Organic complexes built by halogenated molecules: Unexpected in situ C-N bond formation in metal-free solvothermal conditions

Article abstract of DOI:10.1021/cg101550w

Reactions of two halogenated derivatives of bis(4-hydroxyphenyl)sulphone (BPS, 1), tetrabromobisphenol-S (TBBPS, 2), and tetrachlorobisphenol-S (TCBPS, 3), with piperazine (PZ, 4), were investigated by means of the combinational usage of solvothermal and mechanochemical methods. The resultant organic complexes, [(C₆H₂OBr₂)₂SO ₂]?[(C₄H₁₀N₂) ₂CH₂] (5), [(C₆H₂OBr ₂)₂SO₂]₂?(C₄H ₁₂N₂)₂?3(CH₃OH) (6), [(C ₆H₂OCl₂)₂SO₂] ?[(C₄H₁₀N₂)₂CH₂] (7), and [(C₆H₂OCl₂)₂SO ₂]₂?(C₄H₁₂N₂) ₂?3(CH₃OH) (8), were fully characterized by single crystal and powder X-ray diffractions. In the cases of complexes 5 and 7 that were prepared from solvothermal conditions, a rare metal-free in situ ligand formation has been observed, in which the new organic molecule 1,2-bispiperazinylmethane was presumably originated from the double C-N coupling of two piperazines on a carbon atom coming from methanol. In addition, the relevant concomitants 6 and 8 were also isolated from the solutions of 5 and 7, respectively. Complexes 6 and 8 contain 1:1 starting molecules of 2/3 with 4 assembled into helical structures.

Full text of DOI:10.1021/cg101550w

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pubs.acs.org/crystal
Organic Complexes Built by Halogenated Molecules: Unexpected
in Situ CꢀN Bond Formation in Metal-Free Solvothermal Conditions
Jian L€u,† Li-Wei Han,†,‡ Jing-Xiang Lin,† and Rong Cao*,†
†State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fujian, Fuzhou 350002, P. R. China
‡Graduate School, Chinese Academy of Sciences, Beijing 100039, P. R. China
S Supporting Information
b
ABSTRACT: Reactions of two halogenated derivatives of bis(4-hydroxyphenyl)sulphone
(BPS, 1), tetrabromobisphenol-S (TBBPS, 2), and tetrachlorobisphenol-S (TCBPS, 3), with
piperazine (PZ, 4), were investigated by means of the combinational usage of solvothermal
and mechanochemical methods. The resultant organic complexes, [(C6H2OBr2)2SO2] -
3
[(C4H10N2)2CH2] (5), [(C6H2OBr2)2SO2]2 (C4H12N2)2 3(CH3OH) (6), [(C6H2-
3
3
OCl2)2SO2] [(C4H10N2)2CH2] (7), and [(C6H2OCl2)2SO2]2 (C4H12N2)2 3(CH3OH)
3
3
3
(8), were fully characterized by single crystal and powder X-ray diffractions. In the cases of
complexes 5 and 7 that were prepared from solvothermal conditions, a rare metal-free in situ
ligand formation has been observed, in which the new organic molecule 1,2-bispiperazi-
nylmethane was presumably originated from the double CꢀN coupling of two piperazines
on a carbon atom coming from methanol. In addition, the relevant concomitants 6 and 8
were also isolated from the solutions of 5 and 7, respectively. Complexes 6 and 8 contain 1:1
starting molecules of 2/3 with 4 assembled into helical structures.
rystalline materials of organic complexes are notable repre-
sentatives in supramolecular chemistry because of both their
groups and as potential donor sites to form secondary X-bonds
that may direct the hierarchical assemblies.
