Engineering hydrogen-bonded molecular crystals built from derivatives of hexaphenylbenzene and related compounds

Article abstract of DOI:10.1021/ja067571x

Hexakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]benzene (4) incorporates a disc-shaped hexaphenylbenzene core and six peripheral diaminotriazine groups that can engage in hydrogen bonding according to established motifs. Under all conditions examined, compound 4 crystallizes as planned to give closely related noninterpenetrated three-dimensional networks built from sheets in which each molecule has six hydrogen-bonded neighbors. In the structure of compound 4, the number of hydrogen bonds per molecule and the percentage of volume accessible to guests approach the highest values so far observed in molecular networks. Analogue 5 (which has the same hexaphenylbenzene core but only four diaminotriazine groups at the 1,2,4,5-positions) and analogue 7 (in which the two unsubstituted phenyl groups of compound 5 are replaced by methyl groups) crystallize according to a closely similar pattern. Analogues with flatter pentaphenylbenzene or tetraphenylbenzene cores crystallize differently, underscoring the importance of maintaining a consistent molecular shape in attempts to engineer crystals with predetermined properties.

Full text of DOI:10.1021/ja067571x

Published on Web 03/15/2007
Engineering Hydrogen-Bonded Molecular Crystals Built from
Derivatives of Hexaphenylbenzene and Related Compounds
1
2
Kenneth E. Maly, Eric Gagnon, Thierry Maris, and James D. Wuest*
Contribution from the D e´ partement de Chimie, UniVersit e´ de Montr e´ al, Montr e´ al,
Qu e´ bec H3C 3J7, Canada
Received October 30, 2006; E-mail: james.d.wuest@umontreal.ca
Abstract: Hexakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]benzene (4) incorporates a disc-shaped hexaphen-
ylbenzene core and six peripheral diaminotriazine groups that can engage in hydrogen bonding according
to established motifs. Under all conditions examined, compound 4 crystallizes as planned to give closely
related noninterpenetrated three-dimensional networks built from sheets in which each molecule has six
hydrogen-bonded neighbors. In the structure of compound 4, the number of hydrogen bonds per molecule
and the percentage of volume accessible to guests approach the highest values so far observed in molecular
networks. Analogue 5 (which has the same hexaphenylbenzene core but only four diaminotriazine groups
at the 1,2,4,5-positions) and analogue 7 (in which the two unsubstituted phenyl groups of compound 5 are
replaced by methyl groups) crystallize according to a closely similar pattern. Analogues with flatter
pentaphenylbenzene or tetraphenylbenzene cores crystallize differently, underscoring the importance of
maintaining a consistent molecular shape in attempts to engineer crystals with predetermined properties.
Introduction
of new materials. Hydrogen bonds have been widely exploited
in this strategy because their strength and directionality tend to
Designing molecules to form crystals with particular structures
and properties has become a very active area of research. An
especially productive strategy in crystal engineering builds
structures from molecules that engage in multiple specific
interactions with neighbors. Such molecules, which have been
3
favor the formation of crystals in which neighboring molecules
9
are positioned predictably. The resulting structures can be
described as networks of molecules connected by hydrogen
bonds.
4-7
8
These networks often have a significant degree of openness
because efficient packing cannot normally be achieved at the
same time that hydrogen bonding is optimized. In such cases,
an important percentage of the volume of the resulting crystals
can be occupied by included guests. Systematic efforts to
increase the openness of the resulting networks have yielded
called tectons, are well suited for the purposeful construction
(
(
(
1) Fellow of the Natural Sciences and Engineering Research Council of
Canada, 2003-2004.
2) Fellow of the Natural Sciences and Engineering Research Council of
Canada, 2003-2007.
3) Braga, D. Chem. Commun. 2003, 2751-2754. Biradha, K. CrystEngComm
2
003, 5, 374-384. Hollingsworth, M. D. Science 2002, 295, 2410-2413.
Crystal Engineering: From Molecules and Crystals to Materials; Braga,
D., Grepioni, F., Orpen, A. G., Eds.; Kluwer: Dordrecht, Netherlands, 1999.
Desiraju, G. R. Crystal Engineering: The Design of Organic Solids;
Elsevier: Amsterdam, 1989.
molecular crystals in which as much as 75% of the volume is
5,6,10,11
accessible to guests.
Initially, these permeable molecular
crystals were exotic curiosities; increasingly, however, they are
serving as inspiration for scientists studying subjects of im-
mediate practical importance, such as ways to make new porous
(
4) For recent examples, see: Sokolov, A. N.; Fri sˇ cˇ i c´ , T.; MacGillivray, L. R.
J. Am. Chem. Soc. 2006, 128, 2806-2807. Roques, N.; Maspoch, D.; Wurst,
K.; Ruiz-Molina, D.; Rovira, C.; Veciana, J. Chem.sEur. J. 2006, 12,
9
238-9253. Pigge, F. C.; Dighe, M. K.; Rath, N. P. Cryst. Growth Des.
006, 6, 2732-2738. Saha, B. K.; Nangia, A.; Nicoud, J.-F. Cryst. Growth
2
12
materials for selectively storing guests, to make solids react
Des. 2006, 6, 1278-1281. Jayaraman, A.; Balasubramaniam, V.; Valiyaveet-
til, S. Cryst. Growth Des. 2006, 6, 636-642. Suslick, K. S.; Bhyrappa, P.;
Chou, J.-H.; Kosal, M. E.; Nakagaki, S.; Smithenry, D. W.; Wilson, S. R.
Acc. Chem. Res. 2005, 38, 283-291. Aaker o¨ y, C. B.; Desper, J.; Urbina,
J. F. Chem. Commun. 2005, 2820-2822. Braga, D.; Brammer, L.;
Champness, N. R. CrystEngComm 2005, 7, 1-19. Sisson, A. L.; del Amo
Sanchez, V.; Magro, G.; Griffin, A. M. E.; Shah, S.; Charmant, J. P. H.;
Davis, A. P. Angew. Chem., Int. Ed. 2005, 44, 6878-6881. Malek, N.;
Maris, T.; Perron, M.- EÅ .; Wuest, J. D. Angew. Chem., Int. Ed. 2005, 44,
(6) Fournier, J.-H.; Maris, T.; Wuest, J. D. J. Org. Chem. 2004, 69, 1762-
1775.
(7) For recent overviews of the strategy, see: Wuest, J. D. Chem. Commun.
2005, 5830-5837. Hosseini, M. W. Acc. Chem. Res. 2005, 38, 313-323.
(8) Simard, M.; Su, D.; Wuest, J. D. J. Am. Chem. Soc. 1991, 113, 4696-
4697.
(9) For reviews, see: Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48-76.
Prins, L. J.; Reinhoudt, D. N.; Timmerman, P. Angew. Chem., Int. Ed. 2001,
40, 2382-2426.
4
1
021-4025. Voogt, J. N.; Blanch, H. W. Cryst. Growth Des. 2005, 5,
135-1144. Lee, S.-O.; Shacklady, D. M.; Horner, M. J.; Ferlay, S.;
Hosseini, M. W.; Ward, M. D. Cryst. Growth Des. 2005, 5, 995-1003.
Saied, O.; Maris, T.; Wang, X.; Simard, M.; Wuest, J. D. J. Am. Chem.
Soc. 2005, 127, 10008-10009. Custelcean, R.; Gorbunova, M. G.;
Bonnesen, P. V. Chem.sEur. J. 2005, 11, 1459-1466. Moorthy, J. N.;
Natarajan, R.; Venugopalan, P. J. Org. Chem. 2005, 70, 8568-8571.
Soldatov, D. V.; Moudrakovski, I. L.; Ripmeester, J. A. Angew. Chem.,
Int. Ed. 2004, 43, 6308-6311. Alshahateet, S. F.; Nakano, K.; Bishop, R.;
Craig, D. C.; Harris, K. D. M.; Scudder, M. L. CrystEngComm 2004, 6,
(10) We estimate the percentage of volume accessible to guests by using the
1
1
PLATON program. PLATON calculates the accessible volume by
allowing a spherical probe of variable radius to roll over the van der Waals
surface of the network. PLATON uses a default value of 1.20 Å for the
radius of the probe, which is an appropriate model for small guests such
as water.
(11) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht
University: Utrecht, The Netherlands, 2001. van der Sluis, P.; Spek, A. L.
Acta Crystallogr. 1990, A46, 194-201.
(12) Nangia, A. Curr. Opin. Solid State Mater. Sci. 2001, 5, 115-122. Langley,
P. J.; Hulliger, J. Chem. Soc. ReV. 1999, 28, 279-291.
5
-10.
5) Malek, N.; Maris, T.; Simard, M.; Wuest, J. D. J. Am. Chem. Soc. 2005,
27, 5910-5916.
(
1
4306
9
J. AM. CHEM. SOC. 2007, 129, 4306-4322
10.1021/ja067571x CCC: $37.00 © 2007 American Chemical Society

