Serendipity and the search for short N - I halogen bonds

Article abstract of DOI:10.1021/cg401243h

The X-ray structure of the complex formed between N,N-dimethylaminopyridine (DMAP) and 1,2-bis(iodoethynyl)benzene is reported. The N - I halogen bond lengths are 2.654 and 2.662 A, approximately 75% of the sum of the van der Waals radii. On the basis of literature precedent and electrostatic potential calculations, a series of fluorosubstituted iodophenylacetylenes were prepared and individually complexed with dimethylaminopyridine in a search for shorter halogen bonds. A N - I halogen bond distance of 2.680 A was observed in the DMAP complex with 3,5-difluoro(iodoethynyl)benzene, and halogen bond distances of 2.622, 2.676, 2.700, and 2.705 A were observed in the complex of 4-fluoro(iodoethynyl)benzene with DMAP. These N - I bond distances range from 74.3 to 76.6% of the sum of the van der Waals radii.

Full text of DOI:10.1021/cg401243h

Article
pubs.acs.org/crystal
Serendipity and the Search for Short N‑-‑I Halogen Bonds
Eric Bosch*
Department of Chemistry, Missouri State University, Springfield, Missouri 65804, United States
ABSTRACT: The X-ray structure of the complex formed between N,N-
dimethylaminopyridine (DMAP) and 1,2-bis(iodoethynyl)benzene is reported.
The N---I halogen bond lengths are 2.654 and 2.662 Å, approximately 75% of the
sum of the van der Waals radii. On the basis of literature precedent and electrostatic
potential calculations, a series of fluorosubstituted iodophenylacetylenes were
prepared and individually complexed with dimethylaminopyridine in a search for
shorter halogen bonds. A N---I halogen bond distance of 2.680 Å was observed in
the DMAP complex with 3,5-difluoro(iodoethynyl)benzene, and halogen bond
distances of 2.622, 2.676, 2.700, and 2.705 Å were observed in the complex of 4-
fluoro(iodoethynyl)benzene with DMAP. These N---I bond distances range from
74.3 to 76.6% of the sum of the van der Waals radii.
A portion of these crystals were redissolved in dichloromethane and
placed on a short silica column, and the 1,2-bis(iodoethynyl)benzene
was eluted with a 10:1 mixture of hexanes and ethylacetate as an
almost colorless oil. 1H NMR δ (300 Mz, CDCl3) 7.42 (dd, J = 3.4, 5.8
Hz, 2H), 7.26 (dd, J = 3.4, 5.8 Hz, 2H). 13C NMR δ 132.50, 128.33,
126.75, 92.35, 69.67, 11.13.
INTRODUCTION
■
Despite the fact that halogen bonding can be traced back to
1863,1 the interaction has only become recognized as a valuable
tool in crystal engineering over the past two decades.2,3 In this
article we describe the crystal structure of a halogen bonded
complex that we did not intend to form and then describe how
this led to an exploration of other extremely short N---I halogen
bonds. The specific application of iodoalkynes as halogen bond
donors is best known from the elegant synthetic application to
the solid-state formation of polyacetylenes based on halogen
bonding ordering of dialkynes in the solid state.4 We were
interested in preparing a series of bis-iodoalkynes for a crystal
engineering study and used the synthetic procedure published
by Meng, et al.5 We were surprised when NMR analysis of the
crude crystalline product isolated on preparation of 1,2-
bis(iodoethynyl)benzene indicated that this product was in
fact a 2:1 complex with N,N-dimethylaminopyridine. In this
paper we report the molecular structure of that complex and
the beautiful interlocked three-dimensional crystal packing.
This will be followed by the preliminary results of the search for
even stronger N---I halogen bonds using fluorinated
iodoethynylbenzenes.
Complex between N,N-Dimethylaminopyridine and 1,2-Bis-
(iodoethynyl)benzene, A. The complex was intentionally formed in
quantitative yield when the purified bis-iodoalkyne was mixed with 2
equiv of N,N-dimethylaminopyridine in dichloromethane solution.
Synthesis of 4-Fluoro-1-(iodoethynyl)benzene, 2. 4-Fluoropheny-
lacetylene (125 mg, 1.05 mmol) was reacted with iodine (315 mg, 1.24
mmol) in the presence of N,N-dimethylamino pyridine (156 mg, 1.28
mmol) in dichloromethane (3 mL) at room temperature.5 After 16 h
the reaction was treated with aqueous ammonium thiosulfate which
bleached the orange/brown color. The organic layer was diluted with
dichloromethane (10 mL), separated, and dried over sodium sulfate.
