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Crystal Structures of Pigment Red 170 and Derivatives as Determined by X-ray Powder Diffraction.

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Crystal Engineering
DOI: 10.1002/anie.200502468
Crystal Structures of Pigment Red 170 and
Derivatives, as Determined by X-ray Powder
Martin U. Schmidt,* Detlef W. M. Hofmann,
Christian Buchsbaum, and Hans Joachim Metz
Pigment Red 170 (1 a) is currently one of the most important
organic pigments for paints and coatings with an estimated
market share of roughly 50 million euros annually. The g
phase is used for automotive coatings, but the coatings start to
fade after five to ten years. For a better understanding of the
pigment#s properties we determined the crystal structures of
the a and g phases from X-ray powder diagrams, even in the
cases when indexing was not possible. The structures served as
the starting point for structure variations by crystal-engineering methods which finally led to g polymorphs of new
chemical identity with improved durability under weathering
Pigments, which are by definition insoluble in application
media e.g. paints, resins, plastics or inks, develop their
coloristic properties through dispersion. The crystal structures
are not altered during this process and therefore play an
important role in determining properties of the final products
such as hue and photostability.[1] Surprisingly the crystal
structures of the Pigment Red 170 polymorphs were hitherto
not known. The reason lies in the very low solubility of the
pigment in all solvents, impeding the growth of single crystals
[*] Prof. Dr. M. U. Schmidt, Dr. D. W. M. Hofmann,
Dipl.-Chem. C. Buchsbaum
Institut f7r Anorganische und Analytische Chemie
Johann Wolfgang Goethe-Universit<t
Marie-Curie-Strasse 11, 60439 Frankfurt am Main (Germany)
Fax: (+ 49) 69-798-29235
suitable for X-ray analyses. We therefore determined the
crystal structures from powder diffraction data.
Most methods[2] for the determination of crystal structures
from X-ray powder diagrams require the diagram to be
indexed, that is, all lattice parameters and the possible space
groups must be known. There are two alternative approaches:
1) search for an isotypical compound with known structure, or
2) predict the crystal structures by global minimization of the
lattice energy, followed by simulation of powder diagrams and
comparison with the experimental diffractogram.[3] To solve
the structure of a-1 a we had to combine the two approaches.
Pigment 1 a is synthesized industrially by diazotation of paminobenzamide and subsequent coupling with 3-hydroxy-2naphththoic acid (2-ethoxy)anilide. In the solid state these
azo pigments assume the hydrazo form (see formula).[4]
The primary product of the syntheses is a nanocrystalline
precipitate of the a polymorph (a-1 a), which cannot be
recrystallized. The crystal quality is low, with a domain size of
about 10 nm.[5] The X-ray powder diagram contains at best
only about 10 relatively broad reflections (Figure 1 a, black
line). All attempts for indexing the diagram failed.
Dr. H. J. Metz
Clariant GmbH
Div. Pigments & Additives, G834
65926 Frankfurt am Main (Germany)
[**] The authors thank Dr. Felix Grimm and JCrg Wolka (Clariant GmbH,
Frankfurt) for the syntheses of starting materials, Frank Becker,
Dennis Thamm, and Dr. Andreas Wacker (Clariant GmbH, Frankfurt) for the syntheses of the pigments, Prof. Dr. Erich F. Paulus,
Dipl.-Ing. Ursula Conrad (both formerly at Hoechst AG, Frankfurt),
Dr. Martin Ermrich (RCntgenlabor Dr. Ermrich, Reinheim), and
Edith Alig (Univ. of Frankfurt) for X-ray powder diagrams, Prof.
Peter W. Stephens (NSLS Brookhaven) for synchrotron measurements, PD Dr. Robert E. Dinnebier (MPI for Solid-State Research,
Stuttgart), Dr. Stephan R7hl (Univ. of GCttingen) and Jan Schnorr
(Univ. of Frankfurt) for the support on the Rietveld refinements with
GSAS, and Dr. Hans Klee and his group (Clariant GmbH) for
electron microscopy. Financial support from the Deutsche Forschungsgemeinschaft (Forschergruppe 412) is gratefully acknowledged.
