Solid-state structures of ureidoimidazoles

Article abstract of DOI:10.1080/10610278.2010.550289

This work outlines the synthesis and solid-state structures of a series of ureidoimidazole derivatives. The ureidoimidazoles all adopt a common tautomeric configuration and possess remarkably consistent features of supramolecular organisation that are aff

Full text of DOI:10.1080/10610278.2010.550289

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Supramolecular Chemistry
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Solid-state structures of ureidoimidazoles
Andrea M. McGhee a , Jeffrey P. Plante a , Colin A. Kilner a & Andrew J. Wilson a b
a School of Chemistry, University of Leeds, Leeds, UK
b Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
Published online: 15 Apr 2011.
To cite this article: Andrea M. McGhee , Jeffrey P. Plante , Colin A. Kilner & Andrew J. Wilson (2011) Solid-state structures of
ureidoimidazoles, Supramolecular Chemistry, 23:6, 470-479, DOI: 10.1080/10610278.2010.550289
To link to this article: http://dx.doi.org/10.1080/10610278.2010.550289
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Supramolecular Chemistry
Vol. 23, No. 6, June 2011, 470–479
Solid-state structures of ureidoimidazoles
Andrea M. McGheea, Jeffrey P. Plantea, Colin A. Kilnera and Andrew J. Wilsonab*
aSchool of Chemistry, University of Leeds, Leeds, UK; bAstbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
(Received 25 October 2010; final version received 20 December 2010)
This work outlines the synthesis and solid-state structures of a series of ureidoimidazole derivatives. The ureidoimidazoles
all adopt a common tautomeric configuration and possess remarkably consistent features of supramolecular organisation that
are affected by both steric factors and proximal hydrogen-bonding functionality.
Keywords: hydrogen-bonding; linear arrays; self assembly
Introduction
structure determination. The crystal structure of
compound 1 has been previously disclosed by us (16).
Compound 1 crystallises in the monoclinic P21/n space
group, with one molecule present in the asymmetric unit.
Of the two conformational possibilities, intramolecular
urea NH to imidazole N hydrogen bonded and intra-
molecular urea carbonyl to imidazole NH hydrogen bonded,
only the latter is observed (Figure 1(a)). The packing of
compound 1 is mediated by intermolecular hydrogen bonds,
which, based on the intermolecular heteroatom hydrogen
distances, would be described as weak hydrogen bonds.
Bifurcated hydrogen bonding between urea NHs and the
imidazole nitrogen is observed with each monomer
perpendicular to two others, while the backface of the
molecule interacts through carbonyl to imidazole NH
hydrogen bonding creating an infinite 2D structure
(Figure 1(b)). Van der Waals packing is observed between
sheets (Figure 1(c)). Similarly, according to our original
report (16), Barboiu reported a structure of compound 1 that
is virtually identical to the one we reported (17).
The design and synthesis of hydrogen-bonding motifs
exhibiting well-defined supramolecular organisation both in
solution and in solid state is an ongoing area of interest
(1–8). Hydrogen-bonding motifs are important building
blocks for the assembly of supramolecular polymers (8–10)
and more generally of self-assembling gelators (11, 12)
which attract attention as tuneable ‘smart materials’. They
also play a central role in crystalline assemblies, which are
significant in a number of areas including polymorphism of
active pharmaceutical ingredients (13) and solid-state
reactivity (14). Furthermore, solid-state structures can
provide valuable information on molecular recognition
behaviour in solution. Our group have initiated an
investigation concerned with the development of linear
arrays of hydrogen bonds (15, 16) to be used as components
of supramolecular polymers (8–10). The current work
focuses on the ureidoimidazole donor–donor–acceptor
motif previously shown by us to exhibit conformer
independent heterodimerisation with the complementary
amidoisocytosine acceptor–acceptor–donor array (16).
Although our prior studies have illustrated negligible self-
association of the ureidoimidazole motif in solution, the
current results reveal an unusual mode of self-assembly in
the solid state for a series of compounds; this is remarkably
conserved across the series and subtly modulated through
both steric effects and proximal hydrogen-bonding groups.
Compound 2 crystallises in the monoclinic C2/c space
group, with one molecule present in the asymmetric unit.
Again, only intramolecular urea carbonyl to imidazole NH
hydrogen bonding is observed (Figure 2(a)). As for
compound 1, weak bifurcated hydrogen bonding between
urea NHs and the imidazole nitrogen is observed with each
monomer perpendicular to two others; however, no
hydrogen bonds are observed involving the carbonyl and
imidazole NHs on the opposite side of the molecule to the
DDA array (Figure 2(b) and (c)). Therefore, infinite 1D
chains are observed, which are packed in the second and
third dimensions through aromatic p–p edge to face
(ArC–H–p interaction), p–p face to face and Van der
Waals interactions (Figure 2(c)–(e)).
Results and discussion
The ureidoimidazole derivatives 1, 2 and 3a–c were
synthesised using standard procedures as illustrated in
Scheme 1.
Single crystals of each compound suitable for a
diffraction study were obtained as described in the
Experimentalsection,andweresubjectedtocrystallographic
Compound 3a crystallises in the monoclinic P21/n
space group, with two molecules and two solvent methanol
*Corresponding author. Email: a.j.wilson@leeds.ac.uk
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2011 Taylor & Francis
DOI: 10.1080/10610278.2010.550289
http://www.informaworld.com

