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Logo of actae2this articlesearchopen accesssubmitActa Crystallographica Section E: Crystallographic CommunicationsActa Crystallographica Section E: Crystallographic Communications
Acta Crystallogr E Crystallogr Commun. 2017 April 1; 73(Pt 4): 507–510.
Published online 2017 March 14. doi:  10.1107/S2056989017003309
PMCID: PMC5382609

Crystal structure of Pigment Red 254 from X-ray powder diffraction data


The crystal structure of Pigment Red 254 [P.R. 254, C18H10Cl2N2O2; systematic name: 3,6-bis­(4-chloro­phen­yl)-2,5-di­hydro­pyrrolo­[3,4-c]pyrrole-1,4-dione] was solved from laboratory X-ray powder diffraction data using the simulated annealing method followed by Rietveld refinement because the very low solubility of the pigment in all solvents impedes the growth of single crystals suitable for X-ray analysis. The mol­ecule lies across an inversion center. The dihedral angle between the benzene ring and the pyrrole ring in the unique part of the mol­ecule is 11.1 (2)°. In the crystal, mol­ecules are linked via N—H(...)O hydrogen bonds, forming chains along [110] incorporating R 2 2(8) rings.

Keywords: powder diffraction, Pigment Red 254, diketo­pyrrolo-pyrrole (DPP) pigments, simulated annealing, Rietveld refinement

Chemical context  

Within the range of diketo­pyrrolo-pyrrole (DPP) pigments presently offered to the market, P.R. 254 plays the most important role (Herbst & Hunger, 2004  ), this commercially available type the pigment being widely used in industrial paints, for example for automotive finishes, and plastics which are processed at high temperature. P.R. 254 affords medium shades of red in full shades, while reductions made with a white paint are somewhat bluish red. The pigment demonstrates excellent fastness to organic solvents and weather-fastness, as well as good coloristic and fastness properties. It also shows good hiding power and high tinctorial strength.

The pigment exhibits very low solubility in all solvents, impeding the growth of single crystals suitable for X-ray analyses. Pigments are not dissolved in their application media, but finely dispersed. Consequently the final product properties depend on the crystal structure of the pigments. The crystal structure was successfully solved from laboratory X-ray powder diffraction data using the simulated annealing method followed by Rietveld refinement.

An external file that holds a picture, illustration, etc.
Object name is e-73-00507-scheme1.jpg

Structural commentary  

The mol­ecule of the title compound (Fig. 1  ) lies across an inversion center. The dihedral angle between the benzene (C1–C6) and pyrrole (N1/C7–C9/C8 rings is 11.1 (2)°. In the crystal, mol­ecules are linked via N—H(...)O hydrogen bonds, forming one-dimensional chains along [110] incorporating An external file that holds a picture, illustration, etc.
Object name is e-73-00507-efi1.jpg(8) rings.que part of the mol­ecule (C1/C2/C3/C4/C5/C6) and the pyrrole ring [C7/C9/N1/C8/C8(−x + 1, −y + 1, −z + 1)] is 11.1 (2)°. An intra­molecular C—H(...)O hydrogen bond occurs (Table 1  ).

Figure 1
The mol­ecular structure of the title compound. Unlabelled atoms are related by the symmetry code (−x + 1, −y + 1, −z + 1). The atoms are represented by spheres of arbitrary ...
Table 1
Hydrogen-bond geometry (Å, °)

Supra­molecular features  

In the crystal, mol­ecules are linked via N—H(...)O hydrogen bonds, forming chains along [110] incorporating An external file that holds a picture, illustration, etc.
Object name is e-73-00507-efi1.jpg(8) rings (Fig. 2  ). In addition, π–π stacking inter­actions between symmetry-related benzene rings with a centroid–centroid distance of 3.871 (2)° connect these chains along [100] (Fig. 3  ).

Figure 2
Part of the crystal structure of the title compound (viewed along the a axis). Hydrogen bonds are shown as dashed lines.
Figure 3
Layered arrangement in the crystal structure of the title compound. Numerical values refer to distances in Å.

Synthesis and crystallization  

The technical product P.R. 254 (TR008.052.11-F) supplied by Clariant Produkte (Deutschland) GmbH was taken as is.