Supporting information for this article is available on the WWW
under or from the author.
Angew. Chem. Int. Ed. 2006, 45, 1313 ?1317
Figure 1. Rietveld refinement of a) a-1 a (l = 1.540598 ), b) a-1 b
(l = 1.149914 ). Experimental powder diagrams shown in black,
simulated diagrams in red, background curves in green, difference
curves in blue.
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
In the course of our investigations to improve the
properties of the g-1 a phase (see below) we synthesized the
previously unknown methyl derivative 1 b. Comparison of the
powder diagrams of a-1 a and a-1 b revealed that the
structures are isotypic (see Figure 1 and the Supporting
Information). Compounds 1 a and 1 b were shown to form a
continuous series of mixed crystals. Although a-1 b exhibits a
powder diagram of considerably higher quality (Figure 1 b,
black line) than that of a-1 a, a complete indexing of 1 b was
still not possible, because 30 out of 33 observed peaks
correspond to the hk0 reflections; thus the lattice parameters
a*, b* and g*, could be determined, but the information on
the remaining three parameters (c*, a*, b*), as well as on the
crystal system and the space group remained obscure.
The structure of a-1 b was solved by a crystal-structure
prediction[6] using FlexCryst.[7, 8] The molecular geometry was
derived from crystal data of other azo pigments[9, 10] and held
constant during the structure-prediction step. Calculations
were performed with fixed values for a, b, and g in the 11 most
frequent space groups. Simulation of powder diagrams and
automated comparison with the experimental diagram
pointed to a structure having P212121 symmetry. Subsequently
the crystal structure was optimized with CRYSCA[11] including the optimization of the molecular conformation. The
similarity between calculated and experimental powder
diagram increased even further, although there was no fit to
the experimental data in this step. Finally we recorded a highresolution powder diffraction pattern with synchrotron radiation and refined the structure by the Rietveld method with
the program GSAS[12] (Figure 1 b).[13, 14] The structure changed
only very slightly, underlining the accuracy of the CRYSCA
The crystal structure of a-1 b was then used as a starting
point for the Rietveld refinement of a-1 a (Figure 1 a).[15] In a1 a (and a-1 b) the molecules are almost planar. They are
arranged in a herringbone pattern (Figure 2). Each molecule
Figure 2. Section of the crystal structure of the a phase of Pigment
Red 170 (a-1 a) (SCHAKAL plot[28]). View direction [100], b axis
horizontal, c axis vertical. C atoms are shown in black, O in red, N in
blue, H in white.
is connected through four hydrogen bonds (C=OиииH N) to its
neighbors. The CONH2 groups form a helix perpendicular to
the molecular planes, thus creating a three-dimensional
The corresponding derivatives with fluoro-, chloro-,
bromo-, and nitro substituents were synthesized as well (1 c?
f).[16] Their a polymorphs are isotypical to a-1 a and a-1 b. The
Rietveld refinements of a-1 c?f proved the remarkable
similarity between the crystal structures of all a phases (see
the Supporting Information).[17]
For a-1 a?f, the size of the substituents R was calculated
from Hofmann#s volume increments for atoms in molecular
crystals.[18] This leads to the conclusion that medium-sized
substituents produce a preference for the a polymorph. In the
case of the smallest substituent, hydrogen (V = 5.1 C3), the a
polymorph becomes less stable than the b and g phases; the a
structure no longer corresponds to the optimal packing of the
molecules of 1 a; this is also reflected by the lower density of
the a phase (1.395(1) g cm 3) relative to that of the g phase
(1.4020(2) g cm 3), and by the difference in lattice energies (a:
198.17, g: 200.47 kJ mol 1).[19] For larger substituents like
CH3 (V = 29.1 C3) the a phase becomes significantly more
stable; for chlorine (25.8 C3) and bromine (32.7 C3) the a
phase is the only phase known. The nitro substituent, which
requires even more space (34.6 C3, coplanar with the adjacent
phenyl ring), destabilizes the a structure and leads to two new
polymorphs (d and e).[16]
The g phase of Pigment Red 170 (g-1 a) is produced
industrially by thermal treatment of the a polymorph in water
at 130 8C under pressure.[20] g-1 a is a brilliant red pigment and
has been used for many years in car coatings. In the past 30
years empirical search programs have focused on new red
pigments with improved light- and weatherfastness, and
hundreds of derivatives have been synthesized. In terms of
the relevant application properties, however, all of them are
inferior to g-1 a.