Supramolecular Chemistry
471
PhNCO
pyridine,
∆, 78%
(a) (i) NaOH, H2O
(ii) EtOH (anh)
celite
H
N
.0.5H2SO4
N
O
HN
O
HN
H2N
N
N
H
N
H
N
H2N
(b) PhNCO, THF,
NEt3 , 0.02 M
50% (2 steps)
N
O
N
H
N
H
N
H
2
1
(i) Boc2O, NaOH
H2O/acetone
(i) HCl, EtOH (1M)
reflux, 20 hrs
(ii) X-PhNCO, NEt3
THF,
H
N
H
N
N
H
N
(ii) 1-bromopinacolone
N
HCl•NH2
DMF, 42% (2 steps)
O
HN
X
O
NH
H2N
NH
3a X = H, 40%
3b X = CO2Et, 65%
3c X = CF3, 64%
(2 steps)
Scheme 1. Synthesis of compounds 1, 2 and 3a–c.
ꢀ
Compound 3c crystallises in the triclinic P1 space
molecules present in the asymmetric unit. The confor-
mations of each molecule of 3a are only subtly different. As
for the first two examples, only intramolecular urea
carbonyl to imidazole NH hydrogen bonding is observed;
however, the packing structure is significantly different in
the presence of solvent (Figure 3(a)). The same core mode
of dimerisation that is observed for 1 and 2 is observed for
3a in that urea NH bifurcated hydrogen bonding with the
imidazole is observed; however, in this instance, the
solvent molecule acts as a bridge – the interactions are
therefore significantly stronger as evidenced by the shorter
intermolecular distances – and a coplanar rather than the
perpendicular arrangement of 3a is observed, i.e. a self-
complementary dimer is observed bridged by two methanol
molecules (Figure 3(b) and (c)). The infinite 1D polymer is
propagated through self-complementary hydrogen bonds
involving the carbonyl and imidazole NHs on the opposite
side of the molecule to the DDA array as is the case for
compound 1. Packing in the second and third dimensions is
mediated by Van der Waals interactions (Figure 3(d)).
group, with two molecules and two solvent methanol
molecules present in the asymmetric unit. Each molecule
of 3c is only subtly different. Like all other examples, a
single defined conformation is observed, which is dictated
by the intramolecular hydrogen bonding (Figure 5(a)). The
packing structure of 3c is very similar to compound 3a,
and all the same hydrogen-bonding features are present
within the observed infinite 1D polymer with Van der
Waals interactions mediating the packing in the second
and third dimensions (Figure 5(b)–(d)).
Overall, the salient solid-state assembly properties of
the ureidoimidazole series are summarised in Figure 6.
Each structure adopts a common conformation mediated
by intramolecular hydrogen bonding between the imida-
zole NH and the carbonyl functionality of the urea motif to
present a donor–donor–acceptor array. In the absence of
solvent, direct interaction of each urea group with the
acceptor on the imidazole of an adjacent molecule is
observed. The perpendicular orientation (which presum-
ably results from steric constraints imposed by R 1) results
in an infinite 1D chain as is observed for 1 and 2 (Figure
6(a)). Assembly for this series can be propagated in a
second dimension through self-complementary hydrogen
bonding between the rear faces as for 1. This feature is
‘switched-off’ with sterically bulky ureidoimidazoles as
for 2 – the R 2 group in Figure 6(a) is clearly positioned to
influence packing of adjacent molecules. In the presence of
methanol, stronger hydrogen bonding is observed and the
solvent acts as a bridge between the urea NHs and
imidazole Ns on two coplanar ureidoimidazole motifs as is
observed for 3a–c (Figure 6(b)). The infinite 1D chain is
propagated through self-complementary hydrogen bonding
between the rear faces. This interaction is the same as that
which is observed to mediate propagation in the second
dimension, when solvent is absent (i.e. compound 1),
although it should be noted that the presence of additional
hydrogen-bonding functionality on the ureidoimidazole
ꢀ
Compound 3b crystallises in the triclinic P1 space
group, with two molecules and three solvent methanol
molecules present in the unit cell. One of the methanol
molecules is disordered over two equally occupied
positions. There are only minor differences between the
structures of the individual monomer units. Again, the
conformation of 3b is determined by intramolecular urea
carbonyl to imidazole NH hydrogen bonding, and the
DDA array present in the structure is the same as the other
compounds (Figure 4(a)). The solid-state assembly is
similar in nature to 3a. The principle difference is that the
infinite 1D polymer is propagated through self-comp-
lementary hydrogen bonds involving the carbonyl of the
ester (as opposed to the urea) and imidazole NH – an
additional hydrogen bond from the urea carbonyl to a
solvent CH is also observed (Figure 4(b) and (c)). Packing
in the second and third dimensions is mediated by Van der
Waals interactions (Figure 4(d)).

