Crystal engineering in the gem-alkynol family; synthon repetitivity and topological similarity in diphenylethynylmethanols: Structures that lack O - H...O hydrogen bonds

Article abstract of DOI:10.1107/S010876810001154X

The structures of four para-substituted derivatives of diphenylethynylmethanol have been determined [ditolylethynylmethanol, di(4-chlorophenyl)ethynylmethanol, di(4-bromophenyl)ethynylmethanol and bis(4,4′-biphenylyl)ethynylmethanol]. The dimethyl, dichloro, dibromo and diphenyl compounds have been analysed using X-ray diffraction at 150 K, and the dichloro compound has also been studied using neutron diffraction at 150 K. In common with the parent diphenylethynylmethanol [Garcia, Ramos, Rodriguez & Fronczek (1995). Acta Cryst. C51, 2674-2676], all four derivatives fail to form the expected strong O - H...O hydrogen bonds due to steric hindrance. Instead, the supramolecular structural organization in this family of gem-alkynols is mediated by a variety of weaker interactions. The two most acidic protons, O - H and C≡C - H, participate in weak hydrogen bonds to π-acceptors, forming synthons that stabilize all five structures. These primary interactions are reinforced by a variety of other weak hydrogen bonds involving C - H donors and the hydroxy-O as an acceptor, and by halogen...halogen interactions in the dichloro and dibromo compounds.

Full text of DOI:10.1107/S010876810001154X

research papers
Crystal engineering in the gem-alkynol family;
Acta Crystallographica Section B
Structural
Science
synthon repetitivity and topological similarity in
diphenylethynylmethanols: structures that lack
OÐHÁ Á ÁO hydrogen bonds
ISSN 0108-7681
Clair Bilton,a Judith A. K.
Howard,a N. N. L. Madhavi,b
Ashwini Nangia,b Gautam R.
Desiraju,b Frank H. Allenc* and
Chick C. Wilsond
The structures of four para-substituted derivatives of diphe-
nylethynylmethanol have been determined [ditolylethynyl-
Received 31 May 2000
Accepted 22 August 2000
methanol, di(4-chlorophenyl)ethynylmethanol, di(4-bromo-
phenyl)ethynylmethanol and bis(4,40-biphenylyl)ethynyl-
methanol]. The dimethyl, dichloro, dibromo and diphenyl
compounds have been analysed using X-ray diffraction at
150 K, and the dichloro compound has also been studied using
neutron diffraction at 150 K. In common with the parent
diphenylethynylmethanol [Garcia, Ramos, Rodriguez &
Fronczek (1995). Acta Cryst. C51, 2674±2676], all four
derivatives fail to form the expected strong OÐHÁ Á ÁO
hydrogen bonds due to steric hindrance. Instead, the
supramolecular structural organization in this family of gem-
alkynols is mediated by a variety of weaker interactions. The
two most acidic protons, OÐH and C CÐH, participate in
weak hydrogen bonds to ꢀ-acceptors, forming synthons that
stabilize all ®ve structures. These primary interactions are
reinforced by a variety of other weak hydrogen bonds
involving CÐH donors and the hydroxy-O as an acceptor,
and by halogenÁ Á Áhalogen interactions in the dichloro and
dibromo compounds.
aDepartment of Chemistry, University of
Durham, South Road, Durham DH1 3LE,
England, bSchool of Chemistry, University of
Hyderabad, Hyderabad 500 046, India,
cCambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, England, and
dISIS Facility, Rutherford Appleton Laboratory,
Chilton, Didcot, Oxon OX11 0QX, England
Correspondence e-mail: allen@ccdc.cam.ac.uk
1. Introduction
The identi®cation of robust and reproducible supramolecular
synthons (Desiraju, 1995) is a major goal of crystal engi-
neering studies. The aim is to understand these patterns in
terms of the mutual interplay between particular interactions
(Nangia & Desiraju, 1998; Desiraju, 1997) and to establish
correspondences between molecular and crystal structures
(see e.g. Ermer & Eling, 1994; Allen et al., 1997).
Previous papers (Bilton et al., 1999; Madhavi, Bilton et al.,
2000; Madhavi, Desiraju et al., 2000), have discussed the wide
variety of interaction patterns observed in existing structures
in the gem-alkynol family and reported nine crystal structures
of seven novel compounds containing the 1,4-bis(gem-
alkynol) functionality attached to cyclohexane and cyclohexa-
2,5-diene rings. In all cases, the dominant synthon is
constructed from strong cooperative arrangements of OÐ
HÁ Á ÁO hydrogen bonds which form extended chains, helical
trimers, or cyclic tetramers and hexamers.
During our literature surveys, conducted using the
Cambridge Structural Database (CSD; Allen & Kennard,
1993), we became intrigued by the structure of diphenyl-
ethynylmethanol [(1), P21/n, Z = 4; Garcia et al., 1995]. Here
(Fig. 1), inversion-related molecules form dimeric synthons
through OÐHÁ Á Áꢀ(arene) bonds and these dimers are linked
by cooperative chains of C CÐHÁ Á Á ꢀ(ethynyl) bonds. The
# 2000 International Union of Crystallography
Printed in Great Britain ± all rights reserved
ꢀ
Acta Cryst. (2000). B56, 1071±1079
Bilton et al. Crystal engineering in gem-alkynols 1071

research papers
structure is stabilized entirely by weak interactions: the OÐ
HÁ Á ÁO hydrogen bonds that might be expected by consid-
eration of Etter's (1990) rule and from our own previous work
in this series simply do not form.
CCD diffractometer (Bruker Systems Inc., 1999a) using
Mo Kꢁ X-radiation. Data were processed using the SAINT
package (Bruker Systems Inc., 1999b), with structure solution
and re®nement using SHELX97 (Sheldrick, 1997). H atoms
were located in all four structures and re®ned freely with
isotropic displacement parameters. A large (2.5 Â 1.5 Â
0.5 mm3) crystal of (3) was selected for neutron diffraction
study. Diffraction data were collected at 150 K on the SXD
diffractometer (Keen & Wilson, 1996) at the ISIS spallation
source, Rutherford Appleton Laboratory, Chilton, England.