Pigments with desirable properties are generally characterized by very dense packings (e.g., 1.74 g cm 1 for the
triphenedioxazine C22H12Cl2N6O4[3] and 2.03 g cm 1 for the
anthanthrone pigment C22H8Br2O2[6c]). Dense packings
impede photochemical reactions that require a change in
molecular geometry; in the case of photodissociation the
fragments remain trapped at their locations and have a good
chance for recombination. Structures with unfavorable lattice
energies correspond to pigments with enhanced solubilities in
the application medium, increasing the chances for photochemical or radical degradation of the dissolved molecules.
When the ethoxy moiety in 1 a is replaced by a methoxy or
propoxy group, products with increased solubilities and lower
durabilites are obtained. A similar effect is observed when the
position of the ethoxy group is changed. The key reasons for
these observations were unclear hitherto because no crystal
structures were known.
The crystal structure of g-1 a could be solved from a
standard powder diagram recorded in the lab. The diagram
could be indexed by TREOR.[21, 22] The structure was solved
by crystal-structure prediction using the program CRYSCA.
CRYSCA performs global lattice energy mimimizations for
flexible molecules;[6, 11, 23, 24] with this approach we could
recently solve the structure of the violet pigment
C22H12Cl2N6O4 from a non-indexed powder diagram containing only 12 peaks.[3] For g-1 a, several thousand crystal
structures with given lattice parameters were generated with
the symmetries P21/c, P21/n, and P21/a (Z = 4). The lattice
energy was optimized simultaneously with the molecular
geometry. For all energetically favorable structures, the
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 1313 ?1317
simulated powder diagrams were compared with the experimental difractogram, revealing that the calculated structure
with the lowest energy had a powder diagram very similar to
the experimental one. Finally a Rietveld refinement, based on
a carefully recorded data set, was carried out.[25]
The structure of g-1 a features almost planar molecules,
arranged in weakly undulating layers (Figure 3). Within these
layers, each molecule is connected with its neighbors by four
hydrogen bonds (Figure 4). Between the layers there are only
van der Waals interactions.
Figure 3. Crystal structure of the g phase of Pigment Red 170 (g-1 a).
View direction [103], b axis horizontal, a and c axes vertical. C atoms
are shown in black, O in red, N in blue, H in white.
Despite the generally efficient packing of g-1 a, a small
void still remains between the ethoxy group and the phenyl
moiety (marked with an ?X? in Figure 4). In a crystalengineering approach, filling this void with an additional
substituent was predicted to improve the pigment properties
of g-1 a. Previous synthetic studies omitted this substitution
pattern because the percursors are more difficult to synthesize. However, a close examination of the structures led to the
conclusion that no ideal substituent exists: all potential
choices are too large for the void. We therefore chose to fill
only a given fraction of the voids by producing mixed crystals
(solid solutions) of g-1 a and g-1 b?f.
Such solid solutions are readily formed, if the syntheses
are conducted with a mixture of the corresponding diazonium
salts. Experimental evidence proved our hypothesis: while the
new pigments have coloristic properties very similar to those
of g-1 a, some of them exhibit considerably improved lightand weatherfastness; in other words, the corresponding
automotive coatings show less fading.[26, 27] This remarkable
improvement in performance was thought to be impossible
for this chemical class of colorants.
This work shows that it may be possible to determine
crystal structures from X-ray powder diagrams even if the
powder data are of low quality and indexing fails. The only
prerequisite is a sufficiently accurate molecular geometry.
