The synthesis, photophysical characterization, and X-ray structure analysis of two polymorphs of 4,4′-diacetylstilbene

Article abstract of DOI:10.1002/hlca.200900343

A palladium(II) acetate-catalyzed synthesis of 1 that utilizes the novel triazene 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone as a synthon is described. The room temperature absorption spectra of 1 in various solvents exhibited a π→π* transition in the range of 330-350 nm. Compound 1 was observed to be luminescent, with room-temperature solution and solid-state emission spectra that exhibited maxima in the range 400-500 nm. All room-temperature absorption and emission spectra exhibited some degree of vibrational structure. The emission spectrum of 1 at 77 K in propanenitrile glass was broad and featureless with a maximum at 447 nm. Compound 1 crystallized as a yellow and colorless polymorph. X-Ray structure analyses of both of these polymorphs and 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone are presented.

Full text of DOI:10.1002/hlca.200900343

1
162
Helvetica Chimica Acta – Vol. 93 (2010)
The Synthesis, Photophysical Characterization, and X-Ray Structure Analysis
of Two Polymorphs of 4,4’-Diacetylstilbene
a
b
a
by Cameron Pye ), Frank R. Fronczek ), and Ralph Isovitsch* )
a) Department of Chemistry, Whittier College, Whittier CA 90608, USA
(
phone: þ 1-562-907-4200 ext. 4499; e-mail: risovits@whittier.edu)
b) Department of Chemistry, Louisiana State University, Baton Rouge LA 70803, USA
A palladium(II) acetate-catalyzed synthesis of 1 that utilizes the novel triazene 1-{4-[(E)-
morpholin-4-yldiazenyl]phenyl}ethanone as a synthon is described. The room temperature absorption
spectra of 1 in various solvents exhibited a p ! p* transition in the range of 330 – 350 nm. Compound 1
was observed to be luminescent, with room-temperature solution and solid-state emission spectra that
exhibited maxima in the range 400 – 500 nm. All room-temperature absorption and emission spectra
exhibited some degree of vibrational structure. The emission spectrum of 1 at 77 K in propanenitrile glass
was broad and featureless with a maximum at 447 nm. Compound 1 crystallized as a yellow and colorless
polymorph. X-Ray structure analyses of both of these polymorphs and 1-{4-[(E)-morpholin-4-
yldiazenyl]phenyl}ethanone are presented.
Introduction. – For more than 45 years, numerous studies have been undertaken to
characterize the unique excited-state properties of (E)-stilbene [1]. Towards the end of
applying (E)-stilbene derivatives in a wide variety of research areas, this work has
served as a catalyst for investigations into optimizing and tuning these excited-state
properties by altering the functionality of (E)-stilbene [2][3]. Of particular interest is
the preparation of materials that contain an (E)-stilbene moiety. Such materials exhibit
novel photophysical, redox, and electroluminescent properties that have potential
applicability to the construction of light-emitting diodes and liquid-crystal displays [4].
Our research involves the synthesis of unique ligands whose metal-binding moieties
are positioned for the formation of luminescent metal-organic materials. A logical
starting material for our ligands is 4,4’-diacetylstilbene (1; Scheme), with its syntheti-
cally versatile Ac groups and inherent luminescent properties. Since its first synthesis in
1945, its photophysical properties have been incompletely characterized [5]. In this
article, we present a complete photophysical characterization of 1, which was found to
absorb and emit light at longer wavelengths than (E)-stilbene. A new Pd-catalyzed
synthesis of 1 is discussed and illustrated in the Scheme. The crystal structures of the
yellow and colorless polymorphs of 1 are also presented.
Results and Discussion. – Synthesis of 1. Preparation of 4,4’-disubstituted (E)-
stilbene derivatives according to known protocols often have drawbacks that include
numerous steps that utilize protecting groups and purification procedures that often
result in a low yield. The classic synthesis of 1 by Zimmerman and Stille is an illustration
of these difficulties [6].
ꢀ
2010 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 93 (2010)
1163
Scheme. The Synthesis of Compound 1 from 1-(4-Aminophenyl)ethanone
Recently published Heck reaction methodologies that are notable for their high
yields and the use of Pd(OAc) as a ꢂligand-lessꢃ catalyst overcome the difficulties
2
inherent in the literature procedure for the synthesis of 1 [7]. Our synthesis of 1 is an
extension of the work of Sengupta and co-workers, and is shown in the Scheme. This
route to 4,4’-disubstituted (E)-stilbene derivatives was attractive because it stereo-
selectively yields the (E)-stilbene isomer, and uses economical and readily available
starting materials [8]. It also utilizes mild reaction conditions that pose no threat to
reactive substituents, such as an Ac group.
The presented preparation of 1 began with the synthesis of the novel triazene
1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone, an easily prepared and handled
equivalent for the in situ generation of a reactive diazonium ion. This compound was
prepared in good yield (64%) and recrystallized from light petroleum ether.
The triazene exhibited the predicted spectroscopic characteristics, except for the
13
C-NMR spectrum. It exhibited the expected resonances for the aromatic ring and the
Ac group, as well as three broad singlets at 44.1, 51.7, and 66.0 ppm for the morpholine
ring. The assignment of these singlets to the C-atoms of the morpholine ring is
supported by the HMQC-NMR spectrum of the triazene, which showed a clear
13
connection between the broad C resonances and the morpholine H-atoms. Three
signals were observed instead of the expected two, because the rotational dynamics of
the triazene moiety resulted in the nonequivalence of the morpholine C-atoms [9]. The
identity of the triazene was corroborated by an elemental analysis that provided
þ
acceptable values, and a HR-ESI-MS that had an [M þ H] peak at m/z 234.1233, which
was ca. 2.0 ppm less than the calculated value.
Triethoxy(vinyl)silane and the triazene were used together in a Pd(OAc) -catalyzed
2
coupling reaction to prepare compound 1 in moderate yield (48%). The spectra of 1
compared well with those found in the literature [7b]. An acceptable elemental analysis
þ
supported the identity and purity of 1. The HR-ESI-MS of 1 exhibited an [M þ H]
peak at m/z 265.1215 that was ca. 3 ppm lower than the calculated value.
Photophysics of 1. Excitation of an (E)-stilbene molecule leads to the population of
a singlet state, S . The main deactivation pathway of S has been found to involve
1
1
rotation about the central C,C-bond with eventual formation of a mixture of (Z)- and
E)-stilbene. The second deactivation pathway for S is fluorescence [1b][10].
(
1

