Crystal engineering in the gem-alkynol family: Interplay between strong and weak interactions in structures of 2,3,5,6-tetrahalo[F,Cl,Br]-trans-1,4-diethynylcyclohexa-2,5-diene-1,4-diols

Article abstract of DOI:10.1107/S0108768100011496

Structures of the title compounds are all mediated by strong cooperative arrangements of O - H...O hydrogen bonds, supported by a variety of weaker interactions which affect the type of O - H...O synthon that is formed. The tetrafluoro compound contains hexameric O - H...O synthons in a supramolecular chair conformation, together with C≡C -H...F interactions. However, the tetrachloro and tetrabromo compounds both form tetrameric O - H...O synthons. This dominant pattern is supported by halogen...halogen interactions having one C - Cl[Br]...Cl[Br] angle close to 180° and the other close to 90°, and by C≡C - H...Cl[Br] interactions.

Full text of DOI:10.1107/S0108768100011496

research papers
Crystal engineering in the gem-alkynol family:
Acta Crystallographica Section B
Structural
Science
interplay between strong and weak interactions in
structures of 2,3,5,6-tetrahalo[F,Cl,Br]-trans-1,4-
diethynylcyclohexa-2,5-diene-1,4-diols
ISSN 0108-7681
N. N. L. Madhavi,a Gautam R.
Desiraju,a Claire Bilton,b
Judith A. K. Howardb and
Frank H. Allenc*
Structures of the title compounds are all mediated by strong
cooperative arrangements of OÐHÁ Á ÁO hydrogen bonds,
Received 31 May 2000
Accepted 22 August 2000
supported by a variety of weaker interactions which affect the
type of OÐHÁ Á ÁO synthon that is formed. The tetra¯uoro
compound contains hexameric OÐHÁ Á ÁO synthons in a
supramolecular chair conformation, together with CꢁCÐ
HÁ Á ÁF interactions. However, the tetrachloro and tetrabromo
compounds both form tetrameric OÐHÁ Á ÁO synthons. This
dominant pattern is supported by halogenÁ Á Áhalogen interac-
tions having one CÐCl[Br]Á Á ÁCl[Br] angle close to 180ꢂ and
the other close to 90ꢂ, and by CꢁCÐHÁ Á ÁCl[Br] interactions.
aSchool of Chemistry, University of Hyderabad,
Hyderabad 500 046, India, bDepartment of
Chemistry, University of Durham, South Road,
Durham DH1 3LE, England, and cCambridge
Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, England
Correspondence e-mail: allen@ccdc.cam.ac.uk
1. Introduction
Crystal engineering methodologies attempt to identify
common patterns in series of crystal structures of related
molecules in order to understand these patterns in terms of
the mutual interplay between particular types of inter-
molecular interactions (see e.g. Nangia & Desiraju, 1998;
Desiraju, 1997). The identi®cation of robust and reproducible
interaction patterns or supramolecular synthons (Desiraju,
1995) is a major aim of these studies, so as to establish
correspondences between molecular and crystal structures
(see e.g. Ermer & Eling, 1994; Allen et al., 1997).
Supramolecular synthons based on strong hydrogen bonds
have been well documented (Desiraju, 1995) and the most
common patterns formed by such bonds have been char-
acterized (Allen et al., 1999) using the Cambridge Structural
Database (CSD; Allen & Kennard, 1993). The involvement of
weaker interactions, e.g. CÐHÁ Á ÁO bonds, has also attracted
signi®cant attention (see e.g. Desiraju, 1991; Desiraju &
Steiner, 1999), but others such as CÐHÁ Á Áꢀ(arene) (Malone et
al., 1997; Madhavi et al., 1997) and CꢁCÐHÁ Á Áꢀ(CꢁC)
(Steiner et al., 1996; Nishio et al., 1998) are less well under-
stood. A particular dif®culty arises when two or more inter-
actions, strong or weak, are in competition (interaction
interference) and in such cases predicting the likely interac-
tion patterns in crystal structures becomes a highly complex
task.
Recently, we have synthesized a variety of compounds
containing the gem-alkynol functionality. Such structures are
likely to contain both strong OÐHÁ Á ÁO bonds and weaker
interactions involving the acidic proton and the ꢀ-system of
the CꢁCÐH group, thus providing an opportunity to char-
acterize the latter and study their competition with the former.
A CSD study (Madhavi et al., 2000) has shown that the 94
published structures of gem-alkynols exhibit a bewildering
variety of interaction patterns, involving OÐHÁ Á ÁO,
# 2000 International Union of Crystallography
Printed in Great Britain ± all rights reserved
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Madhavi et al. Crystal engineering in gem-alkynols 1063

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CÐHÁ Á ÁO, OÐHÁ Á Áꢀ and CÐHÁ Á Áꢀ contacts. However, the
molecules within this sample are chemically diverse and
sometimes complex. More than half of the sample contain
Our approach, therefore, has been to synthesize a series of
gem-alkynols in which the substituents are varied in a
controlled manner, beginning with compounds (1) (Bilton et
al., 1999), (2), (3) and (4) (Madhavi et al., 2000) which contain
only the gem-alkynol functionality (together with CÐH
groups of differing hydrogen acidity). Structure (1) (Bilton et
al., 1999) represents a unique example of the simultaneous
occurrence of both conformational polymorphism and
conformational isomorphism (Bernstein, 1987), and also forms
a pseudopolymorphic monohydrate. All three forms of (1)
aggregate through helical trimeric OÐHÁ Á ÁO synthons, with
no interference from weaker interactions involving the
CꢁCÐH groups. Structure (2) shows a simple in®nite OÐ
HÁ Á ÁO cooperative chain, reinforced by CꢁCÐHÁ Á ÁO and
C(ring)ÐHÁ Á Áꢀ interactions. In contrast, structures (3) and (4)
both contain the cyclic synthons (5) and (6), each composed of
alternating strong (OÐHÁ Á ÁO) and weak (CꢁCÐHÁ Á ÁO or
CꢁCÐHÁ Á Áꢀ) hydrogen bonds.
