Tracing a common origin of phase transformation, polymorphism, disorder, isosterism, and isostructuralism in fluorobenzoylcarvacryl thiourea

Article abstract of DOI:10.1021/cg300699r

The terms phase transformation, polymorphism, disorder, isosterism, and isostructuralism are often the keywords used in the design and engineering of molecular crystals. Three benzoylcarvacryl thiourea derivatives with [-NH-C(S)-NH-C(O)-] cores generate molecular crystals, which provide the basis for exploring a common link between the structures related by aforementioned terms. The apparent origin of all these structural modifications has been traced to the formation of a planar molecular dimeric chain built with homomeric R₂²(12) and R₂²(8) synthons occurring in tandem, one formed with N-H???O and the other with N-H???S hydrogen bonds.

Full text of DOI:10.1021/cg300699r

Article
pubs.acs.org/crystal
Tracing a Common “Origin” of Phase Transformation, Polymorphism,
Disorder, Isosterism, and Isostructuralism in Fluorobenzoylcarvacryl
Thiourea
Amol G. Dikundwar,† Umesh D. Pete,‡ Chetan M. Zade,‡ Ratnamala S. Bendre,*,‡
and Tayur N. Guru Row*,†
†Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India
‡School of Chemical Sciences, North Maharashtra University, Jalgaon 425 001, India
S
* Supporting Information
ABSTRACT: The terms phase transformation, polymorphism,
disorder, isosterism, and isostructuralism are often the keywords used
in the design and engineering of molecular crystals. Three
benzoylcarvacryl thiourea derivatives with [-NH−C(S)−NH−C(O)-]
cores generate molecular crystals, which provide the basis for exploring
a common link between the structures related by aforementioned
terms. The apparent “origin” of all these structural modifications has
2
2
been traced to the formation of a planar molecular dimeric chain built with homomeric R2 (12) and R2 (8) synthons occurring in
tandem, one formed with N−H···O and the other with N−H···S hydrogen bonds.
cases, the lowering of crystal symmetry is observed upon
lowering the temperature, there are examples resulting in higher
symmetry with lowering of temperature.8,9 More interestingly,
it has been reported that two polymorphs, both stable under
ambient conditions, can reversibly be interconverted into one
another under the given set of temperature conditions.10 In all
these cases, the very existence of a robust synthon in the lower
Z′ form has been well associated with synthons in their
evolutionary stages in the corresponding polymorphs with
higher Z′.11
In the context of crystallography, the atoms or ions with
comparable atomic or ionic volumes are referred to as being
isosteric. Molecules differing only in the substitution of
isosteres at specific positions, in general, result in the formation
of similar crystal structures due to isosterism among the
substituents. A fluorinated analog is geometrically very similar
to its parent molecule and hence satisfies isosteric requirements
in the ensuing crystal structures.12 As a result, compounds with
monofluorophenyl rings, in particular, ortho-fluoro- and meta-
fluorophenyl compounds are commonly found to be orienta-
tionally disordered in the crystal structures.13 However, it is
interesting to note that, in general, if the fluorine atom is
involved in hydrogen bonding (C−H···F, N−H···F; for
example), this orientational disorder is reduced. Isostructurality
with its parent nonfluoro compounds, mainly controlled by a
size factor, is yet another feature observed in fluorinated
analogs. Even though in general isostructurality prevails,3 there
are examples that display significant structural deviations on
INTRODUCTION
■
Growth of a molecular crystal depends on a delicate balance
between a variety of thermodynamic and kinetic factors.1 The
strength and directionality of intermolecular interactions in
molecular crystals control these factors in terms of the
formation of “supramolecular synthons”.2 It is obvious from
the wealth of crystal structure data available that the formation
of high Z′ structures, occurrence of phase transitions with
temperature or pressure, formation of polymorphic modifica-
tions, and disorder in crystal structures are indeed dictated by
the variability offered by synthons. Further, the robustness
associated with synthons can provide a landscape for
isostructurality and isosterism.3 Recently, it has been
demonstrated that synthons can also serve as potential
fragments for the transferability of charge density distributions
in molecular crystals (SBFA methodology).4 However, so far in
the literature, the potency of a synthon to serve as a “common
linker” between polymorphism, disorder, phase transformation,
isostructurality, and isosterism has not been explored. In this
paper, we examine the credibility of a robust synthon to serve
as a common link to generate such a structural diversity in
single molecular species5 (parent molecule and F-substituted
derivatives).
