supplementary materials


gk2567 scheme

Acta Cryst. (2013). E69, o977-o978    [ doi:10.1107/S1600536813013834 ]

Ethyl 7-oxo-7H-benzo[de]imidazo[5,1-a]isoquinoline-11-carboxylate-trifluoroacetic acid (1/1)

R. T. Stibrany and J. A. Potenza

Abstract top

The structure of the title trifluoroacetic acid adduct, C17H12N2O3·C2HF3O2, contains a trifluoroacetic acid molecule hydrogen bonded to the imine N atom of the imidazole ring of a nearly planar four-fused-ring system (r.m.s. deviatiation = 0.013 Å). The carboxylic acid group of the triflouroacetic acid molecule is twisted with respect to the mean plane of the four-fused-ring sytem by 75.9 (2)°. A short intramolecular C-H...O hydrogen bond occurs. In the crystal, the adduct molecules are arranged into stacks along the b axis via [pi]-[pi] interactions between imidazole rings and between imidazole and one of the benzene rings [centroid-centroid distances 3.352 (2) and 3.485 (2) Å, respectively]. Molecules are linked via C-H...O hydrogen bonds, forming an alternating polymeric head-to-head/tail-to-tail stepped chain approximately along the a-axis direction and tilted on an axis bisecting the b and c axes.

Comment top

The title compound, Fig. 1, was isolated as part of our long-term interest in the chemistry of bis (imidazoles), bis(benzimidazoles), and their complexes with metal ions. These species have demonstrated their usefulness as proton sponges (Stibrany et al., 2002), geometrically constraining ligands (Stibrany et al., 2004), agents to study electron transfer (Knapp et al., 1990), polymerization catalysts (Stibrany et al., 2003; Baugh et al., 2006), 19F NMR polymerization catalyst probes (Stibrany, 2003), and in the formation of metal-organic copolymers (Stibrany & Potenza, 2008). Previously, we have shown that 1-methylbenzimidazole can be used in the synthesis of bis(benzimidazole)ketones, which were found to be useful ligands for the chelation of metals (Gorun et al., 1996).

Our investigation into the synthesis of acenapthoimidazoles as building blocks for higher dentate ligands led us to attempt a similar method of preparation as for phenanthroimidazoles (Stibrany & Potenza, 2009). The title compound was isolated by chromatography as a side product of that preparation. The trifluoroacetic acid adduct [C18H12N2O3][C2HF3O2] contains trifluoroacetic acid molecule, hydrogen bonded to the imine nitrogen of the imidazole ring of a nearly-planar, four-fused-ring system (r.m.s. deviatiation = 0.013 Å). A carbonyl-centroid interaction is formed by C41-O11 to the centroid formed by C20, C25/C29 (-x+1, -y, -z+1) with a O11-Cg distance of 3.567 (2) Å and a C41-O11···Cg angle of 78.0 (1)°. In the space group P1 , the adduct molecules are centrosymmetrically disposed about the origin, and form π-π dimers through the imidazole rings along the b cell direction Fig 2. The first Cg-Cg interaction is the imidazole ring (N11, N13, C11/C13) paired to a symmetry related imidazole (-x+1, -y+1, -z+1) at a distance of 3.352 (2) Å. A second Cg-Cg interaction is formed by the imidazole ring and the centroid C21/C26 (-x+1, -y, 1-z) at a distance of 3.485 (2) Å. There are three short intermolecular hydrogen bonds and one short intramolecular hydrogen bond found in the structure and are listed in the hydrogen-bond Table 1. No additional electron density was located near N13 in the difference Fourier maps, likely due to the electron-withdrawing effect of the adjacent ethyl ester group.

Related literature top

For 19F NMR studies of related compounds, see: Stibrany (2003). For polymerization studies, see: Stibrany et al. (2003). For their use as agents to study electron transfer, see: Knapp et al. (1990). For related structures, see: Baugh et al. (2006); Stibrany (2003); Stibrany et al. (2002, 2004); Stibrany & Potenza (2008, 2009); Gorun et al. (1996).