1
164
Helvetica Chimica Acta – Vol. 93 (2010)
The experimental photophysical data for compound 1 and the literature photo-
physical data for (E)-stilbene are listed in Table 1 [10]. Electronic-absorption spectra
for 1 in CHCl and propanenitrile solution are presented in Figs. 1 and 2, respectively.
3
Table 1. Photophysical Data for Compound 1 and (E)-Stilbenea)
lmax,abs [nm] (e)b)
lmax,em [nm] (lexc [nm])
Ffl
CHCl solution
343 (45,300)
339 (50,500), 354 (35,700)
429 (343)
397 (339), 427, 456
447 (339)
0.0015
0.0088
3
MeCH CN solution
2
MeCH CN glass at 77 K
2
Solid state
424 (343), 452, 487, 511
350 (295)
(
E)-Stilbene
295 (28,500), 307 (24,600)
0.023
c
MeCN solution )
a) Spectra were acquired at room temperature unless otherwise noted. ) Extinction coefficient units m
cm . ) See [10].
b
ꢀ1
ꢀ
1
c
Fig. 1. Electronic-absorption and emission spectra of compound 1. Absorption spectrum in CHCl (---);
3
room-temperature emission spectrum in CHCl3 (lexc 343 nm) (—); room-temperature solid-state
emission spectrum (lexc 343 nm) (···).
The room-temperature absorption spectra of 1 in CHCl and propanenitrile were
3
found to be similar. Each possessed an intense absorption assigned to a p ! p*
transition that exhibited varying degrees of vibrational structure [11]. In dilute CHCl
3
solution, one maximum at 343 nm was noted, while two maxima at 339 and 354 nm
were observed in dilute propanenitrile solution. Extinction coefficients for these
ꢀ
1
ꢀ1
maxima ranged from ca. 35,000 to 50,000 m cm , which is not unusual for