Data were processed using SXD97 (Wilson, 1997), and coor-
dinates for C and O atoms from the X-ray re®nement were
used as a starting model for least-squares re®nement against
the neutron data. H atoms were located from the resulting
difference map and included in the neutron re®nement model.
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.
Since there is considerable current interest in weak inter-
actions (see Desiraju & Steiner, 1999), and because of our
ongoing work on gem-alkynols, we decided to synthesize and
study the structures of other members of the diphenylethy-
nylmethanol family. The hope was to add to the growing
literature describing OÐHÁ Á Áꢀ (Steinwender et al., 1993;
Steiner, Starikov & Tamm, 1996) and CÐHÁ Á Áꢀ interactions
(Steiner et al., 1995; Steiner, Tamm et al., 1996; Lutz et al., 1998;
Nishio et al., 1998). In this paper we report the structures of
simple derivatives of (1), which are para-disubstituted by
methyl (2), chloro (3), bromo (4) and phenyl (5) groups. Low-
temperature X-ray diffraction has been used throughout and
for (3) a low-temperature neutron diffraction experiment was
also performed.
3. Results and discussion
Crystal structures of (1) (Garcia et al., 1995) and (2), (3), (4)
and (5) (this work) are illustrated in Figs. 1±5, while Fig. 6
provides schematic drawings of the synthons observed in these
structures. Geometrical details of the intermolecular interac-
tions observed in (2)±(5) are collected in Table 3.
2. Experimental
2.1. Syntheses
3.1. Diphenylethynylmethanol (1) (Garcia et al., 1995)
Inversion-related dimers (synthon I, Fig. 6) are formed
through OÐHÁ Á Áꢀ(arene) interactions, with herringbone
Compounds (2)±(5) were synthesized from appropriately
substituted dibenzophenone derivatives 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 substituted dibenzo-
phenone 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 The product was dried over
magnesium sulfate and the solvent removed. Crystals were
obtained by puri®cation of the crude material (column chro-
matography) followed by recrystallization.
Melting points: (2) 368±369, (3) 345-346, (4) 370 and (5)
430 K. Spectroscopic data have been deposited.1
2.2. Crystal structure analyses
X-ray diffraction intensities for (2)±(5) were collected at
150 K (Oxford Cryosystems cryostat) on a Bruker SMART
1 Supplementary data for this paper are available from the IUCr electronic
archives (Reference: BM0034). Services for accessing these data are described
at the back of the journal.
Figure 1
Perspective views of structure (1), displaying synthon I and other
interactions.
ꢀ
1072 Bilton et al. Crystal engineering in gem-alkynols
Acta Cryst. (2000). B56, 1071±1079

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interactions mediating the packing of dimers (Fig. 1a). The
ethynyl groups project outwards from the two-dimensional
arrangement of dimers, and form cooperative chains of
by a lack of OÐHÁ Á ÁO hydrogen bonding. Figs. 3(a) and 4(a)
show that both structures form dimers through C CÐ
HÁ Á Áꢀ(arene) interactions to form synthon II of Fig. 6. Each
constituent molecule of this synthon is then further dimerized
via a pair of weaker C(phenyl)ÐHÁ Á ÁO interactions to form
stacks along the b axis. The molecular stacks of (3) and (4) are
linked along the a axis (Figs. 3b and 4b) by OÐHÁ Á Áꢀ(arene)
interactions, depicted as synthon III in Fig. 6, a situation which
is further assisted by the weaker C(phenyl)ÐHÁ Á Áꢀ(ethynyl)
interactions.
Figs. 3(a), (b), 4(a) and (b) also show that the molecular
stacks of (3) and (4) are cross-linked along the c axis by
halogenÁ Á Áhalogen interactions. Recent debate concerning the
nature and origin of these interactions is surveyed and illu-
strated in our previous paper (Madhavi, Desiraju et al., 2000).
In summary, intermolecular perturbation theory calculations
(Price et al., 1994; Lommerse et al., 1996) show that carbon-
bound halogens in a suf®ciently electron-withdrawing envir-
onment present an anisotropic charge distribution, ꢂ+ forward
C
CÐHÁ Á Áꢀ(ethynyl) bonds along the b axis (Fig. 1b).
3.2. Ditolylethynylmethanol (2)
The most notable similarity between the structures of
parent (1) and the dimethyl derivative (2) is the lack of OÐ
HÁ Á ÁO hydrogen bonding: molecules of (2) form inversion-
related OÐHÁ Á Áꢀ(arene) dimers (Fig. 2a) as in (1). However,
there is a different mutual arrangement of dimers in (2), where
the two-dimensional packing is now mediated by a variety of
weak interactions involving methyl CÐH donor groups and
ꢀ(arene), ꢀ(ethynyl) and hydroxy-O acceptors. Thus, synthon
I (Fig. 6) is preserved in structure (2). This synthon is also
observed in the very closely related structure of 1,1,2-triphe-
nylethanol (Ferguson et al., 1994).
The ethynyl groups again project outwards from the two-
dimensional arrangement of dimers but, in contrast to (1),
these groups now form C CÐHÁ Á Áꢀ(arene) interactions
which link the molecules along the b axis to form synthon IV
(Fig. 6). This difference in the involvement of the ethynyl
group in structure (2) may be attributed to the bulky methyl
groups, which disturb the structural arrangement adopted for
the parent (1), but not suf®ciently to prevent formation of the
OÐHÁ Á Áꢀ(arene) dimer.