H-Bonded Crystals from Hexaphenylbenzene Derivatives
A R T I C L E S
without using solvents to dissolve them,13 and to create new
types of gels, liquid crystals, films, glasses, and other materials
in which particular degrees of order, porosity, and molecular
diffusion must be maintained.14
Table 1. Summary of Key Structural Features of the
Hydrogen-Bonded Networks in Crystals of Hexaphenylbenzenes
-5 and Related Compounds 6-8
1
number
compound
of hydrogen-
bonded
number
of hydrogen
bonds
dimensionality
of hydrogen-
bonded
Diverse tectons can be made conveniently by attaching
appropriate hydrogen-bonding groups or other sticky sites to
the periphery of cores with well-defined geometries. Many
previously studied networks have been built from tectons with
nominally tetrahedral cores, which tend to favor diamondoid
architectures. In such structures, the volume available for
including guests is often diminished or even eliminated by the
interpenetration of independent networks.15 Increasing the
permeability of molecular crystals requires new types of tectons
that yield networks in which interpenetration is disfavored or
impossible. In addition, to ensure that the resulting networks
are highly robust, each tecton must form many hydrogen bonds
with its neighbors.
As part of a systematic effort to construct highly open and
robust hydrogen-bonded networks, we turned our attention to
tectons with complex aromatic cores related to hexaphenylben-
zene. In noteworthy earlier work in crystal engineering, Koba-
yashi and co-workers showed that compounds 1-3, which have
simple hydrogen-bonding groups attached to each of the six
(
conditions of
% volume
accessible
to guests10,11
crystallization
neighbors
per tectona
in parentheses)
per tectona
network
1 (Et2O)16
(DMF)16
48
42
46
59
48
7
6
4
6
8
6
8
4
12
12
12
12
2D
2D
2D
3D
3D
3D
1
17
2
3
3
(MeOH)
(DMSO)18
18
(n-PrOH/H2O)
18
3 (H2O)
10
c
c
1
0
8
8
6
20
4
4
(DMSO/THF)
(DMSO/toluene)
70
56
72
56
60
55
75
16
16
12
36
12
8
16
14
4
3D
3D
3D
3D
3D
2D
3D
2D
1D
4 (DMSO/benzene)
4
5
6
7
(HCOOH/EtOH)
(DMSO/MeCN)
(DMSO/acetone)
(DMSO/dioxane)
12
6
4
6
4
b
7 (DMSO/MeOH)
39
64
8
(DMSO/acetone)
2
a
Hydrogen bonds involving guests are excluded. b This value is abnor-
mally low in the series of compounds 4-8 because the network is 2-fold
interpenetrated. c The unit cell contains two independent molecules.
together by self-association of the carboxyl groups as cyclic
1
7
hydrogen-bonded pairs. This leads to a structure in which the
number of hydrogen bonds per tecton increases to 12 but the
percentage of accessible volume is still modest (46%). Hexakis-
(4-carbamoylphenyl)benzene (3) was found by Kobayashi and
co-workers to crystallize from three solvent systems as different
1
8
three-dimensional hydrogen-bonded networks. Again, the
percentages of volume accessible to included guests (59%, 48%,
and 7%) are significantly lower than those of the most permeable
5
,6
molecular crystals currently known, and the cohesive forces
are modest, as measured by the number of hydrogen bonds per
tecton.
Tectons 1-3 are structurally similar, but the resulting
networks display widely different architectures for reasons that
have not been delineated. Moreover, the percentages of volume
accessible to guests are all less than 60%, in some cases by a
large margin, and the number of hydrogen bonds per tecton
does not normally exceed 12 (Table 1). Taken together, these
properties do not point to tectons derived from hexaphenylben-
zene as especially promising precursors for engineering highly
permeable molecular crystals. However, we were encouraged
to note that none of the networks formed by compounds 1-3
exhibits interpenetration, possibly because of the geometry of
the hexaphenylbenzene core. These observations encouraged us
to undertake a systematic study of derivatives of hexaphenyl-
benzene as sources of highly porous hydrogen-bonded networks
not compromised by interpenetration.
radiating phenyl arms of hexaphenylbenzene, form open net-
works without interpenetration.1
6-18
A summary of key features
of these structures appears in Table 1. Hexakis(4-hydroxyphen-
yl)benzene (1) was shown to crystallize from two different sol-
vent systems as inclusion compounds that both consist of
hydrogen-bonded sheets.16 In each of these two structures, the
percentage of volume accessible to guests is relatively modest
(42% and 48%), as is the number of hydrogen bonds in which
each tecton participates (four and eight). Hexakis(4-carboxy-
phenyl)benzene (2) also crystallizes as sheets, which are held
(
13) Brunet, P.; Demers, E.; Maris, T.; Enright, G. D.; Wuest, J. D. Angew.
Chem., Int. Ed. 2003, 42, 5303-5306.
(
14) For recent references, see: Lebel, O.; Maris, T.; Perron, M.- EÅ .; Demers,
E.; Wuest, J. D. J. Am. Chem. Soc. 2006, 128, 10372-10373. Nath, K. G.;
Ivasenko, O.; Miwa, J. A.; Dang, H.; Wuest, J. D.; Nanci, A.; Perepichka,
D. F.; Rosei, F. J. Am. Chem. Soc. 2006, 128, 4212-4213. Lebel, O.;
Perron, M.- EÅ .; Maris, T.; Zalzal, S. F.; Nanci, A.; Wuest, J. D. Chem. Mater.
Our initial target was tecton 4, which incorporates six
diaminotriazine groups on the periphery of the hexaphenylben-
zene core. Diaminotriazines are known to self-associate reliably
2
006, 18, 3616-3626. Maly, K. E.; Dauphin, C.; Wuest, J. D. J. Mater.
Chem. 2006, 16, 4695-4700.
5,6,19
in the solid state by forming hydrogen-bonded motifs I-III.
(
15) For discussions of interpenetration in networks, see: Batten, S. R.
CrystEngComm 2001, 76-82. Batten, S. R.; Robson, R. Angew. Chem.,
Int. Ed. 1998, 37, 1460-1494.
Motif I is particularly favorable because it involves hydrogen
bonding remote from sterically congested sites where the
diaminotriazine groups are attached to the molecular core. For
(
(
(
16) Kobayashi, K.; Shirasaka, T.; Sato, A.; Horn, E.; Furukawa, N. Angew.
Chem., Int. Ed. 1999, 38, 3483-3486.
17) Kobayashi, K.; Shirasaka, T.; Horn, E.; Furukawa, N. Tetrahedron Lett.
2
000, 41, 89-93.
18) Kobayashi, K.; Sato, A.; Sakamoto, S.; Yamaguchi, K. J. Am. Chem. Soc.
003, 125, 3035-3045.
(19) Demers, E.; Maris, T.; Wuest, J. D. Cryst. Growth Des. 2005, 5, 1227-
2
1235.
J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007 4307

A R T I C L E S
Maly et al.
this reason, we expected tecton 4 to crystallize by associating
according to motif I. This would lead to the formation of sheets
represented by Figure 1a, in which each tecton has six hydrogen-
bonded neighbors and takes part in a total of 12 hydrogen bonds.
In addition, the sheets shown in Figure 1a could potentially be
further connected by secondary hydrogen-bonding interactions
according to motif II or III, giving a three-dimensional network
and increasing the number of hydrogen bonds per tecton. In
the resulting network, the sheets would be held apart and spaced
by hydrogen bonding. For these reasons, we expected compound
4
to generate structures with higher percentages of volume
accessible to guests, larger numbers of hydrogen bonds per
tecton, and more consistent three-dimensional architectures than
those produced by the simpler hexaphenylbenzenes studied by
Kobayashi et al.1
6-18
In addition, we recognized that the hexaphenylbenzene core
offers an attractive opportunity to modify networks rationally
by changing the number and position of the hydrogen-bonding
substituents. For example, removing selected hydrogen-bonding
groups from the core can produce hexaphenylbenzenes such as
compound 5, and more dramatic mutations of the core itself
can yield derivatives such as pentaphenylbenzene 6 and
tetraphenylbenzenes 7 and 8. We undertook these systematic
alterations with the expectation that analysis of the resulting
structures would deepen our understanding of how molecular
crystals can be engineered.
Figure 1. Schematic representations of possible networks derived from
(
a) a hexaphenylbenzene with six hydrogen-bonding substituents at the
para position of each phenyl group (such as tecton 4); (b) a pentaphenyl-
benzene with five hydrogen-bonding substituents (such as tecton 6); and
(c) a 1,2,4,5-tetraphenylbenzene with four hydrogen-bonding substituents
(such as tecton 7). In all images, red circles represent hydrogen-bonding
substituents.
Results and Discussion
Synthesis of Tecton 4. Target 4 was prepared in four steps
in an overall yield of 47% by the route outlined in Scheme 1.
Hexaphenylbenzene (9) was synthesized in 93% yield via the
Diels-Alder reaction of tetraphenylcyclopentadienone with
20
diphenylacetylene. Treatment with neat bromine then produced
(
20) Fieser, L. F. Org. Synth. 1966, 46, 44-48. Fieser, L. F. Organic Syntheses;
Wiley: New York, 1973; Collect. Vol. V, pp 604-608.
4308 J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007