Supramolecular synthons in high Z′ structures appear to be
in their primitive stages and hence provide clues about possible
nucleation pathways.6 In several recent articles, it has been
discussed that high Z′ structures would indeed allow for
alterations in the packing motifs assisting the prediction of new
polymorphic modifications of lower Z′ (preferably Z′ = 1).7
Systematic studies of high Z′ structures exhibiting pseudosym-
metry elements bring out their susceptibility for temperature or
pressure induced phase transformations.8 Although, in many
Received: May 23, 2012
Revised: July 8, 2012
Published: July 17, 2012
© 2012 American Chemical Society
4530
dx.doi.org/10.1021/cg300699r | Cryst. Growth Des. 2012, 12, 4530−4534

Crystal Growth & Design
Article
substitution of fluorine at the hydrogen positions.14 Indeed,
several recent articles,15 draw attention toward the structure-
directing role of “organic” fluorine in this regard.
strong H-bond donors (N−H) and acceptors (CO and C
S).
Benzoylcarvacryl thiourea [BCTU] derivatives belong to a
class of insect growth regulators with N-acyl thiourea [-NH−
C(S)−NH−C(O)-] functionality and are widely used in the
agricultural industry.16 Three compounds, namely, 2-fluoro
benzoylcarvacryl thiourea [2FBCTU], 2,6-difluoro benzoylcar-
vacryl thiourea [26DFBCTU], and benzoylcarvacryl thiourea
[BCTU] (Scheme 1), have been identified for the evaluation of
EXPERIMENTAL SECTION
■
The compounds 2FBCTU, 26DFBCTU, and BCTU were synthesized
by the reaction of the corresponding benzoyl chlorides with 4-amino-
5-isopropyl-2-methylphenol and ammonium thiocyanate in acetone
(see Supporting Information for detailed synthetic procedures). X-ray
diffraction data were collected on an Oxford Mova diffractometer,17
equipped with an EoS detector, utilizing Mo Kα radiation (λ =
0.71073 Å). All structures were solved by direct methods using
SHELXS-97 and refined against F2 using SHELXL-97.18 H-atoms
except for the ones on nitrogen (N−H) were fixed geometrically and
refined isotropically. The hydrogens of the amino group were located
from difference Fourier maps and refined isotropically. WinGX19 and
OLEX220 were used for structure refinement and production of data
tables, and ORTEP-321 was used for structure visualization. Analysis of
the H-bonded and π interactions was carried out using PLATON.22
Packing diagrams were generated with MERCURY.23
Scheme 1. Chemical Structures of the Compounds 2FBCTU,
26DFBCTU, and BCTU
RESULTS AND DISCUSSION
■
The compound 2-fluoro benzoylcarvacryl thiourea, 2FBCTU,
was crystallized from its saturated solution in ethyl acetate/
hexane (7:3) under ambient conditions. Room-temperature X-
ray diffraction data acquired on a plate-shaped colorless crystal
revealed that the structure belongs to a noncentrosymmetric
space group P1 with four molecules in the asymmetric unit
important structural features associated with interchangeability
of a hydrogen atom and a fluorine atom in the presence of
Table 1. Crystallographic Details of Compounds 2FBCTU, 26DFBCTU, and BCTU
2FBCTU
form IA
form IB
form II
26DFBCTU
BCTU
formula
C18H19O2 F1S1N2
346.4
C18H19O2 F1S1N2
346.4
C18H19O2 F1S1N2
345.4
C18H18O2 F2S1N2
364.4
C18H20O2S1N2
328.4
formula wt
color
colorless
plate
colorless
plate
colorless
block
colorless
block
colorless
block
cryst morphology
cryst size (mm3)
temp (K)
radiation
0.09 × 0.25 × 0.30
295(2)
0.09 × 0.25 × 0.30
90(1)
0.25 × 0.30 × 0.30
100(1)
0.20 × 0.30 × 0.30
100(1)
0.20 × 0.30 × 0.30
110(1)
Mo Kα
Mo Kα
Mo Kα
Mo Kα
Mo Kα
wavelength (Å)
cryst syst
space group
a (Å)
0.71073
triclinic
0.71073
monoclinic
P21
0.71073
monoclinic