The solution was filtered, and the solvent was removed under vacuo.
The crude product was purified by flash chromatography with hexanes
as eluant yielding a colorless oil (182 mg, 71 %). 1H NMR δ (300 Mz,
CDCl3) 7.41 (mdd, J = 5.6, 9.2 Hz, 2H), 7.00 (mt, J = 9.2 Hz, 2H);
13C NMR δ 162.74 (d, JFC = 249.1 Hz), 134.24 (d, JFC = 8.8 Hz),
119.44 (d, JFC = 3.6 Hz), 115.54 (d, JFC = 21.0 Hz), 92.96, 6.06 (C−I);
19F NMR δ −109.66.
Complex between N,N-Dimethylaminopyridine and 4-Fluoro-1-
(iodoethynyl)benzene, B. N,N-Dimethylaminopyridine and 4-fluoro-
1-(iodoethynyl)benzene (0.01 mmol each) were added to a small
screw cap vial and dissolved with the minimum amount of
dichloromethane without heating. The dichloromethane was allowed
to slowly evaporate over several days to form a homogeneous mass of
blocklike crystals. 1H NMR δ (300 Mz, CDCl3) 8.22 (d, J = 5.1 Hz,
2H, dmap), 7.43 (m, 2H), 7.01 (m, 2H), 6.50 (d, J = 5.1 Hz, 2H,
dmap), 3.01 (s, 6H, dmap).
EXPERIMENTAL SECTION
■
Synthesis. Synthesis of 1,2-Bis(iodoethynyl)benzene, 1. 1,2-
Bis(ethynyl)benzene (0.280 g) was reacted with iodine (1.36 g) in
the presence of N,N-dimethylamino pyridine (0.564 g) in dichloro-
methane (8 mL) at 40 °C for 24 h.5 The dark brown reaction mixture
was diluted with more dichloromethane (10 mL) and treated with
aqueous ammonium thiosulfate until the color bleached. The organic
layer was separated and dried over sodium sulfate. The solution was
filtered and the solvent was removed under a vacuum. The crude
product was diluted in 3 mL of dichloromethane and 2 equiv of N,N-
dimethylamino pyridine was added. The mixture was heated to form a
clear brown solution. After two days, large colorless blocklike crystals
of a 1:2 complex had formed. 1H NMR δ (300 Mz) CDCl3) 8.20 (d, J
= 6.6 Hz, 4 H, dmap), 7.41 (dd, J = 3.0, 5.7 Hz, 2H), 7.26 (dd, J = 3.0,
5.7 Hz, 2H), 6.49 (d, J = 6.6 Hz, 4H, dmap), 3.00 (s, 12H, dmap).
Synthesis of 3,5-Fluoro-1-(iodoethynyl)benzene, 3. 3,5-Difluor-
ophenylacetylene (210 mg, 1.52 mmol) was reacted with iodine (445
mg, 1.75 mmol) in the presence of N,N-dimethylamino pyridine (209
mg, 1.71 mmol) in dichloromethane (5 mL) at room temperature.5
Received: August 14, 2013
Revised: November 26, 2013
Published: December 2, 2013
© 2013 American Chemical Society
126
dx.doi.org/10.1021/cg401243h | Cryst. Growth Des. 2014, 14, 126−130

Crystal Growth & Design
Article
After 16 h the organic layer was diluted with dichloromethane (10
mL) and treated with aqueous ammonium thiosulfate. The organic
layer was separated and dried over sodium sulfate. The solution was
filtered and the solvent was removed under vacuo. The crude product
was purified by flash chromatography with hexanes as eluant yielding a
RESULTS AND DISCUSSION
■
This project began when we prepared a few bis-iodoalkynes as
part of an, as yet unpublished, crystal engineering study. We
were surprised to find that 1,2-bis(iodoethynyl)benzene
cocrystallized with dimethylaminopyridine from the crude
1
pale yellow oil (233 mg, 58 %). H NMR δ (300 Mz, CDCl3) 6.94
(md, J = 6 Hz, 2H), 6.80 (mt, J = 9 Hz, 1H); 13C NMR δ 162.47 (dd,
1
reaction product as established by H NMR analysis. A similar
JFC = 247.5, 13.2 Hz), 125.84 (t, JFC = 11.7 Hz), 115.36 (dd, JFC
=
reaction of 1,4-diethynylbenzene yielded uncomplexed 1,4-
bis(iodoethynyl)benzene. Naturally, we decided to investigate
the structure of the cocrystals we isolated.