Structural details, such as bond lengths and bond angles, are
difficult to deduce from powder data, but in many cases
information about the molecular arrangement in the crystal
can lead to new insights in structure?property relationships.
Crystal engineering based on this information can lead to new
materials with improved properties. We are convinced this
approach will be used more and more in organic solid-state
science as well as in application-oriented research.
Experimental Section
Figure 4. Crystal structure of the g phase of Pigment Red 170 (g-1 a).
View direction [301?]. Only one layer is shown. C atoms are shown in
black, O in red, N in blue, H in white. At the position marked with an
X, there a small empty space that may be filled by an additional
Based on these crystal structures we are now able to draw
some conclusions on structure?property relationships: The
ethoxy groups seem to be a good choice to fill the space
between the molecules in one layer, resulting in a quite dense
packing. Replacement of the ethoxy substituent by a methoxy
group would leave space vacant, while a propoxy group in the
standard all-trans conformation would generate steric interactions with neighboring molecules. Similarly other structural
variations, for example, additional substituents on the naphthalene moiety or the phenyl rings, would also lead in most
cases to a less efficient packing resulting in higher solubilities
and poorer application properties.
Angew. Chem. Int. Ed. 2006, 45, 1313 ?1317
1 b: 4-Amino-3-methyl-benzamide (15.0 g, 0.1 mol) was stirred into
5 n hydrochloric acid (60 mL). The mixture was diluted with water
and diazotized at 10 8C with 5 n sodium nitrate (20 mL). Subsequently
glacial acetic acid (7 mL) and 2 n sodium acetate (50 mL) were added.
Meanwhile 3-hydroxy-2-naphthoic acid (2-ethoxy)anilide (?Naphtol
AS-PH?, technical grade, 30 g, 0.1 mol) was dissolved in water
(450 mL) and 5 n NaOH (42 mL) at elevated temperature. This
solution was added slowly over 1 h to the stirred solution of the
diazonium salt, which was cooled at 10 to 15 8C. The a-1 b precipitated
as a fine red powder, which was isolated by filtration and washed with
water. Yield: 350 g press cake. To improve crystallite size and crystal
quality, the water-containing press cake of 1 b was suspended in
800 mL of N-methylpyrrolidone (NMP) and heated to 105 8C for 1 h.
The pigment powder was isolated by filtration, washed with NMP and
then with water, and dried in vacuo at 50?60 8C, giving 44.5 g (95 %) of
a-1 b. When the final treatment was conducted with chlorobenzene at
120 8C under pressure, g-1 b formed.
The a phases of 1 c?f were synthesized analogously from the
appropriately substituted 4-aminobenzamide derivatives. The final
treatment was done with glacial acetic acid at 114 8C for 1 c (R = F),
with water under pressure at 160 8C for 1 d (R = Cl), and with water at
140 8C for 1 e (R = Br). The a phase of 1 f (R = NO2) formed when the
press cake was heated in dimethylformamide at 106 8C for 35 min;
when the press cake was stirred in water at 98 8C for 2 h, d-1 f resulted
with small admixtures of the a phase; heating in water at 140 8C for
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1 h resulted in the formation of the e phase with small amounts of the
a and d phases.
Solid solutions of 1 a and 1 d (9:1 and 4:1) in the g phase: The
corresponding amounts of 4-aminobenzamide and 4-amino-3-chlorobenzamide were combined, diazotized, and coupled with 3-hydroxy2-naphthoic acid (2-ethoxy)anilide, as described for 1 b. For the final
treatment the press cake was suspended in water and heated under
pressure to 140 8C for 1 h, then filtered and dried. The solid solutions
formed with a yield of 95 %.
(5 g, 0.032 mol) was dissolved in acetone (25 mL). This solution was
cooled while 30 % H2O2 solution (16 mL), tetrabutylammonium
hydrogen sulphate (2.4 g), and 20 % NaOH (15 mL) were added. The
mixture was stirred at 30?40 8C for 90 min, and an alkaline pH was
maintained. The mixture was neutralized with sulfuric acid, and
extracted with chloroform (25 mL). When a saturated NaCl solution
(50 mL) was added to the organic phase, the product precipitated.