The supramolecular chemistry of bis(4-hydroxyphe-
nyl)sulphone (BPS, 1) was investigated and showed efficient
and robust ability to form organic complexes with a series of
C
structural complexity and physical property of interest, in which
the role of hydrogen bonds (H-bonds), as predominant driven
forces, has been well-established.1,2 Most hydrogen bonds are
primarily electrostatic in nature and flexible in strength, accord-
ing to the different electron donors and acceptors. Of note,
relatively simple covalent modifications in external conditions of
organic molecules can change the balance of weak interactions
and alter the secondary structures. In addition, halogen atoms
have been known to form well-defined adducts with electron
donor species through noncovalent halogen bonds (X-bonds).
However, it is only recently that heuristic principles are presented
to develop a rational crystal engineering of halogen bonded
organic complexes, relying on the directional and predictive
nature of these intermolecular cohesive interactions.3 As a
consequence, halogen bonding has soon been proven as an
effective supramolecular interaction in self-assembly processes
and awakens considerable research interest in many practical
realms, including molecular recognition, drugꢀreceptor interac-
tion, supramolecular organic conductors, and liquid crystals.4
Our current strategy focuses on investigating the effects of
halogenation on traditional organic modules in construction of
supramolecular organic complexes. In the current systems,
halogen atoms were introduced onto the organic precursors that
possess terminal hydroxyl groups; thus, the halogen atoms are
able to play dual roles both as modification to adjust the primary
hydrogen bonds formed by the H-bond donating hydroxyl
organoamines via charge-assisted Ohydroxyl
H
N hydrogen
3 3 3 3 3 3
bonds with or without proton transfer.5 We target on the
halogenated BPS as modeling molecules based on the following
considerations: (i) the ability of the hydroxyl groups on haloge-
nated BPS to form hydrogen bonds can be boosted due to the
substitution of electron-withdrawing halogen atoms; (ii) H-bond
strengths of the halogenated BPS molecules can be carefully
tuned through relatively simple covalent modifications with
different halogen atoms,1d which, we believe, may endow some
superiority in directing the molecular assembly and recognition;
(iii) the halogenated BPS molecules are able to generate sec-
ondary halogen bonds due to the introduction of X-bond donors,
which may result in new and interesting supramolecular assem-
blies. We have successfully demonstrated that tetrabromobi-
sphenolsulphone (TBBPS, 2) crystallized with 1,3-bis(4-pyridyl)
propane (BPP), among others, differently from the parent BPS
and resulted in an organic cocrystal with an unprecedented
braidlike molecular assembly.6 As part of the extension into a more
complex sysmtem, we report herein the reactions of two halogenated
Received: November 22, 2010
Revised:
March 29, 2011
Published: April 22, 2011
r
2011 American Chemical Society
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dx.doi.org/10.1021/cg101550w Cryst. Growth Des. 2011, 11, 2035–2038
|

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Scheme 1. Synthesis of TBBPS/TCBPS and complexes 5ꢀ8
Figure 1. View of the hydrogen bonds between the BPZM and TBBPS
(a and b); and the 3D supramolecular structure in complex 5 (c).
molecules, tetrabromobisphenolsulphone (2) and tetrachlorobisphe-
nolsulphone (TCBPS, 3), with piperazine (PZ, 4) by the combina-
tional usage of solvothermal and mechanochemical methods.
transꢀtrans configuration (defined by the central sp3 carbon),
and the terminal piperazinyl N N distance is 7.554 Å, which is
3 3 3
The halogenated organic molecules, TBBPS and TCBPS,
were prepared from the reactions of BPS with bromine or
chlorine in glacial acetic acid at 85 °C (see Supporting Informa-
tion in detail), respectively (Scheme 1). The solvothermal
method was introduced because of the poor solubilities of
TBBPS and TCBPS in methanol. Moreover, white precipitate
appeared immediately when solutions of TBPPS/TCBPS and
piperazine were mixed, which detered the further crystallization
of single crystals. Reaction of 1:1 TBBPS and PZ in methanol at
135 °C yielded a small amount of colorless and irregular crystal-
line solids, which is insoluble in water and common organic
solvents. Single crystal X-ray diffraction indicated an unexpected
somewhat shorter than the actual donorꢀdonor distance
(Ohydroxyl Ohydroxyl) of 9.072 Å in TBBPS. Each BPZM
3 3 3
connects to four TBBPS, and the TBBPS in turn interacts with
four BPZM to form a three-dimensional (3D) supramolecular
network. Topological analysis7 considering H-bonds as primary
intermolecular forces of complex 5 indicates that it possesses a
four-connected uninodal sra (SrAl2) net (point symbol
(42 63 8), vertex symbol [4 6 4 6 6 82]) by choosing the
3
3
3 3 3 3 3
two types of organic molecules as simple nodes.