H-Bonded Crystals from Hexaphenylbenzene Derivatives
A R T I C L E S
Scheme 1
hexakis(4-bromophenyl)benzene (10) in 96% yield.21,22 Reaction
in 31% yield. Finally, the reaction of pentanitrile 17 with
dicyandiamide under standard conditions gave compound 6 in
76% yield.
of hexabromide 10 with CuCN gave hexakis(4-cyanophenyl)-
benzene (11) in 63% yield,2
3,24
and treatment of the product
with dicyandiamide under basic conditions provided target 4
in 88% yield.
Synthesis of Tecton 7. Tetraphenylbenzene 7 was prepared
from the commercially available dimer of 2,5-dimethyl-3,4-
diphenylcyclopentadienone, which reacted with diphenyl-
acetylene in hot diphenyl ether to give 1,4-dimethyl-2,3,5,6-
tetraphenylbenzene (18) in 81% yield (Scheme 4). Bromination
using neat bromine produced the desired tetrabromide 19 in 81%
yield. This reaction was carried out in the dark to avoid benzylic
bromination. The subsequent reaction of tetrabromide 19 with
CuCN in DMF provided the corresponding tetranitrile 20
in 66% yield. Finally, treatment of compound 20 with di-
cyandiamide under standard conditions gave target 7 in 78%
yield.
2
5
Synthesis of Tecton 5. To synthesize derivative 5, in which
two diaminotriazine groups have been removed from opposing
positions on the hexaphenylbenzene core, we took advantage
of the flexibility inherent in the Diels-Alder strategy employed
in Scheme 1. The reaction of 4,4′-dibromobenzil with 1,3-
diphenylacetone gave dibrominated tetraphenylcyclopentadi-
29
26
enone 12 in 85% yield (Scheme 2). The Diels-Alder reaction
of compound 12 with bis(4-bromophenyl)acetylene,2 followed
by loss of CO, produced tetrabrominated hexaphenylbenzene
7
1
3 in 84% yield. Treatment of compound 13 with CuCN gave
the corresponding tetranitrile 14 in 60% yield, and further
reaction with dicyandiamide under standard conditions provided
target 5 in 83% yield.
Synthesis of Tecton 6. Pentaphenylbenzene 6 was prepared
by an analogous route (Scheme 3). The reaction of tetraphen-
ylcyclopentadienone with phenylacetylene in refluxing diphenyl
ether gave pentaphenylbenzene (15) in 91% yield.28 Subsequent
bromination in neat bromine produced pentakis(4-bromophenyl)-
benzene (16) in 58% yield. Treatment of compound 16 with
CuCN in DMF provided pentakis(4-cyanophenyl)benzene (17)
Synthesis of Tecton 8. Tetraphenylbenzene 8 was most
conveniently prepared by an alternative approach involving a
fourfold Suzuki-Miyaura coupling of commercially available
30
1
,2,4,5-tetrabromobenzene with 4-cyanophenylboronic acid to
give 1,2,4,5-tetrakis(4-cyanophenyl)benzene (21) in 82% yield
Scheme 5). Subsequent treatment of tetranitrile 21 with
(
dicyandiamide under standard conditions gave target 8 in 83%
yield.
Structures of Crystals of Tecton 4. Hexaphenylbenzene 4
showed low solubility in most organic solvents but could be
crystallized by allowing vapors of suitable cosolvents to diffuse
into solutions in DMSO or formic acid. Crystals suitable for
study by X-ray diffraction were obtained from DMSO/THF,
DMSO/toluene, DMSO/benzene, and formic acid/methanol.
Their structures were solved to allow comparison of the resulting
hydrogen-bonded networks.
(
(
(
(
(
21) Rathore, R.; Burns, C. L.; Guzei, I. A. J. Org. Chem. 2004, 69, 1524-
1
530. Rathore, R.; Burns, C. L. Org. Synth. 2004, 82, 30-33.
22) Wu, J.; Watson, M. D.; Zhang, L.; Wang, Z.; M u¨ llen, K. J. Am. Chem.
Soc. 2004, 126, 177-186.
23) Maly, K. E.; Maris, T.; Gagnon, E.; Wuest, J. D. Cryst. Growth Des. 2006,
6
, 461-466.
24) Kobayashi, K.; Kobayashi, N.; Ikuta, M.; Therrien, B.; Sakamoto, S.;
Yamaguchi, K. J. Org. Chem. 2005, 70, 749-752.
25) Simons, J. K.; Saxton, M. R. Org. Synth. 1953, 33, 13-15. Simons, J. K.;
Saxton, M. R. Organic Syntheses; Wiley: New York, 1963; Collect. Vol.
IV, pp 78-80.
Structure of Crystals of Tecton 4 Grown from DMSO/
THF. The crystals were found to belong to the triclinic space
(
(
(
26) Coan, S. B.; Trucker, D. E.; Becker, E. I. J. Am. Chem. Soc. 1955, 77,
6
0-66.
27) Misumi, S.; Kuwana, M.; Nakagawa, M. Bull. Chem. Soc. Jpn. 1962, 35,
(29) Padwa, A.; Goldstein, S. I.; Rosenthal, R. J. J. Org. Chem. 1987, 52, 3278-
3285. Regan, T. H.; Miller, J. B. J. Org. Chem. 1967, 32, 592-596.
(30) Nishimura, M.; Ueda, M.; Miyaura, N. Tetrahedron 2002, 58, 5779-
5787.
1
35-142. Barber, H. J.; Slack, R. J. Chem. Soc. 1944, 612-615.
28) K u¨ bel, C.; Eckhardt, K.; Enkelmann, V.; Wegner, G.; M u¨ llen, K. J. Mater.
Chem. 2000, 10, 879-886.
J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007 4309

A R T I C L E S
Scheme 2
Maly et al.
Scheme 3
group P 1h and to have the approximate composition 4‚9DMSO‚
of the central aromatic ring and those of the six aryl substituents
lie in the range 62.3(2)°-68.4(2)° (Table 2). The sheets consist
of equal numbers of the two enantiomers.
A subtle but important element in the design of hexaphenyl-
benzene 4, modified tectons 5-8, and related compounds is
the strong tendency of 2-phenyl-1,3,5-triazines to adopt con-
formations in which the phenyl and triazine rings are nearly
coplanar. In 2,4,6-triphenyl-1,3,5-triazine, for example, the
planes of the three phenyl substituents are tilted by an average
of only 8.5° with respect to the plane of the triazine core.33
3
1
7
THF‚xH2O. As anticipated (Figure 1a), the six diaminotri-
azine groups of each tecton form hydrogen bonds according to
motif I with six neighbors, thereby defining parallel sheets held
together by 12 hydrogen bonds per tecton (Figure 2a). The
hexaphenylbenzene core of compound 4 adopts a character-
istic chiral propeller-shaped conformation with approximate
6
-fold symmetry, as observed in many other derivatives of
23,32
hexaphenylbenzene.
The angles between the average plane
(
31) The composition was estimated by X-ray diffraction and by 1H NMR
spectroscopy of dissolved samples. The amount of any H
not be determined accurately.
2
O included could
(32) Gagnon, E.; Maly, K. E.; Maris, T.; Wuest, J. D. Acta Crystallogr. 2007,
C63, o4-o6.
4310 J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007

H-Bonded Crystals from Hexaphenylbenzene Derivatives
A R T I C L E S
Scheme 4
Scheme 5
interpenetration of independent networks is observed; instead,
a single open network is favored, and 70% of the volume of
the crystal is accessible to guests, which are partly disor-
1
0,11
dered.
The guests occupy interconnected channels that in
principle give new guests access to the interior of the crystal.
The largest channels are triangular and aligned with the b-axis,
and smaller channels run along the a-axis (Figure 4).
Examination of the overall structure confirms that multiple
key features result predictably from design. In particular, com-
pound 4 crystallizes as a non-interpenetrated three-dimensional
hydrogen-bonded network built from sheets in which each tecton
interacts as planned with six neighbors. In this design, the natural
tendency of hexaphenylbenzenes and other disc-shaped mol-
ecules to form layered structures is strongly reinforced by
intrasheet hydrogen bonding. As planned, the six diaminotriazine
groups of compound 4 are nearly coplanar with the phenyl arms
of the hexaphenylbenzene core, thereby extending its propeller
conformation predictably. This ensures the formation of ad-
ditional intersheet hydrogen bonds, although we acknowledge
that the precise mode of stacking of the sheets and the nature
of the resulting channels could not have been foreseen with
confidence. As measured by the volume accessible to guests
and the number of hydrogen bonds per tecton, the network
formed by compound 4 is significantly more open and robust
than those built from simpler analogues 1-3, placing it among
the most impressive molecular networks observed so far.
Similar conformational preferences have been noted in many
other simple phenyltriazines.34 Data compiled in the Cambridge
Structural Database (Version 5.27) demonstrate that torsional
angles in 2-phenyl-1,3,5-triazines (Figure 3a) tend to be
significantly smaller than those observed for biphenyls (Figure
3
b), and those found in 2-phenylpyrimidines are similarly
3
5
small. In crystals of tecton 4 grown from DMSO/THF, the
average deviation from coplanarity is 12.9(3)°. This ensures that
the diaminotriazine groups are oriented in a way that extends
the propeller shape of the hexaphenylbenzene core and directs
hydrogen-bonding sites out of the plane defined by each tecton
and its six principal neighbors.
As a result, each tecton can form another four hydrogen bonds
of type III to two additional neighbors in adjacent sheets (Figure
Structure of Crystals of Tecton 4 Grown from DMSO/
Toluene. Our assertion that key features of the structure resulted
from rational design was tested rigorously by searching for
pseudopolymorphs formed under other conditions. Crystals
grown by allowing vapors of toluene to diffuse into a solution
of tecton 4 in DMSO also proved to belong to the triclinic space
group P 1h . Their composition was determined by crystallography
to be 4‚6DMSO‚H2O. Again, each tecton interacts with six
neighbors according to hydrogen-bonding motif I to define
2b). This links the sheets into a three-dimensional network, and
each tecton participates in a total of 16 intertectonic hydrogen
bonds involving eight neighbors (Table 1). As expected, no
(
33) Damiani, A.; Giglio, E.; Ripamonti, A. Acta Crystallogr. 1965, 19, 161-
1
68.
(
34) Ishi-i, T.; Kuwahara, R.; Takata, A.; Jeong, Y.; Sakurai, K.; Mataka, S.
Chem.sEur. J. 2006, 12, 763-776. Janczak, J.; Kubiak, R. J. Mol. Struct.
2
005, 751, 74-84. D ´ı az-Ortiz, AÄ .; Elguero, J.; Foces-Foces, C.; de la Hoz,
A.; Moreno, A.; Mateo, M. d. C.; S a´ nchez-Migall o´ n, A.; Valiente, G. New
J. Chem. 2004, 28, 952-958.
3
5
(
35) See the Supporting Information for details.
sheets. The hexaphenylbenzene core is characteristically
J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007 4311

A R T I C L E S
Maly et al.
Figure 2. (a) View of the structure of crystals of tecton 4 grown from DMSO/THF, showing a central molecule (red) and its eight hydrogen-bonded
neighbors (blue and green). Six of the neighbors (blue) lie approximately in the plane of the central molecule and interact according to motif I, and the other
two (green) lie above and below the plane and form hydrogen bonds of type III with the central molecule (red). (b) Side view showing the two neighbors
in green above and below the plane. In both views, guests are omitted for clarity, and hydrogen bonds are represented by broken lines.
Table 2. Conformations Adopted by the Arylbenzene Cores in
Crystals of Hexaphenylbenzenes 4-5 and Related Compounds
triangular channels that run along the a-axis and are similar to
those observed in crystals grown from DMSO/THF (Figure 4a),
but they are not interconnected by other significant channels.
Despite these minor differences, the structures of crystals grown
from DMSO/THF and DMSO/toluene show close overall
similarity, supporting the conclusion that the observed networks
are the result of logical design.
6-8
compound (conditions of
angles (deg) between the average planes of the aryl
substituents and central ring of the arylbenzene core
crystallization in parentheses)
4
4
4
4
5
6
7
7
8
(DMSO/THF)
(DMSO/toluene)
(DMSO/benzene) 66.08(11)
(HCOOH/EtOH)
(DMSO/MeCN)
(DMSO/acetone)
(DMSO/dioxane) 84.50(12)
(DMSO/MeOH)
(DMSO/acetone)
67.0(2), 63.3(2), 68.4(2), 67.7(2), 62.3(2), 66.2(2)
66.4(3), 74.1(2), 89.8(2)
88.88(15)
Structure of Crystals of Tecton 4 Grown from DMSO/
Benzene. A further test of this conclusion was carried out by
analyzing crystals grown by the diffusion of vapors of benzene
into a solution of tecton 4 in DMSO. The resulting crystals were
found to belong to the trigonal space group R 3h and to have the
approximate composition 4‚12DMSO‚12benzene‚xH2O.31 The
network formed is similar to the two already described, although
some new features appear. Again, each tecton interacts directly
with six neighbors by hydrogen bonding according to motif I.
However, the neighbors lie alternately above and below the
plane defined by the central tecton, giving rise to an irregular
sheet in which the neighbors cannot interact directly but instead
are bridged by hydrogen bonds to intervening molecules of
DMSO (Figure 5). In this way, each molecule of hexaphenyl-
benzene 4 participates in 12 hydrogen bonds with neighboring
59.88(9), 80.48(9), 85.63(9) (2x), 88.59(10) (2x)
41.9(2) (2x), 56.09(19), 62.4(2) (2x)
67(1), 72(1), 80(1), 81(1)
40.06(16) (2x), 65.17(16) (2x)
nonplanar (Table 2), allowing four additional hydrogen bonds
to link each tecton to two neighbors located in adjacent sheets.
35
The resulting network is three-dimensional and held together
by a total of 16 hydrogen bonds per tecton (Table 1), like that
found in crystals grown from DMSO/THF. The only significant
architectural difference between the two networks is in the
precise way the sheets are connected.35 Packing of the sheets
appears to be somewhat more efficient in crystals grown from
DMSO/toluene, leading to a smaller percentage of volume
accessible to guests (56%).1 The guests occupy large parallel
0,11
4312 J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007

