Concomitant polymorphs of 2,2′,6,6′-tetramethyl-4,4′- terphenyldiol: The β-quinol network reproduced in a metastable polymorph

Article abstract of DOI:10.1039/b500665a

The striking resemblance of the rhombohedral and monoclinic forms of the title molecule to β- and γ-quinol provides a crystal engineering approach to new polymorphic systems. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b500665a

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Concomitant polymorphs of 2,29,6,69-tetramethyl-4,49-terphenyldiol:
the b-quinol network reproduced in a metastable polymorph{
Srinivasulu Aitipamula and Ashwini Nangia*
Received (in Columbia, OR, USA) 14th January 2005, Accepted 27th April 2005
First published as an Advance Article on the web 24th May 2005
DOI: 10.1039/b500665a
The striking resemblance of the rhombohedral and monoclinic
forms of the title molecule to b- and c-quinol provides a crystal
engineering approach to new polymorphic systems.
Crystallization of 1 from EtOAc gave needle-shaped crystals
of form 1b (monoclinic P2 /c).{ Screw-axis related molecules form
an infinite chain of O–H O hydrogen bonds (1.84 A, 153.5u;
Fig. 2), similar to the structure of c-hydroquinone. The ring and
1
…
˚
1
H. M. Powell reported the crystal structure of hydroquinone (1,4-
8
chain polymorphs of 1 have different topologies mediated via
…
benzenediol, quinol in the older literature) and its polymorphs and
phenol O–H O hydrogen bonds. Photomicrographs in Fig. 3
clathrates in the 1940s and 50s. a-Hydroquinone is the stable form
˚
R-3, a 5 38.46, c 5 5.65 A) with 54 molecules in the triple
show that the hexagonal and needle-shaped crystals, 1a and 1b,
can be grown from EtOAc/ether and EtOAc without any morph
contamination.
(
h
primitive hexagonal unit cell. The metastable c modification
crystallizes in the monoclinic system P2 /c (a 5 8.07, b 5 5.20,
1
Crystallization of 1 from MeOH afforded crystals of both
hexagonal and needle morphology that correspond to the unit cell
˚
c 5 13.20 A, b 5 107.0u). b-Hydroquinone clathrates are the most
well studied forms because of the resemblance of the rhombohe-
9
of the rhombohedral and monoclinic forms. Mechanical grinding
dral host lattice to b-polonium and its ability to include small and
2
S, MeOH, C60) in the doubly
with a drop of MeOH or n-PrOH added also afforded both
modifications in the same batch. The exact amount of these forms
varies in different experiments but hexagonal crystals far out-
numbered needle-shaped ones. Thus, concomitant polymorphs 1a
and 1b can be isolated from the same flask by employing
appropriate crystallization solvents or the solvent-drop grinding
large guest molecules (Ne, HF, H
˚
interpenetrated cubic cage (R-3, a 5 16.61, c 5 5.47 A, no guest).
2
h
3
A dense d form is obtained at high pressure. The structural
chemistry of hydroquinone is the genesis of clathrate, host–guest
and lattice inclusion compounds in modern-day supramolecular
4
chemistry. It is therefore surprising that the fascinating rhombohe-
9
method. Since the central phenyl ring adopts different conforma-
dral structure of b-hydroquinone has not been reproduced in another
diphenolic compound for over half a century. We report a fourfold
interpenetrated rhombohedral structure of 2,29,6,69-tetramethyl-
tions in these structures,{ the dimorphic cluster of 1 is classified as
concomitant, conformational polymorphs. These observations
6
suggest that crystal lattice energies must be comparable (form 1a
2
1
21
245.16 kcal mol , form 1b 246.57 kcal mol , per molecule of
4,49-terphenyldiol (1){ as well as a monoclinic modification,
referred to as forms 1a and 1b. These structures are strikingly
similar to b- and c-hydroquinone. Our ‘‘phenylogous series’’
crystal engineering approach for developing a new polymorphic
1).§ However, crystal density of the metastable form 1a is higher
3
10
than that of 1b (1.261 vs. 1.231 g/cm ) but packing fraction of 1b
(72.1%) is higher. That the kinetic polymorph 1a is the dominant
form in the grinding experiment is judged from powder X-ray
diffraction (PXRD).{
5,6
system is novel in the extensive literature on polymorphism.