472
A.M. McGhee et al.
Figure 1. (a) X-ray crystal structure of compound 1, (b) structure packing diagram of compound 1 shown in CPK format,
˚
(c) stick representation of (b), key distances: H4–O7 2.31 A (intramolecular), H4–O7 2.11 A, N1–H6 2.09 A, N1–H8 2.25 A
˚
˚
˚
(intermolecular), (d) solid-state structure of 1 illustrating intrasheet packing.

Supramolecular Chemistry
473
Figure 2. (a) X-ray crystal structure of compound 2, (b) structure packing diagram of compound 2 shown in CPK format,
˚
(c) stick representation of (b), key distances: H3–O1 2.04 A (intramolecular), H2–N3 2.19 A, H1–N3 2.11 A (intermolecular), (d) and
˚
˚
(e) solid-state structure of 2 illustrating intrasheet packing.
can play a role as is the case for 3b, where Y ¼ CO2Et (the
size of R 2 is also anticipated to influence assembly).
the ureidoimidazole motif has been shown by us to
participate in self-association to a negligible extent
(,10 M21) (16); however, hydrogen bonding plays a
significant role in determining the solid-state structures that
are observed. In the absence of a bridging solvent, the
intermolecular distances for these interactions indicate that
Conclusions
We have reported the synthesis and solid-state structure of a
series of ureidoimidazole motifs. In solution (chloroform),

474
A.M. McGhee et al.
Figure 3. (a) X-ray crystal structure of compound 3a, (b) structure packing diagram of compound 3a shown in CPK format,
˚
(c) stick representation of (b), key distances: O7A–H4A 2.29 A (intramolecular), N1A–H2S 1.89 A, H6A–O1S 2.16 A, H8A–O1S
˚
˚
˚
2.03 A, O7A–H4B 2.29 A (intermolecular), (d) solid-state structure of 3a illustrating intrasheet packing.
˚
these interactions are weak, which reinforces the solution
observations. The urea motif has a strong tendency to
engage in bifurcated hydrogen bonding involving both its
NHs (2), and this seems to play a prominent role here
in controlling the solid-state assembly. These observations
will be used in our ongoing efforts to design and synthesise
novel linear arrays of hydrogen-bonding groups for
supramolecular assembly.