Yield: 3.5 g (63 %). Purity (HPLC-MS): 98.7 % (M+ = 170). 1H NMR
(400 MHz, [D6]DMSO, 25 8C, TMS): d = 7.76 (d, 5J = 2 Hz, 1 H; H2),
7.66 (s, 1 H; CONH), 7.58 (dd, 4J = 9 Hz, 5J = 2 Hz, 1 H; H6), 7.00 (s,
1 H; CONH), 6.76 (d, 4J = 9 Hz, 1 H; H5), 5.86 ppm (s, 2 H; NH2). IR:
n? = 3439 (m), 3328 (m), 3144 (m), 1703 (w), 1665 (m), 1618 (s), 1508
(w), 1430 (s), 1387 (s), 1309 (m), 1169 (m), 1117 cm 1 (m).
X-ray powder diagrams: All measurements were performed in
transmission geometry on a STOE-STADI-P diffractometer equipped with a curved Ge(111) primary monochromator and a linearposition-sensitive detector. CuKa1 radiation (l = 1.540598 C) was
used. The diffractogram of a-1 a was additionally recorded with
synchrotron radiation (NSLS Brookhaven, beamline X3B1, l =
1.149914 C).
Rietveld refinements: All refinements were carried out with the
program GSAS, using restraints for bond lengths, bond angles, and
planar groups.
Keywords: crystal engineering и dyes/pigments и
Rietveld refinement и X-ray powder diffraction
[1] W. Herbst, K. Hunger, Industrial Organic Pigments, 3rd ed.,
Wiley-VCH, Weinheim, 2004.
[2] For structure solution by direct methods see e.g.: a) G. Cascarano, L. Favia, C. Giacovazzo, J. Appl. Crystallogr. 1992, 25, 310 ?
317; b) A. Altomare, M. C. Burla, M. Camalli, B. Carrozzini,
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H. Schenk, Z. Kristallogr. 1998, 213, 1 ? 3; j) W. I. F. David, K.
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m) A. A. Coelho, J. Appl. Crystallogr. 2000, 33, 899 ? 908; n) S.
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o) S. G. Zhukov, V. V. Chernyshev, E. V. Babaev, E. J. Sonne-
Received: July 14, 2005
Revised: October 25, 2005
Published online: January 20, 2006
veld, H. Schenk, Z. Kristallogr. 2001, 216, 5 ? 9; p) A. Le Bail,
Mater. Sci. Forum 2001, 378?381, 65 ? 70; q) V. Favre-Nicolin, R.
Cerny, J. Appl. Crystallogr. 2002, 35, 734 ? 743; r) J. C. Johnston,
W. I. F. David, A. J. Markvardsen, K. Shankland, Acta Crystallogr. Sect. A 2002, 58, 441 ? 447.
M. U. Schmidt, M. Ermrich, R. E. Dinnebier, Acta Crystallogr.
Sect. B 2005, 61, 37 ? 45.
E. F. Paulus, Z. Kristallogr. 1982, 160, 235 ? 243.
Estimated from the peak widths in the powder diagram by
applying the formula of Scherrer (P. Scherrer, Nachr. K. Ges.
Wiss. G:ttingen 1918, 98 ? 100), cf.: R. Allmann, R:ntgenpulverdiffraktometrie, Verlag Sven von Loga, Cologne, 1994, p. 194.
The total particle sizes are approximately 100 nm, as shown by
transmission electron microscopy.
a) J. P. M. Lommerse, W. D. S. Motherwell, H. L. Ammon, J. D.
Dunitz, A. Gavezzotti, D. W. M. Hofmann, F. J. J. Leusen,
W. T. M. Mooij, S. L. Price, B. Schweizer, M. U. Schmidt, B. P.
van Eijck, P. Verwer, D. E. Williams, Acta Crystallogr. Sect. B
2000, 56, 697 ? 714; b) W. D. S. Motherwell, H. L. Ammon, J. D.