Crystallization of 1 from EtOAc/ether afforded wine-red colored
hexagonal-shaped single crystals. The X-ray structure of form 1a
¯
Melting point determination (Fisher–Johns) shows that both
forms melt at 257–259 uC. Tonset of the melting endotherm in
differential scanning calorimetry (DSC) is also very close: 1a
257.62 uC, 1b 257.74 uC (Fig. 4). Closer inspection of phase 1a (see
insert) reveals a micro-endotherm at 251 uC just before the onset of
melting, whereas the DSC profile of 1b shows melting only. This
(R3 space group in the hexagonal setting){ shows a chair
…
˚
cyclohexane ring of O–H O hydrogen bonds (1.79 A, 163.0u;
neutron-normalized geometry) with the terphenyl groups oriented
axially. The inversion-related phenol group is part of an identical
…
O–H O hexamer having length of 2.75 A on each side. Each
˚
11
oxygen atom behaves as a three-connected 3D node which builds
difference in thermal behavior could mean that the metastable
2
up to produce the 6.10 network of b-quinol. The rhombohedral
7
polymorph 1a transforms to the thermodynamic form 1b before
5,12
melting (enantiotropic situation).
cage structure of 1a (Fig. 1), constructed by joining the centers of
…
The dimorphic cluster 1
13
O–H O hexamers, is about twice as long compared to
˚
b-hydroquinone (10.13 vs. 17.96 A). The fourfold interpenetrated
follows Ostwald’s Rule of Stages: the metsatable form is isolated
first which then transforms to the stable modification upon
heating. That the micro-endotherm in form 1a is a phase transition
was confirmed by heat–cool–heat cycle in DSC. The metastable
form 1a was heated to 251 uC (just beyond the micro-endo peak)
and cooled to room temperature; reheating to 300 uC now shows
only the major melting endotherm at 257–258 uC for the stable
phase 1b. We did not observe any phase transition in crystal-
lization batches from MeOH/PrOH on the laboratory time scale of
hours to days.
dense network of 1a (packing fraction 71.7%) eschews guest
inclusion in contrast to the doubly interlocked b-hydroquinone
inclusion clathrates.
{ Electronic supplementary information (ESI) available: Synthesis of 1
and 2, conformation overlay diagram, and PXRD pattern of polymorphs.
See http://www.rsc.org/suppdata/cc/b5/b500665a/
*ashwini_nangia@rediffmail.com
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Chem. Commun., 2005, 3159–3161 | 3159

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…
Fig. 1 (a) Chair cyclohexane ring of O–H O hydrogen bonds in polymorph 1a. (b) Hydrogen bonding of the axially oriented terphenyl groups to six
…
different O–H O hexamers forms the super cube of the rhombohedral b-quinol network (blue lines). H atoms are omitted except OH groups. (c) Fourfold
interpenetrated network of the cubic lattice in 1a.
Fig. 4 DSC thermogram to show the phase transition of 1a (see insert)
prior to the melting endotherm. Form 1b is stable. Note the absolutely flat
background in DSC runs.
intramolecular H-bonding is kinetically favored due to entropic
…
factors. The infinite O–H O chain of form 1b is thermodynami-
cally stable because of extended s-bond cooperativity. Our model
is consistent with the observation that solvent-drop grinding with
…
Fig. 2 Infinite chain of O–H O hydrogen bonds along [010] in
MeOH/n-PrOH type solvents affords both forms concomitantly.
polymorph 1b. The middle phenyl ring is disordered over two orientations
Both types of crystal nuclei form extended clusters with these
(s.o.f. 0.69, 0.31). H atoms are omitted except OH groups.
hydrogen bond donor–acceptor solvents, and then loose the
solvent as the nucleus grows to give form 1a and 1b
simultaneously. On the other hand, EtOAc and ether are hydrogen
…
bond terminating type solvents and so substrate O–H
O
hydrogen bond synthons are able to discriminate in the outcome
of crystallization, giving either form 1a or form 1b.
1
5
Crystal engineering is about structural control and modular
self-assembly. Polymorphism is its antithesis, wherein hydrogen
bonding and packing motifs cannot be easily predicted. We have
designed a new polymorphic system from hydroquinone using the
idea of structural insulation through phenyl spacer units.
Hydroquinone led us to think of 4,49-terphenyldiol 2 so that the
inversion center would reside on the central phenyl ring and the
hydrogen bonding groups will extend out. Crystallization of 2
from DMSO afforded a solvated form (2.dmso,{ Fig. 5),
suggesting that the phenol OH groups should be made less
accessible to the solvent. The addition of ortho-methyl groups
resulted in the title molecule 1 which exhibits polymorphism and
network structures akin to hydroquinone. We have therefore
Fig. 3 Hexagonal crystals of the rhombohedral form 1a (a) and needle-
shaped crystals of the monoclinic form 1b (b), grown from different
solvents.