Thus encouraged that structural repetitivity can be
preserved in such a fragile system, we have now selectively
embellished structure (2) with the tetrahalo functionality of
(7) (F4), (8) (Cl4) and (9) (Br4), whose structures are reported
in this paper. Here the C(ring)ÐH donors are all replaced by
halogens and the interest is to see how possible halogen-
Á Á Áhalogen and CÐHÁ Á Áhalogen interactions might interfere
with, or reinforce, the OÐHÁ Á ÁO bonds observed in (2)
(Madhavi et al., 2000). Further, it is of interest to see if
structural repetitivity is preserved in two or more structures of
this series and to compare any synthons which may occur with
those [(5) and (6)] which were observed in structures (3) and
(4).
The role of halogen atoms in weak interactions is a matter
of long-standing interest (see Desiraju & Steiner, 1999) and
the nature of halogenÁ Á Áhalogen interactions, particularly CÐ
ClÁ Á ÁClÐC, has been the subject of considerable debate over
the past decade. Desiraju & Parthasarathy (1989) and Pedir-
eddi et al. (1994) used the CSD to identify the occurrence of
two interaction types. If we denote the larger of the two CÐ
ClÁ Á ÁCl angles as ꢁ1, and the smaller as ꢁ2, then type I inter-
actions (10) have ꢁ1 = ꢁ2 and type II have ꢁ1 = 180ꢂ and ꢁ2 =
90ꢂ. Linear CÐClÁ Á ÁClÐC systems, ꢁ1 = ꢁ2 = 180ꢂ, are seldom
observed. The vast majority of type I examples arise from
interactions across a crystallographic centre of symmetry,
while type II interactions (11) were deemed to arise due to the
increasing polarizability of the halogen (F < Cl < Br < I).
Calculations of interaction energies using intermolecular
perturbation theory (Hayes & Stone, 1984) have been carried
out for CÐClÁ Á ÁClÐC interactions (Price et al., 1994) and CÐ
ClÁ Á ÁO interactions (Lommerse et al., 1996). In broad terms,
these authors agree that carbon-bound halogens in suf®ciently
electron-withdrawing environments present an anisotropic
charge distribution, ꢂ+ forward of the halogen along the C±
halogen bond vector (ꢁ1 = 180ꢂ), and ꢂ perpendicular to the
bond vector (ꢁ2 = 90ꢂ). In these cases, stabilizing interaction
other functional groups which are capable of acting as strong
hydrogen-bond donors or acceptors (or both), and this
introduces a wholly avoidable complication into the study of a
chemical system in which strong and weak interactions are in a
delicate balance.
1
energies of up to 10 kJ mol can be attained for linear CÐ
ClÁ Á ÁO interactions, about one-third of the interaction energy
for a strong hydrogen bond (Lommerse et al., 1996). These
ꢀ
1064 Madhavi et al. Crystal engineering in gem-alkynols
Acta Cryst. (2000). B56, 1063±1070

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authors also provide computational evidence that the inter-
actions become stronger for the more readily polarisable
halogens, Br and I, but are not exhibited by F.
centres at 0, 0.5, 0; 0.5, 0, 0.5 and 0.5, 0.5, 0.5, as illustrated in
Fig. 1. The dominant interaction pattern is formed by six OÐ
HÁ Á ÁO hydrogen bonds in a supramolecular chair conforma-
tion (Fig. 2a). All hydroxy groups are involved in forming this
synthon, which is located on the inversion centre at 0, 0.5, 0.5.
The hydrogen-bond geometry (Table 3) describes three strong
OÐHÁ Á ÁO bonds, which deviate by a maximum of 19ꢂ from
linearity at H. The three independent molecules each contri-
bute two OH groups to synthon formation and the molecules
of each independent pair are located at 1,4 positions
(numbering only O atoms in the synthon ring) relative to one
another, such that they adopt an antiparallel disposition (Fig.
2a). Each hexameric synthon is therefore connected to six
others through molecular spacers, and acts as an octahedral
supramolecular node, which extends the network in three
dimensions.
2. Experimental
2.1. Syntheses
Compounds (7), (8) and (9) were synthesized from the
appropriate diketone, 2,3,5,6-tetrahalo[X]-cyclohexa-2,5-
diene-1,4-dione, using a two-step procedure. All operations
were carried out in a dry nitrogen atmosphere using standard
syringe-septum techniques.
(i) A solution of trimethylsilylacetylene (4.4 mmol) in thf
(15 ml) was mixed with n-butyllithium (4.2 mmol) at 195 K.
After stirring for 15 min a solution of the appropriate ketone,
X = F, Cl or Br, was added dropwise and stirring was continued
for 30 min at 195 K and for a further 1 h at room temperature.
Brine was added to the reaction mixture and the products
were extracted with diethylether. The organic phase was dried
over magnesium sulfate, ®ltered and the ether removed.