Dunitz, A. Dzyabchenko, P. Erk, A. Gavezzotti, D. W. M.
Hofmann, F. J. J. Leusen, J. P. M. Lommerse, W. T. M. Mooij,
S. L. Price, H. Scheraga, B. Schweizer, M. U. Schmidt, B. P.
van Eijck, P. Verwer, D. E. Williams, Acta Crystallogr. Sect. B
2002, 58, 647 ? 661; c) G. M. Day, W. D. S. Motherwell, H. L.
Ammon, S. X. M. Boerrigter, R. G. Della Valle, E. Venuti, A.
Dzyabchenko, J. D. Dunitz, B. Schweizer, B. P. van Eijck, P. Erk,
J. C. Facelli, V. E. Bazterra, M. B. Ferraro, D. W. M. Hofmann,
F. J. J. Leusen, C. Liang, C. C. Pantelides, P. G. Karamertzanis,
S. L. Price, T. C. Lewis, H. Nowell, A. Torrisi, H. A. Scheraga,
Y. A. Arnautova, M. U. Schmidt, P. Verwer, Acta Crystallogr.
Sect. B 2005, 61, 511 ? 527.
D. W. M. Hofmann, J. Apostolakis, J. Mol. Struct. 2003, 647, 17 ?
D. W. M. Hofmann, L. N. Kuleshova, M. Yu. Antipin, Cryst.
Growth Des. 2004, 4, 1395 ? 1402.
Cambridge Structural Database, Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge, UK.
D. Kobelt, E. F. Paulus, W. Kunstmann, Z. Kristallogr. 1974, 139,
15 ? 32.
M. U. Schmidt, H. Kalkhof, CRYSCA. Program for Crystal
Structure Calculations for Flexible Molecules, Frankfurt am
Main, 1999.
A. C. Larson, R. B. von Dreele, General Structure Analysis
System (GSAS), Los Alamos National Laboratory Report
LAUR 1994, pp. 86?748.
a-1 b: Red powder, C27H24N4O4, Mr = 468.50, orthorhombic,
P212121, Z = 4, a = 24.6208(9) C, b = 22.8877(9) C, c =
1calcd =
3.9388(2) C,
a = b = g = 908,
V = 2219.6(2) C3,
1.4020(2) g cm 3, Rwp = 6.65 %, Rp = 5.19 %, red. c2 = 4.459.
CCDC-270077 (a-1 a), 270078 (a-1 b), 270079 (a-1 e), 270080 (a1 f), 270081 (a-1 c), 270082 (a-1 d), and 276530 (g-1 a) contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge Crystallographic Data Centre via
a-1 a: Red powder, C26H22N4O4, Mr = 454.48, orthorhombic,
P212121, Z = 4, a = 23.960(9) C, b = 23.234(9) C, c = 3.887(1) C,
a = b = g = 908, V = 2164(1) C3, 1calcd = 1.395(1) g cm 3, Rwp =
4.95 %, Rp = 3.70 %, red. c2 = 23.16. Restraints for planar
groups were applied for each of the the two phenyl rings, and
for the naphthalene moiety, but not for the relative movement of
these fragments or for the conformation of the ethoxy group.
Nevertheless a chemically sensible, almost planar molecular
conformation was obtained. A previous careful and cautious fit
of the strongly anisotropic peak shapes turned out to be crucial.
a) M. U. Schmidt, A. Wacker, H. J. Metz (Clariant GmbH),
German Patent DE 10224279A1, 2003; b) M. U. Schmidt, A.