Helvetica Chimica Acta – Vol. 93 (2010)
1165
Fig. 2. Electronic-absorption and emission spectra of compound 1. Absorption spectrum in propane-
nitrile (---); room-temperature emission spectrum in propanenitrile (lexc 339 nm) (—); emission
spectrum in propanenitrile glass at 77 K (lexc 339 nm) (···).
disubstituted (E)-stilbene derivatives. The observed absorption spectral data for 1 in
CHCl and propanenitrile corresponded to the reported ones [6][11a].
3
The emission spectra of 1 in CHCl and propanenitrile varied in their degree of
3
ꢀ
5
vibrational-structure resolution. Excitation of a dilute (1.0 ꢁ 10 m) CHCl solution of
3
1
at room temperature yielded an emission spectrum (Fig. 1) with a maximum at
4
29 nm and poorly resolved vibrational structure at wavelengths greater than 429 nm.
ꢀ6
The room-temperature emission spectrum of a 4.0 ꢁ 10 m propanenitrile solution of 1
(
Fig. 2) resolved this vibrational structure as two maxima at 427 and 456 nm. A shorter
wavelength maximum at 397 nm was also observed.
The room-temperature solid-state emission spectrum of 1 (Fig. 1) yielded the best
resolution of the vibrational structure that was first observed in the solution-state
ꢀ
1
spectra. The energy difference between the best-resolved maxima in Fig. 1 is 1461 cm ,
and assigned to a vibrational mode of the phenyl ring of 1 [1a].
The excitation of a propanenitrile solution of 1 at 77 K yielded a featureless
emission spectrum (Fig. 2) with a narrower band that had a maximum at 447 nm. The
lack of vibrational structure in this spectrum is explained by the low temperature, which
permitted relaxation of S from a single preferred vibrational level.
1
The low fluorescence efficiency of 1 was illustrated by its small quantum yields in
CHCl and propanenitrile solution, 0.0015 and 0.0088, respectively. Other 4-substituted
3
stilbenes with electron-withdrawing substituents have been shown to have similar
quantum yields that result from the electron-withdrawing groups making fluorescence
a less favored excited-state deactivation pathway [12]. The larger quantum yield
observed for 1 in propanenitrile resulted from stabilization of the S1 state via

1
166
Helvetica Chimica Acta – Vol. 93 (2010)
interactions with the solvent, which caused the fluorescence deactivation pathway to be
slightly more likely to occur.
X-Ray Analysis of 1 and Its Precursor. Recrystallization of the triazene precursor to
1
from light petroleum ether yielded orange microplates that were suitable for X-ray
analysis. Selected bond lengths for the triazene derivative are listed in Table 2, while its
ORTEP representation is shown in Fig. 3. The N¼N bond substituents adopted an (E)-
configuration, with a N(3)ꢀN(2)ꢀN(1) bond angle of 114.08(7)8. The triazene moiety
exhibited p-delocalization that was evidenced by N(1)ꢀN(2) and N(2)ꢀN(3) bond
lengths of 1.3361(10) and 1.2766(10) ꢄ, respectively. These values are between
2
3
literature value of 1.222 ꢄ for a N¼N bond and 1.420 ꢄ for a N(sp )ꢀN(sp ) single
bond [13]. The morpholine ring adopted a conventional chair conformation. The
structure of 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone is similar to the
structure of related triazenes [14].
Table 2. Selected Bond Lengths [ꢄ] and Angles [8] for the Colorless Polymorph of 1 and Its Triazene
Precursor
Triazene
1a)
O(1)ꢀC(1)
1.4315(11)
1.5186(12)
1.4622(11)
1.3361(10)
1.2766(10)
1.4206(11)
1.3970(12)
1.4905(12)
1.2271(11)
1.5076(12)
109.78(7)
110.69(7)
114.08(7)
112.33(7)
119.65(8)
121.01(8)
O(1)ꢀC(8)
C(8)ꢀC(9)
C(5)ꢀC(8)
C(4)ꢀC(5)
C(1)ꢀC(2)
1.229(2)
1.499(8)
1.489(3)
1.394(3)
1.467(3)
1.338(4)
C(1)ꢀC(2)
N(1)ꢀC(2)
N(1)ꢀN(2)
N(2)ꢀN(3)
i
N(3)ꢀC(5)
C(1)ꢀC(1 )
C(5)ꢀC(6)
C(8)ꢀC(11)
O(2)ꢀC(11)
C(11)ꢀC(12)
C(1)ꢀO(1)ꢀC(4)
O(1)ꢀC(1)ꢀC(2)
N(3)ꢀN(2)ꢀN(1)
N(2)ꢀN(30ꢀC(5)
C(6)ꢀC(5)ꢀC(10)
O(2)ꢀC(11)ꢀC(12)
i
C(1 )ꢀC(1)ꢀC(2)
125.7(2)
C(5)ꢀC(8)ꢀC(9)
O(1)ꢀC(8)ꢀC(9)
C(3)ꢀC(4)ꢀC(5)
119.31(16)
120.18(18)
120.43(16)
a) Symmetry code i is defined as ꢀ x, 1 ꢀ y, ꢀ z.
A yellow and a colorless polymorph of compound 1 simultaneously formed when it
was recrystallized from benzene. Polymorphs of different color have been observed in a
variety of stilbene derivatives [15]. Selected bond lengths for the colorless polymorph
of 1 are listed in Table 2, while its ORTEP representation is shown in Fig. 4.
Molecules of 1 in each polymorph were observed to have crystallographic inversion
symmetry, and essentially identical bond lengths and angles. The colorless polymorph
i
of 1 adopted (E)-geometry about the C¼C bond, with a C(1 )ꢀC(1)ꢀC(2) bond angle
of 125.7(2)8 (symmetry code i for the colorless polymorph is defined as ꢀ x, 1 ꢀ y, ꢀ z).
The observed C¼C bond length of 1.338(4) ꢄ as well as other bond lengths and angles
in 1 correlated with the values for a similar stilbene derivative [16]. The only difference