(ii) The solid product from step (i) was dissolved in
methanol and methanolic KOH was added slowly and stirred
for 1 h at room temperature. Water was added to the reaction
mixture and the product was extracted with ethylacetate. The
product was dried over magnesium sulfate and the solvent
removed. Crystals were obtained by puri®cation of the crude
material (column chromatography) followed by recrystalliza-
tion.
Two of the three independent ethynyl groups form three
CÐHÁ Á ÁFÐC interactions (Table 3) within a van der Waals
Ê
Ê
radius sum of 2.67 A [v(F) = 1.47 A (Bondi, 1964); v(H) =
Ê
1.20 A (Rowland & Taylor, 1996)]. The shortest of these has a
Ê
hydrogen-normalized HÁ Á ÁF distance of only 2.34 A, with
directionality angles ꢁ(H) and ꢁ(F) of 171 and 142ꢂ, respec-
tively. One of the CÐHÁ Á ÁF bonds forms a dimeric motif
between molecules related by an a-translation, and this dimer
and the OÐHÁ Á ÁO hexamer alternate along the b axis. Other
CÐHÁ Á ÁF interactions link translation-related molecules
along the b axis. There are two FÁ Á ÁF contacts (Table 3) which
are respectively just below and just above the van der Waals
Ê
Ê
sum of 2.94 A. The shortest of these [2.86 (2) A] has ꢁ1, ꢁ2 =
Melting points: (7) 405±406 K; (8) 478±479 K (with sublima-
tion); (9) 493 K (with decomposition). Spectroscopic data
have been deposited.1
173.72 (7) and 90.58 (6)ꢂ, respectively, which is very close to
2.2. Crystal structure analyses
X-ray diffraction intensities for (7), (8) and (9) were
collected at 150 K (Oxford Cryosystems cryostat) on a Bruker
SMART CCD diffractometer (Bruker Systems Inc., 1999a)
using Mo Kꢃ X-radiation. Data were processed using the
Bruker SAINT package (Bruker Systems Inc., 1999b), with
structure solution and re®nement using SHELX97 (Sheldrick,
1997). Data for (9) were corrected for absorption using
SADABS (Sheldrick, 1996). H atoms were located in all three
structures and re®ned freely with isotropic displacement
parameters. Crystal data and details of data collections,
structure solutions and re®nements are given in Table 1.
Atomic coordinates for non-H atoms are given in Table 2.
3. Results and discussion
3.1. 2,3,5,6-Tetrafluoro-trans-1,4-diethynylcyclohexa-2,5-
diene-1,4-diol (7)
ꢀ
Compound (7) crystallizes in space group P1 with three
symmetry-independent molecules occupying distinct inversion
1 Supplementary data for this paper are available from the IUCr electronic
archives (Reference: BM0033). Services for accessing these data are described
at the back of the journal.
Figure 1
Packing diagram of trimeric (7), viewed down the c axis and with the b
axis vertical
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Madhavi et al. Crystal engineering in gem-alkynols 1065

research papers
Table 1
Experimental details.
(7)
(8)
(9)
Crystal data
Chemical formula
Chemical formula weight
Cell setting
C10H4F4O2
232.13
Triclinic
P1
8.9002 (18)
9.2388 (18)
9.6721 (19)
93.73 (3)
98.73 (3)
114.46 (3)
708.3 (2)
3
C10H4Cl4O2
297.93
Tetragonal
I41=a
16.758 (2)
16.758 (2)
8.865 (2)
90
C10H4Br4O2
475.77
Triclinic
P1
8.9147 (3)
12.6402 (5)
12.6547 (5)
85.738 (1)
69.625 (1)
72.72 (1)
1275.76 (8)
4
Space group
Ê
a (A)
Ê
b (A)
Ê
c (A)
ꢃ ꢃꢂ†
ꢄ ꢃꢂ†
ꢅ ꢃꢂ†
90
90
3
Ê
V (A )
2489.6 (7)
8
1.590
Mo Kꢃ
0.71073
505
Z
Dx (Mg m
3
)
Radiation type
1.633
2.477
Mo Kꢃ
0.71073
999
Mo Kꢃ
0.71073
510
Ê
Wavelength (A)
No. of re¯ections for cell
parameters
ꢁ range (ꢂ)
0.16±30.57
0.165
150
5.26±25.31
0.930
150
5.10±23.72
12.599
150
1
ꢆ (mm
)
Temperature (K)
Crystal form
Crystal size (mm)
Crystal colour
Block
0.7 Â 0.3 Â 0.2
Block
0.3 Â 0.3 Â 0.2
Block
0.3 Â 0.2 Â 0.2
Colourless
Colourless
Colourless
Data collection
Diffractometer
Data collection method
Absorption correction
Tmin
Bruker SMART CCD
! scans
Empirical
0.289
0.382
Bruker SMART CCD
! scans
Multi-scan
0.665
0.830
Bruker SMART CCD
! scans
Multi-scan
0.0180
0.0737
Tmax
No. of measured re¯ections
No. of independent re¯ections
No. of observed re¯ections
Criterion for observed re¯ections
Rint
8674
3722
3376
I > 2ꢇ(I)
0.0288
29.88
8404
1421
1202
I > 2ꢇ(I)
0.0432
27.39
14 367
5818
4966
I > 2ꢇ(I)
0.0431
27.48
ꢁmax (ꢂ)
Range of h, k, l
12 ! h ! 12
12 ! k ! 12
13 ! l ! 13
21 ! h ! 20
21 ! k ! 19
9 ! l ! 11
11 ! h ! 11
16 ! k ! 16
16 ! l ! 16
Re®nement
Re®nement on