Supramolecular Chemistry
475
Figure 4. (a) X-ray crystal structure of compound 3b, (b) structure packing diagram of compound 3b shown in CPK format, (c) stick
˚
representation of (b), key distances: H4–O7 2.26 A (intramolecular), N1–H1S 1.87 A, H6–O1S 2.14 A, H8–O2S 2.01 A, H4–015
˚
˚
˚
˚
˚
2.13 A, H1S3–07 2.05 A (intermolecular), (d) solid-state structure of 3b illustrating intrasheet packing.
Experimental
AMD300 spectrometers operating at 500 or 300 MHz for
1H spectra and 125 or 75 MHz for 13C spectra as stated.
Proton spectra are referenced to TMS at 0.00 ppm, and
carbon spectra to CDCl3 at 77.4 ppm, unless otherwise
stated. Melting points were determined using a Griffin D5
variable temperature apparatus and are uncorrected. IR
spectra were obtained using Perkin-Elmer FTIR spec-
trometer. Microanalysis was carried out on a Carlo Erba
Elemental Analyser MOD 1106 instrument. High Resol-
ution Mass Spectra (HRMS) were recorded on a
Micromass GCT Premier using electron impact ionisation
or a Bruker Daltonics micrOTOF using electro spray
ionisation (ESI).
All reagents were purchased from Aldrich or Alfa Aesar
and used without further purification unless otherwise
stated. Where anhydrous solvents were required, THF was
freshly distilled from sodium benzophenone ketyl radical,
CH2Cl2 was freshly distilled from calcium hydride and
CHCl3 was freshly distilled from calcium chloride under a
nitrogen atmosphere. Anhydrous DMF was obtained ‘sure-
sealed’ from Sigma-Aldrich (Poole, Dorset, UK). Triethyl-
amine was distilled from calcium hydride and stored,
under nitrogen, over potassium hydroxide pellets. All non-
aqueous reactions were carried out under a nitrogen
atmosphere. Analytical thin layer chromatography was
conducted using Merck Kieselgel 0.25 mm silica gel pre-
coated aluminium plates with fluorescent indicator active
at UV245. Purification by column chromatography was
carried out using Merck Kieselgel 60 silica gel. NMR
spectra were obtained using Bruker DMX500 or Bruker
N-tert-Butoxycarbonylguanidine (16)
The title compound was prepared as described pre-
viously (16).

476
A.M. McGhee et al.
Figure 5. (a) X-ray crystal structure of compound 3c, (b) structure packing diagram of compound 3c shown in CPK format, (c) stick
˚
representation of (b), key distances: H4–O7 2.35 A (intramolecular), N1–H1S 1.88 A, H6–O1S 1.99 A, H8–O1S 2.12 A, H4–O7 2.26 A
˚
˚
˚
˚
(intermolecular), (d) solid-state structure of 3c illustrating intrasheet packing.
2-tert-Butoxyamido-4-tert-butylimidazole (16)
After 20 min, a precipitate began to form, and after 1 h
the reaction mixture was cooled and filtered to give a
white solid (0.340 g). The filtrate was then poured into
water to give a precipitate (0.366 g) that was filtered
and dried. Both samples were found to be identical
giving a total yield of product (0.706 g, 87%) as a
white solid, which was not purified further,
m.p. decomposes . 236.08C; dH (500 MHz, DMSO-
d6); 7.01 (1H, t, J ¼ 7.0, ArCH), 7.06 (2H, dd, J ¼ 5.5,
3.2, ArCH), 7.31 (2H, t, J ¼ 8.0, ArCH), 7.37 (2H, dd,
J ¼ 5.5, 3.2, ArCH), 7.57 (2H, d, J ¼ 7.7, ArCH), 9.57
(1H, br s, NH) 11.32 (1H, br s, NH); dC (75 MHz,
DMSO-d6) 118.4, 118.5, 118.9, 121.3, 122.1, 122.7,
129.1, 139.69, 140.0, 150.0, 152.9; nmax/cm21; 3278
The title compound was prepared as described pre-
viously (16).
N-Phenyl-N0-(imidazo-2-yl)urea 1
The title compound was prepared as described pre-
viously (16).
1-(1H-Benzo[d]imidazol-2-yl)-3-phenylurea 2
A stirred solution of 2-aminobenzimidazole (0.500 g,
3.75 mmol) in anhydrous pyridine under nitrogen was
brought to 1008C. Phenylisocyanate (0.387 ml, 0.4245 g,
3.57 mmol) was then added, and stirring was continued.