H-Bonded Crystals from Hexaphenylbenzene Derivatives
A R T I C L E S
Figure 4. Views of the structure of crystals of tecton 4 grown from DMSO/
THF, showing (a) large triangular channels along the b-axis and (b) smaller
channels along the a-axis. Both views show a 3 × 2 × 3 array of unit
cells. Guests are omitted for clarity, and atoms are represented by spheres
of van der Waals radii to show the cross sections of the channels. Atoms
of hydrogen appear in white; carbon in gray; and nitrogen in blue.
ordered, whereas included benzene and the phenyl arms of the
hexaphenylbenzene core are statistically disordered (Table 2).
Structure of Crystals of Tecton 4 Grown from Formic
Acid/Methanol. The marked tendency of hexaphenylbenzene
4
to form three-dimensional networks built from sheets in which
each tecton interacts with six neighbors by forming 12 hydrogen
bonds according to motif I was further tested by growing crystals
under distinctly different conditions. Vapors of methanol were
allowed to diffuse into a solution of compound 4 in formic acid,
and the resulting crystals were found to belong to the trigonal
space group R 3h . Included solvent proved to be disordered, and
the composition could not be determined accurately by crystal-
lography. Again, each tecton interacts with six neighbors in the
expected way, leading to the formation of sheets closely similar
to those observed in crystals grown from DMSO/THF and
Figure 3. Histograms showing the frequency of torsional angles between
the average planes of the aromatic rings in 2-phenyl-1,3,5-triazines and
biphenyls, as observed in crystal structures compiled in the Cambridge
Structural Database (Version 5.27). Structures containing metals or with
atoms other than hydrogen at the indicated positions were not included in
the analysis to avoid torsional effects arising from coordination or from
ortho substitution. In addition, phenyltriazines in which the atoms of nitrogen
were protonated or otherwise substituted were removed individually from
the set of data.
35
DMSO/toluene. In each tecton, the six phenyl arms of the
hexaphenylbenzene core are virtually perpendicular to the central
benzene ring (Table 2). This conformation allows each tecton
to engage in a total of 24 additional hydrogen bonds of type
III with six other neighbors, of which three are in each of the
3
5
two adjacent sheets. The resulting network is three-dimen-
sional, each tecton participates in a total of 36 hydrogen bonds,
and 56% of the volume is accessible to guests (Table 1).1 In
this structure, adjacent sheets are offset in a way that prevents
the formation of conspicuous channels perpendicular to the plane
of the characteristic sheets (Figure 7).
0,11
tectons and 12 more with included molecules of DMSO (Table
1). The resulting network is highly open, and 72% of the volume
is accessible to guests, which occupy interconnected chan-
Together, the structures of the four pseudopolymorphs
described above provide strong evidence that tecton 4 has been
successfully engineered to favor crystals with the following
specific features: (1) Each structure is built from a heptameric
1
0,11
nels.
The largest channels are triangular and aligned with
the c-axis (Figure 6), and smaller channels lie in other directions.
The included DMSO is hydrogen-bonded to tecton 4 and
J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007 4313

A R T I C L E S
Maly et al.
Figure 5. View of the structure of crystals of tecton 4 grown from DMSO/benzene, showing a central molecule (red) and its six hydrogen-bonded neighbors
blue). The six neighbors (blue) lie alternately above and below the plane of the central molecule (red), and they are bridged by hydrogen bonds to molecules
of DMSO (yellow). Guests are omitted for clarity, and hydrogen bonds are represented by broken lines.
(
Figure 7. Representation of the structure of crystals of tecton 4 grown
Figure 6. View of the structure of crystals of tecton 4 grown from DMSO/
benzene, showing a 2 × 2 × 2 array of unit cells along the c-axis. Guests
are omitted for clarity, and atoms are represented by spheres of van der
Waals radii to show the cross sections of the channels. Atoms of hydrogen
appear in white; carbon in gray; and nitrogen in blue.
from formic acid/methanol, showing a 2 × 2 × 2 array of unit cells viewed
along the c-axis. Three successive offset sheets are colored in red, blue,
and green. Guests are omitted for clarity, and atoms are represented by
spheres of van der Waals radii to confirm the absence of channels
perpendicular to the sheets.
unit in which a central tecton forms hydrogen bonds of type I
with six neighbors; (2) further association of these heptameric
units leads to the formation of sheets; (3) the characteristic
nonplanar conformations adopted by the hexaphenylbenzene
core, in conjunction with the tendency of the triazine rings to
lie close to the planes of the phenyl arms to which they are
grafted, promote hydrogen bonding between sheets, thereby
leading to the formation of three-dimensional networks held
together by up to 36 hydrogen bonds per tecton; (4) no
interpenetration of independent networks is observed; and (5)
spaces between and within the sheets allow the inclusion of
guests, and the percentage of accessible volume (56%-72%)
consistently approaches the highest values so far observed in
molecular networks. Although the networks produced by tecton
molecular tectonics: molecules with well-defined geometries
and multiple sites of strong directional interactions do not tend
to crystallize in widely divergent polymorphic forms.7
Hydrogen-Bonded Networks Formed by Mutated Tectons
5-8. Having demonstrated an important degree of control in
constructing networks from hexaphenylbenzene 4, we then put
our understanding to a further test by probing the effect of
selected structural modifications. Analogues 5-8 were synthe-
sized and crystallized to reveal how removal of specific
diaminotriazine groups or phenyl groups from the hexaphenyl-
benzene core would change how crystallization occurs.
Structure of Crystals of Tecton 6 Grown from DMSO/
Acetone. In tecton 6, one of the phenyl arms of the hexa-
phenylbenzene core has been excised, thereby producing a
pentaphenylbenzene with five attached diaminotriazine groups.
4
under different conditions of crystallization are not strictly
identical, their close similarity supports a key principle of
4314 J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007

H-Bonded Crystals from Hexaphenylbenzene Derivatives
A R T I C L E S
maintained by multiple hydrogen bonds of type I is retained,
and the resulting network is noninterpenetrated and highly
porous.
Structure of Crystals of Tecton 5 Grown from DMSO/
Acetonitrile. The behavior of pentaphenylbenzene 6 helped
clarify the importance of the conformation of the core and
suggested that analysis of derivatives of tecton 4 with an intact
hexaphenylbenzene core but less than six diaminotriazine groups
would be informative. Crystals of tetrasubstituted hexaphenyl-
benzene 5 were grown by allowing vapors of acetonitrile to
diffuse into a solution in DMSO. The crystals were found to
belong to the monoclinic space group C2/c and to have the
composition 5‚8DMSO‚6CH3CN. The observed structure is
closely consistent with the pattern established by hexasubstituted
analogue 4. In particular, tecton 5 engages in a total of eight
hydrogen bonds of type I with four neighbors, and the resulting
pentameric unit defines a sheet (Figure 10a). The hexaphenyl-
benzene core of each tecton adopts a characteristic nonplanar
conformation (Table 2), which permits the formation of four
additional hydrogen bonds to two other tectons in adjacent sheets
Figure 8. View of the structure of crystals of tecton 6 grown from DMSO/
acetone, showing a central molecule (in red) and its four coplanar neighbors
(blue), which are linked to the central molecule by hydrogen bonds of type
I. Guests are omitted for clarity, and hydrogen bonds are represented by
broken lines.
(Figure 10b). The resulting network is noninterpenetrated and
highly open, with 60% of the volume of the crystal accessible
1
0,11
to guests (Table 1).
Again, the guests occupy channels that
run perpendicular to the plane of the sheets (Figure 11), and
the unsubstituted phenyl groups face one another across the
channels, as represented schematically by Figure 1c. The closely
parallel behavior of hexaphenylbenzenes 4 and 5 provides a
compelling example of successful crystal engineering and under-
scores the importance of maintaining a consistent molecular
shape.
Structure of Crystals of Tecton 7 Grown from DMSO/
Dioxane. In tetraphenylbenzene 7, the two unsubstituted phenyl
groups of hexaphenylbenzene 5 have been replaced by methyl
groups. The new substituents were chosen to be (1) large enough
to force tecton 7 to adopt a conformation similar to that of tecton
Figure 9. View of the structure of crystals of tecton 6 grown from DMSO/
acetone, showing a 2 × 2 × 2 array of unit cells viewed along the b-axis
with successive sheets colored in red and blue. Guests are omitted for clarity,
and atoms are represented by spheres of van der Waals radii.
Crystals grown by diffusion of vapors of acetone into a solution
of tecton 6 in DMSO proved to belong to the monoclinic space
group C2/c and to have the approximate composition 6‚8DMSO‚
xH2O.31 In the resulting structure, each tecton uses four of its
five diaminotriazine groups to form a total of eight hydrogen
bonds of type I with four neighbors (Figure 8). The fifth group
does not form hydrogen bonds with neighboring tectons and
interacts instead with included molecules of DMSO. The
resulting pentameric motif generates the hydrogen-bonded sheets
represented by Figure 1b and shown from the side in Figure 9.
Removal of one of the arms of the hexaphenylbenzene core
allows the remaining phenyl spacers to adopt orientations closer
to the plane of the central benzene ring (Table 2). This flattening
of the molecular structure prevents tectons in one sheet from
engaging in direct hydrogen bonding with tectons in adjacent
sheets. Instead, the sheets are linked into an offset three-
dimensional network by hydrogen bonds involving bridging
molecules of DMSO. No interpenetration is observed, and 55%
5
, with the remaining four phenyl groups held well out of the
plane of the central aromatic ring, but (2) small enough to yield
crystals in which the volume accessible to guests is increased
significantly. Crystals were obtained by allowing dioxane to
diffuse slowly into a solution of compound 7 in DMSO. The
crystals proved to belong to the monoclinic space group C2/m,
31
to have the approximate composition 7‚10DMSO‚xH2O and
to adopt a structure in close agreement with expectations. In
particular, tecton 7 forms eight hydrogen bonds of type I with
four neighbors to define a sheet (Figure 12a). As planned, the
methyl groups enforce a conformation in which the central
aromatic ring forms large dihedral angles with the four remain-
ing phenyl arms (Table 2). Moreover, the established preference
for nearly coplanar alignment of the triazines then allows the
formation of four additional hydrogen bonds of type III to two
tectons in adjacent sheets (Figure 12b). The resulting network
10,11
of the volume of the crystal is accessible to guests (Table 1).
is noninterpenetrated and defines large channels (Figures 13-
Guests occupy distinct channels that lie along the c-axis and
incorporate the unpaired diaminotriazine groups. The accessible
volume is slightly lower than that observed in structures of
tecton 4, even though removal of a significant part of the
molecule might have been expected to increase porosity. This
is presumably because the flattened pentaphenylbenzene core
permits closer packing of the sheets. Despite this important
change, however, mutated tecton 6 continues to resemble
hexaphenylbenzene 4 in key ways. Specifically, a sheet structure
36
1
5). The most impressive are aligned with the c-axis and
2
measure approximately 9.6 × 15 Å , and 75% of the volume
10,11
of the crystals is accessible to guests (Table 1).
The porosity
equals the current record for crystals built from small mol-
5,6
ecules. By yielding a network with an architecture closely
similar to that of model 5, and by increasing the volume
(
36) Representations of channels were generated by the Cavities option in the
program ATOMS Version 5.1 (Shape Software, 521 Hidden Valley Road,
Kingsport, Tennessee 37663 U.S.A.; www.shapesoftware.com).
J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007 4315