R‰F2>2ꢇꢃF2†Š
wRꢃF2†
F 2
0.0336
0.0928
1.031
F 2
0.0489
0.1245
1.091
F 2
0.0336
0.0781
1.148
S
No. of re¯ections used in re®nement 3722
1421
82
5818
321
No. of parameters used
H-atom treatment
Weighting scheme
242
All H-atom parameters re®ned
All H-atom parameters re®ned
All H-atom parameters re®ned
w = 1/[ꢇ2(Fo2) + (0.0484P)2 + 0.2454P], w = 1/[ꢇ2(Fo2) + (0.0383P)2 + 5.8833P], w = 1/[ꢇ2(Fo2) + (0.0218P)2 + 4.0324P],
where P = (Fo + 2Fc2)/3
0.001
0.456
0.239
SHELXL (Sheldrick, 1997)
0.080 (5)
where P = (Fo + 2Fc2)/3
0.001
0.589
0.437
SHELXL (Sheldrick, 1997)
0.0178 (11)
International Tables for
Crystallography (1992, Vol. C,
Tables 4.2.6.8 and 6.1.1.4)
where P = (Fo + 2Fc2)/3
0.005
0.797
1.052
None
±
International Tables for
Crystallography (1992, Vol. C,
Tables 4.2.6.8 and 6.1.1.4)
2
2
2
ꢃÁ=ꢇ†
max
3
Ê
Ê
Áꢈmax (e A
)
3
Áꢈmin (e A
Extinction method
)
Extinction coef®cient
Source of atomic scattering factors
International Tables for
Crystallography (1992, Vol. C,
Tables 4.2.6.8 and 6.1.1.4)
Computer programs
Data collection
SMART (Bruker Systems Inc.,
1999a)
SMART (Bruker Systems Inc.,
1999a)
SMART (Bruker Systems Inc.,
1999a)
Cell re®nement
Data reduction
SMART (Bruker Systems Inc.,
1999a)
SAINT (Bruker Systems Inc.,
1999b)
SMART (Bruker Systems Inc.,
1999a)
SAINT (Bruker Systems Inc.,
1999b)
SMART (Bruker Systems Inc.,
1999a)
SAINT (Bruker Systems Inc.,
1999b)
Structure solution
Structure re®nement
Preparation of material for
publication
SHELXS97 (Sheldrick, 1997)
SHELXL97 (Sheldrick, 1997)
SHELXL97 (Sheldrick, 1997)
SHELXS97 (Sheldrick, 1997)
SHELXL97 (Sheldrick, 1997)
SHELXL97 (Sheldrick, 1997)
SHELXS97 (Sheldrick, 1997)
SHELXL97 (Sheldrick, 1997)
SHELXL97 (Sheldrick, 1997)
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1066 Madhavi et al. Crystal engineering in gem-alkynols
Acta Cryst. (2000). B56, 1063±1070

research papers
the geometry (11) expected for type II halogenÁ Á Áhalogen
interactions. Given the hardness of F coupled with existing
computational evidence, we regard this geometry as arising
from crystal packing effects rather than from any speci®c
attractive forces.
3.2. 2,3,5,6-Tetrachloro-trans-1,4-diethynylcyclohexa-2,5-
diene-1,4-diol (8)
Compound (8) crystallizes in the high-symmetry space
group I41/a, with the molecules located on inversion centres
(Z = 8), as illustrated in Fig. 3. Once again, the dominant
interaction pattern is formed by OÐHÁ Á ÁO hydrogen bonds,
ꢀ
but here the synthon is tetrameric and arranged about a 4 axis
(Fig. 2b). The hydrogen-bond geometry is reported in Table 3.
Each molecule of (8) connects two tetramer units, such that
each synthon is connected to four others through molecular
spacers which extend the network to three dimensions.
The fundamental OÐHÁ Á ÁO architecture is supported by a
number of weaker interactions described in Table 3. Both
symmetry-independent Cl atoms are involved in type II
ClÁ Á ÁCl interactions (11), i.e. four such interactions per
molecule, at contact distances that are slightly more than twice
Ê
the isotropic van der Waals radius of Cl (1.75 A; Bondi, 1964),
but within the ranges discussed by Price et al. (1994) and
Lommerse et al. (1996). The shorter of these interactions
Ê
[3.605 (1) A] forms a helical arrangement about a 41 axis,
Ê
while the longer interaction [3.731 (2) A] forms a closed
tetrameric Cl4 synthon, which alternates with the OÐHÁ Á ÁO
ꢀ
tetramer along a 4 axis. This halogen arrangement is remi-
niscent of the recently reported triangulo-trichloro and trian-
gulo-tribromo synthons (Anthony et al., 1998; Thalladi et al.,
1998; Jetti et al., 1999; Broder et al., 2000). Table 3 also reports
a long CꢁCÐHÁ Á ÁCl contact.
3.3. 2,3,5,6-Tetrabromo-trans-1,4-diethynylcyclohexa-2,5-
diene-1,4-diol (9)
Compound (9) crystallizes with each of the four symmetry-
independent molecules located on distinct inversion centres,
as illustrated in Fig. 4. The dominant interaction pattern is
again formed by OÐHÁ Á ÁO hydrogen bonds (see Table 3 for
geometrical details). Each independent molecule contributes
one OH group to the formation of a tetrameric synthon (Fig.
2c) and links adjacent tetramers into a three-dimensional
network that is topologically analogous to that observed in the
chloro compound (8).