Supramolecular Chemistry
477
Y
(a)
Y
H
N
N
R1
Y
O
N
R1
N
H
H
R2
R2
H
R1
H
N
O
N
N
N
R2
N
N
N
H
H
N
N
H
H
N
N
H
H
H
O
N
N
N
N
O
H
R2
H
H
N
N
O
R1
R2
H
R2
N
H
N
R1
O
R1
Y
N
H
Y
R1
Y
R2
Y
N
N
O
(b)
H
N
N
H
H
N
H
H
R1
R
O
R2
H
O
H
N
N
Y
H
N
N
N
N
N
O
H
R2
H
H
Y
R1
O
N
N
N
H
R
O
N
H
H
R2
Y
R1
Figure 6. Solid-state assembly behaviour of ureidoimidazole compounds (a) 1 and 2, (b) 3a–c.
(NH), 1717 (CO), 1599 (CO), 1557, 1498, 1447, 1313,
1233; m/z (ESI-MS) 253 [M þ H]þ.
concentrated under reduced pressure before purification
by column chromatography.
General procedure: synthesis of ureido-4-tert-
butylimidazoles
1-(4-tert-Butyl-1H-imidazol-2-yl)-3-phenylurea 3a (16)
Adopting minor modifications to our published method
(16), the general procedure using 2-tert-butoxyamido-4-
tert-butylimidazole (1.94 g, 10.0mmol) and phenylisocya-
nate (1.08 ml, 10.0mmol) provided a yellow/brown solid,
which was purified by column chromatography (gradient
elution: 2:3 EtOAc–hexane to 1:19 MeOH–EtOAc) and
crystallised (1:1 MeOH:MeCN–H2O) to give the title
compound (1.04 g, 40%) as a cream coloured solid;
m.p. 70–738C (MeOH:MeCN–H2O), [Lit. decomp . 1478
C]; Rf 0.24 (1:19 MeOH–CH2Cl2); dH (500MHz, CDCl3);
7.34 (2H, d, J ¼ 7.7 Hz, ArCH), 7.26 (2H, d, J ¼ 7.7 Hz,
ArCH), 7.04 (1H, t, J ¼ 7.7 Hz, ArCH), 6.29 (1H, s, ArCH),
1.25 (9H, s, tBu); dC (75 MHz, CDCl3); 154.9, 144.3, 138.6,
128.9, 123.3, 120.1, 119.8, 30.6, 29.7; nmax/cm21 3281,
2960, 1669, 1592, 1551, 1499, 1449, 1310, 1238, 1198,
1156, 1082; ESI-HRMS found m/z 259.1553 [M þ H]þ,
C14H19N4O requires 259.1553.
2-tert-Butoxyamido-4-tert-butylimidazole (1.0 equiv.)
was stirred in 20% HCl/EtOH (100 ml per 1.0 g of starting
material) for 1 h. The solution was concentrated, and the
residue was dried under vacuum for 1 h. The resulting
material was dissolved in dry THF (40 ml per 1.0 g of
material) at room temperature under N2, and triethylamine
(1.5 equiv.) was added. The reaction mixture was heated to
reflux, and the appropriate isocyanate (1.0 equiv., 1.0 M in
THF) was added dropwise. The reaction mixture was
stirred at reflux for 16 h. After cooling to room
temperature, the volatiles were removed under reduced
pressure, and the residue was partitioned between EtOAc
and water. The layers were separated, and the aqueous
phase was extracted with EtOAc. The combined organics
were washed with aqueous saturated NH4Cl, aqueous
saturated NaHCO3 and brine, dried (Na2SO4) and