Crystal data, data collection and structure refinement details are summarized in Table 2  . Rietveld refinement was carried out with TOPAS (Coelho, 2007  ) using all diffraction data. The TOPAS input file (including all crystallographic constraints and chemical restraints) was generated automatically by the DASH-to-TOPAS link.

Table 2
Experimental details

Simulated annealing method (SA) was used to solve the crystal structure from the powder pattern in direct space. The starting mol­ecular geometry was built from known crystal structure of similar compound from the Cambridge Structural Database (CSD; Groom et al., 2016  ). The half of the mol­ecule has three flexible torsion angles, which combined with three translational and three orientational degrees of freedom corresponds to a total of nine degrees of freedom. The program DASH (David et al., 2006  ) was used for structure solution. DASH allows the torsion angles to be restricted to inter­vals that significantly reduce the search space. These three flexible torsion angles and their allowed ranges are shown in Fig. 4  . The powder pattern was truncated to a real space resolution of 2.6 Å, which for Cu Kα1 radiation corres­ponds to 34.6° in 2θ. The background was subtracted with a Bayesian high-pass filter (David & Sivia, 2001  ). The number of SA runs was increased to 50 to get better statistics regarding reproducibility. The background subtraction, peak fitting, Pawley refinement and SA algorithms were used as implemented in the program DASH.

Figure 4
The three flexible torsion angles and their allowed ranges in the structure solution step.

Accurate peak positions for indexing were obtained by fitting 20 manually selected peaks with an asymmetry-corrected Voigt function. Indexing was done with the program DICVOL91 (Boultif & Louër, 1991  ). A triclinic unit cell was determined with M(20) = 40.7 (de Wolff et al., 1968  ), F(20) = 82.8 (Smith & Snyder, 1979  ). From volume considerations, the unit cell can contain one mol­ecule of P.R. 254 (Z = 1). The mol­ecule has an inversion centre, which means the asymmetric unit must consist of a one half of the mol­ecule.

Pawley refinement (Pawley, 1981  ) was carried out for refining the background, unit-cell parameters, zero-point error, peak-width and peak-asymmetry parameters. It allows extracting integrated intensities and their correlations. All intensities were refined without reference to a structural model and the result is the best fit that is theoretically possible: Rwp = 13.57, Rexp  = 11.20, χ2 = 1.467.

Suitable chemical restraints were applied for all bond lengths, valence angles and the planarity of the aromatic ring systems (including the five-membered condensed system). Anisotropic peak broadening was included to allow the peak profiles to be described accurately. The discrepancies between the observed and the calculated profile appeared to systematically depend on the hkl indices of the reflections, indicating preferred orientation in the [001] direction. The March–Dollase formula (Dollase, 1986  ) was used. The diffraction profiles and the differences between the measured and calculated profiles are shown in Fig. 5  .

Figure 5
Rietveld plot of P.R. 254. The experimental data points are shown as crosses, the calculated pattern as a solid line and the difference curve as line under the profiles. Tick marks are shown as vertical dashes (laboratory data).

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S2056989017003309/lh5832sup1.cif

Rietveld powder data: contains datablock(s) I. DOI: 10.1107/S2056989017003309/lh5832Isup2.rtv

CCDC reference: 1517793

Additional supporting information: crystallographic information; 3D view; checkCIF report


Professor Dr Martin Schmidt (Frankfurt University) is gratefully acknowledged for the technical product P.R. 254 (TR008.052.11-F). Dr Lothar Fink and Edith Alig (Frankfurt University) are gratefully acknowledged for the collection of the powder diffraction patterns.

supplementary crystallographic information

Crystal data

C18H10Cl2N2O2V = 380.45 (3) Å3
Mr = 357.19Z = 1
Triclinic, P1Dx = 1.57 Mg m3
a = 3.871 (1) ÅCu Kα1 radiation, λ = 1.54056 Å
b = 6.553 (1) ÅT = 293 K
c = 15.292 (1) ÅParticle morphology: powder
α = 92.773 (3)°red
β = 94.656 (3)°flat_sheet, 10 × 10 mm
γ = 99.627 (2)°