The four symmetry-independent molecules are cross-linked
by six different BrÁ Á ÁBr interactions. Four of these are shorter
Ê
than 3.70 A [v(Br) = 1.85 A; Bondi, 1964] and represent
Ê
interpenetration of the van der Waals spheres, while the
Ê
remaining two interactions are up to 0.20 A longer than this
comparator. All six interactions are clearly of type II (11), as
shown by the geometrical data of Table 3. It is clear that the
BrÁ Á ÁBr interactions in (9) are shorter relative to van der
Waals sums than the ClÁ Á ÁCl interactions in (8), in line with the
increased polarizability of Br, and in agreement with indica-
tions from the ab initio calculations of Price et al. (1994) and
Figure 2
(a) Hexameric OÐHÁ Á ÁO synthon in (7); (b) tetrameric OÐHÁ Á ÁO
synthon in (8); (c) tetrameric OÐHÁ Á ÁO synthon in (9).
ꢀ
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Madhavi et al. Crystal engineering in gem-alkynols 1067

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Table 2
Fractional atomic coordinates and equivalent isotropic displacement
Table 2 (continued)
2
parameters (A ).
Ê
x
y
z
Ueq
Ueq ˆ ꢃ1=3†ÆiÆjUijaiajai:aj:
C34
C35
0.1752 (5)
0.1068 (5)
0.0377 (3)
0.0694 (3)
0.9406 (3)
0.9688 (3)
0.0187 (8)
0.0187 (8)
x
y
z
Ueq
(7)
F1
F2
Lommerse et al. (1996). However, in contrast to (8), the
BrÁ Á ÁBr interactions do not form either closed or helical
tetramers.
0.13140 (9)
0.10278 (9)
0.54677 (9)
0.18252 (8)
0.45397 (9)
0.18494 (8)
0.09274 (10)
0.24851 (10)
0.70633 (11)
0.46278 (16)
0.31531 (14)
0.13028 (13)
0.06470 (13)
0.05022 (13)
0.21624 (16)
0.27270 (14)
0.34702 (13)
0.52767 (13)
0.34023 (13)
0.85068 (17)
0.76156 (14)
0.65179 (13)
0.47257 (14)
0.34131 (13)
0.32812 (9)
0.82232 (8)
0.58373 (9)
0.32907 (9)
0.00542 (9)
0.15228 (9)
0.60128 (10)
0.53620 (9)
0.25896 (9)
0.73049 (19)
0.66562 (14)
0.58530 (12)
0.40977 (13)
0.66421 (12)
0.17711 (15)
0.29858 (13)
0.44886 (12)
0.54587 (13)
0.40981 (12)
0.02473 (16)
0.02754 (13)
0.09123 (12)
0.00009 (12)
0.07603 (12)
0.85824 (8)
0.99013 (8)
1.23827 (7)
1.54950 (8)
0.78559 (7)
0.66778 (7)
0.76376 (8)
1.34412 (8)
0.57778 (9)
0.99717 (14)
0.95594 (11)
0.91000 (10)
0.92853 (11)
0.99688 (11)
1.19891 (14)
1.27786 (12)
1.37978 (11)
1.36766 (11)
1.52821 (11)
0.66346 (15)
0.62251 (12)
0.56684 (11)
0.64633 (10)
0.58808 (11)
0.02992 (17)
0.02855 (17)
0.03106 (18)
0.03013 (17)
0.02882 (17)
0.02902 (17)
0.02489 (18)
0.02313 (17)
0.02384 (17)
0.0373 (3)
0.0248 (2)
0.0196 (2)
0.0205 (2)
0.0204 (2)
0.0305 (2)
0.0235 (2)
0.0197 (2)
0.0212 (2)
0.0207 (2)
0.0344 (3)
0.0246 (2)
0.0197 (2)
0.0204 (2)
0.0205 (2)
F11
F12
F21
F22
O1
O11
O21
C1
C2
C3
C4
C5
C11
C12
C13
C14
C15
C21
C22
C23
C24
C25
Three of the four independent ethynyl groups form CꢁCÐ
HÁ Á ÁBr contacts which, with normalized H-atom positions
(Table 3), have HÁ Á ÁBr distances that are at or just below the
Ê
sum of v(Br) and v(H) of 3.05 A. The fourth ethynyl H atom is
directed towards the ꢀ density of a CꢁC bond (Table 3).
3.4. Structural relationships in the trans-1,4-diethynylcyclo-
hexa-2,5-diene-1,4-diols (2), (7)±(9)
Strong cooperative arrangements of OÐHÁ Á ÁO hydrogen
bonds are fundamental to all four structures in this series. In
all cases these arrangements are supported by a variety of
weaker interactions that have signi®cant effects on the type of
OÐHÁ Á ÁO synthon that is formed. Parent 2 (Madhavi et al.,
2000) is the most straightforward, comprising in®nite coop-
erative OÐHÁ Á ÁO chains, together with CꢁCÐHÁ Á ÁO and
C(sp2)ÐHÁ Á Áꢀ(ethynyl) hydrogen bonds.