Complex between 1,2-Bis(iodoethynyl)benzene and
N,N-Dimethylaminopyridine, A. The single crystal X-ray
structure of the 1:2 complex is shown in Figure 1A with the
asymmetric unit labeled.
19.1, 8.1 Hz), 105.21 (t, JFC = 25.6 Hz), 91.81 (t, JFC = 3.6 Hz),
10.22(C−I); 19F NMR δ −109.31.
Complex between N,N-Dimethylaminopyridine and 3,5-Fluoro-
1-(iodoethynyl)benzene, C. N,N-Dimethylaminopyridine and 3,5-
fluoro-1-(iodoethynyl)benzene (0.01 mmol each) were added to a
small screw cap vial and dissolved with the minimum amount of
dichloromethane without heating. The dichloromethane was allowed
to evaporate over several days to form homogeneous plate-like crystals.
1H NMR δ (300 Mz, CDCl3) 8.20 (dd, J = 1.7, 5.1 Hz, 2H, dmap),
The two halogen bonds are almost linear with C1−I−N1 and
C10−I2−N3 bond angles of 174.92 and 174.17°, respectively.
The nitrogen−iodine distance of 2.654 and 2.662 Å for I1−N1
and I2−N3 respectively are 75.2 and 75.4% of the sum of the
van der Waals radii. The iodine atoms are above the plane of
the N,N-dimethylaminopyridine rings to which they are bound
with angles I1−N1−C13 and I2−N3−C20 of 160.87 and
163.84° respectively. The N,N-dimethylaminopyridine mole-
cules in the complex are almost parallel to each other with a
tweezer-like orientation and a centroid−centroid distance of
7.099 Å. This distance between the two N,N-dimethylamino-
pyridine rings accommodates a N,N-dimethylaminopyridine
molecule from another 2:1 complex with a reversed orientation
for a good electronic interaction. This amino pyridine ring is
slightly asymmetrically π-stacked. Thus the closest interaction
between the entrapped N,N-dimethylaminopyridine molecule
and one of the two other N,N-dimethylaminopyridine rings is
about 3.45 Å, whereas the distance to the other pyridine is
about 3.69 Å. This interaction results in a series of interlocked
complexes where the pyridines are all π-stacked. This is
illustrated in the space filling model shown in Figure 1B. These
interlocked complexes then form two-dimensional sheets with
the benzene rings fitting together like a zipper as shown in
Figure 2A. There are no exceptionally close interactions
between adjacent benzene rings. The two-dimensional sheets
fit neatly on top of each other as shown in Figure 2B. There is a
weak C−H---benzene interaction between the N,N-dimethyla-
minopyridine rings and the benzene ring with one H of each
pyridine positioned above the centroid of the benzene ring with
H18-benzene centroid and H12-benzene centroid distances of
2.661 and 2.752 Å respectively. Rather than intermolecular
forces controlling the three-dimensional structure, it is the close
packing of appropriately sized one-dimensional strands of the
interlocked molecular complexes in both of the other two
dimensions that controls the three-dimensional structure.
On examination of N---I halogen bonds reported in the
Cambridge Crystallographic Database,9 we were surprised to
discover that the halogen bond distance of 2.622 Å is in fact
shorter that any N---I halogen bond reported to date. A short
N---I interaction of 2.633 was evident in the structure of
trimethylsilylamino triphenylphosphonium iodocyanide.10 Two
of the next three shortest N---I bond distances in the database
were reported for complexes between the halogen bond
acceptor N,N-dimethylaminopyridine. The N---I distance for
the complex with 1,4-diiodotetrafluorobenzene is 2.667 Å11 and
that with iodopentafluorobenzene is 2.693 Å.12 The N---I bond
distance in the complex between (S)-(−)-(1-(dimethylamino)-
ethyl)ferrocene and 1,4-diiodoperfluorobutane is 2.689 Å.13
Interestingly three of the 11 shortest N---I bond distances
6.92 (m, 2H), 6.79 (m, 1H), 6.50 (dd, J = 1.7, 5.1 Hz, 2H, dmap), 3.00
(s, 6H, dmap).
X-ray Structure Determination. For each complex a single
crystal was mounted on a Kryoloop using viscous hydrocarbon oil.