A possible reaction mechanism concerning the formation of
the new BPZM molecule is proposed and illustrated in Scheme
S1 (Supporting Information). Reportedly, a similar reaction can
be achieved in the presence of Al2O3.8ꢀ10 Attempts at carrying
out the reactions using the nonbrominated reagent 1 (BPS)
afforded no outcome of expecting reactions. This result supports
the hypothesis that the halogenated reagents 2 (TBBPS) and 3
(TCBPS) promote the CꢀN coupling under the metal-free
solvothermal conditions.
Single-crystal X-ray crystallographic analysis reveals that com-
plex 6 crystallizes in tetragonal space group P41212 (flack
parameter 0.02(2)). In the structure of 6, TBBPS and PZ form
a 1:1 complex with three MeOH solvent molecules per formula
unit (Figure 2a and b). The assembly of complex 6 is directed
crystal phase, formulated as [(C6H2OBr2)2SO2] [(C4H10N2)2
3
CH2] (complex 5), in which a new organic molecule formed
in situ. The above solution was allowed to evaporate in ambient
condition and resulted in light-yellow block crystals together
with some unidentified yellow slurry. The structure of the block
crystals was determined by single crystal X-ray diffraction and
formulated as [(C6H2OBr2)2SO2]2 (C4H12N2)2 3(CH3OH)
3
3
(complex 6). The bulk of complex 5 can be obtained from
optimized reactions with 1:2 TBBPS and PZ in methanol.
However, the pure bulk of complex 6 was perturbed by both
the low yield and slurry impurities. Fortunately, mechanochem-
ical reaction by manual grinding of 1:1 TBBPS and PZ in a agate
mortar with several drops of methanol gave a bulky sample of
complex 6 that was confirmed by XRPD (Figure S2 of the
Supporting Information). Reactions using TCBPS to replace
TBBPS gave complexes 7 and 8 accordingly.
by Ohydroxyl HꢀN hydrogen bonds between the hydroxyl O
3 3 3
atoms of TBBPS and the piperazinyl nitrogen atoms of PZ
(Ohydroxyl HꢀN 2.581ꢀ2.688 Å), which are considerably
3 3 3
shorter than the O HꢀN hydrogen bonds in complex 5
3 3 3
(2.720ꢀ2.777 Å). The TBBPS and PZ connect to each other
in a way that the TBBPS molecules pack into double helices due
to their “bent” nature and the PZ molecules locate in between the
two helical chains (Figure 2c). The double helices pack along the
crystallographic c axis into a 3D supramolecular structure invol-
ving secondary halogen bonds between Br atoms of TBBPS and
Complexes 5 and 7 are isomorphous; therefore, only the
structure of complex 5 is presented (Figure 1). Single-crystal
X-ray crystallographic analysis shows that complex 5 crystallizes
in monoclinic space group P21/n. It is evident that a new organic
molecule, 1,2-bispiperazinylmethane (BPZM for short), was
formed during the solvothermal reaction. The in situ generated
BPZM molecules form a 1:1 complex with TBBPS (5). The
O donors of methanol (Br Omethanol = 3.276 Å) (Figure 2d).