(8)
Cl1
Cl2
O1
C1
C2
C3
C4
C5
The structure type observed for (2) is not available to (7),
where the four C(sp2)ÐH are replaced by ¯uorines. In
accordance with recent work (Dunitz & Taylor, 1997), no OÐ
HÁ Á ÁF bonds are formed. However, evidence from structures
that contain only C, H and F would indicate that F atoms do
participate in CÐHÁ Á ÁF bonds (Suzuki et al., 1992; Rodham et
al., 1993; Thalladi et al., 1998). CꢁCÐHÁ Á ÁF interactions are
indeed observed in (7), rather than the CꢁCÐHÁ Á ÁO bonds of
(2), and the OÐHÁ Á ÁO bonds now form the hexameric
synthon of Fig. 2(a). We note that the ¯uoro compound (7)
0.77134 (5)
0.61323 (6)
0.89228 (11)
0.8625 (2)
0.84570 (16)
0.82653 (13)
0.75598 (14)
0.68998 (14)
0.61807 (5)
0.71900 (6)
0.72875 (11)
0.5634 (2)
0.62493 (16)
0.70177 (13)
0.69120 (14)
0.73415 (15)
0.00252 (9)
0.01517 (12)
0.1540 (3)
0.3678 (5)
0.3155 (3)
0.2419 (3)
0.1362 (3)
0.1411 (3)
0.0642 (3)
0.0813 (4)
0.0533 (6)
0.0714 (10)
0.0462 (6)
0.0363 (6)
0.0379 (6)
0.0402 (6)
(9)
Br1
Br2
Br11
Br12
Br21
Br22
Br31
Br32
O1
O2
O3
O4
C1
0.79084 (7)
0.84216 (7)
0.78564 (6)
0.48669 (6)
0.26974 (6)
0.40392 (6)
0.40744 (6)
0.23387 (6)
1.0803 (5)
0.7898 (4)
0.0988 (4)
0.0960 (4)
0.7190 (7)
0.8281 (6)
0.9714 (5)
0.9092 (5)
0.9306 (6)
0.5609 (7)
0.5913 (6)
0.6262 (5)
0.6176 (5)
0.5043 (5)
0.1280 (6)
0.0946 (5)
0.0620 (5)
0.1214 (5)
0.1746 (5)
0.2033 (8)
0.1482 (6)
0.0778 (5)
0.18445 (4)
0.08758 (5)
0.43745 (4)
0.68322 (4)
0.38542 (4)
0.42595 (5)
0.09732 (4)
0.17095 (4)
0.1357 (3)
0.3546 (3)
0.3802 (3)
0.1677 (3)
0.0528 (5)
0.0123 (4)
0.0412 (3)
0.0793 (4)
0.0423 (4)
0.2152 (5)
0.2906 (4)
0.3856 (3)
0.4770 (4)
0.5748 (4)
0.6166 (4)
0.5578 (3)
0.4806 (3)
0.4505 (3)
0.4672 (3)
0.2869 (5)
0.2131 (4)
0.1231 (3)
0.59429 (4)
0.33470 (4)
0.62350 (4)
0.67843 (4)
1.13043 (4)
0.85341 (4)
0.86395 (4)
0.93445 (4)
0.6498 (3)
0.3984 (3)
1.1712 (3)
0.8614 (2)
0.8056 (4)
0.7218 (4)
0.6199 (3)
0.5363 (4)
0.4334 (4)
0.6053 (5)
0.5515 (4)
0.4816 (3)
0.5572 (3)
0.5760 (3)
1.2985 (4)
1.2199 (4)
1.1266 (3)
1.0519 (3)
0.9417 (4)
1.0836 (5)
1.0344 (4)
0.9671 (3)
0.03404 (12)
0.03575 (13)
0.03124 (12)
0.02516 (10)
0.02820 (11)
0.03255 (12)
0.02761 (11)
0.02955 (11)
0.0273 (7)
0.0202 (6)
0.0233 (7)
0.0207 (6)
0.0330 (11)
0.0240 (9)
0.0185 (8)
0.0218 (9)
0.0215 (9)
0.0385 (13)
0.0233 (9)
0.0186 (8)
0.0178 (8)
0.0183 (8)
0.0268 (10)
0.0201 (8)
0.0182 (8)
0.0187 (8)
0.0183 (8)
0.0367 (13)
0.0222 (9)
0.0163 (8)
ꢀ
crystallizes in space group P1 with Z = 3, a situation also
C2
C3
C4
C5
C11
C12
C13
C14
C15
C21
C22
C23
C24
C25
C31
C32
C33
Figure 3
Packing diagram of tetragonal (8) viewed down the c axis.
ꢀ
1068 Madhavi et al. Crystal engineering in gem-alkynols
Acta Cryst. (2000). B56, 1063±1070

research papers
Table 3
Intermolecular interaction geometries.
F. Whilst short FÁ Á ÁF contacts
do occur in (7), they do not
make a systematic contribution
to that structure. However, in
(8) the ClÁ Á ÁCl interactions form
both closed and helical tetra-
meric units, which are important
to structural integrity. These
could not form within the
framework adopted by the
¯uoro compound, hence there is
a major change which results in
the high-symmetry OÐHÁ Á ÁO
and ClÁ Á ÁCl synthons of (8).