C2/c
0.71073
monoclinic
C2/c
0.71073
monoclinic
C2/c
P1
10.0715(4)
14.8192(7)
11.8886(6)
87.715(4)
90.239(3)
89.911(3)
1772.96(14)
4
10.0148(18)
14.7799(27)
11.6010(21)
90
23.5271(12)
10.7467(6)
13.5653(9)
90
23.4200(19)
10.7880(9)
13.5978(12)
90
23.4872(11)
10.7385(5)
13.6376(8)
90
b (Å)
c (Å)
α (deg)
β (deg)
90.796(3)
90
97.631(5)
90
95.991(3)
90
98.421(5)
90
γ (deg)
vol (Å3)
1716.99(5)
4
3399.46(24)
8
3416.8(5)
8
3402.54(27)
8
Z
density (g/mL)
μ (1/mm)
F (000)
1.30
1.34
1.35
1.42
1.28
0.205
0.211
0.213
0.224
0.201
727.9
727.9
1447.8
1519.8
1391.8
θ (min, max)
no. unique reflns
no. of params
hmin,max
2.4, 25.0
11871
2.0, 25.0
6040
2.5, 25.0
2994
1.8, 25.0
3005
2.5, 25.0
2963
881
450
239
238
214
−11, 11
−17, 17
−14, 14
0.084, 0.085
0.047, 0.078
−0.180, 0.221
0.85
−11, 11
−17, 17
−13, 13
0.072, 0.084
0.046, 0.075
−0.269, 0.293
0.99
−27, 27
−12, 12
−16, 16
0.042, 0.090
0.033, 0.086
−0.233, 0.271
1.06
−27, 26
−8, 12
−16, 15
0.047, 0.112
0.042, 0.109
−0.249, 0.648
1.04
−27, 18
−12, 11
−16, 15
0.067, 0.103
0.045, 0.093
−0.298, 0.334
1.01
kmin,max
lmin,max
R_all, wR2_all
R_obs, wR2_obs
Δρmin, Δρmax (e Å−3
)
GOF
4531
dx.doi.org/10.1021/cg300699r | Cryst. Growth Des. 2012, 12, 4530−4534

Crystal Growth & Design
Article
[2FBCTU, form IA; Table 1]. These molecules are held in
tive C−H···π contact is an important factor stabilizing a
nonplanar conformation of these dimers (Figure 1).
pairs as two independent dimers with the connecting N−H···O
2
hydrogen bonds of dissimilar lengths forming an R2 (12) motif
Single Crystal to Single Crystal Transformation (SST)
in 2FBCTU. In order to precisely determine the wide range of
intermolecular interactions offered by four symmetry-inde-
pendent molecules, data were collected at 90 K on the same
crystal. Interestingly, crystal structure at this temperature was
solved in the monoclinic space group P21, now with two
symmetry-independent molecules [2FBCTU, form IB; Table
1]. A slight rearrangement of the four symmetry-independent
molecules in form IA upon cooling of the crystal is clearly
reflected by the small, yet significant, changes in the
representative torsion angles [given in Supporting Information,
Table S2]. Upon cooling, the N−H···O and N−H···S hydrogen
(Supporting Information; Figure S1, Table S1). Figure 1 shows
2
bonds reorganize slightly such that the dimeric R2 (12) and
2
R2 (8) motifs attain a little more planarity. Although slender,
the concomitant conformational changes in all four independ-
ent molecules in P1 manifest in such a way that the molecular
conformation and the dimeric conformation in both dimers
becomes identical, and as a result, a pseudo-21-screw in form IA
actually becomes operational forcing the structure into the
space group P21 (form IB), obviously without much significant
changes in the cell parameters (Table 1). Figure 2a,b provides a
comparison between the packing arrangements of form IA and
form IB. In order to determine the temperature at which the
phase transformation (SST) occurs, complete sets of data were
collected on the same crystal every 20 K from room
temperature, and the phase change from P1 to P21 was
observed at 190(1) K with the transformation being reversible.
Details of variable-temperature single-crystal XRD experiments
along with CIFs have been provided in the Supporting
Information. It is important to note that, although the molecule
does not contain any chiral center, it prefers to pack in a
noncentrosymmetric space group, P1, and reversibly transforms
to a space group P21 mainly because of adoption of a
conformationally chiral dimeric unit owing to the molecular
flexibility of 2FBCTU.