Experimental top

The title compound was isolated as a minor side product in the condensation of acenaphthaquinone in place of phenanthroquinone (Stibrany & Potenza, 2009). A small yellow–orange band was isolated by chromatography on silica gel using ethyl acetate as the eluent. Two X-ray quality crystals were obtained by slow evaporation of a 10:1 v/v methanol/trifluoroacetic acid solution of the title compound.

Refinement top

Hydrogen atoms were positioned geometrically and refined using a riding model, with C—H = 0.97 (methylene), 0.96 (methyl) and 0.93 Å (aromatic), and with Uiso(H) = 1.2–1.5Ueq (C). The carboxylic hydrogen atom was freely refined.

Computing details top

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of the title compound showing the atom-numbering scheme. Displacement ellipsoids are shown at the 40% probability level. H atoms are shown as spheres of arbitrary radius.
[Figure 2] Fig. 2. Packing of the π-π stacked imidazole dimers approximately along the b axis in the unit cell viewed approximately down the a axis.
Ethyl 7-oxo-7H-benzo[de]imidazo[5,1-a]isoquinoline-11-carboxylate–trifluoroacetic acid (1/1) top
Crystal data top
C17H12N2O3·C2HF3O2Z = 2
Mr = 406.31F(000) = 416
Triclinic, P1Dx = 1.583 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 7.642 (3) ÅCell parameters from 800 reflections
b = 8.111 (4) Åθ = 2.5–26.0°
c = 14.043 (6) ŵ = 0.14 mm1
α = 97.539 (8)°T = 100 K
β = 98.055 (8)°Spike, yellow
γ = 92.695 (8)°0.48 × 0.10 × 0.07 mm
V = 852.6 (6) Å3
Data collection top
Bruker SMART CCD area-detector
diffractometer
3380 independent reflections
Radiation source: fine-focus sealed tube2642 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.032
φ and ω scansθmax = 26.2°, θmin = 2.5°
Absorption correction: multi-scan
(SADABS; Bruker, 2000; Blessing, 1995)
h = 99
Tmin = 0.711, Tmax = 1.00k = 1010
7689 measured reflectionsl = 1717
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)] = 0.050Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.140H atoms treated by a mixture of independent and constrained refinement
S = 1.00 w = 1/[σ2(Fo2) + (0.0934P)2 + 0.124P]
where P = (Fo2 + 2Fc2)/3
3380 reflections(Δ/σ)max < 0.001
267 parametersΔρmax = 0.42 e Å3
0 restraintsΔρmin = 0.28 e Å3
Crystal data top
C17H12N2O3·C2HF3O2γ = 92.695 (8)°
Mr = 406.31V = 852.6 (6) Å3
Triclinic, P1Z = 2
a = 7.642 (3) ÅMo Kα radiation
b = 8.111 (4) ŵ = 0.14 mm1
c = 14.043 (6) ÅT = 100 K
α = 97.539 (8)°0.48 × 0.10 × 0.07 mm
β = 98.055 (8)°
Data collection top
Bruker SMART CCD area-detector
diffractometer
3380 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2000; Blessing, 1995)
2642 reflections with I > 2σ(I)
Tmin = 0.711, Tmax = 1.00Rint = 0.032