3.3. Di(4-chlorophenyl)ethynylmethanol (3) and di(4-
bromophenyl)ethynylmethanol (4)
Compounds (3) and (4) are isostructural, a not unexpected
outcome (Pedireddi et al., 1992), and are again characterized
Figure 3
Perspective views of structure (3), displaying synthons II and III and
halogenÁ Á Áhalogen interactions.
Figure 2
Perspective views of structure (2), displaying synthons I and IV.
ꢀ
Acta Cryst. (2000). B56, 1071±1079
Bilton et al. Crystal engineering in gem-alkynols 1073

research papers
Table 1
Experimental details.
(2)
(3) X-ray
(3) Neutron
(4)
(5)
Crystal data
Chemical formula
Chemical formula
weight
C17H16O
236.3
C15H10Cl2O
277.13
C15H10Cl2O
277.13
C15H10Br2O
366.05
C27H20O
360.43
Cell setting
Space group
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
Ê
a (A)
6.8286 (14)
8.2407 (16)
12.658 (3)
106.73 (3)
98.71 (3)
101.39 (3)
652.0 (2)
2
5.7082 (1)
11.3645 (2)
11.5167 (1)
117.268 (1)
99.257 (1)
96.726 (1)
639.734 (17)
2
5.7280 (1)
11.3620 (2)
11.5210 (1)
117.240 (1)
99.250 (1)
96.860 (1)
641.865 (17)
2
5.7906 (12)
11.325 (2)
11.907 (2)
115.67 (3)
99.43 (3)
97.91 (3)
674.8 (2)
2
5.6413 (3)
10.2599 (5)
17.3238 (9)
100.450 (2)
97.790 (2)
95.477 (2)
969.51 (9)
2
Ê
b (A)
Ê
c (A)
ꢁ ꢁꢂ†
ꢃ ꢁꢂ†
ꢄ ꢁꢂ†
3
Ê
V (A )
Z
Dx (Mg m
3
)
Radiation type
1.204
Mo Kꢁ
0.71073
1.439
1.433
1.801
1.235
Mo Kꢁ
0.71073
500
Neutron
±
25
Mo Kꢁ
0.71073
998
Mo Kꢁ
0.71073
927
Ê
Wavelength (A)
No. of re¯ections for cell 512
parameters
ꢅ range (ꢂ)
5.33±29.35
0.073
150
Block
5.44±29.17
0.490
150
±
±
150
4.26±30.50
5.990
150
10.15±26.52
0.073
150
1
ꢆ (mm
)
Temperature (K)
Crystal form
Crystal size (mm)
Crystal colour
Block
0.5 Â 0.4 Â 0.4
Block
2.5 Â 1.5 Â 1.0
Block
0.4 Â 0.3 Â 0.2
Plate
0.4 Â 0.25 Â 0.1
0.3 Â 0.3 Â 0.2
Colourless
Colourless
Colourless
Colourless
Colourless
Data collection
Diffractometer
Data collection method ! scans
Bruker SMART CCD
Bruker SMART CCD
! scans
SXD
Bruker SMART CCD
! scans
Bruker SMART CCD
! scans
Time-of-¯ight LAUE
diffraction
Empirical
0.51
0.89
10 674
Absorption correction
Multi-scan
0.784
1.000
Multi-scan
0.284
0.332
Empirical
0.344
0.766
Empirical
0.681
0.884
Tmin
Tmax
No. of measured re¯ec- 4775
tions
4371
5364
12 424
No. of independent
re¯ections
2964
2826
2929
3456
5270
No. of observed re¯ec-
tions
2362
2617
2928
2879
3419
Criterion for observed
re¯ections
Rint
ꢅmax (ꢂ)
I > 2ꢇ(I)
I > 2ꢇ(I)
I > 2ꢇ(I)
I > 2ꢇ(I)
I > 2ꢇ(I)
0.0176
27.48
0.0425
27.31
0.062
16.16
0.0287
30.16
0.0426
30.45
Range of h, k, l
8 ! h ! 8
10 ! k ! 7
14 ! l ! 16
6 ! h ! 7
11 ! k ! 14
14 ! l ! 12
0 ! h ! 12
20 ! k ! 21
19 ! l ! 10
6 ! h ! 8
15 ! k ! 12
15 ! l ! 16
7 ! h ! 7
14 ! k ! 13
21 ! l ! 23
Re®nement
Re®nement on
R‰F2>2ꢇꢁF2†Š
wRꢁF2†
F2
0.0478
0.1317
1.033
F2
F2
F2
F2
0.0378
0.1043
1.110
2826
0.0668
0.1281
5.444
2929
0.0276
0.0718
1.071
3456
0.0759
0.2336
1.038
5270
S
No. of re¯ections used in 2964
re®nement
No. of parameters used 231
203
253
All H-atom parameters All H-atom parameters All H-atom parameters
re®ned
w = 1/[ꢇ2(Fo2)]
203
322
H-atom treatment
All H-atom parameters Mixed
re®ned
w = 1/[ꢇ2(Fo2) +
re®ned
w = 1/[ꢇ2(Fo2) +
re®ned
w = 1/[ꢇ2(Fo2) +
Weighting scheme
w = 1/[ꢇ2(Fo2) +
(0.0618P)2 + 0.2678P],
(0.0467P)2 + 0.3533P],
(0.0393P)2 + 0.1818P],
(0.1193P)2 + 0.5780P],
2
2
2
2
where P = (Fo
2Fc2)/3
+
where P = (Fo
2Fc2)/3
+
where P = (Fo
2Fc2)/3
+
where P = (Fo
2Fc2)/3
+
ꢁÁ=ꢇ†
0.028
0.205
0.197
0.000
0.332
0.354
0.000
0
0
Becker±Coppens
Lorentzian model
0.296
0.001
0.862
0.433
0.000
0.503
0.433
max
3
Ê
Ê
Áꢈmax (e A
)
3
Áꢈmin (e A
Extinction method
)
None
None
None
None
Extinction coef®cient
Source of atomic scat-
tering factors
±
±
±
±
International Tables for International Tables for International Tables for International Tables for International Tables for
