2—C8—C4126.0 (2)
N1—C4—H4110.2O3—C8—C4109.5 (2)
C8—C4—H4110.2O3—C9—H9A109.5
C5—C4—H4110.2O3—C9—H9B109.5
C6—C5—C4104.1 (2)H9A—C9—H9B109.5
C6—C5—H5A110.9O3—C9—H9C109.5
C4—C5—H5A110.9H9A—C9—H9C109.5
C6—C5—H5B110.9H9B—C9—H9C109.5
C4—N1—C2—C3178.7 (3)C7—N1—C4—C5−17.7 (3)
C7—N1—C2—C34.9 (4)N1—C4—C5—C632.4 (3)
C4—N1—C2—C1−0.9 (4)C8—C4—C5—C6−86.2 (2)
C7—N1—C2—C1−174.7 (2)C4—C5—C6—C7−35.3 (3)
O1—C1—C2—N14.5 (4)C2—N1—C7—C6170.6 (2)
C3i—C1—C2—N1−174.4 (2)C4—N1—C7—C6−4.1 (3)
O1—C1—C2—C3−175.1 (2)C5—C6—C7—N124.3 (3)
C3i—C1—C2—C36.1 (3)C9—O3—C8—O22.6 (4)
N1—C2—C3—C1i179.1 (3)C9—O3—C8—C4−178.7 (2)
C1—C2—C3—C1i−1.4 (3)N1—C4—C8—O2−13.2 (3)
C2—N1—C4—C8−71.0 (3)C5—C4—C8—O2101.3 (3)
C7—N1—C4—C8103.3 (2)N1—C4—C8—O3168.10 (19)
C2—N1—C4—C5168.0 (2)C5—C4—C8—O3−77.4 (2)
Symmetry code: (i) −x, y, −z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C3—H3···O2ii0.952.563.400 (3)147
C5—H5b···O1iii0.992.543.407 (3)146
C9—H9b···O1iv0.982.383.186 (4)139
Symmetry codes: (ii) −x+1/2, y−1/2, −z; (iii) x+1/2, y−1/2, z; (iv) −x+1/2, y+1/2, −z+1.

Experimental details

Crystal data
Chemical formulaC18H22N2O6
Mr362.38
Crystal system, space groupMonoclinic, C2
Temperature (K)120
a, b, c (Å)11.4728 (5), 7.1556 (4), 11.7882 (7)
β (°) 111.230 (3)
V (Å3)902.07 (8)
Z2
Radiation typeMo Kα
µ (mm−1)0.10
Crystal size (mm)0.24 × 0.12 × 0.08
Data collection
DiffractometerNonius KappaCCD area-detector
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2007)
Tmin, Tmax0.896, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections		6840, 1114, 1008
Rint0.034
(sin θ/λ)max (Å−1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.038, 0.136, 1.23
No. of reflections1114
No. of parameters119
No. of restraints1
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å−3)0.64, −0.63

Computer programs: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg, 2006), publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C3—H3···O2i0.952.563.400 (3)147
C5—H5b···O1ii0.992.543.407 (3)146
C9—H9b···O1iii0.982.383.186 (4)139
Symmetry codes: (i) −x+1/2, y−1/2, −z; (ii) x+1/2, y−1/2, z; (iii) −x+1/2, y+1/2, −z+1.
 

Footnotes

‡Additional correspondence author, e-mail: j.wardell@abdn.ac.uk.

Acknowledgements

The use of the EPSRC X-ray crystallographic service at the University of Southampton, England, and the valuable assistance of the staff there is gratefully acknowledged. JLW acknowledges support from CAPES (Brazil), and SJG thanks CNPq and FAPERJ (Brazil) for financial support.

References

First citationBrandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany.  Google Scholar
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ISSN: 2056-9890
Volume 66| Part 8| August 2010| Page o2071
https://doi.org/10.1107/S1600536810027947
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