Figure 1. View of a noncentric dimer of 2FBCTU (form IA and form
IB) built with N−H···O hydrogen bonds and C−H···π interactions.
a view of one of the dimers formed with N−H···O hydrogen
bonds. The individual dimers are held together by two N−H···S
2
hydrogen bonds (forming an R2 (8) motif) generating a
distorted molecular dimeric chain along the a-axis. Figure 2a
shows a packing diagram of the structure wherein four
symmetry-independent molecules are color coded. The dimers
(formed between red−yellow and blue−green molecules) are
further related by a pseudo-21-screw axis along the b-direction,
which is not operative mainly because of the subtle conforma-
tional differences among the four molecules and hence among
the two dimers (see Supporting Information; Figure S1, Table
S2). Notably, the molecules in the adjacent dimers are
interlinked through their hydroxy ends via O−H···O hydrogen
bonds (Supporting Information, Figure S2), a feature
commonly observed in high Z′ structures of hydroxy-containing
compounds with the occurrence pseudosymmetry.8 A suppor-
Polymorphism in 2FBCTU. A detailed Cambridge
Structural Database24 [ConQuest 1.14; Feb 2012 update]
analysis (provided in Supporting Information) revealed that the
commonly adopted packing motif for molecules with N-acyl
thiourea [-NH−C(S)−NH−C(O)-] linkage is a planar
molecular dimeric chain formed through centrosymmetric
2
2
R2 (12) and R2 (8) packing motifs built with N−H···O and
N−H···S hydrogen bonds as shown in Figure 3.
Figure 2. Packing diagram of (a) form IA, space group P1, Z′ = 4, and (b) form IB, space group P21, Z′ = 2, of 2FBCTU. Symmetry-independent
molecules are color coded. Molecular dimeric chains running along the a-axis (perpendicular to plane of the paper) are formed via N−H···O/N−
H···S hydrogen bonds: red with yellow molecules and green with blue molecules.
4532
dx.doi.org/10.1021/cg300699r | Cryst. Growth Des. 2012, 12, 4530−4534

Crystal Growth & Design
Article
Figure 3. Planar molecular dimeric chain formed with N−H···S and
N−H···O dimers from the [-NH−C(S)−NH−C(O)-] units, both
across the center of inversion. Color codes: sulfur, yellow; oxygen, red;
nitrogen, blue; carbon, gray; hydrogen, white.
In order to probe a structure with lower Z′ value (preferably
Z′ = 1) following the most preferred packing pattern (Figure
3), crystallization of 2FBCTU was attempted under different
experimental conditions. Indeed, an anticipated centrosym-
metric structure with Z′ = 1 was obtained for a block-shaped
crystal grown from a relatively polar solvent, acetonitrile, at
room temperature. It is of interest to note that though the
crystals belong to the monoclinic space group C2/c (Z′ = 1),
the ortho-fluorine atom is rendered disordered! Figure 4 shows
an ORTEP view of the structure [form II, 2FBCTU; Table 1]
with partial occupancies of the disordered fluorine atom.
Figure 5. Molecular dimeric chains in (a) form IA, form IB, and (b)
form II of 2FBCTU. Compare these figures in terms of the N−H···O
and N−H···S dimers; notice the change in molecular orientations from
panel a to b and positional disorder of F-atom in panel b.
These are the best candidates to verify the isosterism of F and
H in the presence of strong H-bond partners and to examine
the influence of asymmetric monofluoro substitution (at o-
position) in the formation of high Z′ structure (form IA),
associated phase transition (form IB), and disorder-mediated
polymorphism (form II) in 2FBCTU.
Figure 4. ORTEP diagram of form II of 2FBCTU (C2/c; Z′ = 1) at
50% ellipsoidal probability. Notice the disorder of F-atom over two
ortho-positions with partial occupancies of 44% and 56%.
An orientational disorder of fluorine over the two ortho
positions and its noninvolvement in any significant structure-
guiding interactions in form II of 2FBCTU implies the
isostructural models for compounds 26DFBCTU and BCTU
keeping in view the intact nature of strong N−H···O and N−
The molecular conformation in this structure is slightly
different from that of forms IA and IB (Supporting
Information, Table S2). The molecules form similar N−
2
H···O and N−H···S mediated dimers but now with the R2 (12)
2
2
2
and R2 (8) motifs being exactly planar and devoid of any C−
H···S driven R2 (12) and R2 (8) synthons in 2FBCTU. Indeed,
the compounds 26DFBCTU and BCTU adopt the same space
group C2/c with comparable cell parameters (Table 1). Figure
6 shows a packing overlay diagram depicting the isostructural
features of 2FBCTU (form II), 26DFBCTU, and BCTU.