3 3 3
Complex 8 possesses an identical packing pattern as 6 but
crystallized with an opposite absolute configuration (space group
P43212, flack parameter ꢀ0.02(9)).
molecular aggregation of complex 5 is dominated by Ohydroxyl
3
HꢀN hydrogen bonds between the hydroxyl O atoms of
3 3
TBBPS and the piperazinyl nitrogen atoms of BPZM (Ohydroxyl
Binary and ternary organic complexes formed by means of chiral
crystallization from achiral molecular building blocks have been
HꢀN 2.720ꢀ2.777 Å). The BPZM molecule adopts a
3 3 3
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Crystal Growth & Design
COMMUNICATION
bonds, Ohydroxyl HꢀN (2.579 Å) and Ohydroxyl Hꢀ
3 3 3
3 3 3
Ohydroxyl (2.560 Å), respectively (Figure S3a, Supporting Infor-
mation).5 The ring chains are further extended by week
Osulfuryl HꢀN (2.918 Å and 2.985 Å) and Osulfuryl HꢀC
3 3 3
3 3 3
(2.975 Å) hydrogen bonds into a 3D supramolecular structure
(Figure S3b, Supporting Information). Thestructureofcomplex9
is somewhat straightforward and significantly different from those of
complexes 6 and 8 built by halogenated modules with PZ.
In summary, the present work serves to explore the effects of
halogenations on the structures and physical properties of the
new organic complexes. Furthermore, we introduce the sol-
vothermal method in the synthesis of organic complexes in
solving the problem related to the competition between hetero-
meric and homomeric crystallizations in conventional synthesis.
It has been shown that the modification on traditional organic
molecules would be a successful synthetic strategy to construct
supramolecular organic complexes thanks to the hierarchy of
intermolecular interactions. In the reaction system of haloge-
nated BPS (TBBPS and TCBPS) with piperazine, the strength of
primary O HꢀN H-bonds has been rationally modified by
3 3 3
the electron-withdrawing halogen atoms, and the inclusion of
secondary Br O X-bonds results in various changes in the
3 3 3
crystal packing. Of note, the unexpected in situ ligand formation
by CꢀN coupling in complex 5/7 is related to the halogenated
modules, although a clear mechanism is awaiting disclosure.
Figure 2. View of the hydrogen bonds between the PZ and TBBPS
(a) and (b); the double helical subunit (c); and the 3D packing pattern
of complex 7 (d).
’ CRYSTAL STRUCTURE DETERMINATION
rationalized in the system of benzoic acid with organic amines. A key
factor has been the multiple roles that the carboxyl group and amino
nitrogen atom play as electron donors and acceptors, giving birth to
Crystallographic data were collected on a Rigaku Mercury CCD/
AFC diffractometer equipped with graphite-monochromated Mo
KR radiation with a radiation wavelength of 0.71073 Å by using the
ω-scan technique. All absorption corrections were performed us-
ing the CrystalClear program.14 Structures were solved by direct
methods and refined on F2 by full matrix least-squares using the
SHELXL-97 program package.15 All the non-hydrogen atoms were
refined anisotropically. The active H atoms on organic molecules
were found on a Fourier-difference map, and other H atoms were
generated geometrically. CCDC-775137 (5), 784281 (6), 784280
(7), and 784282 (8) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
Crystal/Refinement Details for 5. C21H26Br4N4O4S, M =
750.16, monoclinic, P21/n, a = 10.2780(4), b = 12.0006(3),
c = 21.9936(6), β = 95.190(3), V = 2701.62(2), Z = 4, R1
[I > 2σ(I)] = 0.0490, wR2 = 0.1386. For 6: C17.5H22Br4N2O5.5S,
M = 700.07, tetragonal, P41212, a = 15.8417(6), b = 15.8417(6),
c = 19.1079(1), V = 4795.3(4), Z = 8, R1 [I > 2σ(I)] = 0.0626,
wR2 = 0.1882. For 7: C21H26Cl4N4O4S, M = 572.32, monoclinic,
P21/n, a = 10.3884(4), b = 11.4896(3), c = 21.6902(6), β =
94.662(3), V = 2580.35(1), Z = 4, R1 [I > 2σ(I)] = 0.0520, wR2 =
0.1808. For 8: C17.5H22Cl4N2O5.5S, M = 522.23, tetragonal,
P43212, a = 15.543(3), b = 15.543(3), c = 19.210(5), V =
4641.1(2), Z = 8, R1 [I > 2σ(I)] = 0.0555, wR2 = 0.1705.