Crystallography
(1992, Vol. C, Tables
4.2.6.8 and 6.1.1.4)
Crystallography
(1992, Vol. C, Tables
4.2.6.8 and 6.1.1.4)
Crystallography
(1992, Vol. C, Tables
4.4.4.1)
Crystallography
(1992, Vol. C, Tables
4.2.6.8 and 6.1.1.4)
Crystallography
(1992, Vol. C, Tables
4.2.6.8 and 6.1.1.4)
ꢀ
1074 Bilton et al. Crystal engineering in gem-alkynols
Acta Cryst. (2000). B56, 1071±1079

research papers
Table 1 (continued)
(2)
(3) X-ray
(3) Neutron
(4)
(5)
Computer programs
Data collection
SMART (Bruker
Systems Inc., 1999a)
SMART (Bruker
Systems Inc., 1999a)
SMART (Bruker
Systems Inc., 1999a)
SMART (Bruker
Systems Inc., 1999a)
SXD (Keen & Wilson,
1996)
SXD (Keen & Wilson,
1996)
SMART (Bruker
SMART (Bruker
Systems Inc., 1999a)
SMART (Bruker
Systems Inc., 1999a)
Systems Inc., 1999a)
SMART (Bruker
Systems Inc., 1999a)
Cell re®nement
Data reduction
SAINT (Bruker Systems SAINT (Bruker Systems SXD (Keen & Wilson,
SAINT (Bruker Systems SAINT (Bruker Systems
Inc., 1999b)
SHELXS97 (Sheldrick,
1997)
Inc., 1999b)
SHELXS97 (Sheldrick,
1997)
1996)
SHELXS97 (Sheldrick,
1997)
Inc., 1999b)
SHELXS97 (Sheldrick,
1997)
Inc., 1999b)
SHELXS97 (Sheldrick,
1997)
Structure solution
Structure re®nement
SHELXL97 (Sheldrick, SHELXL97 (Sheldrick, SHELXL97 (Sheldrick, SHELXL97 (Sheldrick, SHELXL97 (Sheldrick,
1997) 1997) 1997) 1997) 1997)
Preparation of material SHELXL97 (Sheldrick, SHELXL97 (Sheldrick, SHELXL97 (Sheldrick, SHELXL97 (Sheldrick, SHELXL97 (Sheldrick,
for publication 1997) 1997) 1997) 1997) 1997)
of the halogen along the C±halogen bond vector, and ꢂ
perpendicular to the bond vector. Thus, an electrostatic C1Ð
Cl1Á Á ÁCl2ÐC2 interaction would be predicted to have ꢅ1 =
C1ÐCl1Á Á ÁCl2 = 180ꢂ and ꢅ2 = Cl1Á Á ÁCl2ÐC2 = 90ꢂ. This is in
accord with the type II interactions identi®ed in crystal
structures by Desiraju & Parthasarathy (1989) and Pedireddi
et al. (1994) from a CSD analysis; their type I interactions (ꢅ1 =
ꢅ2) arising from ClÁ Á ÁCl contacts across an inversion centre.
The halogenÁ Á Áhalogen interactions observed in (3) and (4)
(Table 3) have almost perfect type II geometry, with the
ClÁ Á ÁCl and BrÁ Á ÁBr distances shorter than the appropriate
Ê
van der Waals limits by 0.12 and 0.20 A, respectively. The
Figure 4
Perspective views of structure (4), displaying synthons II and III and
halogenÁ Á Áhalogen interactions.
Figure 5
Perspective views of structure (5), displaying synthons II and III.
ꢀ
Acta Cryst. (2000). B56, 1071±1079
Bilton et al. Crystal engineering in gem-alkynols 1075

research papers
Table 2
Fractional atomic coordinates and equivalent isotropic displacement
Table 2 (continued)
2
parameters (A ).
Ê
x
y
z
Ueq
Ueq ˆ ꢁ1=3†ÆiÆjUijaiajai:aj:
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
0.7950 (4)
0.9410 (4)
1.1362 (4)
1.1801 (4)
1.0325 (4)
0.8406 (4)
0.6726 (4)
0.5266 (4)
0.6082 (4)
0.8365 (4)
0.9833 (4)
0.8996 (4)
0.2749 (2)
0.3879 (2)
0.3768 (2)
0.2507 (2)
0.1356 (2)
0.1481 (2)
0.2554 (2)
0.1636 (2)
0.1394 (2)
0.2090 (2)
0.3029 (2)
0.3258 (2)
1.1894 (2)
1.2966 (2)
1.3750 (2)
1.3444 (2)
1.2387 (2)
1.1613 (2)
0.9690 (2)
0.8476 (2)
0.7376 (2)
0.7505 (2)
0.8698 (2)
0.9790 (2)
0.0220 (4)
0.0283 (5)
0.0297 (5)
0.0261 (4)
0.0274 (4)
0.0263 (4)
0.0208 (4)
0.0242 (4)
0.0260 (4)
0.0247 (4)
0.0263 (4)
0.0250 (4)
x
y
z
Ueq
(2)
O1
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
0.36138 (16)
0.7141 (3)
0.6603 (2)
0.5790 (2)
0.6155 (2)
0.4550 (2)
0.4927 (3)
0.6903 (2)
0.7306 (3)
0.8508 (2)
0.8142 (2)
0.6815 (2)
0.5842 (2)
0.6724 (3)
0.8597 (2)
0.9529 (3)
0.9569 (2)
0.8691 (2)
0.14659 (15)
0.0109 (2)
0.09261 (19)
0.21385 (18)
0.39365 (18)
0.4686 (2)
0.16398 (10) 0.0278 (3)
0.29487 (14) 0.0344 (4)
0.25638 (13) 0.0266 (3)