A R T I C L E S
Maly et al.
Figure 10. (a) View of the structure of crystals of tecton 5 grown from DMSO/acetonitrile, showing a central molecule (red) and its six hydrogen-bonded
neighbors (blue and green). Four of the neighbors (blue) lie approximately in the plane of the central molecule and form hydrogen bonds to it via motif I.
The remaining two neighbors (green) lie above and below the sheet. (b) Side view of the central molecule (red) and its six hydrogen-bonded neighbors (blue
and green). In both views, guests are omitted for clarity, and hydrogen bonds are represented by broken lines.
Structure of Crystals of Tecton 7 Grown from DMSO/
Methanol. To test the reliability of these guidelines, we searched
for pseudopolymorphs formed under other conditions. Crystals
grown by slow diffusion of methanol into a solution of
compound 7 in DMSO were found to belong to the monoclinic
space group P21/c and to have the composition 7‚8DMSO‚4H2O.
In the resulting structure, one of the diaminotriazine groups is
disordered over two positions, which complicates analysis of
the hydrogen bonding. Each tecton forms hydrogen bonds with
four neighbors, thereby generating a sheet (Figure 16). Unlike
all previously analyzed structures, in which the characteristic
sheets are maintained by hydrogen bonds of type I, those
generated when tecton 7 is crystallized from DMSO/methanol
are held together by hydrogen bonds of types II and III.
Moreover, adjacent sheets do not appear to form hydrogen bonds
with each other, despite the nonplanar conformation of tecton
7
(Table 2). In addition, the network is 2-fold interpene-
trated (Figure 17), and only 39% of the volume is access-
ible to guests (Table 1). Together, the observations of signifi-
cantly lower porosity, interpenetration, and deviations from
established patterns of hydrogen bonding show that signif-
icant alterations of the hexaphenylbenzene core of tectons 4
and 5 can have subtle and unexpected effects. In the partic-
ular case of tecton 7, key conformational features of the aro-
matic core are successfully maintained, but the smaller methyl
groups appear to allow neighboring molecules to approach more
closely.
Figure 11. Representation of the structure of crystals of tecton 5 grown
from DMSO/acetonitrile, showing two successive offset hydrogen-bonded
sheets in red and blue. The image shows a 1 × 2 × 2 array of unit cells
viewed along the c-axis, with guests omitted for clarity and atoms
represented by spheres of van der Waals radii to reveal the cross sections
of channels.
accessible to guests from 60% to 75%, tecton 7 behaved
according to plan, demonstrating how new structures with
predictable features can be engineered by following the guide-
lines of molecular tectonics.
4316 J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007

H-Bonded Crystals from Hexaphenylbenzene Derivatives
A R T I C L E S
Figure 12. (a) View of the structure of crystals of tecton 7 grown from DMSO/dioxane, showing a central molecule (red) and its six hydrogen-bonded
neighbors (blue and green). Four of the neighbors (blue) interact according to motif I and lie approximately in the plane of the central molecule, and the
other two (green) form hydrogen bonds of type III and lie above and below the plane. (b) Side view showing the two neighbors in green above and below
the plane. In both views, guests are omitted for clarity, and hydrogen bonds are represented by broken lines.
Figure 13. Representation of the structure of crystals of tecton 7 grown
from DMSO/dioxane, showing three successive offset sheets colored in red,
blue, and green. Guests are omitted for clarity, and atoms are represented
by spheres of van der Waals radii.
Figure 14. View of the structure of crystals of tecton 7 grown from DMSO/
dioxane, showing a 2 × 2 × 2 array of unit cells along the c-axis. Guests
Structure of Crystals of Tecton 8 Grown from DMSO/
Acetone. Further confirmation of the importance of an intact
hexaphenylbenzene core was obtained by studying the behavior
of tecton 8, which is derived from 1,2,4,5-tetraphenylbenzene.
Crystals grown by diffusion of vapors of acetone into a solu-
tion of compound 8 in DMSO were found to belong to the
monoclinic space group P21/c and to have the composition
are omitted for clarity, and atoms are represented by spheres of van der
Waals radii to show the cross sections of the channels. Atoms of hydrogen
appear in white; carbon in gray; and nitrogen in blue.
phenylbenzenes. Only two diaminotriazine groups in each tecton
interact with those of neighbors, thereby producing chains that
extend along the b-axis and are held together by hydrogen bonds
of type I (Figure 18a). The remaining diaminotriazine groups
engage in hydrogen bonding with included molecules of DMSO,
which form bridges to neighboring tectons (Figure 18b). The
8‚12DMSO. As expected, tecton 8 adopts a flattened conforma-
tion (Table 2) and generates a hydrogen-bonded network that
is very different from those derived from analogous hexa-
J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007 4317

A R T I C L E S
Maly et al.
Together, these results provide an impressive demonstration of
the ability of molecular tectonics to control crystallization, and
they suggest that new tectons with more complex nonplanar
aromatic cores and multiple sites of hydrogen bonding can be
designed to produce networks with even higher degrees of
porosity and robustness.
Our results also demonstrate that major structural alterations
of the hexaphenylbenzene core can change the architecture of
the resulting network significantly. In particular, analogues with
flatter pentaphenylbenzene and tetraphenylbenzene cores yield
crystals with different features. It is important to note that we
have not been able to compare the structures of crystals of
tectons 4-8 grown under identical conditions. However, our
thorough investigation of the pseudopolymorphs of compound
4
has established that key structural features are maintained in
Figure 15. Representation of channels along the c-axis in the network
resulting from crystallization of tecton 7 from DMSO/dioxane. The image
shows a 2 × 2 ×2 array of unit cells. The outsides of the channels appear
in dark gray, and light gray is used to show where the channels are cut by
the boundaries of the array. The surface of the channels is defined by the
possible loci of the center of a sphere of diameter 6 Å as it rolls over the
all crystals examined. Moreover, the networks generated by
tectons 4-8 have many shared properties despite significant
differences in the conditions of crystallization. For these reasons,
we believe that our work defines the current state of the art in
crystal engineering and illustrates primarily the systematic effect
of modifying the molecular components of crystals, not the
conditions of crystallization.
3
6
surface of the ordered network.
resulting network is open, and 64% of the volume is accessible
to guests (Table 1).
Experimental Section
All reagents and solvents were purchased from commercial sources
and used without further purification unless otherwise indicated.
Hexakis(4-cyanophenyl)benzene (11) was prepared from hexakis(4-
Conclusions
Our study of hydrogen-bonded networks derived from
hexaphenylbenzene and related compounds, together with earlier
work reported by Kobayashi et al.,16-18 has yielded a deeper
understanding of how to create molecular crystals by design.
By examining the behavior of a single compound under multiple
conditions of crystallization, and by analyzing the effects of a
series of systematic structural modifications, we have tested
molecular tectonics as a strategy for engineering crystals with
predetermined properties, and we have clearly delineated its
current strengths and limitations.
bromophenyl)benzene (10)2
1,22
as described previously. Anhydrous
23
and oxygen-free solvents (DMF and toluene) were obtained by passage
through columns packed with activated alumina and supported copper
catalyst (Glass Contour, Irvine, CA). NMR spectra were recorded using
a Bruker AV400 spectrometer, and high-resolution mass spectra were
obtained using an Agilent LC-MSD TOF spectrometer. Elemental
analyses were performed at the Universit e´ de Montr e´ al.
Hexakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]benzene (4).
2
3,24
Hexakis(4-cyanophenyl)benzene (11) (315 mg, 0.460 mmol)
combined with dicyandiamide (474 mg, 5.64 mmol) and KOH (75 mg,
.34 mmol) in 2-methoxyethanol (10 mL), and the mixture was heated
was
Our results underscore the importance of the geometry of
the hexaphenylbenzene core, which reliably adopts nonplanar
conformations and has a disclike shape that inherently favors
parallel molecular packing and the formation of layered
structures. In tectons 4 and 5, this tendency has been powerfully
reinforced by grafting diaminotriazine groups to the periphery
of the hexaphenylbenzene core, thereby ensuring the formation
of multiple hydrogen bonds in the molecular plane. Simulta-
neously, the characteristic nonplanar conformation of the core,
along with the preference for nearly coplanar alignment of
phenyl-substituted triazines, ensures that additional hydrogen
bonds are formed between the sheets, creating three-dimensional
networks. Our results show that when a consistent molecular
shape is maintained, the results of crystallization have a high
degree of predictability. Under all conditions examined, hexa-
phenylbenzene 4 crystallizes as planned to give noninterpen-
etrated three-dimensional networks built from sheets in which
each tecton forms hydrogen bonds of type I with six neighbors.
In addition, the behavior of analogues 5 and 7, which have
conformationally similar cores but only four diaminotriazine
groups, is closely parallel. In these structures, the number of
hydrogen bonds per tecton and the percentage of volume
accessible to guests consistently exceed those reported for the
simpler derivatives studied earlier by Kobayashi et al., and they
reach the highest values so far observed in molecular networks.
1
at reflux for 15 h. The resulting mixture was then cooled to 25 °C, and
volatiles were removed by evaporation in vacuo. The residue was
suspended in water, and the solid fraction was separated by filtration
and then washed with hot water, ethanol, and methanol. The product
was dried to give hexakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]-
benzene (4; 467 mg, 0.393 mmol, 85%) as a colorless solid. A sample
was further purified for analysis by recrystallization from formic acid/
1
ethyl acetate: mp > 300 °C; H NMR (400 MHz, DMSO-d
(
6
) δ 6.62
3
3
13
s, 24H), 6.96 (d, 12H, J ) 8 Hz), 7.67 (d, 12H, J ) 8 Hz);
C
NMR (100 MHz, DCOOD) δ 127.3, 127.6, 132.4, 139.6, 146.0, 160.7,
1
63.4; HRMS (ESI) calcd for C60 30 + H m/e 1189.47510, found
H
48
N
1
189.47404. Anal. Calcd for C60H N30 + HCOOH: C, 59.31; H, 4.08;
48
N, 34.02. Found: C, 59.79; H, 4.11; N, 33.83.
3,4-Bis(4-bromophenyl)-2,5-diphenyl-2,4-cyclopentadien-1-one
(12).26 A solution of KOH (0.29 g, 5.2 mmol) in ethanol (5 mL) was
added to a mixture of 4,4′-dibromobenzil (3.68 g, 10.0 mmol) and 1,3-
diphenylacetone (2.10 g, 10.0 mmol) in ethanol (20 mL). The resulting
mixture was heated at reflux for 1 h. The mixture was then cooled to
0
°C, and the resulting precipitate was collected by filtration and dried
to give 3,4-bis(4-bromophenyl)-2,5-diphenyl-2,4-cyclopentadien-1-one
1
(
12; 4.61 g, 8.50 mmol, 85%) as a dark purple solid: H NMR (400
3
MHz, CDCl ) δ 6.80 (d, 4H, J ) 8.4 Hz), 7.1-7.3 (m, 10H), 7.35 (d,
H, J ) 8.4 Hz); C NMR (100 MHz, CDCl ) δ 123.6, 126.3, 128.3,
3
3
13
4
3
1
28.7, 130.5, 130.6, 131.4, 131.9, 132.1, 153.0, 200.0.
1,2,4,5-Tetrakis(4-bromophenyl)-3,6-diphenylbenzene (13). A
mixture of 3,4-bis(4-bromophenyl)-2,5-diphenyl-2,4-cyclopentadien-
4318 J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007