Interestingly, the intermolecular interactions in all the three
structures are notably similar with the C−H···π in BCTU
replaced by C−F···π in 2FBCTU (form II) and 26DFBCTU
(Supporting Information, Table S1). Further, a short F···F
[F2···F2, 2.42 Å] contact appears in 26DFBCTU as a
consequence of preserving the isostructural features with a
disordered monofluoro and a nonfluoro compound. Notably,
the probability ellipsoid of F2 appears to be slightly elongated
indicating its disorder, and hence this rather short F···F contact
between the symmetrically equivalent F-atoms suggests that the
F2 atoms in the adjacent molecules are disordered in a counter
phase fashion.
H···π interactions. Figure 5a,b gives a clear picture for the
comparison of molecular and supramolecular features of form I
(A and B) and form II structures, respectively.
Clearly, a driving force for both the phase transformation and
the polymorphism in 2FBCTU is the formation of a planar
2
molecular dimeric chain built with a pair of homomeric R2 (12)
2
and R2 (8) synthons occurring in tandem, one formed with N−
H···O and the other with N−H···S hydrogen bonds. The
concomitant conformational changes on lowering of the
temperature transform the distorted dimeric chain in form IA
toward a slightly better planar one in form IB. Whereas, the
requirement of this feature demands the molecule to disorder
the ortho-positioned fluorine atom in form II, 2FBCTU.
Isostructuralism through Isosterism. The compounds
26DFBCTU and BCTU were specially designed as a difluoro
and a nonfluoro analog of 2FBCTU, respectively (Scheme 1).
4533
dx.doi.org/10.1021/cg300699r | Cryst. Growth Des. 2012, 12, 4530−4534

Crystal Growth & Design
Article
REFERENCES
■
(1) (a) Bernstein, J. Polymorphism in Molecular Crystals; Clarendon
Press: Oxford, 2002. (b) Kuleshova, L. N.; Antipin, M. Yu. Crystallogr.
Rep. 2002, 47, 268.
(2) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311−2327.
(3) Nangia, A. New J. Chem. 2000, 24, 1049−1055.
(4) Hathwar, V. R.; Thakur, T. S.; Guru Row, T. N.; Desiraju, G. R.
Cryst. Growth Des. 2011, 11, 616−623.
(5) Desiraju, G. R. Cryst. Growth Des. 2008, 8, 3−5.
(6) Anderson, K. M.; Goeta, A. E.; Steed, J. W. Cryst. Growth Des.
2008, 8, 2517−2524. Thakur, T. S.; Sathishkumar, R.; Dikundwar, A.
G.; Guru Row, T. N.; Desiraju, G. R. Cryst. Growth Des. 2010, 10,
4246−4249.
(7) Steed, J. W. CrystEngComm 2003, 5, 169−179. Desiraju, G. R.
CrystEngComm 2007, 9, 91−92. Nangia, A. Acc. Chem. Res. 2008, 41,
595−604. Nichol, G. S.; Clegg, W. CrystEngComm 2007, 9, 959−960.
Bernstein, J.; Dunitz, J. D.; Gavezzotti, A. Cryst. Growth Des. 2008, 8,
2011−2018. Gavezzotti, A. CrystEngComm 2008, 10, 389−398.
(8) Kuleshova, L. N.; Antipin, M. Yu.; Komkov, I. V. J. Mol. Struct.
2003, 647, 41−51.
(9) Shilov, G. V.; Zhilyaeva, E. I.; Flakina, A. M.; Torunova, S. A.;
Lyubovskii, R. B.; Aldoshin, S. M.; Lyubovskaya, R. N. CrystEngComm
2011, 13, 1467−1473.
(10) Das, D.; Engel, E.; Barbour, L. J. Chem. Commun. 2010, 46,
1676−1678.
Figure 6. A packing overlay diagram of the three isostructural (C2/c; Z
= 8) compounds: 2FBCTU (form II), 26DFBCTU, and BCTU. The
hydrogen atoms have been omitted for clarity. Molecular dimeric
chains (shown in Figure 3) formed via N−H···S/N−H···O hydrogen
bonds are along the b-axis, that is, running out of plane of the paper.
CONCLUSION
■
(11) Mahapatra, S.; Thakur, T. S.; Joseph, S.; Varughese, S.; Desiraju,
G. R. Cryst. Growth Des. 2010, 10, 3191−3202. Das, D.; Banerjee, R.;
Mondal, R.; Howard, J. A. K.; Boese, R.; Desiraju, G. R. Chem.
Commun. 2006, 555−557.