0.20481 (12) 0.0229 (3)
0.29666 (12) 0.0224 (3)
0.31962 (14) 0.0277 (3)
0.40489 (14) 0.0303 (4)
0.46824 (12) 0.0263 (3)
0.56227 (15) 0.0356 (4)
0.44306 (13) 0.0281 (3)
0.35843 (13) 0.0272 (3)
0.10758 (12) 0.0222 (3)
0.02815 (13) 0.0260 (3)
0.06040 (13) 0.0282 (3)
0.07268 (13) 0.0266 (3)
0.17029 (15) 0.0362 (4)
0.00761 (13) 0.0266 (3)
0.09667 (13) 0.0248 (3)
0.6303 (2)
0.71997 (19)
0.8924 (2)
0.6444 (2)
(5)
O1
C1
C2
C3
C4
C5
C6
C7
C8
C8A
C9
C9A
C9B
C10
C10A
C10B
C11
C11A
C11B
C12
C12A
C12B
C13
C13A
C13B
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
C27
0.0883 (3)
0.0423 (4)
0.1443 (4)
0.2633 (4)
0.3638 (4)
0.2812 (6)
0.3804 (7)
0.5632 (4)
0.6933 (12)
0.6508 (10)
0.7488 (13)
0.8893 (16)
0.755 (2)
0.26591 (16)
0.0743 (3)
0.0348 (2)
0.1735 (2)
0.1901 (2)
0.2778 (3)
0.2913 (4)
0.2191 (2)
0.2569 (7)
0.2181 (6)
0.1532 (8)
0.1860 (9)
0.1131 (15)
0.3032 (10)
0.1971 (11)
0.1373 (12)
0.1854 (10)
0.2539 (14)
0.2489 (10)
0.4169 (8)
0.2654 (12)
0.3675 (13)
0.3910 (7)
0.2510 (11)
0.3512 (11)
0.1299 (3)
0.1155 (3)
0.2080 (2)
0.1103 (2)
0.1467 (2)
0.2812 (2)
0.3190 (2)
0.2522 (2)
0.2851 (2)
0.3860 (3)
0.4552 (3)
0.4217 (2)
0.3784 (2)
0.3425 (2)
0.32794 (10) 0.0326 (4)
0.29797 (15) 0.0354 (5)
0.30668 (13) 0.0297 (5)
0.31647 (13) 0.0277 (4)
0.24024 (13) 0.0275 (4)
0.19456 (17) 0.0510 (8)
0.12649 (19) 0.0662 (10)
0.10295 (15) 0.0387 (5)
0.0337 (4)
0.0279 (3)
0.0184 (4)
0.0183 (5)
0.0142 (9)
0.0909 (6)
0.0516 (7)
0.0838 (6)
0.0857 (6)
0.1172 (8)
0.1105 (6)
0.0341 (5)
0.1054 (7)
0.0672 (8)
0.0277 (4)
0.0363 (7)
0.0001 (7)
0.14867 (16) 0.0410 (6)
0.21671 (17) 0.0418 (6)
0.38763 (13) 0.0265 (4)
0.41913 (14) 0.0302 (5)
0.48245 (14) 0.0291 (5)
0.51612 (12) 0.0248 (4)
0.58493 (12) 0.0247 (4)
0.58795 (14) 0.0287 (5)
0.65346 (15) 0.0342 (5)
0.71682 (16) 0.0414 (6)
0.71411 (15) 0.0385 (6)
0.64876 (14) 0.0299 (5)
0.48418 (13) 0.0262 (4)
0.42013 (13) 0.0272 (4)
0.4830 (2)
0.23500 (17)
0.29838 (19)
0.3212 (2)
0.28299 (18)
0.3045 (2)
0.22143 (19)
0.19732 (19)
0.0444 (16)
0.0345 (13)
0.0479 (17)
0.0309 (18)
0.047 (3)
0.079 (2)
0.045 (2)
0.032 (2)
0.070 (2)
0.051 (4)
0.0241 (19)
0.076 (2)
0.051 (3)
0.054 (3)
0.0614 (16)
0.042 (2)
0.044 (2)
(3) X-ray
O1
C1
C2
C3
C4
C5
C6
C7
Cl1
C8
C9
C10
C11
C12
C13
Cl2
C14
C15
1.1132 (2)
1.0066 (3)
0.9579 (3)
0.9001 (3)
0.8200 (3)
0.9651 (3)
0.8855 (3)
0.6591 (3)
0.04963 (8)
0.5132 (3)
0.5949 (3)
0.6949 (3)
0.6523 (3)
0.4577 (3)
0.3042 (3)
0.55431 (8)
0.3448 (3)
0.5417 (3)
0.31881 (11)
0.02664 (17)
0.08150 (16)
0.21751 (15)
0.24719 (14)
0.34161 (15)
0.36662 (16)
0.29600 (16)
0.26483 (5)
0.20033 (17)
0.17631 (17)
0.22598 (15)
0.35366 (15)
0.36638 (17)
0.25021 (17)
0.32701 (5)
0.12307 (17)
0.11124 (16)
0.44629 (13) 0.0267 (3)
0.30273 (19) 0.0305 (4)
0.35028 (16) 0.0235 (3)
0.40912 (16) 0.0214 (3)
0.53893 (15) 0.0201 (3)
0.66530 (16) 0.0243 (3)
0.78075 (17) 0.0270 (3)
0.76799 (16) 0.0249 (3)
0.9392 (17)
0.984 (2)
0.8428 (18)
0.8695 (17)
0.776 (3)
0.857 (2)
0.9046 (16)
0.595 (2)
0.758 (2)
0.7765 (13)
0.5090 (19)
0.654 (2)
0.6400 (5)
0.5424 (5)
0.4697 (4)
0.5842 (4)
0.7747 (4)
0.8535 (3)
1.0514 (3)
1.2571 (4)
1.4380 (4)
1.4181 (5)
1.2180 (4)
1.0358 (4)
0.7358 (4)
0.5500 (4)
0.05839 (5)
0.03706 (14)
0.64306 (17) 0.0272 (3)
0.52931 (16) 0.0252 (3)
0.31106 (15) 0.0214 (3)
0.33946 (17) 0.0253 (3)
0.26036 (17) 0.0276 (3)
0.15251 (16) 0.0271 (3)
0.91110 (4)
0.12157 (17) 0.0291 (3)
0.20127 (17) 0.0264 (3)
0.03824 (15)
(3) Neutron
O1
Cl1
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
Cl2
C14
C15
1.1102 (4)
0.0542 (3)
1.0047 (4)
0.9559 (3)
0.8984 (3)
0.8194 (3)
0.9649 (3)
0.8860 (4)
0.6603 (3)
0.5148 (4)
0.5950 (3)
0.6940 (3)
0.6513 (4)
0.4579 (4)
0.3053 (4)
0.5579 (3)
0.3467 (4)
0.5422 (4)
0.3181 (2)
0.4452 (3)