Helvetica Chimica Acta – Vol. 93 (2010)
1167
Fig. 3. ORTEP View of 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone. Ellipsoids are represented
at the 50% probability level.
Fig. 4. ORTEP View of the colorless polymorph of 1. Ellipsoids are represented at the 50% probability
level.

1
168
Helvetica Chimica Acta – Vol. 93 (2010)
between individual molecules of 1 was that the yellow polymorph deviated from
planarity more than individual molecules of 1 in the colorless polymorph. The former
i
had a C(1 )ꢀC(1)ꢀC(2)ꢀC(3) torsion angle of 175.55(16)8 (symmetry code i for the
yellow polymorph is defined as 2 ꢀ x, 1 ꢀ y, 1 ꢀ z), the corresponding angle of the latter
was 165.3(2)8.
Each polymorph was found to have different unit-cell dimensions. Crystals of the
colorless polymorph were found to have parallel stacks of 1 arranged at an angle of
62.18 to each other in a herringbone pattern. The distance between molecules of 1 in
each stack was 3.5 – 3.6 ꢄ. No overlap of the p-systems of the phenyl rings was
observed. The yellow polymorph was found to consist of parallel planes of 1 separated
by a distance of ca. 3.5 ꢄ. The yellow color of this polymorph is attributed to the slight
overlap of the p-systems of the phenyl rings, whose centroids were separated by ca.
4.2 ꢄ. Similar variations in color and crystal packing have been observed in other
stilbene derivatives [15d].
Conclusions. – A convenient Pd-catalyzed synthesis of compound 1 was presented.
Room-temperature solution-state absorption spectra of 1 in CHCl and propanenitrile
3
were found to be similar, with each having an intense absorption that resulted from a
p ! p* transition. Emission of 1 in differing media was observed from ca. 400 to
500 nm. Both the absorption and emission spectra of 1 exhibited vibrational structure.
The quantum yields of 1 point to its low fluorescence efficiency, which is not unusual for
E)-stilbene derivatives that are substituted with electron-withdrawing groups.
(
Recrystallization of 1 from benzene resulted in the formation of a yellow and colorless
polymorph whose crystal structures were determined. The main difference between the
two was in their crystal packing. The yellow polymorph exhibited overlap of its p-
systems, while the colorless polymorph did not. Bond angles and lengths of individual
molecules of 1 were essentially the same.
The authors would like to thank the Fletcher Jones Foundation for funds that allowed the purchase of
the fluorometer. Whittier College is acknowledged for the funds that supported this research. Dr.
Andrew Maverick is acknowledged for helpful discussion.
Experimental Part
General. Synthetic procedures were carried out using standard techniques. Solvents and reagents
were used as received. Anthracene used as a quantum-yield standard was of > 99% purity. M.p.: in open
1
capillaries; uncorrected. IR Spectra: as KBr disks on a JASCO 460 FT-IR spectrophotometer. H- and
13
C-NMR spectra: JEOL ECX 300 MHz spectrometer; TMS as the internal standard. MS: provided by
the Washington University Mass Spectrometry Resource with support from the NIH National Center for
Research Resources (Grant No. P41RR0954). Elemental analyses: performed by M-H-W Laboratories
of Tucson, Arizona.
Photophysical Measurements. Emission and absorption spectra were recorded at r.t. in spectropho-
tometric-grade CHCl3 and propanenitrile (99% purity) utilizing a HoribaJobinYvon FluoroMax-4
fluorometer and a Hewlett Packard 8453 diode array spectrometer. All solns. were deoxygenated with Ar
prior to luminescence measurements. All emission spectra were corrected for detector response utilizing
a correction curve supplied by the fluorometer manufacturer.
Fluorescence quantum yields were measured at r.t. in deoxygenated soln. of CHCl and propane-
3
nitrile (lex 343 and 339 nm, resp.) by comparison with anthracene (lmax,em 366 – 475 nm; F ¼ 0.27 in
fl