H-Bonded Crystals from Hexaphenylbenzene Derivatives
A R T I C L E S
Figure 16. (a) View of the structure of crystals of tecton 7 grown from DMSO/methanol, showing a central molecule (red) and its four hydrogen-bonded
neighbors (blue). (b) View of the resulting hydrogen-bonded sheet, with atoms of hydrogen appearing in white; carbon in gray; and nitrogen in blue. In both
views, guests are omitted for clarity, and hydrogen bonds are represented by broken lines.
with ethanol. The precipitate was collected by filtration, washed with
ethanol and hexane, and dried to give 1,2,4,5-tetrakis(4-bromophenyl)-
3
,6-diphenylbenzene (13; 2.83 g, 3.33 mmol, 84%) as a nearly colorless
solid: 1H NMR (400 MHz, CDCl
3
3
) δ 6.67 (d, 8H, J ) 8.4 Hz), 6.78
3
(m, 4H), 6.94 (m, 6H), 7.04 (d, 8H, J ) 8.4 Hz). Anal. Calcd for
C
42
H26Br
4
: C, 59.33; H, 3.08. Found: C, 59.11; H, 2.75.
1,2,4,5-Tetrakis(4-cyanophenyl)-3,6-diphenylbenzene (14). 1,2,4,5-
Tetrakis(4-bromophenyl)-3,6-diphenylbenzene (13; 1.70 g, 2.00 mmol)
was combined with CuCN (1.08 g, 12.1 mmol) in dry DMF (10 mL).
The mixture was heated at reflux under N for 21 h. The resulting
2
mixture was then cooled to 25 °C and diluted with water. The precipitate
was collected by filtration, washed with a mixture of water and
ethylenediamine, and extracted with CH
several times with a mixture of water and ethylenediamine, 1 M aqueous
HCl, and brine. The organic phase was then dried (MgSO ) and fil-
2 2
Cl . The extracts were washed
4
tered, and volatiles were removed by evaporation under reduced
pressure. The crude residue was purified by passage through a short
column of silica gel (100% CH Cl ) to yield 1,2,4,5-tetrakis(4-
2 2
Figure 17. Representation of the structure of crystals of tecton 7 grown
from DMSO/methanol, showing the 2-fold interpenetration of hydrogen-
bonded sheets (red and blue). Guests are omitted for clarity, and atoms are
represented by spheres of van der Waals radii.
cyanophenyl)-3,6-diphenylbenzene (14; 780 mg, 1.23 mmol, 61%) as
1
a nearly colorless solid: mp > 300 °C; H NMR (400 MHz, CDCl
3
)
3
1
-one (12; 2.16 g, 3.98 mmol) and bis(4-bromophenyl)acetylene (1.34
δ 6.72 (m, 4H), 6.90 (d, 8H, J ) 8.2 Hz), 6.94 (m, 6H), 7.21 (d, 8H,
J ) 8.2 Hz); C NMR (100 MHz, CDCl
2
7
3
13
g, 3.99 mmol) in diphenyl ether (5 mL) was heated at reflux under
for 48 h. The resulting mixture was cooled to 25 °C and then diluted
3
) δ 110.7, 118.8, 127.3,
N
2
128.0, 131.1, 131.5, 132.0, 138.4, 139.8, 140.9, 144.6; HRMS (ESI)
J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007 4319

A R T I C L E S
Maly et al.
Figure 18. (a) View of the structure of crystals of tecton 8 grown from DMSO/acetone, showing how molecules are linked into chains by hydrogen bonds
of motif I. Atoms of hydrogen appear in white; carbon in gray; and nitrogen in blue. (b) Additional view of the structure showing how hydrogen bonds
involving bridging molecules of DMSO link each tecton (red) to two additional neighbors in adjacent chains (green).
3
3
calcd for C46
for C46 : C, 87.04; H, 4.13; N, 8.83. Found: C, 86.93; H, 3.77;
N, 8.88.
,2,4,5-Tetrakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]-3,6-
diphenylbenzene (5). 1,2,4,5-Tetrakis(4-cyanophenyl)-3,6-diphenyl-
benzene (14; 160 mg, 0.252 mmol) and dicyandiamide (106 mg, 1.26
mmol) were added to a solution of KOH (55 mg, 0.98 mmol) in
H
26
N
4
+ H m/e 635.2230, found 635.2232. Anal. Calcd
3
CDCl ) δ 6.59 (d, 2H, J ) 8.4 Hz), 6.65 (d, 4H, J ) 8.4 Hz), 6.95
3
3
3
H N
26 4
(d, 4H, J ) 8.4 Hz), 7.07 (d, 2H, J ) 8.4 Hz), 7.13 (d, 4H, J ) 8.3
3
13
Hz), 7.32 (d, 4H, J ) 8.4 Hz), 7.45 (s, 1H); C NMR (100 MHz,
CDCl ) δ 120.8, 121.0, 121.6, 129.3, 130.9, 131.1, 131.5, 131.7, 133.1,
133.2, 138.4, 138.7, 138.7, 140.1, 140.5, 141.0. Anal. Calcd for
: C, 50.69; H, 2.48. Found: C, 51.29; H, 2.39.
Pentakis(4-cyanophenyl)benzene (17). Pentakis(4-bromophenyl)-
1
3
36 5
C H21Br
2
-methoxyethanol (5 mL), and the mixture was heated at reflux for 12
benzene (16; 1.34 g, 1.57 mmol) and CuCN (1.05 g, 11.7 mmol) were
h. The resulting mixture was cooled to 25 °C and diluted with water.
The precipitate was collected by filtration, washed with hot water and
ethanol, and dried to give 1,2,4,5-tetrakis[4-(2,4-diamino-1,3,5-triazin-
combined in dry DMF (10 mL), and the mixture was heated at reflux
under N for 18 h. The resulting mixture was then cooled to 25 °C and
2
poured into water. The precipitate was collected by filtration and washed
with water and then with water/ethylenediamine (3:1 v/v). The solid
residue was suspended in CH Cl and washed repeatedly with water/
6
-yl)phenyl]-3,6-diphenylbenzene (5; 204 mg, 0.210 mmol, 83%) as a
1
colorless solid: mp > 300 °C; H NMR (400 MHz, DMSO-d
6
) δ 6.61
2
2
3
(
br s, 16H), 6.8-6.9 (m, 10H), 6.95 (d, 8H, J ) 8.4 Hz), 7.67 (d, 8H,
ethylenediamine until the aqueous washings were colorless. The organic
phase was then washed with 1 M aqueous HCl and brine, dried over
3
13
J ) 8.4 Hz); C NMR (100 MHz, DCOOD) 126.7, 126.7, 127.2,
27.5, 131.3, 132.5, 138.8, 139.6, 140.4, 147.1, 160.8, 163.4; HRMS
ESI) calcd for C54
1
MgSO , and filtered. Removal of volatiles by evaporation under reduced
4
(
H
42
N
20 + H m/e 971.3974, found 971.4007.
pressure left a residue that was purified by flash chromatography (100%
Pentaphenylbenzene (15).28 Tetraphenylcyclopentadienone (3.84 g,
CH
2 2
Cl ) to give pentakis(4-cyanophenyl)benzene (17; 0.280 g, 0.480
1
9
.99 mmol) and phenylacetylene (1.1 mL, 10 mmol) were combined
mmol, 31%) as a colorless solid: mp > 300 °C; H NMR (400 MHz,
CDCl ) δ 6.85 (d, 2H, J ) 8.2 Hz), 6.91 (d, 4H, J ) 8.2 Hz), 7.20
3
(d, 4H, J ) 8.3 Hz), 7.27 (d, 2H, J ) 8.2 Hz), 7.32 (d, 4H, J ) 8.2
Hz), 7.52 (d, 4H, J ) 8.3 Hz), 7.56 (s, 1H); C NMR (100 MHz,
CDCl ) δ 111.6, 111.8, 112.1, 118.3, 118.3, 118.6, 130.7, 131.8, 131.9,
132.0, 132.1, 132.2, 132.5, 138.7, 140.5, 140.8, 143.1, 143.4, 144.6;
HRMS (ESI) calcd for C41 + Na m/e 606.16892, found
606.16852. Anal. Calcd for C41 + 0.25 CH Cl : C, 81.91; H,
3.58; N, 11.58. Found: C, 82.03; H, 3.59; N, 11.63.
3
3
in diphenyl ether (10 mL), and the mixture was heated at reflux under
for 30 min. During this time, the mixture became light orange. The
3
3
3
N
2
3
13
mixture was cooled to 25 °C and diluted with ethanol (150 mL). The
resulting precipitate was collected by filtration, washed with ethanol
3
and hexane, and dried to give pentaphenylbenzene (15; 4.16 g, 9.07
1
mmol, 91%) as a colorless solid: H NMR (400 MHz, CDCl
(
3
) δ 6.83
21 5
H N
m, 2H), 6.90 (m, 7H), 6.96 (m, 6H), 7.19 (m, 10 H), 7.63 (s, 1H); 13
C
H
21
N
5
2
2
NMR (100 MHz, CDCl ) δ 125.8, 126.0, 126.7, 127.1, 127.4, 128.0,
3
1
30.4, 131.8, 131.9, 132.0, 139.7, 140.4, 140.8, 141.2, 142.1, 142.2.
Pentakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]benzene (6).
Pentakis(4-cyanophenyl)benzene (17; 255 mg, 0.437 mmol), dicyan-
diamide (370 mg, 4.40 mmol), and KOH (123 mg, 2.19 mmol) were
combined in 2-methoxyethanol (5 mL), and the mixture was heated at
reflux for 19 h. The resulting mixture was cooled to 25 °C and poured
into water. The precipitate was collected by filtration, washed with
hot water and methanol, and then dried to give pentakis[4-(2,4-diamino-
1,3,5-triazin-6-yl)phenyl]benzene (6; 335 mg, 0.334 mmol, 76%) as a
Pentakis(4-bromophenyl)benzene (16). Pentaphenylbenzene (1.73
g, 3.77 mmol) was spread in a thin layer at the bottom of a beaker and
covered with neat bromine (6.5 mL, 130 mmol). The mixture was
allowed to stand overnight at 25 °C. The crude product was washed
with ethanol and hexane, dried, recrystallized from xylenes, and dried
again to give pure pentakis(4-bromophenyl)benzene (16; 1.88 g, 2.20
1
mmol, 58%) as a colorless solid: mp > 300 °C; H NMR (400 MHz,
4320 J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007