0.05897 (17) 0.0421 (4)
0.3033 (2) 0.0333 (5)
0.35113 (19) 0.0223 (4)
0.40894 (17) 0.0187 (3)
0.53838 (16) 0.0171 (3)
0.66423 (18) 0.0236 (4)
0.78000 (19) 0.0269 (4)
0.76792 (18) 0.0236 (4)
0.0268 (5)
0.26511 (16)
0.02661 (18)
0.08311 (16)
0.21786 (15)
0.24703 (14)
0.34106 (16)
0.36646 (17)
0.29618 (17)
0.2012 (2)
0.17659 (18)
0.22635 (15)
0.35329 (16)
0.36662 (18)
0.25032 (18)
0.32699 (17)
0.12323 (18)
0.11157 (17)
0.6435 (2)
0.0278 (4)
0.52866 (19) 0.0247 (4)
0.31199 (17) 0.0193 (3)
0.34004 (19) 0.0248 (4)
0.2611 (2)
0.15295 (19) 0.0266 (4)
0.91032 (17) 0.0434 (4)
more signi®cant interpenetration of the Br spheres is
suggested by both the theoretical and database analyses cited
above and re¯ects the increased polarizability of Br.
0.0282 (4)
0.1226 (2) 0.0299 (4)
0.20187 (19) 0.0265 (4)
3.4. Bis(4,40-biphenylyl)ethynylmethanol (5)
The structure of (5), in which one of the substituent phenyl
rings is disordered over three positions with relative site
occupancies in the ratio 2:1:1, is very similar to those of (3) and
(4). Inversion-related molecules form dimers through a pair of
C CÐHÁ Á Áꢀ(arene) bonds (Fig. 5a) to the ordered phenyl
substituent. The synthon thus formed is a variant of synthon II
(4)
O1
Br1
Br2
C1
0.3788 (3)
1.45503 (4)
0.95564 (5)
0.4884 (4)
0.5352 (4)
0.5921 (4)
0.17949 (17)
0.23580 (3)
0.17469 (3)
0.5239 (3)
0.4170 (2)
0.2826 (2)
1.05754 (17) 0.0280 (3)
1.44526 (2)
0.60197 (2)
1.1907 (3)
1.1473 (2)
1.0935 (2)
0.03392 (8)
0.03739 (8)
0.0314 (5)
0.0243 (4)
0.0222 (4)
C2
C3
ꢀ
1076 Bilton et al. Crystal engineering in gem-alkynols
Acta Cryst. (2000). B56, 1071±1079

research papers
Table 3
Intermolecular interaction geometries.
acceptor density, e.g. the ꢀ-
density of arene rings or ethynyl
bonds. Both of these situations
occur in structure (3).
The neutron-derived geom-
for
etry
the
OÐHÁ Á Á
Experimental
H-normalized
ꢅ (ꢂ)
Ê
ꢀ(arene), C CÐHÁ Á Áꢀ(arene),
CÐHÁ Á ÁO and C(phenyl)Ð
ꢅ (ꢂ)
d (A)
Ê
D (A)
Ê
d (A)
HÁ Á Áꢀ(ethynyl)
interactions
(2)
OÐHÁ Á ÁX1²³
3.324
3.987
3.705 (2)
3.525
3.794
3.463
3.472
3.330 (2)
3.776
2.484
3.137
2.90 (3)
2.768
2.996
2.743
2.722
2.47 (2)
2.858
3.375 (6)
2.569
2.637
2.361 (4)
2.759
3.394 (2)
2.835
2.684
2.56 (3)
2.970
167.9
149.5
139 (2)
138.4
139.0
157.4
138.8
152 (1)
157.6
172.96 (6), 93.54 (5)
158.43
137.7
150.2 (3)
157.1
173.0 (1), 93.85 (9)
159.2
148.1
157 (2)
156.0
2.358
3.025
2.831
2.662
2.922
2.544
2.608
2.341
2.756
167.2
148.2
138
136.3
137.8
155.52
136.2
151
is given in Table 3. It
is clear that the relevant CÐH
donor vectors are not collinear
with the centres of arene or
ethynyl ꢀ-density and this is not
unexpected. A combination of
C
CÐHÁ Á ÁX1²³
CÐHÁ Á ÁO
CÐHÁ Á ÁX1²³
CÐHÁ Á ÁX2²§
OÐHÁ Á ÁX1²³
(3) X-ray
(3) Neutron
(4)
C
CÐHÁ Á ÁX1²³
CÐHÁ Á ÁO
CÐHÁ Á ÁX2§
ClÁ Á ÁCl
156.7
IR
(Steiner et al., 1996) and
neutron diffraction data
(Steiner et al., 1997) have shown
spectroscopic
studies
OÐHÁ Á ÁX1²³
3.471
3.481
3.341 (3)
3.781
C
CÐHÁ Á ÁX1²³
CÐHÁ Á ÁO
CÐHÁ Á ÁX2§
ClÁ Á ÁCl
that
ꢀ(arene)
off-centre
OÐHÁ Á Á
OÐHÁ Á ÁX1²³
3.560
3.483
3.378 (3)
3.840
2.633
2.532
2.37
157.5
145.9
155
interactions
do
C
CÐHÁ Á ÁX1²³
indeed exhibit hydrogen-bond
characteristics, while gas-phase
studies (Suzuki et al., 1992) have
shown that the acceptor direc-
tionality of aromatic rings is
extremely soft, allowing for a
wide range of geometries to
exist that have closely similar
CÐHÁ Á ÁO
CÐHÁ Á ÁX2§
BrÁ Á ÁBr
2.833
154.7
3.502 (1)
2.630
2.641
173.79 (7), 93.42 (7)
157.0
151.8
(5)
OÐHÁ Á ÁX1²³
3.451
3.446
2.530
2.468
156.0
149.6
C
CÐHÁ Á ÁX1²³
² Distances and angles measured to the mid-point of the triple bond and aromatic ring. ³ X1 is the centroid of an aromatic
ring. § X2 is the centroid of the triple bond.