7689 measured reflectionsθmax = 26.2°
Refinement top
R[F2 > 2σ(F2)] = 0.050H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.140Δρmax = 0.42 e Å3
S = 1.00Δρmin = 0.28 e Å3
3380 reflectionsAbsolute structure: ?
267 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
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
xyzUiso*/Ueq
F10.25760 (19)0.12397 (17)0.05463 (9)0.0435 (4)
F20.0782 (2)0.27375 (17)0.01973 (9)0.0460 (4)
F30.0070 (2)0.13711 (19)0.08785 (10)0.0550 (5)
O10.1872 (2)0.51438 (18)0.12697 (11)0.0390 (4)
O20.2409 (2)0.32127 (17)0.22686 (10)0.0300 (4)
O110.79755 (19)0.70261 (18)0.38002 (10)0.0310 (4)
O120.60779 (18)0.52898 (16)0.27167 (9)0.0242 (3)
O300.08434 (17)0.69206 (16)0.60128 (9)0.0250 (3)
N110.3148 (2)0.69116 (18)0.51474 (11)0.0185 (3)
N130.3464 (2)0.54546 (18)0.37627 (11)0.0201 (4)
C10.1900 (3)0.3743 (2)0.14513 (13)0.0242 (4)
C20.1289 (3)0.2258 (3)0.06570 (14)0.0276 (5)
C110.4856 (2)0.7380 (2)0.49858 (13)0.0183 (4)
C120.5023 (2)0.6433 (2)0.41081 (12)0.0189 (4)
C130.2372 (2)0.5763 (2)0.43870 (12)0.0199 (4)
H130.12300.52720.43250.024*
C200.5334 (3)1.1120 (2)0.80732 (13)0.0260 (5)
H200.59711.19230.85430.031*
C210.5911 (2)0.8628 (2)0.57107 (12)0.0185 (4)
C220.7608 (2)0.9217 (2)0.56293 (13)0.0217 (4)
H220.81270.87940.50960.026*
C230.8557 (3)1.0438 (2)0.63361 (14)0.0248 (4)
H230.96891.08220.62620.030*
C240.7837 (3)1.1071 (2)0.71340 (14)0.0247 (4)
H240.84831.18770.75990.030*
C250.6110 (3)1.0504 (2)0.72550 (13)0.0224 (4)
C260.5131 (2)0.9275 (2)0.65349 (13)0.0193 (4)
C270.3396 (3)0.8738 (2)0.66789 (13)0.0205 (4)
C280.2685 (3)0.9367 (2)0.74925 (13)0.0241 (4)
H280.15530.89930.75730.029*
C290.3665 (3)1.0565 (2)0.81947 (14)0.0281 (5)
H290.31881.09860.87440.034*
C300.2317 (2)0.7487 (2)0.59630 (13)0.0191 (4)
C410.6521 (2)0.6321 (2)0.35499 (13)0.0206 (4)
C420.7451 (3)0.5121 (3)0.20891 (14)0.0274 (5)
H42A0.83810.44690.23580.033*
H42B0.79700.62100.20270.033*
C430.6566 (3)0.4257 (3)0.11143 (14)0.0346 (5)
H43A0.61120.31610.11810.052*
H43B0.74130.41720.06680.052*
H43C0.56100.48860.08720.052*
H2O0.284 (4)0.419 (4)0.281 (2)0.061 (8)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
F10.0536 (9)0.0426 (8)0.0288 (7)0.0170 (6)0.0016 (6)0.0117 (6)
F20.0704 (10)0.0429 (8)0.0192 (6)0.0082 (7)0.0094 (6)0.0009 (5)
F30.0627 (10)0.0589 (9)0.0352 (8)0.0337 (8)0.0193 (7)0.0232 (7)
O10.0595 (11)0.0267 (8)0.0269 (8)0.0030 (7)0.0062 (7)0.0029 (6)
O20.0476 (9)0.0231 (7)0.0164 (7)0.0031 (6)0.0007 (6)0.0004 (6)
O110.0297 (8)0.0378 (8)0.0236 (7)0.0072 (6)0.0089 (6)0.0049 (6)
O120.0290 (7)0.0273 (7)0.0157 (6)0.0000 (6)0.0065 (5)0.0020 (5)
O300.0243 (7)0.0270 (7)0.0231 (7)0.0040 (6)0.0063 (5)0.0000 (5)
N110.0216 (8)0.0182 (8)0.0153 (7)0.0011 (6)0.0027 (6)0.0016 (6)
N130.0258 (8)0.0189 (8)0.0149 (7)0.0004 (6)0.0013 (6)0.0025 (6)