Why is the hydrogen-bonded hexamer 1a formed faster than the
infinite chain 1b? We surmise that clusters of 5–6 hydrogen-
bonded molecules are dominant in solution because this is the
…
14
taper-off limit for cooperative stabilization in O–H O chains.
The formation of cyclohexane ring polymorph 1a through
3
160 | Chem. Commun., 2005, 3159–3161
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2
least-squares refinement on F with anisotropic displacement parameters
for non-H atoms using SHELXL-97. All H atoms in 2.dmso and hydroxy
H atoms in 1a and 1b are refined isotropically. All other non-hydroxy H
atoms in 1a and 1b were placed in calculated positions. CCDC 261093–
261095. See http://www.rsc.org/suppdata/cc/b5/b500665a/ for crystallo-
graphic data in CIF or other electronic format.
2
Computed in Cerius , Compass force field. www.accelrys.com.
§
" The Cambridge Structural Database (http://www.ccdc.cam.ac.uk) has
only one phenylogous pair of PhOH polymorphs, phenol (PHENOL) and
…
biphenylol (BOPSAA). These structures have infinite O–H O chains as
the common motif. They are not a case of polymorph engineering.
1
D. E. Palin and H. M. Powell, J. Chem. Soc., 1947, 208; H. M. Powell,
J. Chem. Soc., 1948, 61; H. M. Powell, J. Chem. Soc., 1973, 61.
…
Odmso hydrogen bonding in linear chains of molecular
Fig. 5 O–H
2 (a) O. Ermer, Helv. Chim. Acta, 1991, 74, 1339; (b) O. Ermer and
C. R o¨ bke, J. Am. Chem. Soc., 1993, 115, 10077; (c) K. Hermansson,
J. Chem. Phys., 2000, 112, 835.
…
complex 2.dmso and C–H O interactions between the chains (O–H O:
…
˚
…
˚
1
.80 A, 163.8u; C–H O: 2.28 A, 158.7u).
3
M. Naoki, T. Yoshizawa, N. Fukushima, M. Ogiso and M. Yoshino,
J. Phys. Chem. B, 1999, 103, 6309.
reproduced the fascinating rhombohedral network of b-quinol
after more than five decades by deliberate design, and not just as a
chance observation. Several crystallizations of 4,49-biphenyldiol 3
4 (a) J. W. Steed and J. L. Atwood, Supramolecular Chemistry, Wiley,
Chichester, 2000, pp. 251–387; (b) G. R. Desiraju, Nature, 2001, 412,
3
97; (c) T. C. W. Mak and C.-K. Lam, in Encyclopedia of
Supramolecular Chemistry, Vol. 1, J. L. Atwood and J. W. Steed
Eds.), Marcel Dekker, 2004, pp. 679–685.
5 J. Bernstein, R. J. Davey and J.-O. Henck, Angew. Chem. Int. Ed., 1999,
8, 3440; J. Bernstein, Polymorphism in Molecular Crystals, Clarendon,
Oxford, 2002; R. J. Davey, Chem. Commun., 2003, 1463; R. D. Rogers
Ed.), Special Issue on Polymorphism in Crystals, Cryst. Growth Des.,
004, 4, 1087–1441.
16
afforded the reported monoclinic cell of the close-packed
c-hydroquinone type structure. We are searching for an open
framework structure of 3, or its tetramethyl derivative, to complete
this phenylogous series of polymorphic structures." Supramo-
lecular homology is not common in crystal engineering, and only
two well documented examples are known: benzene, biphenyl,
(
3
(
2
6 V. S. S. Kumar, A. Addlagatta, A. Nangia, W. T. Robinson,
C. K. Broder, R. Mondal, I. R. Evans, J. A. K. Howard and
F. H. Allen, Angew. Chem. Int. Ed., 2002, 41, 3848; L. Yu,
G. A. Stephenson, C. A. Mitchell, C. A. Bunnell, S. V. Snorek,
J. J. Bowyer, T. B. Borchardt, J. G. Stowell and S. R. Byrn, J. Am.
Chem. Soc., 2000, 122, 585.
1
7
p-terphenyl; and phenylogous-diol–diamine complexes. We now
show that even the less predictable polymorphic systems are
amenable to a degree of structural control. This result has wider
implications because the search for polymorphs and a better
control over new solid forms is a major challenge in pharmaceu-
7
A. F. Wells, Three-dimensional Nets and Polyhedra, Wiley, New York,
1977, p. 82.
1
8
19
tical formulations and nonlinear optical materials.