Data were collected using a Bruker Apex1 CCD diffractometer
equipped with Mo Kα radiation with λ = 0.71073 Å. Data collection at
100 K was facilitated by use of a Kryoflex system with an accuracy of
1 K. Initial data processing was carried out using the Apex II software
suite.6 Structures were solved by direct methods using SHELXS-97
and refined against F2 using SHELXL-20137 using the program X-
Seed as a graphical interface.8 Hydrogen atoms were located in the
difference maps but were placed in idealized positions and refined with
a riding model. Crystallographic details are collected in Table 1.
Table 1. Crystallographic Data for Complexes A−C
A, 1·(N,N-dmap)2 B, 2·(N,N-dmap) C, 3·(N,N-dmap)
formula
C10H4I2·
2(C7H10N2)
C8H4FI·C7H10N2 C8H3F2I·
C7H10N2
formula weight 311.14
368.18
386.17
crystal dim.
(mm3)
0.45 × 0.25 × 0.15 0.31 × 0.20 ×
0.40 × 0.20 ×
0.05
0.20
crystal system
space group
triclinic
monoclinic
C2/c
orthorhombic
Pbca
P1
̅
́
a (Å)
9.8722(5)
10.1925(5)
13.8977(6)
110.3020(10)
90.0060(10)
112.9040(10)
4
25.481(8)
19.4100(8)
24.5312(10)
90
7.5059(5)
12.9763(9)
30.407(2)
90
́
b (Å)
́
c (Å)
α (deg)
β (deg)
γ (deg)
Z
121.2270(1)
90
90
90
28
8
3
́
V (Å )
1193.27(10)
1.732
10365.7(7)
1.651
2961.6(3)
1.732
ρcalcd (mg m−3
)
T (K)
μ (mm−1
100
100
100
)
2.653
2.161
2.175
reflections/
unique
14321/5293
66248/11538
34394/3289
data/restraints/ 5293/0/275
parameters
11538/0/611
3289/0/183
goodness of fit 1.065
1.084
1.060
R1/wR2
0.0258/0.0579
0.0334/0.0615
0.0260/0.0486
0.0331/0.0508
0.0302/0.0516
0.0458/0.0564
R1/wR2 (all
data)
XPRD Determination. The bulk product was ground in a glass
mortar and pestle and packed in a clear plexiglass holder. The data
were collected using a Bruker D8 Discover X-ray diffractometer at
room temperature with a 2θ range from 10 deg to 40 deg using 0.05
deg increments. Simulated XPRD spectra were obtained using
Mercury software from CCDC.
127
dx.doi.org/10.1021/cg401243h | Cryst. Growth Des. 2014, 14, 126−130

Crystal Growth & Design
Article
Figure 1. (A) Oblique view of the 1:2 complex, A, formed between 1,2-bis(iodoethynyl)benzene and N,N-dimethylaminopyridine with thermal
ellipsoids drawn at the 50% probability level. (B) Space-filling side view of the interaction between two of the 1:2 halogen bonded complexes formed
between 1,2-bis(iodoethynyl)benzene and N,N-dimethylaminopyridine.
Figure 2. (A) View of a portion of the two-dimensional sheet of interlocked 1:2 complexes formed between 1,2-bis(iodoethynyl)three-
dimensionalbenzene and N,N-dimethylaminopyridine. (B) View along (0 1 1) showing packing between the two-dimensional layers of the 1:2
complex formed between 1,2-bis(iodoethynyl)three-dimensionalbenzene and N,N-dimethylaminopyridine.
correspond to N-iodoalkyne halogen bonds.14−16 There are
Scheme 1. Electrostatic Potential of Various Halogen
Bonding Donors20
currently a total of 17 iodoalkyne structures in the Cambridge
Database.15,17,18
Clearly, the effect of the sp-C on the halogen bond donor
properties of the attached iodine is great, and we wondered if
we could increase that halogen bond donor ability by adding
electron-withdrawing fluoro substitutents to the phenyl ring.
This idea was based on several elegant halogen bonding studies.
For example, Bruce et al. studied the halogen bonding between
a series of differentially fluorinated iodobenzenes and N,N-
dimethylaminopyridine.12 In this study, Bruce clearly demon-
strated that progressive addition of fluorine substituents onto
the iodobenzene ring resulted in a uniform decrease in the N---I
bond distance. A similar effect was reported in the studies of
Pennington et al., who reported and compared the structures of
1,4-diiodobenzene and tetrafluoro-1,4-diiodobenzene with a
variety of N-acceptors.19 In all cases, the N---I bond distances
were much shorter for the perfluorinated diiodoarene.