O
H
N supramolecular interactions as the main driven forces
3 3 3 3 3 3
in the molecular packing.11 Moreover, remnant functional groups
capable of generating weaker intermolecular forces are also respon-
sible for the chiral crystallization processes. Similarly, in the reaction
system of halogenated bisphenol derivatives with piperazine, the
Ohydroxyl HꢀN interactions direct the molecular packing and the
3 3 3
potential halogen bonding sites offer the opportunity for weaker
molecular interactions, which, we believe, is the determinant of the
chiral crystallizaiton. However, no legible circular dichroism (CD)
has been observed for either a bulky sample (prepared by mechan-
ochemical method) or single crystals. It is possible that the crystal-
line MeOH solvent molecules, which are extensively involved in
secondary halogen bonds, are lost during the preparation of KCl
discs by grinding and compressing, resulting in the disappearance of
chirality.12 Since complexes 6 and 8 display identical structures with
opposite absolute configurations, it is also possible that the bulk
samples are racemic and contain nearly equivalent crystals with
opposite absolute configurations. One reliable but very time-con-
sumingmethodwouldbetodeterminetheabsoluteconfiguration of
all single crystals in one batch.
Proton transfer from TBBPS/TCBPS to PZ is observed in all
cases; thus, complexes 5ꢀ8 are organic salts. Moreover, the
distances of Ohydroxyl HꢀN hydrogen bonds are shorter than
3 3 3
the ordinary H-bond (2.8/2.9 Å, minimum/average distances),
and they are thus considered as double charge-assisted H-bonds
comprised by strong 1/2-D Hþ A1/2ꢀ interactions (D =
’ ASSOCIATED CONTENT
3 3 3
3 3 3
H-bond donor; A = H-bond acceptor).13 However, the reaction
of parent BPS (1) with PZ (4) afforded a 2:1 salt (complex 9)
having 1D ring chain subunits, in which the doubly protonated
PZ molecules connect the rings formed by face-to-face half
deprotonated BPS moieties via two types of strong hydrogen
S
Supporting Information. Experimental details and general
b
1
characterizations, H NMR, XRPD, figures, and crystallographic
data in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
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COMMUNICATION
’ AUTHOR INFORMATION
(10) Reference for ligand formation in the presence of dihalomethane
as solvents. See for example:Miyano, S.; Mori, A.; Hokari, H.; Ohta, K.;
Hashimoto, H. Bull. Chem. Soc. Jpn. 1982, 55, 1331.
Corresponding Author
*E-mail: rcao@fjirsm.ac.cn.
(11) Tan, T.-F.; Han, J.; Pang, M.-L.; Song, H.-B.; Ma, Y.-X.; Meng,
J.-B. Cryst. Growth Des. 2006, 6, 1186.
ꢁ
(12) Lennartson, A.; Hakansson, M. CrystEngComm 2009, 11, 1979.
(13) (a) Gilli, P.; Bertolasi, V.; Ferretti, V.; Gilli, G. J. Am. Chem. Soc.
2000, 122, 10405. (b) Gilli, P.; Bertolasi, V.; Pretto, L.; Ferretti, V.; Gilli,
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5209, USA, and Rigaku Corporation, 3-9-12 Akishima, Tokyo, Japan.
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’ ACKNOWLEDGMENT
Financial support from the 973 Program (2011CB932504,
2007CB815303), NSFC (20731005, 20821061, and 21001105),
NSF of Fujian Province (E0520003), and Key Project from CAS
are gratefully acknowledged. J.L. thanks Prof. Hui Zhang of
Xiamen University (China) and Mr. Yanchuan Zhao of the
Shanghai Institute of Organic Chemistry (Chinese Academy of
Sciences) for helpful discussions.
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