Helvetica Chimica Acta – Vol. 93 (2010)
1169
deoxygenated abs. EtOH at r.t.) [17]. The absorbances of the anthracene standard soln., and CHCl and
3
propanenitrile soln. of 1 were kept below 0.1 to avoid inner filter effects and matched to within 6 and 8%,
resp. The fluorescence quantum yield values reported in Table 1 are averages of six trials.
Preparation of 1-{4-[(E)-Morpholin-4-yldiazenyl]phenyl}ethanone. 1-(4-Aminophenyl)ethanone
(
1.50 g, 11.1 mmol) was added to 3.7 ml of 6m HCl and heated on a hot water bath to yield a clear
orange soln., which was cooled to 08 to induce the formation of a light orange solid. This solid was
maintained at 08, and a soln. of 0.81 g (11.7 mmol) of NaNO in 2.0 ml of H O was added dropwise under
2
2
stirring over 10 min. A deep-orange-brown soln. resulted. To this stirred soln., 1.1 ml (1.06 g, 12.2 mmol)
of morpholine were added dropwise over 10 min; a deep-orange solid formed. The mixture was allowed
to reach r.t. and then brought to pH 8 with sat. aq. KHCO . The orange solid was collected by suction
3
filtration, washed well with H O, and dried in air. The crude product was recrystallized from light
2
petroleum ether to give 1.66 g (64%) of 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone orange
1
crystalline microplates. M.p. 84.5 – 85.08. IR (KBr): 3020, 2970, 1668, 1597, 1431. H-NMR (300 MHz,
3
3
13
(
(
D )acetone): 2.54 (s, 3 H); 3.82 (s, 8 H); 7.50 (d, J ¼ 8.6, 2 H); 7.95 (d, J ¼ 8.9, 2 H). C-NMR
6
75 MHz, (D )acetone): 25.7; 44.1; 51.7; 66.0; 120.3; 129.3; 134.7; 153.7; 196.3. HR-ESI-MS: 234.1233
6
Table 3. Crystal Data and Structure Refinement of the Polymorphs of 1 and Their Triazene Precur-
sor.
Triazene
1
colorless polymorph
yellow polymorph
C H O
Chemical Formula
Formula weight
Crystal size [mm]
Crystal system
Space group
Unit cell dimensions
a [ꢄ]
b [ꢄ]
c [ꢄ]
b [8]
V [ꢄ3]
C H N O
233.27
C H O
12
15
3
2
18 16
2
18 16
2
264.31
264.31
0.27 ꢁ 0.20 ꢁ 0.19
0.33 ꢁ 0.27 ꢁ 0.02
0.27 ꢁ 0.08 ꢁ 0.07
monoclinic
monoclinic
monoclinic
P2 /c
1
P2 /c
1
P2 /c
1
6.2107 (10)
27.632 (5)
7.1969 (15)
114.003 (7)
1128.3 (4)
4
8.595 (3)
11.571 (4)
7.269 (3)
108.788 (18)
684.4 (4)
2
5.6895 (15)
16.042 (4)
7.421 (2)
96.210 (14)
673.3 (3)
2
Z
3
D [Mg/m ]
m [mm
1.373
0.10
1.283
0.08
1.304
0.08
x
ꢀ1
]
q Range [8]
Index ranges
2.5 – 31.5
ꢀ 9 ꢂ h ꢂ 9
2.5 – 27.1
ꢀ 11 ꢂ h ꢂ 11
ꢀ 14 ꢂ k ꢂ 14
ꢀ 9 ꢂ l ꢂ 9
5712
2.5 – 27.1
ꢀ 7 ꢂ h ꢂ 7
ꢀ 20 ꢂ k ꢂ 20
ꢀ 9 ꢂ l ꢂ 9
8371
1493
1148
0.023
ꢀ
ꢀ
35 ꢂ k ꢂ 40
10 ꢂ l ꢂ 10
Reflections collected
Independent reflections
Reflections with I > 2s(I)
R (int)
12393
3553
3068
0.023
1508
936
0.043
2
Refinement method
R /wR
Full-least squares matrix on F
0.039/0.108
1.04
0.049/0.121
1.02
0.041/0.106
1.05
1
2
2
Goodness-of-fit on F
Refined parameters
156
93
93
Extinction coefficient
Residual density [eꢄꢀ3]
CCDC deposition No.
0.021(5)
0.46, ꢀ 0.24
739503
0.018(5)
0.22, ꢀ 0.24
739504
0.010(3)
0.26, ꢀ 0.19
739505