(Fig. 6) in which, by comparison with the occurrence of this
synthon in (3) and (4), there is an intervening phenyl ring.
Molecules related by an a translation are linked by OÐ
HÁ Á Áꢀ(arene) interactions (synthon III, Fig. 6) in exactly the
same way as the a-translated molecules in (3) and (4) (cf. Fig.
5b with Figs. 3b and 4b), leading to the close similarity in the a
cell dimensions in all three structures (Table 1).
interaction energies. We note that the directionality at H in the
XÐH interactions with ꢀ-systems in (3) is at least as good, i.e.
as close to linear, as it is in the CÐHÁ Á ÁO interaction.
The single-structure observations in (3) are fully corrobo-
rated by an examination of the relevant scatterplots in IsoStar
(Bruno et al., 1997), the knowledge base of intermolecular
Molecular packing along the c axis is mediated by
herringbone interactions between ordered and disordered
peripheral phenyl rings. These interactions substitute for the
type II halogenÁ Á Áhalogen interactions in (3) and (4), a factor
reinforced by the similar (perpendicular) topologies of the two
interaction types. Thus, the overall packing arrangement of
(5), as depicted in Figs. 5(a) and (b), bears a striking resem-
blance to the arrangements in (3) and (4) (Figs. 3a, b, 4a and
b). Note that the disordered phenyl ring is involved in the
looser herringbone interactions, while the ring involved in
synthon II is ordered, thus indicating the relative strength of
the C CÐHÁ Á Áꢀ(arene) interaction.
3.5. Neutron study of di(4-chlorophenyl)ethynylmethanol (3)
The importance of neutron diffraction results to the accu-
rate study of hydrogen-bond geometries is unquestionable.
This is especially true (a) where the chemical nature of the
donor group makes it dif®cult to estimate true H-atom posi-
tions with any degree of certainty, e.g. in the case of OÐH
donors, and (b) in the study of hydrogen bonds to diffuse
Figure 6
Synthons I, II, III and IV.
ꢀ
Acta Cryst. (2000). B56, 1071±1079
Bilton et al. Crystal engineering in gem-alkynols 1077

research papers
interactions derived from the CSD, and distributed as part of
CSD system releases. Fig. 7 shows (static) scatterplots of the
approach of CÐH contact groups to (a) phenyl rings, and (b)
and (c) ethynyl groups. These plots are derived primarily from
X-ray data, the dominant experimental source in the CSD, but
with X-ray determined H-atom positions normalized so that
their CÐH distance re¯ects the mean value obtained in
neutron experiments, but with the X-ray determined CÐH
vector direction unchanged. In Table 3, we also compare the
neutron-derived hydrogen-bond geometries in (3) with those
from the low-temperature X-ray study in which the H-atom
positions have been normalized in this way. The hydrogen-
bond distances and hydrogen-bond directionalities at H
derived from the normalized X-ray data are reassuringly close
to those in the low-temperature neutron study. This provides
some evidence, albeit from a single structure, of the value of
the hydrogen-normalization procedure, now regarded as best
practice in the analysis of hydrogen-bond geometries from X-
ray data. Thus encouraged, we are now undertaking a more
complete comparison of hydrogen-bond geometries deter-
mined by neutron diffraction with those derived from
normalized X-ray data, using the CSD to identify suitable
structures determined by both techniques.
3.6. Structural comparison of gem-alkynols (1)±(5)
The complete lack of the expected strong OÐHÁ Á ÁO
hydrogen bonds in parent (1) is observed throughout the
series (2)±(5) studied here. However, the OH group in gem-
alkynols is already sterically hindered by the extended ethynyl
moiety and this dif®culty is accentuated by the presence of
additional phenyl substituents at the gem-alkynol centre. Thus,
rather than forming OÐHÁ Á ÁO bonds, the two most acidic
protons, OÐH and C CÐH, participate in weak hydrogen
bonds to ꢀ-acceptors, which stabilize all ®ve structures
through the formation of synthons I±IV of Fig. 6. These
primary interactions are reinforced by a variety of other weak
interactions involving C(ethynyl)ÐH, C(phenyl)ÐH and
even C(methyl)ÐH as donors and the hydroxy-O as acceptor,
together with halogenÁ Á Áhalogen interactions in (3) and (4).
Figure 7
Scatterplots from IsoStar (Bruno et al., 1997) showing the approach of alkyl CÐH to (a) phenyl rings, and (b) and (c) to ethynyl groups. Part (b) views the
interaction space along the ÐC CÐH vector, and (c) is a slice through this space viewed perpendicular to the ÐC CÐH vector.
ꢀ
1078 Bilton et al. Crystal engineering in gem-alkynols
Acta Cryst. (2000). B56, 1071±1079

research papers
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.