C10.0257 (10)0.0276 (11)0.0189 (9)0.0026 (8)0.0027 (7)0.0021 (8)
C20.0310 (11)0.0327 (11)0.0188 (10)0.0023 (9)0.0038 (8)0.0023 (8)
C110.0205 (9)0.0189 (9)0.0162 (9)0.0016 (7)0.0023 (7)0.0049 (7)
C120.0228 (9)0.0183 (9)0.0149 (8)0.0000 (7)0.0002 (7)0.0027 (7)
C130.0229 (9)0.0201 (9)0.0156 (9)0.0016 (7)0.0002 (7)0.0029 (7)
C200.0382 (12)0.0202 (10)0.0166 (9)0.0002 (8)0.0010 (8)0.0023 (7)
C210.0239 (9)0.0167 (9)0.0140 (8)0.0004 (7)0.0002 (7)0.0027 (7)
C220.0254 (10)0.0217 (9)0.0179 (9)0.0017 (7)0.0024 (7)0.0036 (7)
C230.0237 (10)0.0239 (10)0.0259 (10)0.0004 (8)0.0004 (8)0.0054 (8)
C240.0291 (11)0.0193 (9)0.0225 (10)0.0035 (8)0.0042 (8)0.0009 (7)
C250.0306 (10)0.0183 (9)0.0173 (9)0.0024 (8)0.0009 (8)0.0027 (7)
C260.0249 (10)0.0167 (9)0.0160 (9)0.0012 (7)0.0010 (7)0.0038 (7)
C270.0272 (10)0.0191 (9)0.0156 (9)0.0027 (8)0.0023 (7)0.0041 (7)
C280.0291 (11)0.0244 (10)0.0201 (9)0.0025 (8)0.0064 (8)0.0045 (7)
C290.0398 (12)0.0272 (11)0.0166 (9)0.0052 (9)0.0053 (8)0.0016 (8)
C300.0222 (10)0.0209 (9)0.0153 (8)0.0029 (7)0.0046 (7)0.0039 (7)
C410.0277 (10)0.0185 (9)0.0158 (9)0.0001 (8)0.0036 (7)0.0027 (7)
C420.0315 (11)0.0321 (11)0.0209 (10)0.0041 (9)0.0109 (8)0.0038 (8)
C430.0412 (13)0.0452 (13)0.0183 (10)0.0076 (10)0.0086 (9)0.0013 (9)
Geometric parameters (Å, º) top
F1—C21.326 (3)C20—H200.9300
F2—C21.322 (2)C21—C221.386 (3)
F3—C21.332 (2)C21—C261.426 (3)
O1—C11.197 (2)C22—C231.402 (3)
O2—C11.294 (2)C22—H220.9300
O2—H2O1.03 (3)C23—C241.368 (3)
O11—C411.210 (2)C23—H230.9300
O12—C411.338 (2)C24—C251.418 (3)
O12—C421.462 (2)C24—H240.9300
O30—C301.211 (2)C25—C261.425 (3)
N11—C131.368 (2)C26—C271.425 (3)
N11—C111.399 (2)C27—C281.381 (3)
N11—C301.423 (2)C27—C301.463 (3)
N13—C131.302 (3)C28—C291.397 (3)
N13—C121.390 (2)C28—H280.9300
C1—C21.537 (3)C29—H290.9300
C11—C121.390 (3)C42—C431.506 (3)
C11—C211.461 (2)C42—H42A0.9700
C12—C411.475 (3)C42—H42B0.9700
C13—H130.9300C43—H43A0.9600
C20—C291.373 (3)C43—H43B0.9600
C20—C251.410 (3)C43—H43C0.9600
C1—O2—H2O111.3 (16)C23—C24—C25120.26 (17)
C41—O12—C42115.50 (15)C23—C24—H24119.9
C13—N11—C11108.78 (15)C25—C24—H24119.9
C13—N11—C30124.09 (15)C20—C25—C24121.70 (17)
C11—N11—C30127.13 (15)C20—C25—C26118.99 (18)
C13—N13—C12107.70 (15)C24—C25—C26119.30 (18)
O1—C1—O2129.19 (18)C25—C26—C27117.75 (17)
O1—C1—C2120.89 (18)C25—C26—C21119.44 (17)
O2—C1—C2109.92 (17)C27—C26—C21122.81 (16)
F2—C2—F1107.05 (17)C28—C27—C26121.52 (17)
F2—C2—F3107.57 (17)C28—C27—C30118.02 (18)
F1—C2—F3107.45 (18)C26—C27—C30120.46 (17)
F2—C2—C1112.15 (17)C27—C28—C29120.05 (19)
F1—C2—C1111.43 (16)C27—C28—H28120.0
F3—C2—C1110.95 (16)C29—C28—H28120.0
C12—C11—N11103.93 (15)C20—C29—C28119.86 (19)
C12—C11—C21138.42 (17)C20—C29—H29120.1
N11—C11—C21117.65 (16)C28—C29—H29120.1