Accordingly, we first evaluated the extent of the positive hole
on the iodine atom in a series of readily available fluorinated
iodophenylacetylenes using the Spartan Molecular Modeling
program.20 The ground state equilibrium geometry and
electrostatic potential was calculated using the Hartree−Fock
method with the 3-21G basis set assuming vacuum. The results
are compared to pentafluoroiodobenzene and perfluoro-1,4-
diiodobutane in Scheme 1. On the basis of these calculations,
we expected the mono and difluorinated iodophenylacetylenes
2 and 3 to be stronger halogen bond donors than 1,2-
bisiodoethynylbenzene and comparable pentafluoroiodoben-
zene and 1,4-diiodoperfluorobutane possibly resulting in
shorter halogen bond distances with N,N-dimethylaminopyr-
idine than we observed in complex A.
Accordingly we prepared representative iodoalkynes 2 and 3
to evaluate the possibility that, on complexation with N,N-
dimethylaminopyridine, these would yield even shorter halogen
bond distances than previously observed. On mixing 4-fluoro-1-
(2′-iodoethynyl)benzene, 2, and N,N-dimethylaminopyridine
in dichloromethane at room temperature and allowing the
solvent to slowly evaporate a homogeneous mass of crystals
formed. X-ray analysis of a single crystal revealed a complex
arrangement with four independent iodoalkyne-dimethylami-
nopyridine complexes as shown in Figure 3. One of the
complexes lies on a C2 axis. Repeated attempts to grow crystals
from different solvents and under different conditions did not
yield crystal suitable for X-ray analysis.
The N---I bond distances are 2.700, 2.676, 2.705, and 2.622
Å for I1−N1, I2−N3, I3−N5, and I4−N7 respectively with C−
I−N bond angles of 176.37, 174.86, 174.29, and 180°. Similar,
mixing 3,5-difluoro-1-(2′-iodoethynyl)benzene, 4, and N,N-
dimethylaminopyridine in dichloromethane at room temper-
128
dx.doi.org/10.1021/cg401243h | Cryst. Growth Des. 2014, 14, 126−130

Crystal Growth & Design
Article
Figure 3. Asymmetric unit of the complex B formed between 4-fluoro-
1-(2′-iodoethynyl)benzene, 4, and N,N-dimethylaminopyridine with
thermal ellipsoids drawn at the 50% probability level.
ature and allowing the solvent to slowly evaporate yielded a
homogeneous batch of plate-like crystals. X-ray analysis of a
single crystal revealed the iodoalkyne-dimethylaminopyridine
complex shown in Figure 4.
Figure 5. (A) Simulated XPRD pattern experimental XPRD pattern of
complex A (1·2(C7H10N2), compared to the experimental XPRD
shown in (B).
AUTHOR INFORMATION
Corresponding Author
*Phone: 417-836-4277. FAX: 417-836-5507. E-mail:
ericbosch@missouristate.edu.
■
Notes
The authors declare no competing financial interest.
Figure 4. Asymmetric unit of the complex, C, formed between 3,5-
difluoro-1-(2′-iodoethynyl)benzene, 4, and N,N-dimethylaminopyr-
idine with thermal ellipsoids drawn at the 50% probability level.
ACKNOWLEDGMENTS
■
The Missouri State University Provost Incentive Fund funded
the purchase of the X-ray diffractometer. I thank Jerrod R.
McCleod for his initial work on the synthesis of bis-
(iodoethynyl)benzenes.
Despite the significantly more positive σ-hole on the iodine
atom in the difluoro derivative (Scheme 1), the halogen bond
defined by a distance, N1---I1, of 2.684 Å and angles C1−N1−
I1 and C11−N1−I1 of 175.11 and 167.02° respectively was
similar to the others reported in this manuscript.
The identity between the single crystal structures and the
bulk material obtained for complex A, 1·2(C7H10N2), was
confirmed by comparison of the predicted XPRD pattern21
simulated from the single crystal X-ray analysis with the
experimental XPRD pattern obtained from the bulk material as
shown in Figure 5. Similar analysis of compounds B and C was
unsuccessful and gave variable results primarily due to
decomposition during sample preparation.
REFERENCES
(1) Guthrie, F. J. Chem. Soc. 1863, 16, 239.
(2) Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G.
Angew. Chem., Int. Ed. 2008, 47, 6114. Metrangolo, P.; Resnati, G.