Bruker Systems Inc. (1999a). SMART. Bruker Systems Inc., Madison,
Wisconsin, USA.
Comparison of the structures reveals interesting transitions
along the series (1)±(5). Thus, in parent (1) the OH groups
participate in the cyclic synthon I, while the ethynyl group
takes part in a cooperative chain. The replacement of the
para-H atoms by methyl groups retains synthon I in (2), but
the ethynyl groups now participate in another ꢀ-directed
synthon IV. In structures (3), (4) and (5), where the para-H are
now replaced by halogen or phenyl substituents having their
own capacity to form non-covalent interactions, the gem-
alkynol functionality now participates in synthons II and III,
albeit in an extended form of II in (5). The formation of
different ꢀ-acceptor synthons in the different structures is
clearly related to the interaction possibilities and require-
ments of the various substituents. Thus, although the dimethyl
derivative (2) and the dichloro derivative (3) resemble each
other in forming OÐHÁ Á Áꢀ(arene) and C CÐHÁ Á Á ꢀ(arene)
bonds, the synthons formed are very different (I versus II),
and their overall structures are very different, owing to the
interaction requirements of the methyl CÐH against CÐCl.
Although it has been observed (Desiraju & Sarma, 1986) that
methyl/chloro interchange does not disrupt structures where
these groups merely play a space-®lling role, it seems clear that
this cannot be the case when interactions involving these
groups are intimately involved in structural organization.
While structures (1)±(5) do show a degree of synthon
repetitivity, synthon I being preserved in (1) and (2), and
synthon II in structures (3), (4) and (5), this repetitivity is not
complete across the series. However, the topological similarity
of synthons I and II is obvious, the former being mediated by
OÐH donors and the latter by C CÐH. It is known (James
et al., 1996; Davis et al., 1996) that hydroxy and ethynyl groups
are capable of forming equivalent synthons when hydrogen-
bonded to themselves. The present structures indicate that
such an equivalence can also occur when these groups are
involved in hydrogen bonds to other acceptors as weak as
phenyl rings. The synthon similarity across the series (1)±(5),
combined with the robustness of the synthons formed, points
to their further application in crystal engineering.
Bruker Systems Inc. (1999b). SAINT. Bruker Systems Inc., Madison,
Wisconsin, USA.
Bruno, I. J., Cole, J. C., Lommerse, J. P. M., Rowland, R. S., Taylor, R.
& Verdonk, M. L. (1997). J. Comput.-Aided Mol. Des. 11, 525±537.
Davis, P. L., Veldman, N., Grove, D. M., Spek, A. L., Lutz, B. T. G. &
van Koten, G. (1996). Angew. Chem. Int. Ed. Engl. 35, 1959±1961.
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. & Sarma, J. A. R. P. (1986). Proc. Indian Acad. Sci.
(Chem. Sci.) 96, 599±605.
Desiraju, G. R. & Steiner, T. (1999). The Weak Hydrogen Bond in
Structural Chemistry and Biology. Oxford University Press.
Ermer, O. & Eling, A. (1994). J. Chem. Soc. Perkin Trans. 2, pp. 925±
944.
Etter, M. C. (1990). Acc. Chem. Res. 23, 120±126.
Ferguson, G., Gallagher, J. F., Glidewell, C. & Zakaria, C. M. (1994).
Acta Cryst. C50, 70±73.
Garcia, J. G., Ramos, B. & Rodriguez, A. (1995). Acta Cryst. C51,
2674±2676.
Keen, D. A. & Wilson, C. C. (1996). Technical Report RAL-TR-96-
083. Single Crystal Diffraction at ISIS. User Guide for the SXD
Instrument. CCLRC Rutherford Appleton Laboratory, Chilton,
England.
James, S. L., Verspui, G., Spek, A. L. & van Koten, G. (1996). Chem.
Commun. pp. 1309±1310.
Lommerse, J. P. M., Stone, A. J., Taylor, R. & Allen, F. H. (1996). J.
Am. Chem. Soc. 118, 3108±3116.
Lutz, B., Kanters, J. A., van der Maas, J., Kroon, J. & Steiner, T.
(1998). J. Mol. Struct. pp. 81±87.
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., Desiraju, G. R., Bilton, C., Howard, J. A. K. &
Allen, F. H. (2000). Acta Cryst. B56, 1063±1070.
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.
Pedireddi, V. R., Sarma, J. A. R. P. & Desiraju, G. R. (1992). J. Chem.
Soc. Perkin Trans. 2, pp. 311±320.
Price, S. L., Stone, A. J., Lucas, J., Rowland, R. S. & Thornley, A. E.
(1994). J. Am. Chem. Soc. 116, 4910±4918.
È
Sheldrick, G. M. (1997). SHELX97. University of Gottingen,
Germany.
Steiner, T., Mason, S. A. & Tamm, M. (1997). Acta Cryst. B53, 843±
848.
Steiner, T., Starikov, E. B., Amado, A. M. & Teixeira-Dias, J. J. C.
(1995). J. Chem. Soc. Perkin Trans. 2, pp. 1321±1326.
Steiner, T., Starikov, E. B. & Tamm, M. (1996). J. Chem. Soc. Perkin
Trans. 2, pp. 67±71.
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.
Steiner, T., Tamm, M., Lutz, B. & van der Maas, J. H. (1996). Chem.
Commun. pp. 1127±1128.
Steinwender, E., Lutz, E. T. G., van der Maas, J. H. & Kanters, J. A.
(1993). Vib. Spectrosc. 4, 217±229.
Suzuki, S., Green, P. G., Bumgarner, R. E., Dasgupta, S., Goddard III,
W. A. & Blake, G. A. (1992). Science, 257, 942±944.
Wilson, C. C. (1997). J. Mol. Struct. pp. 207±217.
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.
ꢀ
Acta Cryst. (2000). B56, 1071±1079
Bilton et al. Crystal engineering in gem-alkynols 1079