478
A.M. McGhee et al.
(observed reflections 0.0580) and wR(F 2) was 0.1144 (all
Ethyl 4-(3-(4-tert-butyl-1H-imidazol-2-
yl)ureido)benzoate 3b
data 0.1333) for 175 parameters. CCDC 795260 contains
the supplementary crystallographic data for this paper.
These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
The general procedure, using 2-tert-butoxyamido-4-tert-
butylimidazole (820 mg, 3.4 mmol) and 4-ethoxycarbo-
nylphenylisocyanate (721 mg, 3.8 mmol) provided a pale
yellow solid that was purified by column chromatography
(1:1 EtOAc–hexane) to give the title compound (804 mg,
65%) as a cream coloured solid; Rf 0.17 (EtOAc); dH
(500 MHz, CDCl3); 7.95 (2H, d, J ¼ 8.7 Hz, ArCH), 7.47
(2H, d, J ¼ 8.7 Hz, ArCH), 6.31 (1H, s, CHN), 4.35 (2H, q,
J ¼ 7.2 Hz, CH3CH2), 1.38 (3H, t, J ¼ 7.2 Hz, CH3CH2),
Crystal structure determination for 3a
Single crystals were grown by the slow evaporation of a
solution of 3a in moist acetonitrile/methanol. X-ray
diffraction data were collected at the University of Leeds
using a Bruker APEX2 instrument. Crystal data:
C15H22N4O2, M ¼ 290.37, crystal size 0.33 £ 0.15 £
t
1.29 (9H, s, Bu); dC (75 MHz, DMSO-d6); 165.8, 154.8,
144.9, 140.0, 130.7, 122.9, 117.7, 107.4, 60.6, 31.0, 29.9,
14.6; nmax/cm21 3312, 2963, 1696, 1591, 1541, 1273,
1172, 1105 cm21; ESI-HRMS found m/z 331.1760
[M þ H]þ, C17H23N4O3 requires 331.1765.
0.05 mm, Monoclinic, a ¼ 12.0588(9), b ¼ 9.5465(7),
3
˚
˚
c ¼ 29.231(2) A, b ¼ 96.888(4)8, U ¼ 3340.8(4) A , T ¼
150(2)K, P21/n, Z ¼ 8, m ¼ 0.079 mm21, l ¼ 0.71073 A
˚
[Mo Ka], 58508 reflections measured, 8178 unique
(Rint ¼ 0.042), observed 5905 (I . 2s(I)). The final R1
was 0.0562 (observed reflections 0.0839) and wR(F 2) was
0.1398 (all data 0.1523) for 413 parameters. CCDC 795261
contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
1-(4-tert-Butyl-1H-imidazol-2-yl)-3-(4-
(trifluoromethyl)phenyl)urea 3c
The general procedure using 2-tert-butoxyamido-4-tert-
butylimidazole (842 mg, 3.50 mmol) and 4-trifluoro-
methylphenylisocyanate (0.53 ml, 3.8 mmol) provided a
pale yellow solid that was purified by column chromatog-
raphy (2:3 EtOAc–hexane to EtOAc) and crystallised (1:1
MeOH–MeCN) to give the title compound (729 mg, 64%)
as a colourless solid; m.p. 178–1818C (1:1 MeOH–
MeCN); Rf 0.65 (EtOAc); dH (300 MHz, CDCl3); 7.48
(2H, d, J ¼ 8.7 Hz, ArCH), 7.42 (2H, d, J ¼ 8.7 Hz,
ArCH), 6.24 (1H, s, CHN), 1.23 (9H, s, tBu); dC (75 MHz,
CDCl3); 155.3, 145.2, 143.6, 141.8, 126.3, 124.6 (q),
122.4, 118.5, 108.3, 30.5, 29.6; nmax/cm21 3391, 2958,
1712, 1598, 1541, 1445, 1412, 1320, 1183, 1155, 1110,
1071, 1060, 1016, 987, 885; ESI-HRMS found m/z
327.1420 [M þ H]þ, C15H18 F3N4O requires 327.1427.
Crystal structure determination for 3b
Single crystals were grown by the slow evaporation of a
solution of 3b in moist acetonitrile/methanol. X-ray
diffraction data were collected at the University of Leeds
using a Bruker APEX2 instrument. Crystal data:
C37H56N8O9, M ¼ 756.9, crystal size 0.35 £ 0.22 £
0.04 mm, Triclinic, a ¼ 8.0694(11), b ¼ 9.3523(13),
˚
c ¼ 14.6137(18) A, a ¼ 99.815(5)8, b ¼ 103.015(5)8,
3
˚
ꢀ
g ¼ 102.771(5)8, U ¼ 1019.4(2) A , T ¼ 150(2) K, P1,
Z ¼ 1, m ¼ 0.089 mm21, l ¼ 0.71073 A [Mo Ka], 19,367
˚
Crystal structure determination for 1
reflections measured, 5107 unique (Rint ¼ 0.0272),
observed 3904 (I . 2s(I)). The final R1 was 0.0587
(observed reflections 0.0587) and wR(F 2) was 0.1664
(all data 0.1798) for 247 parameters. CCDC 795262
contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
The single crystal diffraction study for compound 1 has
been reported previously (16). We note that, since the
publication of our paper, a further report of the structure of
1 has appeared in the literature (17).
Crystal structure determination for 2
Single crystals were grown by the slow evaporation of a
solution of 2 in chloroform/methanol. X-ray diffraction
data were collected at the University of Leeds using a
Bruker APEX2 instrument. Crystal data: C14H12N4O,
M ¼ 252.27, crystal size 0.40 £ 0.40 £ 0.10 mm, Mono-
Crystal structure determination for 3c
Single crystals were grown by the slow evaporation of a
solution of 3c in moist acetonitrile/methanol. X-ray
diffraction data were collected at the University of Leeds
using a Bruker APEX2 instrument. Crystal data:
C16H21F3N4O2, M ¼ 358.37, crystal size 0.27 £ 0.21 £
0.06 mm, Triclinic, a ¼ 7.5470(9), b ¼ 11.2615(13),
˚
clinic, a ¼ 24.2248(6), b ¼ 6.9079(2), c ¼ 16.2372(5) A,
3
˚
b ¼ 119.482(2)8, U ¼ 2365.33(12) A , T ¼ 150(2) K,
C2/c, Z ¼ 6, m ¼ 0.108 mm21, l ¼ 0.71073 A [Mo Ka],
˚
21,752 reflections measured, 3739 unique (Rint ¼ 0.0287),
observed 2957 (I . 2s(I)). The final R1 was 0.0418
˚
c ¼ 11.8882(12) A, a ¼ 108.721(5)8, b ¼ 99.122(5)8,