It has been shown that the propensity to form a planar
molecular dimeric chain through centrosymmetric R2 (12) and
2
2
R2 (8) synthons built with well-defined N−H···O and N−H···S
hydrogen bonds dictates the phase transformation, poly-
morphism, and disorder in compound 2FBCTU. Indeed the
same “symmetry-driven, geometry-controlled” requirement
brings in isosterism and isostructuralism in the crystals of
2FBCTU (form II), BCTU, and 26DFBCTU. The potential of
a conserved synthon to serve as a common “origin” for
polymorphism, disorder, phase transformation, isostructuralism,
and isosterism in a single molecular species (parent molecule
and F-substituted derivatives) has been illustrated.
(12) (a) Ojima, I., McCarthy, J. T., Welch, J. T., Eds. Biomedical
Frontiers of Fluorine Chemistry; ACS Symposium Series 639; American
Chemical Society: Washington, DC, 2000. (b) Ramachandran, P. V.
Asymmetric Fluoroorganic Chemistry: Synthesis, Applications and Future
Directions; ACS Symposium Series 746; American Chemical Society,
Washington, DC, 2000.
(13) Nayak, S. K.; Reddy, M. K.; Chopra, D.; Guru Row, T. N.
CrystEngComm 2012, 14, 200.
(14) Dikundwar, A. G.; Sathishkumar, R.; Guru Row, T. N.; Desiraju,
G. R. Cryst. Growth Des. 2011, 11, 3954−3963.
(15) Dunitz, J. D.; Taylor, R. Chem.Eur. J. 1997, 3, 89. Dunitz, J. D.
ChemBioChem 2004, 5, 614. Dunitz, J. D.; Schweizer, W. B. Chem.
Eur. J. 2006, 12, 6804. Cozzi, F.; Bacchi, S.; Filippini, G.; Pilati, T.;
Gavezzotti, A. Chem.Eur. J. 2007, 13, 7177. Shimoni, L.; Glusker, J.
P. Struct. Chem. 1994, 5, 383. Howard, J. A. K.; Hoy, V. J.; O’Hagan,
D.; Smith, G. T. Tetrahedron 1996, 52, 12613. Reichenbacher, K.; Suss,
H. I.; Hulliger, J. Chem. Soc. Rev. 2005, 34, 22−30. Chopra, D.; Guru
Row, T. N. CrystEngComm 2011, 13, 2175−2186.
(16) Krishnamurthy, R.; Govindaraghavan, S.; Narayanasamy, J.
Pestic. Sci. 1999, 52, 145−151. Pete, U. D.; Zade, C. M.; Bhosale, J. D.;
Tupe, S. G.; Chaudhary, P. M.; Dikundwar, A. G.; Bendre, R. S. Bioorg.
Med. Chem. Lett. 2012, in press.
ASSOCIATED CONTENT
■
S
* Supporting Information
Detailed procedure for the synthesis of compounds 2FBCTU,
BCTU, and 26DFBCTU with spectroscopic data, CSD search
details with REFCODES, crystallographic information files
(CCDC 805403, 870457-60) of 2FBCTU (form IA, form IB,
and form II), BCTU, and 26DFBCTU, and details of variable-
temperature single-crystal XRD experiments with CIFs. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(17) Oxford Diffraction (2009). CrysAlis CCD and CrysAlisPro
RED, Version 1.171.33.34d. Oxford Diffraction Ltd., Abingdon,
Oxfordshire, England.
AUTHOR INFORMATION
■
(18) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
(19) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838.
(20) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.;
Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339−341.
(21) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(22) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7−13.
(23) Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.;
Shields, G. P.; Taylor, R.; Towler, M.; Van de Streek, J. J. Appl.
Crystallogr. 2006, 39, 453−457.
Corresponding Author
*Fax: +91-80-23601310. Tel: +91-80-22932796. E-mail:
ssctng@sscu.iisc.ernet.in (T.N.G.R.). Fax: +91-257-2258403.
Tel: +91-257-2257435. E-mail:bendrers@rediffmail.com
(R.S.B.).
Notes
The authors declare no competing financial interest.
(24) Allen, F. R. Acta Crystallogr. 2002, B58, 380−388.
ACKNOWLEDGMENTS
■
A.G.D. thanks CSIR, New Delhi, for Senior Research
Fellowship; U.D.P. and R.S.B. are thankful to UGC, New
Delhi, for financial assistance. T.N.G. thanks DST, India, for J.
C. Bose fellowship.
4534
dx.doi.org/10.1021/cg300699r | Cryst. Growth Des. 2012, 12, 4530−4534