Experimental
H-normalized
ꢁ (ꢂ)
Ê
ꢁ (ꢂ)
d (A)
Ê
D (A)
Ê
d (A)
(7)
OÐHÁ Á ÁO
2.756 (2)
2.718 (2)
2.733 (1)
1.88 (2)
1.87 (2)
1.95 (2)
2.86 (2)
2.95 (1)
2.48 (2)
2.62 (2)
2.72 (2)
1.93 (4)
3.605 (1)
3.731 (2)
3.14 (5)
2.08 (7)
2.13 (9)
2.08 (6)
3.421 (7)
3.661 (7)
3.515 (6)
3.680 (6)
3.882 (7)
3.899 (5)
3.20 (7)
3.23 (7)
3.02 (6)
2.954
174 (2)
179 (2)
162 (2)
173.72 (7), 90.58 (6)
134.52 (7), 122.52 (7)
171 (1), 142.0 (4)
146.9 (5), 132 (1)
158 (1), 129.8 (4)
160 (3)
161.86 (9), 78.48 (9)
166.0 (1), 127.7 (6)
123 (3), 126.8 (1)
153 (7)
145 (1)
165 (7)
163.0 (1), 116.1 (1)
157.8 (1), 75.5 (1)
172.9 (1), 110.8 (1)
167.2 (1), 120.6 (1)
166.8 (1), 68.1 (1)
152.3 (1), 116.6 (1)
134 (6), 120 (1)
134 (6), 138 (1)
129 (4), 113 (1)
125.7
1.78
1.74
1.79
174
179
161
FÁ Á ÁF
CꢁCÐHÁ Á ÁF
3.409 (2)
3.347 (2)
3.630 (2)
2.653 (3)
2.34
2.54
2.61
1.716
170.6, 142.2
145.0, 130.9
157.1, 130.6
157.97
There is
a
reduction in
(8)
(9)
OÐHÁ Á ÁO
ClÁ Á ÁCl
symmetry in moving to the
bromo compound (9), although
the tetrameric OÐHÁ Á ÁO unit is
preserved. This synthon repeti-
tivity is reminiscent of struc-
tures (3) and (4) (Madhavi et al.,
2000), in which the synthons (5)
and (6) have obvious topolo-
gical relationships with the OÐ
HÁ Á ÁO tetramers (Figs. 2b and c)
in (8) and (9), but are formed by
CꢁCÐHÁ Á ÁCl
OÐHÁ Á ÁO
3.695 (4)
2.724 (5)
2.688 (5)
2.72 (5)
3.025
1.830
1.862
1.772
120.5, 126.9
149.8
139.9
162.2
BrÁ Á ÁBr
CꢁCÐHÁ Á ÁBr
CꢁCÐHÁ Á Áꢁ²
3.900 (5)
3.751 (7)
3.720 (5)
3.507
3.074
2.974
2.951
2.821
133.6, 121.0
128.9, 140.7
128.2, 112.5
121.3
cooperation
HÁ Á ÁO
between
OÐ
and
CꢁCÐHÁ Á ÁO
² Distances and angles measured to the mid-point of the triple bond.
bonds.
The topological similarities
between the supramolecular
observed for the more ¯exible saturated cyclohexane
compound (1) (Bilton et al., 1999). However, in (1) the
dominant OÐHÁ Á ÁO bonds form a helical trimeric synthon in
both of its polymorphs and in its pseudopolymorph.
The OÐHÁ Á ÁO network undergoes a further signi®cant
change to the tetrameric synthon (Figs. 2b and c) in structures
(8) and (9), where the more polarisable Cl and Br now replace
structures of (8) and (9) are re¯ected in the relationship
between their unit cells. The Niggli reduced cell of the tetra-
Ê
gonal (8) has a = 8.870, b = 12.654, c = 12.654 A, ꢃ = 82.94, ꢄ =
69.48, ꢅ = 69.48ꢂ, values which are very close to the triclinic
cell dimensions of (9). Clearly, (9) is pseudo-tetragonal with its
a axis unique in that symmetry, and with b,c (9) ' 0.75 a,b (8).
The symmetry reduction allows the most polarizable halogen
in this series (Br) to form a larger number [by comparison with
(7) and (8)] of short halogenÁ Á Áhalogen contacts which
contribute signi®cantly to structural stability, but which no
longer form the higher-level tetrameric units seen in (8).
4. Conclusions
Crystal structures are the result of the interplay between
intermolecular interactions of varying strengths, directional-
ities and distance dependence characteristics. The present
structures typify this statement ± the dominant tendency is to
form OÐHÁ Á ÁO hydrogen bonds, but the particular arrange-
ment of these bonds depends strongly on the nature of the
weaker interactions, dictated in this case by the type of
halogen present in the molecule. Thus, the structures of (2),
(7), (8) and (9) illustrate the pitfalls of attempting to dissect
crystal structures into modular units based on hierarchies of
interactions. Rather, a crystal structure is a supramolecular
entity in which any particular synthon results from a large
Figure 4
Packing diagram of triclinic (9) viewed down the pseudotetragonal a axis.
ꢀ
Acta Cryst. (2000). B56, 1063±1070
Madhavi et al. Crystal engineering in gem-alkynols 1069

research papers
Bruker Systems Inc. (1999b). SAINT. Bruker Systems Inc., Madison,
Wisconsin, USA.
number of concurring or competing forces. Another theme
that develops here is the chemical similarity between OÐ
HÁ Á ÁO hydrogen bonds and type II halogenÁ Á Áhalogen inter-
actions. This has previously been noted by Robinson et al.
(1998) and by Desiraju & Steiner (1999: p. 178). In a recent
interesting example, Brehmer et al. (2000) show that hydrogen
bonds and halogenÁ Á Áhalogen interactions are actually
mutually replaceable in tetrameric synthons, but the levels of
interaction mimicry are not so high in the structures reported
in the present paper.
Desiraju, G. R. (1991). Acc. Chem. Res. 24, 270±276.
Desiraju, G. R. (1995). Angew. Chem. Int. Ed. Engl. 34, 2311±2327.
Desiraju, G. R. (1997). Chem. Commun. pp. 1475±1476.
Desiraju, G. R. & Parthasarathy, R. (1989). J. Am. Chem. Soc. 111,
8725±8726.