Cryst. Growth Des. 2012, 12, 5835−5838.
(3) Halogen Bonding: Fundamentals and Applications; Metrangolo, P.;
Resnati, G., Eds.; Springer: Berlin, 2008.
■
(4) See for example: Goroff, N. S.; Curtis, S. M.; Webb, J. A.; Fowler,
F. W.; Lauher, J. W. Org. Lett. 2005, 7, 1891−1893. Lauher, J. W.;
Fowler, F. W.; Goroff, N. S. Acc. Chem. Res. 2008, 41, 1215−1229.
(5) Meng, L. G.; Cai, P. J.; Guo, Q. X.; Xue, S. Synth. Commun. 2008,
38, 1257.
(6) ApexII Suite; Bruker AXS Ltd.: Madison, WI, 2006.
(7) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.
(8) Barbour, L.; Atwood, J. A. Cryst. Growth Des. 2001, 3, 3.
(9) Allen, F. H. Acta Crystallogr. 2002, B58, 380−388.
(10) Kempe, R.; Kessenich, E.; Schulz, A. Inorg. Chem. 2001, 40,
5182.
(11) Roper, L. C.; Prasang, C.; Kozhevnikov, V. N.; Whitwood, A. C.;
Karadakov, P. B.; Bruce, D. W. Cryst. Growth Des. 2010, 10, 3710.
(12) Prasang, C.; Whitwood, A. C.; Bruce, D. W. Cryst. Growth Des.
2009, 9, 5319.
(13) Amati, M.; Lelj, F.; Liantonio, R.; Metrangolo, P.; Luzzati, S.;
Pilati, T.; Resnati, G. J. Fluorine Chem. 2004, 125, 629.
(14) Batsanov, A. S.; Howard, J. A. K. Acta Crystallogr., Sect. C: Cryst.
Struct. Commun. 2000, 56, 252.
CONCLUSIONS
■
The N---I halogen bond distances reported in this manuscript
for a series of halogen bonded complexes between iodoalkynes
and N,N-dimethylaminopyridine are marginally shorter than
previously reported halogen bonded complexes. We did not,
however, observe the expected reduction in N---I bond
distances on addition of electron withdrawing fluorine
substituents to the iodoethynyl compounds. It is clear that
the hybridization of the carbon atom to which the iodine atom
is attached has a profound effect on the extent of the σ-hole on
iodine and the halogen bond donor strength. This is a
consequence of the higher s-character of the orbitals and the
higher electronegativity of sp-C’s.22
(15) Perkins, C.; Libri, S.; Adams, H.; Brammer, L. CrystEngComm
2012, 14, 3033.
(16) Bouchmella, K.; Boury, B.; Dutremez, S. G.; van der Lee, A.
Chem.Eur. J. 2007, 13, 6130.
129
dx.doi.org/10.1021/cg401243h | Cryst. Growth Des. 2014, 14, 126−130

Crystal Growth & Design
Article
(17) (a) Goroff, N. S.; Curtis, S. M.; Webb, J. A.; Fowler, F. W.;
Lauher, J. W. Org. Lett. 2005, 7, 1891. (b) Wilhelm, C.; Boyd, S. A.;
Chawda, S.; Fowler, F. W.; Goroff, N. S.; Halada, G. P.; Grey, C. P. J.
Am. Chem. Soc. 2008, 130, 4415.
(18) Sun, A.; Lauher, J. W.; Goroff, N. S. Science 2006, 312, 1030.
(19) Walsh, R. B.; Padgett, C. W.; Metrangolo, P.; Resnati, G.;
Hanks, T. W.; Pennington, W. T. Cryst. Growth Des. 2001, 1, 165.
(20) Spartan ’10 running on a Windows platform, as provided by
Wavefunction, Inc., 18401 Von Karman Ave., Suite 370, Irvine, CA
92612 (www.wavefun.com).
(21) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.;
McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; van de
Streek, J.; Wood, P. A. J. Appl. Crystallogr. 2008, 41, 466−470.
(22) (a) Huheey, J. E. J. Phys. Chem. 1966, 70, 2086. (b) Advanced
Organic Chemistry, Part A: Structure and Mechanism, 4th ed.; Carey, F.
A.; Sundberg, R. J.; Kluwer Academic/Plenum Publishers: New York,
2000.
130
dx.doi.org/10.1021/cg401243h | Cryst. Growth Des. 2014, 14, 126−130