Data collection

Stoe Stadi-P with linear PSD diffractometerData collection mode: transmission
Radiation source: sealed X-ray tubeScan method: step
Primary focussing, Ge 111 monochromatormin = 2.00°, 2θmax = 60.00°, 2θstep = 0.01°
Specimen mounting: sample was prepared between two polyacetate films


Refinement on Inet115 parameters
Least-squares matrix: full with fixed elements per cycle44 restraints
Rp = 6.5060 constraints
Rwp = 8.578All H-atom parameters refined
Rexp = 7.467Weighting scheme based on measured s.u.'s w = 1/σ[Yobs)2
5800 data points(Δ/σ)max = 0.001
Excluded region(s): noneBackground function: Chebyshev function with 20 terms
Profile function: fundamental parametersPreferred orientation correction: March–Dollase formula (Dollase, 1986), (001) direction

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

C10.8418 (7)0.4738 (6)0.6911 (3)0.05373
C20.7516 (10)0.2631 (7)0.7088 (3)0.05373
C30.8543 (9)0.1967 (6)0.7905 (3)0.05373
C41.0452 (8)0.3351 (7)0.8528 (3)0.05373
C51.1403 (8)0.5402 (7)0.8377 (3)0.05373
C61.0380 (9)0.6065 (7)0.7573 (3)0.05373
C70.7380 (7)0.5404 (6)0.6038 (3)0.05373
C80.4818 (10)0.5527 (8)0.4587 (4)0.05373
C90.8702 (6)0.7478 (4)0.5715 (2)0.05373
H20.606 (5)0.157 (2)0.6614 (15)0.06447
H30.796 (4)0.039 (2)0.8095 (13)0.06447
H51.286 (4)0.644 (2)0.8892 (16)0.06447
H61.113 (4)0.767 (2)0.7484 (14)0.06447
H70.774 (5)0.879 (2)0.4529 (17)0.06447
O11.0679 (7)0.8859 (6)0.6108 (3)0.05373
N10.7025 (7)0.7478 (5)0.4806 (3)0.05373
Cl11.1601 (7)0.2385 (4)0.9528 (3)0.05373

Geometric parameters (Å, º)

C1—C21.411 (6)C3—H31.08 (2)
C1—C61.388 (5)C5—H51.07 (2)
C1—C71.470 (6)C6—H61.06 (1)
C2—C31.392 (6)C9—O11.186 (4)
C3—C41.362 (6)C9—N11.485 (5)
C4—C51.369 (6)N1—C81.422 (5)
C5—C61.374 (6)N1—H70.98 (2)
C7—C91.492 (5)C4—Cl11.736 (6)
C2—H21.04 (2)
C2—C1—C6117.3 (4)C2—C3—H3125 (1)
C2—C1—C7119.3 (3)C4—C3—H3115 (1)
C6—C1—C7123.4 (3)C6—C5—H5122 (1)
C1—C2—C3120.0 (3)C4—C5—H5119 (1)
C1—C6—C5122.5 (4)C7—C9—O1126.8 (4)
C1—C7—C9124.4 (3)C7—C9—N1106.4 (2)
C2—C3—C4119.8 (4)C9—N1—C8108.8 (4)
C6—C5—C4118.5 (4)O1—C9—N1126.8 (3)
C3—C4—C5121.8 (4)C3—C4—Cl1116.6 (4)
C1—C2—H2120 (1)C5—C4—Cl1121.6 (3)
C3—C2—H2119.7 (9)C9—N1—H7113 (1)
C1—C6—H6121 (1)C8—N1—H7138 (1)
C5—C6—H6116 (1)

Hydrogen-bond geometry (Å, º)

N1—H7···O1i0.985 (17)1.904 (18)2.884 (5)173 (2)
C2—H2···O1ii1.04 (2)2.542 (18)3.489 (6)151.2 (16)
C2—H2···N1iii1.04 (2)2.55 (2)3.255 (6)124.8 (11)
C6—H6···O11.062 (14)2.28 (2)2.959 (6)119.9 (14)

Symmetry codes: (i) −x+2, −y+2, −z+1; (ii) x−1, y−1, z; (iii) −x+1, −y+1, −z+1.


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