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 1313 ?1317
Wacker, H. J. Metz (Clariant GmbH), International Patent WO
2003099936A1, 2003 [Chem. Abstr. 140, 6180].
a-1 c?1 f: Red powders, orthorhombic, P212121, Z = 4. a-1 c:
C26H21N4O4F, Mr = 472.47, a = 24.429(9) C, b = 23.014(9) C, c =
3.816(3) C, V = 2145(2) C3, 1calcd = 1.463(2) g cm 3, Rwp = 8.28 %,
Rp = 6.60 %, red. c2 = 13.39; a-1 d: C26H21N4O4Cl, Mr = 488.92,
a = 25.370(6) C, b = 23.573(5) C, c = 3.958(3) C, V = 2367(2) C3,
1calcd = 1.372(2) g cm 3, Rwp = 5.51 %, Rp = 4.17 %, red. c2 =
3.581; a-1 e: C26H21N4O4Br, Mr = 533.37, a = 24.58(7) C, b =
1calcd =
22.74(7) C,
c = 3.914(12) C,
V = 2188(20) C3,
1.62(1) g cm , Rwp = 9.97 %, Rp = 6.45 %, red. c2 = 6.080; a-1 f:
C26H21N5O6, Mr = 499.47, a = 24.270(3) C, b = 23.713(2) C, c =
3.9164(4) C, V = 2253.9(3) C3, 1calcd = 1.4719(2) g cm 3, Rwp =
5.63 %, Rp = 4.50 %, red. c2 = 6.258. Rietveld plots of a-1 c?1 f
as well as figures of the crystal structures of a-1 a?1 f are included
in the Supporting Information.
D. W. M. Hofmann, Acta Crystallogr. Sect. B 2002, 58, 489 ? 493;
these atomic volumes were derived from a fit to more than
200 000 molecular crystal structures.
Dreiding force field (S. L. Mayo, B. D. Olafson, W. A. Goddard III, J. Phys. Chem. 1990, 94, 8897 ? 8909); atomic charges
calculated according to J. Gasteiger, M. Marsili, Tetrahedron
1980, 36, 3219 ? 3228.
J. Ribka (Hoechst AG), German Patent DE 2043482, 1970
[Chem. Abstr. 77, 36 379].
P.-E. Werner, Z. Kristallogr. 1964, 120, 375 ? 389.
a = 10.855 C, b = 24.097 C, c = 8.354 C, b = 100.2258, V =
2150.6 C3, Z = 4, space group ambiguous.
M. U. Schmidt, Kristallstrukturberechnungen metallorganischer
Molek@lverbindungen, Shaker Verlag, Aachen, 1995.
M. U. Schmidt, U. Englert, J. Chem. Soc. Dalton Trans. 1996,
2077 ? 2082.
g-1 a: Red powder, C26H22N4O4, Mr = 454.48. Sample measured
in capillary, 2q = 38 to 808; 85 distinguishable peaks or peak
groups, 1458 Bragg positions, max. intensity 730 000 counts.
Monoclinic, space group P21/n (No. 14), a = 10.8222(3) C, b =
24.1690(15) C,
c = 8.3623(5) C,
b = 100.576(3)8,
2150.1(2) C3, 1calcd = 1.4040(2) g cm 3, Rwp = 7.7 %, Rp = 5.4 %,
red. c2 = 8.00. (Rietveld plot included in the Supporting Information.)
For example, a coating containing a solid solution (g phase) of
90 % 1 a and 10 % 1 d shows only a slight color change (color
difference DE = 2.2) during a 2000-hour weatherfastness test in a
rapid-weathering apparatus (Xenotest Beta X1200). In contrast,
the simultaneously tested coating containing the pure g-1 a
showed a remarkably stronger color change (DE = 3.3). A solid
solution with 5 % 1 d resulted in color changes of medium extent
(DE = 2.6). Lightfastness tests gave corresponding results. Physical mixtures of g-1 a und a-1 d exhibit considerably poorer lightand weatherfastness.
M. U. Schmidt, A. Wacker, H. J. Metz (Clariant GmbH),
International Patent WO 2005019346A1, 2005 [Chem. Abstr.
142, 263 085].
E. Keller, SCHAKAL99. Kristallographisches Institut der UniversitSt, Freiburg, 1999.
Angew. Chem. Int. Ed. 2006, 45, 1313 ?1317
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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crystals, powder, 170, structure, pigment, determiners, red, diffraction, ray, derivatives
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