Supramolecular Chemistry
479
3
˚
ꢀ
(5) Sijbesma, R.P.; Meijer, E.W. Chem. Commun. 2003, 5–16.
(6) Sessler, J.L.; Jayawickramarajah, J. Chem. Commun. 2005,
1939–1949.
(7) Sivakova, S.; Rowan, S.J. Chem. Soc. Rev. 2005, 34, 9–21.
(8) Wilson, A.J. Soft Matter 2007, 3, 409–425.
(9) de Greef, T.F.A.; Meijer, E.W. Nature 2008, 453, 171–173.
(10) Fox, J.D.; Rowan, S.J. Macromolecules 2009, 42,
6823–6835.
(11) van Esch, J.H.; Feringa, B.L. Angew. Chem. Int. Ed. 2000,
39, 2263–2266.
(12) Estroff, L.A.; Hamilton, A.D. Chem. Rev. 2004, 104,
1201–1218.
g ¼ 98.695(6)8, U ¼ 922.50(18) A , T ¼ 150(2) K, P1,
Z ¼ 2, m ¼ 0.107 mm21, l ¼ 0.71073 A [Mo Ka], 19,211
˚
reflections measured, 4408 unique (Rint ¼ 0.0279), observed
3488 (I . 2s(I)). The final R1 was 0.0448 (observed
reflections 0.0588) and wR(F 2) was 0.1114 (all data 0.1208)
for 231 parameters. CCDC 795263 contains the supplemen-
tary crystallographic data for this paper. These data can be
obtainedfreeofchargefromtheCambridgeCrystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
(13) Vishweshwar, P.; McMahon, J.A.; Bis, J.A.; Zaworotko,
M.J. J. Pharm. Sci. 2006, 95, 499–516.
This work was supported by the EPSRC [EP/C007638/1].
ˇ
(14) MacGillivray, L.R.; Papaefstathiou, G.S.; Frisi, T.;
Hamilton, T.D.; Buar, D.-K.; Chu, Q.; Varshney, D.B.;
Georgiev, I.G. Acc. Chem. Res. 2008, 41, 280–291.
(15) Gooch, A.; McGhee, A.M.; Renton, L.C.; Plante, J.P.;
Lindsay, C.I.; Wilson, A.J. Supramol. Chem. 2009, 21,
12–17.
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