Desiraju, G. R. & Steiner, T. (1999). The Weak Hydrogen Bond in
Structural Chemistry and Biology. Oxford University Press.
Dunitz, J. D. & Taylor, R. (1997). Chem. Eur. J. 3, 89±98.
Ermer, O. & Eling, A. (1994). J. Chem. Soc. Perkin Trans. 2, pp. 925±
944.
Hayes, I. C. & Stone, A. J. (1984). Mol. Phys. 53, 83±105.
Jetti, R. K. R., Xue, F., Mak, T. C. W. & Nangia, A. (1999). Cryst.
Engng, 2, 215±224.
Lommerse, J. P. M., Stone, A. J., Taylor, R. & Allen, F. H. (1996). J.
Am. Chem. Soc. 118, 3108±3116.
Madhavi, N. N. L., Bilton, C., Howard, J. A. K., Allen, F. H., Nangia,
A. & Desiraju, G. R. (2000). New J. Chem. 24, 1±4.
Madhavi, N. N. L., Katz, A. K., Carrell, H. L., Nangia, A. & Desiraju,
G. R. (1997). J. Chem. Soc. Chem. Commun. pp. 1953±1954.
Malone, J. F., Murray, C. M., Charlton, M. H., Docherty, R. & Lavery,
A. (1997). J. Chem. Soc. Faraday Trans. 93, 3429±3436.
Nangia, A. & Desiraju, G. R. (1998). Top. Curr. Chem. 198, 57±95.
Nishio, M., Hirota, M. & Umezama, Y. (1998). The CH/ꢀ Interaction,
Evidence, Nature and Consequences. New York: Wiley.
Pedireddi, V. R., Reddy, D. S., Goud, B. S., Craig, D. C., Rae, A. D. &
Desiraju, G. R. (1994). J. Chem. Soc. Perkin Trans. 2, pp. 2353±
2360.
The EPSRC (UK) are thanked for ®nancial support to CB
and JAKH (Senior Research Fellowship), and the CSIR
(India) for ®nancial support to NNLM. This work has been
conducted under the Indo-UK bilateral cooperation project
No. INT/UK/P-15/99 of the Department of Science and
Technology, Government of India and the British Council.
References
Allen, F. H., Hoy, V. J., Howard, J. A. K., Thalladi, V. R. & Desiraju,
G. R. (1997). J. Am. Chem. Soc. 119, 3477±3480.
Allen, F. H. & Kennard, O. (1993). Chem. Des. Autom. News, 8, 1, 31±
37.
Allen, F. H., Motherwell, W. D. S., Raithby, P. R., Shields, G. P. &
Taylor, R. (1999). New J. Chem. pp. 25±34.
Price, S. L., Stone, A. J., Lucas, J., Rowland, R. S. & Thornley, A. E.
(1994). J. Am. Chem. Soc. 116, 4910±4918.
Anthony, A., Desiraju, G. R., Jetti, R. K. R., Kuduva, S. S., Madhavi,
N. N. L., Nangia, A., Thaimattam, R. & Thalladi, V. R. (1998). Cryst.
Engng. 1, Mater. Res. Bull. Suppl. S, 1±18.
Bernstein, J. (1987). Organic Solid State Chemistry, edited by G. R.
Desiraju, pp. 471±518. London: Elsevier.
Robinson, J. M. A., Kariuki, B. M., Harris, K. D. M. & Philp, D.
(1998). J. Chem. Soc. Perkin Trans. 2, pp. 2459±2469.
Rodham, D. A., Suzuki, S., Suenram, R. D., Lovas, F. J., Dasgupta, S.,
Goddard III, W. A. & Blake, G. A. (1993). Nature, 362, 735±737.
Rowland R. S. & Taylor, R. (1996). J. Phys. Chem. 100, 7384±7391.
È
Sheldrick, G. M. (1996). SADABS. University of Gottingen,
Germany.
Sheldrick, G. M. (1997). SHELX97. University of Gottingen,
Bilton, C., Howard, J. A. K., Madhavi, N. N. L., Nangia, A., Desiraju,
G. R., Allen, F. H. & Wilson, C. C. (1999). J. Chem. Soc. Chem.
Commun. pp. 1675±1676.
È
Bondi, A. (1964). J. Phys. Chem. 68, 441±451.
Brehmer, T. H., Weber, E. & Cano, F. H. (2000). J. Phys. Org. Chem
13, 63±74.
Germany.
Steiner, T., Tamm, M., Lutz, B. & van der Maas, J. (1996). J. Chem.
Soc. Chem. Commun. pp. 1127±1128.
Broder, C. K., Howard, J. A. K., Keen, D. A., Wilson, C. C., Allen,
F. H., Jetti, R. K. R., Nangia, A. & Desiraju, G. R. (2000). Acta
Cryst. B56, 1080±1084.
Bruker Systems Inc. (1999a). SMART. Bruker Systems Inc., Madison,
Wisconsin, USA.
Suzuki, S., Green, P. G., Bumgarner, R. E., Dasgupta, S., Goddard III,
W. A. & Blake, G. A. (1992). Science, 257, 947±944.
Thalladi, V. R., Brasselet, S., Weiss, H.-C., Blaser, D., Katz, A. K.,
Carrell, H. L., Boese, R., Zyss, J., Nangia, A. & Desiraju, G. R.
(1998). J. Am. Chem. Soc. 120, 2563±2577.
ꢀ
1070 Madhavi et al. Crystal engineering in gem-alkynols
Acta Cryst. (2000). B56, 1063±1070