8
J. A. MacMahon, M. J. Zaworotko and J. F. Remenar, Chem.
Commun., 2004, 278.
This work is supported by the DST (SR/S5/OC-02/2002). SA
thanks the CSIR for fellowship. We thank DST and UGC for the
X-ray CCD diffractometer and the UPE program. We thank Prof.
M. Jask o´ lski (A. Mickiewicz University, Poland) and L. Sreenivas
Reddy (University of Hyderabad) for assistance with X-ray data.
9 N. Shan, F. Toda and W. Jones, Chem. Commun., 2002, 2372;
A. V. Trask, W. D. S. Motherwell and W. Jones, Chem. Commun.,
2004, 890.
10 The metastable form being more dense is uncommon but there are
precedents in other polymorphic systems like hydroquinone (ref. 3),
trimethoxytriazine and trinitrobenzene: N. Fridman, M. Kapon,
Y. Sheyin and M. Kaftory, Acta Cryst., 2004, B60, 97;
P. K. Thallapally, R. K. R. Jetti, A. K. Katz, H. L. Carrell, K. Singh,
K. Lahiri, S. Kotha, R. Boese and G. R. Desiraju, Angew. Chem. Int.
Ed., 2004, 43, 1149.
Srinivasulu Aitipamula and Ashwini Nangia*
School of Chemistry, University of Hyderabad, Hyderabad, 500 046,
India. E-mail: ashwini_nangia@rediffmail.com
1
1 T. Hatakeyama and Z. Liu (Eds.), Handbook of Thermal Analysis,
Notes and references
Wiley, Chichester, 1998.
2 R. G. Gonnade, M. M. Bhadbhade and M. S. Shashidhar, Chem.
1
{ X-ray data for 1a and 1b were collected on Bruker SMART APEX CCD
area detector and for 2.dmso on Nonius Kappa CCD detector with
graphite-monochromated Mo–Ka radiation. Crystal data. Form 1a.
Commun., 2004, 2530.
3 W. Ostwald, Z. Phys. Chem., 1897, 22, 289.
1
¯
, M 5 318.40, hexagonal, space group R3, a 5 b 5 20.8580(12),
c 5 10.0116(12) A, V 5 3772.1(5) A , Z 5 9, D 5 1.261 g cm , T 5
c
21
14 P. K. Thallapally, A. K. Katz, H. L. Carrell and G. R. Desiraju, Chem.
Commun., 2002, 344; G. A. Jeffrey, An Introduction to Hydrogen
Bonding, OUP, New York, 1997.
C
H O
22 22 2
3
23
˚
˚
˚
1
1
00 K, F(000) 5 1530, l 5 0.71073 A, m 5 0.079 mm , R1 5 0.0392 for
514 Fo . 2s(Fo). Form 1b. C22 , M 5 318.40, monoclinic, space
group P2 /c, a 5 9.553(2), b 5 4.5252(11), c 5 20.210(5) A, b 5 100.555(3),
V 5 858.9(4) A , Z 5 2, D
15 G. R. Desiraju, Angew. Chem., Int. Ed. Engl., 1995, 34, 2311.
22 2
H O
˚
16 M. A. Jackisch, F. R. Fronczek, C. C. Geiger, P. S. Hale, W. H. Daly
and L. G. Butler, Acta Cryst., 1990, C46, 919.
17 A. Dey, G. R. Desiraju, R. Mondal and J. A. K. Howard, Chem.
Commun., 2004, 2528.
1
3
23
˚
c
5 1.231 g cm , T 5 100 K, F(000) 5 340,
21
˚
l 5 0.71073 A, m 5 0.077 mm , R1 5 0.0632 for 1393 Fo . 2s(Fo).
.dmso. C20 S, M 5 340.42, orthorhombic, space group Pnma,
a 5 7.1305(14), b 5 34.505(7), c 5 6.8846(14) A, V 5 1693.9(6) A , Z 5 4,
2
20 3
H O
3
¨
18 C. R. Gardner, C. T. Walsh and O. Almarsson, Nature Reviews, 2004, 3,
˚
˚
23
˚
c
D 5 1.335 g cm , T 5 100 K, F(000) 5 720, l 5 0.71073 A, m 5
21
.206 mm , R1 5 0.0577 for 1883 Fo . 2s(Fo). Crystal structures were
926.
19 S. George, A. Nangia, C.-K. Lam, T. C. W. Mak and J.-F. Nicoud,
Chem. Commun., 2004, 1202.
0
solved by direct methods using SHELXS-97 and refined by full-matrix
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 3159–3161 | 3161