1
170
Helvetica Chimica Acta – Vol. 93 (2010)
þ
(
[M þ H] ; calc. 234.1243). Anal. calc. for C H N O (233.27): C 61.79, H 6.48, N 18.01; found: C 62.00,
12
15
3
2
H 6.36, N 17.96.
Preparation of 1,1’-[(E)-Ethene-1,2-diyldibenzene-4,1-diyl]diethanone (1). To a stirred suspension of
-{4-[(E)-morpholin-4-yldiazenyl]phenyl}ethanone (2.00 g, 8.6 mmol) in 20.0 ml of MeOH at 08, 2.2 ml
1
(
17.2 mmol) of 40% HBF were added dropwise over 10 min. This mixture was brought to r.t. and stirred
4
for 15 min until a clear orange-red soln. formed. To this soln., 0.020 g (0.086 mmol) of Pd(OAc) was
2
added, which was followed by the dropwise addition of a soln. of 0.90 ml (4.29 mmol) triethoxy-
(
vinyl)silane in 3.0 ml of MeOH over 5 min. A second portion of 0.020 g (0.086 mmol) of Pd(OAc) was
2
added, and the mixture was stirred at r.t. for 30 min, then heated at 408 for 20 min, and heated to reflux
for 15 min. The volume of the mixture was reduced by half, and then 20 ml of H O were added. The
2
resulting olive-green solid was collected by suction filtration, washed with H O, and air-dried. The crude
2
product was recrystallized twice from benzene to give 0.54 g (48%) of pure 1 as a mixture of yellow
1
needles and colorless plates. M.p. 207 – 2108. IR (KBr): 3028, 1672, 1598. H-NMR (300 MHz, CD Cl ):
2
2
3
3
13
2
1
.57 (s, 6 H); 7.27 (s, 2 H); 7.62 (d, J ¼ 8.3, 4 H); 7.93 (d, J ¼ 8.3, 4 H). C-NMR (75 MHz, CD Cl ): 26.4;
2
2
þ
26.6; 128.5; 129.8; 136.5; 141.3; 197.2. HR-ESI-MS: 265.1215 ([M þ H] ; calc. 265.1229). Anal. calc. for
C H O (264.32): C 81.79, H 6.10; found: C 81.75, H 6.03.
18
16
2
X-Ray Crystal-Structure Analyses of 1-{4-[(E)-Morpholin-4-yldiazenyl]phenyl}ethanone and the
Polymorphs of 1 (Table 3). X-Ray-quality crystals of 1-{4-[(E)-morpholin-4-yldiazenyl]phenyl}etha-
none and the colorless and yellow polymorphs of 1 were used for data collection at T¼ 90 K on a Nonius
KappaCCD diffractometer equipped with an Oxford Cryosystems Cryostream chiller and graphite-
monochromated MoKa radiation (l ¼ 0.71073 ꢄ). Structures were solved by direct methods, and
structure refinement was carried out using SHELXL-97 [18]. All H-atoms were visible in difference
maps, but were placed in idealized positions during refinement, with a torsional parameter refined for
each Me group.
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Received September 25, 2009