C11—C12—N13109.43 (16)O30—C30—N11119.32 (16)
C11—C12—C41130.92 (17)O30—C30—C27126.38 (17)
N13—C12—C41119.64 (16)N11—C30—C27114.30 (16)
N13—C13—N11110.16 (16)O11—C41—O12123.27 (17)
N13—C13—H13124.9O11—C41—C12125.94 (17)
N11—C13—H13124.9O12—C41—C12110.78 (16)
C29—C20—C25121.82 (17)O12—C42—C43106.77 (16)
C29—C20—H20119.1O12—C42—H42A110.4
C25—C20—H20119.1C43—C42—H42A110.4
C22—C21—C26119.02 (16)O12—C42—H42B110.4
C22—C21—C11123.35 (17)C43—C42—H42B110.4
C26—C21—C11117.63 (17)H42A—C42—H42B108.6
C21—C22—C23121.24 (18)C42—C43—H43A109.5
C21—C22—H22119.4C42—C43—H43B109.5
C23—C22—H22119.4H43A—C43—H43B109.5
C24—C23—C22120.73 (19)C42—C43—H43C109.5
C24—C23—H23119.6H43A—C43—H43C109.5
C22—C23—H23119.6H43B—C43—H43C109.5
O1—C1—C2—F20.6 (3)C20—C25—C26—C270.5 (3)
O2—C1—C2—F2178.97 (17)C24—C25—C26—C27179.78 (16)
O1—C1—C2—F1120.6 (2)C20—C25—C26—C21179.23 (16)
O2—C1—C2—F159.0 (2)C24—C25—C26—C210.5 (3)
O1—C1—C2—F3119.7 (2)C22—C21—C26—C250.1 (3)
O2—C1—C2—F360.7 (2)C11—C21—C26—C25179.51 (16)
C13—N11—C11—C120.7 (2)C22—C21—C26—C27179.83 (16)
C30—N11—C11—C12178.48 (16)C11—C21—C26—C270.8 (3)
C13—N11—C11—C21179.02 (15)C25—C26—C27—C280.7 (3)
C30—N11—C11—C211.8 (3)C21—C26—C27—C28178.95 (17)
N11—C11—C12—N130.52 (19)C25—C26—C27—C30179.58 (16)
C21—C11—C12—N13179.2 (2)C21—C26—C27—C300.7 (3)
N11—C11—C12—C41178.54 (17)C26—C27—C28—C290.4 (3)
C21—C11—C12—C411.8 (4)C30—C27—C28—C29179.91 (17)
C13—N13—C12—C110.1 (2)C25—C20—C29—C280.5 (3)
C13—N13—C12—C41179.07 (16)C27—C28—C29—C200.2 (3)
C12—N13—C13—N110.4 (2)C13—N11—C30—O301.5 (3)
C11—N11—C13—N130.7 (2)C11—N11—C30—O30177.63 (16)
C30—N11—C13—N13178.53 (15)C13—N11—C30—C27179.09 (15)
C12—C11—C21—C220.7 (3)C11—N11—C30—C271.8 (3)
N11—C11—C21—C22178.98 (16)C28—C27—C30—O300.8 (3)
C12—C11—C21—C26180.0 (2)C26—C27—C30—O30178.88 (17)
N11—C11—C21—C260.4 (2)C28—C27—C30—N11179.81 (15)
C26—C21—C22—C230.5 (3)C26—C27—C30—N110.5 (2)
C11—C21—C22—C23178.86 (16)C42—O12—C41—O112.9 (3)
C21—C22—C23—C240.7 (3)C42—O12—C41—C12178.27 (15)
C22—C23—C24—C250.3 (3)C11—C12—C41—O113.7 (3)
C29—C20—C25—C24179.62 (18)N13—C12—C41—O11175.24 (18)
C29—C20—C25—C260.1 (3)C11—C12—C41—O12177.52 (18)
C23—C24—C25—C20179.44 (17)N13—C12—C41—O123.5 (2)
C23—C24—C25—C260.3 (3)C41—O12—C42—C43166.99 (16)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C22—H22···O110.932.152.981 (3)148
O2—H2O···N131.03 (3)1.58 (3)2.597 (2)170 (3)
C13—H13···O30i0.932.283.143 (3)154
C23—H23···O11ii0.932.463.320 (3)155
Symmetry codes: (i) x, y+1, z+1; (ii) x+2, y+2, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C22—H22···O110.932.152.981 (3)148
O2—H2O···N131.03 (3)1.58 (3)2.597 (2)170 (3)
C13—H13···O30i0.932.283.143 (3)154
C23—H23···O11ii0.932.463.320 (3)155
Symmetry codes: (i) x, y+1, z+1; (ii) x+2, y+2, z+1.
references
References top