H-Bonded Crystals from Hexaphenylbenzene Derivatives
A R T I C L E S
1
3J ) 8.3 Hz); HRMS (ESI) calcd for C44
found 847.3663.
colorless solid: mp > 300 °C; H NMR (400 MHz, DMSO-d
6
) δ 6.6-
H
38
N
20 + H m/e 847.3661,
3
3
6
7
(
.8 (br m, 20H), 6.93 (d, 2H, J ) 8.4 Hz), 6.97 (d, 4H, J ) 8.2 Hz),
.27 (d, 4H, J ) 8.2 Hz), 7.69 (s, 1H), 7.70 (d, 2H, J ) 8.4 Hz), 7.75
d, 4H, J ) 8.2 Hz), 8.02 (d, 4H, J ) 8.2 Hz); C NMR (100 MHz,
DMSO-d ) δ 127.0, 127.3, 128.0, 130.4, 131.9, 132.0, 132.0, 135.4,
35.7, 136.2, 139.5, 141.0, 141.8, 142.8, 143.2, 144.2, 168.1, 168.2,
3
3
1,2,4,5-Tetrakis(4-cyanophenyl)benzene (21). A mixture of 1,2,4,5-
tetrabromobenzene (0.394 g, 1.00 mmol) and 4-cyanophenylboronic
acid (0.882 g, 6.00 mmol) in toluene (80 mL), ethanol (40 mL), and
aqueous K CO (40 mL, 2 M) was degassed by allowing N to bubble
3
3
13
6
1
1
1
2
3
2
68.2, 170.7, 170.9, 170.9; HRMS (ESI) calcd for C51
004.40495, found 1004.40531.
41
H N25 + H m/e
3 4
through it. Pd(PPh ) (115 mg, 0.100 mmol) was then added, and the
mixture was degassed again. The mixture was heated at 90 °C for 24
h under N and was then exposed to air for 1 h to oxidize the catalyst.
1
,4-Dimethyl-2,3,5,6-tetraphenylbenzene (18).29 A stirred mixture
of the dimer of 2,5-dimethyl-3,4-diphenylcyclopentadienone (2.00 g,
.84 mmol) and diphenylacetylene (2.05 g, 11.5 mmol) in diphenyl
ether (5 mL) was heated at reflux for 2 h. During this time, the mixture
turned deep red and then faded to orange. Slow cooling yielded crystals
after 24 h, which were collected by filtration and washed with hexane.
The product was further purified by recrystallization from xylenes,
giving 1,4-dimethyl-2,3,5,6-tetraphenylbenzene (18; 2.54 g, 6.19 mmol,
1%) as a colorless solid: mp > 300 °C (lit. 363-365 °C); H NMR
400 MHz, CDCl ) δ 1.80 (s, 6H), 7.05 (m, 12H), 7.13 (m, 8H).
,4-Dimethyl-2,3,5,6-tetrakis(4-bromophenyl)benzene (19). 1,4-
Dimethyl-2,3,5,6-tetraphenylbenzene (3.50 g, 8.52 mmol) was powdered
and covered with neat bromine (35 mL). The mixture was kept at 25
2
The resulting mixture was partitioned between toluene (100 mL) and
aqueous NaOH (50 mL, 1 M). The organic phase was separated and
treated with acetone cyanohydrin (3 mL) and triethylamine (3 mL).
As the mixture was stirred for 1 h, it turned from black to yellow. The
mixture was filtered through silica gel, using CHCl to help elute the
3
product. Volatiles were then removed from the filtrate by evaporation
under reduced pressure. Recrystallization of the residue from dioxane,
3
2
9
1
8
3
followed by repeated dissolution of the product in CHCl and
evaporation to eliminate dioxane, yielded 1,2,4,5-tetrakis(4-cyano-
(
3
phenyl)benzene (21; 0.396 g, 0.821 mmol, 82%) as a colorless solid:
1
1
3
mp > 300 °C; H NMR (400 MHz, DMSO-d
6
) δ 7.44 (d, 8H, J ) 8.2
3
13
Hz), 7.63 (s, 2H), 7.80 (d, 8H, J ) 8.2 Hz); C NMR (100 MHz,
6
DMSO-d ) 111.06, 119.49, 131.61, 133.13, 133.66, 139.52, 144.98;
°
C in the dark for 24 h and was then added to stirred ethanol (125 mL)
precooled to -78 °C. The resulting solid was separated by filtration
HRMS (ESI) calcd for C34
18 4
H N
+ H m/e 483.16042, found 483.15952.
and washed with cold ethanol (25 mL) and then with small portions of
1,2,4,5-Tetrakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]ben-
zene (8). 1,2,4,5-Tetrakis(4-cyanophenyl)benzene (0.340 g, 0.705
mmol), dicyandiamide (0.296 g, 3.52 mmol), and powdered KOH
(0.198 g, 3.53 mmol) were suspended in 2-methoxyethanol (10 mL).
The mixture was heated at reflux for 24 h, cooled to 25 °C, and treated
with water (10 mL). The resulting suspension was filtered, and the
solid was washed with boiling water and then with cold methanol.
Drying in air yielded 1,2,4,5-tetrakis[4-(2,4-diamino-1,3,5-triazin-6-
yl)phenyl]benzene (8; 0.479 g, 0.585 mmol, 83%) as a colorless solid.
Further purification was achieved by dissolving the product in hot
DMSO, filtering, and reprecipitating the solid by adding four volumes
of ethyl acetate. The product was collected by filtration and freed of
5
% (w/v) aqueous Na
xylenes afforded 1,4-dimethyl-2,3,5,6-tetrakis(4-bromophenyl)benzene
19; 5.00 g, 6.89 mmol, 81%) as a colorless solid. An analytically pure
2 2 3
S O (total of 75 mL). Recrystallization from
(
sample was obtained by further recrystallization from toluene: mp >
1
3
3
8
5
00 °C; H NMR (400 MHz, CDCl
3
) δ 1.72 (s, 6H), 6.88 (d, 8H, J )
3
.2 Hz), 7.31 (d, 8H, J ) 8.2 Hz). Anal. Calcd for C32
2.93; H, 3.05. Found: C, 52.57; H, 2.72.
H22Br
4
: C,
1
,4-Dimethyl-2,3,5,6-tetrakis(4-cyanophenyl)benzene (20). A mix-
ture of 1,4-dimethyl-2,3,5,6-tetrakis(4-bromophenyl)benzene (0.500 g,
.689 mmol) and CuCN (0.617 g, 6.89 mmol) in dry DMF (40 mL)
was heated at reflux under N for 42 h. The mixture was cooled to 25
C, water (80 mL) was added, and the resulting precipitate was collected
0
2
1
DMSO by trituration with ethyl acetate: mp > 300 °C; H NMR (400
°
3
MHz, DMSO-d
(
1
6
) δ 6.75 (br s, 16H), 7.32 (d, 8H, J ) 8.3 Hz), 7.65
by filtration. The solid was then washed with a 30% aqueous solution
of ethylenediamine until the washings were colorless. The solid was
3
13
s, 2H), 8.10 (d, 8H, J ) 8.3 Hz); C NMR (100 MHz, DMSO-d
6
) δ
27.4, 129.4, 132.1, 135.6, 139.0, 142.6, 167.3, 169.8; HRMS (ESI)
20 + H m/e 819.3348, found 819.3346.
treated with CH
ethylenediamine, then with water, and finally with brine. The organic
phase was dried over anhydrous MgSO and filtered, and volatiles were
then removed by evaporation under reduced pressure. Flash chroma-
tography on silica gel (100% CH Cl ) afforded 1,4-dimethyl-2,3,5,6-
tetrakis(4-cyanophenyl)benzene (20; 0.231 g, 0.452 mmol, 66%) as a
2 2
Cl , and the suspension was washed with 30% aqueous
34
calcd for C42H N
X-ray Crystallographic Studies. Data were collected using (1) a
Bruker AXS SMART 4K/Platform diffractometer or (2) a Bruker
Microstar diffractometer with Cu KR radiation at 100, 200, or 240 K.
Structures were solved by direct methods using SHELXS-97 and refined
4
2
2
1
37
colorless solid: mp > 300 °C; H NMR (400 MHz, CD
6
2
Cl
2
) δ 1.72 (s,
using SHELXL-97. All non-hydrogen atoms were refined anisotro-
3
3
13
H), 7.15 (d, 8H, J ) 8.4 Hz), 7.50 (d, 8H, J ) 8.4 Hz); C NMR
pically, whereas hydrogen atoms were placed in ideal positions and
defined as riding atoms.
(
100 MHz, CD Cl ) δ 19.5, 111.3, 119.1, 131.3, 131.7, 132.4, 140.3,
2
2
1
5
45.7; HRMS (ESI) calcd for C36
11.19221.
H
22
N
4
+ H m/e 511.19172, found
Structure of Crystals of Hexakis[4-(2,4-diamino-1,3,5-triazin-6-
yl)phenyl]benzene (4) Grown from DMSO/THF. Crystals were found
to belong to the triclinic space group P 1h with a ) 17.770(2) Å, b )
1,2,4,5-Tetrakis[4-(2,4-diamino-1,3,5-triazin-6-yl)phenyl]-3,6-di-
2
1
1.235(3) Å, c ) 21.691(2) Å, R ) 98.400(6)°, â ) 110.518(5)°, γ )
methylbenzene (7). 1,4-Dimethyl-2,3,5,6-tetrakis(4-cyanophenyl)ben-
zene (0.200 g, 0.392 mmol), dicyandiamide (0.527 g, 6.27 mmol), and
powdered KOH (0.056 g, 1.0 mmol) were suspended in 2-methoxy-
ethanol (5 mL). The reaction mixture was heated at reflux for 24 h,
cooled to 25 °C, and treated with water (5 mL). The resulting precipitate
was separated by filtration and washed successively with boiling water,
methanol, and dichloromethane to give 1,2,4,5-tetrakis[4-(2,4-diamino-
3
3
03.475(6)°, V ) 7217.9(14) Å , Dcalcd ) 1.128 g/cm , and Z ) 2.
2
Full-matrix least-squares refinements on F led to final residuals R
f
)
0
>
.1160, R
2σ(I).
Structure of Crystals of Hexakis[4-(2,4-diamino-1,3,5-triazin-6-
w
) 0.2902, and GOF ) 1.096 for 23 987 reflections with I
yl)phenyl]benzene (4) Grown from DMSO/Toluene. Crystals were
found to belong to the triclinic space group P 1h with a ) 8.4178(11)
Å, b ) 16.424(2) Å, c ) 20.251(3) Å, R ) 105.291(5)°, â ) 97.289-
1,3,5-triazin-6-yl)phenyl]-3,6-dimethylbenzene (7; 0.260 g, 0.307 mmol,
7
8%) as a colorless solid. Further purification could be achieved by
3
3
(1) dissolving the compound (40 mg) in DMSO (20 mL) with the
(6)°, γ ) 93.544(6)°, V ) 2665.7(6) Å , Dcalcd ) 1.347 g/cm , and Z
2
assistance of slight heating and sonication, (2) filtering the resulting
mixture through a 0.45 µm PTFE filter, (3) adding a supernatant layer
of anhydrous ethanol (120 mL) on top of the filtered solution, and (4)
) 2. Full-matrix least-squares refinements on F led to final residuals
R
f
) 0.0792, R
w
) 0.1865, and GOF ) 1.045 for 5999 reflections
with I > 2σ(I).
keeping the mixture undisturbed in a closed vessel overnight until small
Structure of Crystals of Hexakis[4-(2,4-diamino-1,3,5-triazin-6-
yl)phenyl]benzene (4) Grown from DMSO/Benzene. Crystals were
found to belong to the trigonal space group R 3h with a ) b ) 38.6740-
1
crystals appeared: mp > 300 °C; H NMR (400 MHz, DMSO-d
6
) δ
3
1
.79 (s, 6H), 6.68 (br s, 16H), 7.17 (d, 8H, J ) 8.3 Hz), 8.00 (d, 8H,
J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007 4321

A R T I C L E S
Maly et al.
3
3
3
3
(
9) Å, c ) 10.010(3) Å, V ) 12966(4) Å , Dcalcd ) 1.177 g/cm , and
) 104.885(2)°, V ) 6307.2(4) Å , Dcalcd ) 0.940 g/cm , and Z ) 2.
2
2
Z ) 3. Full-matrix least-squares refinements on F led to final residuals
) 0.0587, R ) 0.1369, and GOF ) 1.028 for 5226 reflections
with I > 2σ(I).
Full-matrix least-squares refinements on F led to final residuals R
f
)
R
f
w
0.0730, R
w
) 0.1611, and GOF ) 1.181 for 1988 reflections with I >
2σ(I).
Structure of Crystals of Hexakis[4-(2,4-diamino-1,3,5-triazin-6-
yl)phenyl]benzene (4) Grown from Formic Acid/Methanol. Crystals
Structure of Crystals of 1,2,4,5-Tetrakis[4-(2,4-diamino-1,3,5-
triazin-6-yl)phenyl]-3,6-dimethylbenzene (7) Grown from DMSO/
Methanol. Crystals were found to belong to the monoclinic space group
were found to belong to the trigonal space group R 3h with a ) b )
3
2
2.8070(9) Å, c ) 17.2915(16) Å, V ) 7789.3(8) Å , Dcalcd ) 0.761
1
P2 /c with a ) 34.706(2) Å, b ) 14.9704(9) Å, c ) 12.064(7) Å, â )
3
2
3
3
g/cm , and Z ) 3. Full-matrix least-squares refinements on F led to
final residuals R ) 0.0614, R ) 0.1513, and GOF ) 1.048 for 1912
reflections with I > 2σ(I).
91.318(2)°, V ) 6246.8(7) Å , Dcalcd ) 1.271 g/cm , and Z ) 4. Full-
2
matrix least-squares refinements on F led to final residuals R
f
) 0.0794,
f
w
R
w
) 0.1704, and GOF ) 1.115 for 8635 reflections with I > 2σ(I).
Structure of Crystals of 1,2,4,5-Tetrakis[4-(2,4-diamino-1,3,5-
triazin-6-yl)phenyl]benzene (8) Grown from DMSO/Acetone. Crys-
tals were found to belong to the monoclinic space group P2 /c with a
8.9750(3) Å, b ) 22.7525(6) Å, c ) 21.9316(8) Å, â ) 101.4980-
Structure of Crystals of 1,2,4,5-Tetrakis[4-(2,4-diamino-1,3,5-
triazin-6-yl)phenyl]-3,6-diphenylbenzene (5) Grown from DMSO/
Acetonitrile. Crystals were found to belong to the monoclinic space
group C2/c with a ) 40.3960(13) Å, b ) 20.6327(7) Å, c ) 12.0265-
1
)
3
3
3
3
(10)°, V ) 4388.6(2) Å , D
least-squares refinements on F led to final residuals R ) 0.0651, R
) 1.329 g/cm , and Z ) 2. Full-matrix
(
)
R
4) Å, â ) 99.926(2)°, V ) 9873.8(6) Å , Dcalcd ) 1.239 g/cm , and Z
calcd
2
2
4. Full-matrix least-squares refinements on F led to final residuals
) 0.0622, R ) 0.1476, and GOF ) 1.003 for 6853 reflections
with I > 2σ(I).
f
w
)
0.1491, and GOF ) 1.085 for 7838 reflections with I > 2σ(I).
f
w
Acknowledgment. We are grateful to the Natural Sciences
Structure of Crystals of Pentakis[4-(2,4-diamino-1,3,5-triazin-
-yl)phenyl]benzene (6) Grown from DMSO/Acetone. Crystals were
found to belong to the monoclinic space group C2/c with a ) 31.282-
and Engineering Research Council of Canada, the Minist e` re de
l’ EÄ ducation du Qu e´ bec, the Canada Foundation for Innovation,
the Canada Research Chairs Program, and Universit e´ de
Montr e´ al for financial support. We thank Dr. Alexandra Furtos
and Karine Venne for obtaining mass spectra. In addition, we
are grateful to Prof. Jurgen Sygusch for providing access to a
diffractometer equipped with a rotating anode.
6
(
8
15) Å, b ) 24.617(3) Å, c ) 11.704(9) Å, â ) 108.302(4)°, V )
3
3
557(8) Å , Dcalcd ) 1.265 g/cm , and Z ) 4. Full-matrix least-squares
2
refinements on F led to final residuals R
f
) 0.0890, R ) 0.1426, and
w
GOF ) 1.00 for 8129 reflections with I > 2σ(I).
Structure of Crystals of 1,2,4,5-Tetrakis[4-(2,4-diamino-1,3,5-
triazin-6-yl)phenyl]-3,6-dimethylbenzene (7) Grown from DMSO/
Dioxane. Crystals were found to belong to the monoclinic space group
C2/m with a ) 20.4638(8) Å, b ) 21.4603(8) Å, c ) 15.8607(6) Å, â
Supporting Information Available: Additional crystallo-
graphic details, including ORTEP drawings and tables of
structural data for compounds 4-8. This material is available
free of charge via the Internet at http://pubs.acs.org.
(
37) Sheldrick, G. M. SHELXS-97, Program for the Solution of Crystal Structures
and SHELXL-97, Program for the Refinement of Crystal Structures;
Universit a¨ t G o¨ ttingen: Germany, 1997.
JA067571X
4322 J. AM. CHEM. SOC.
9
VOL. 129, NO. 14, 2007