Baugh, L. S., Sissano, J. A., Kacker, S., Berluche, E., Stibrany, R. T., Schulz, D. N. & Rucker, S. P. (2006). J. Polym. Sci. Part A Polym. Chem. 44, 1817–1840.

Blessing, R. H. (1995). Acta Cryst. A51, 33–38.

Bruker (2000). SAINT and SMART. Bruker AXS Inc., Madison, Wisconsin, USA.

Burnett, M. N. & Johnson, C. K. (1996). ORTEPIII. Report ORNL-6895. Oak Ridge National Laboratory, Tennessee, USA.

Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854.

Gorun, S. M., Stibrany, R. T., Katritzky, A. R., Slawinski, J. J., Faid-Allah, H. & Brunner, F. (1996). Inorg. Chem. 35, 3–4.

Knapp, S., Keenan, T. P., Zhang, X., Fikar, R., Potenza, J. A. & Schugar, H. J. (1990). J. Am. Chem. Soc. 112, 3452–3464.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Stibrany, R. T. (2003). Copper-Based Olefin Polymerization Catalysts: High-Pressure 19F NMR Catalyst Probe, ACS Symp. Series 857, Beyond Metallocenes, edited by G. G. Hlatky & A. O. Patil, pp. 210–221. Washington, DC: ACS Press.

Stibrany, R. T., Lobanov, M. V., Schugar, H. J. & Potenza, J. A. (2004). Inorg. Chem. 43, 1472–1480.

Stibrany, R. T. & Potenza, J. A. (2008). Acta Cryst. C64, m213–m216.

Stibrany, R. T. & Potenza, J. A. (2009). Acta Cryst. C65, o406–o409.

Stibrany, R. T., Schugar, H. J. & Potenza, J. A. (2002). Acta Cryst. E58, o1142–o1144.

Stibrany, R. T., Schulz, D. N., Kacker, S., Patil, A. O., Baugh, L. S., Rucker, S. P., Zushma, S., Berluche, E. & Sissano, J. A. (2003). Macromolecules, 36, 8584–8586.