Coordination polymers of organic polymers synthesized via photopolymerization of single crystals: Two-dimensional hydrogen bonding layers with amazing shock absorbing nature

Article abstract of DOI:10.1039/c4cc00625a

Crystalline coordination polymers of organic polymers (CPOPs) were synthesized via photopolymerization of Ag(i) coordination polymers of dienes which have a self-templating nature due to the formation of N-H...O hydrogen bonded layers. The shock absorbing nature of the H-bonded layer facilitated the SCSC [2+2] transformation upon irradiation to produce CPOPs. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4cc00625a

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Coordination polymers of organic polymers
synthesized via photopolymerization of single
crystals: two-dimensional hydrogen bonding
layers with amazing shock absorbing nature†
Cite this: Chem. Commun., 2014,
0, 3568
5
Received 24th January 2014,
Accepted 10th February 2014
Mousumi Garai and Kumar Biradha*
DOI: 10.1039/c4cc00625a
www.rsc.org/chemcomm
Crystalline coordination polymers of organic polymers (CPOPs)
were synthesized via photopolymerization of Ag(I) coordination
polymers of dienes which have a self-templating nature due to
the formation of N–Hꢀ ꢀ ꢀO hydrogen bonded layers. The shock
absorbing nature of the H-bonded layer facilitated the SCSC [2+2]
transformation upon irradiation to produce CPOPs.
Scheme 1
Coordination polymers (CPs) are of current interest due to their
intriguing structures, multifunctional aspects and dynamic
1
–3
aspects.
Several thousands of CPs have been reported to bonding layers provides an excellent opportunity for producing
date by linking transition metals with small organic molecules. unprecedented crystalline CPs of organic polymers (CPOPs),
However, CPs formed using an organic polymer (OP) as a linker the first reports, via single-crystal-to-single-crystal transforma-
6
between the metal atoms have not been reported to date given the tion (Scheme 1).
lower solubility of organic polymers and difficulty in obtaining
Molecule 1a was found to be photostable in its crystalline state as
single crystals of such complexes. Here, we demonstrate very rare it forms a b-sheet network, which places the double bonds at
examples of CPs of OPs. In the literature, there are some examples unreactive distances. Single crystals of CPs of 1a and 1b with Ag(I)
where the solid state photo-dimerization was used as a tool for are prepared in anticipation of the hydrogen bonding layer which
7
increasing the dimensionality of the network, as the molecules can polymerize the molecules of 1. The single crystals of complex 2,
belonging to the neighbouring networks dimerize via [2+2] [Ag(1a)(ClO
reaction in a SCSC fashion. However, such reactions to date EtOH and a drop of NH
4
)]
n
, were obtained by the reaction of 1a with AgClO
4
in
4
4
OH. The single crystal analysis reveals that
have not been used for polymerization of the organic ligands 2 contains one-dimensional zig-zag chains of Agꢀ1a which are cross-
containing olefin moieties that serve as the backbone of CPs. linked by disordered perchlorate ions. The asymmetric unit is
Recently we have reported that 1b upon photo-irradiation constituted by half unit each of Ag(I), 1a and ClO
4
ions. The Ag(I)
5
polymerizes to produce 1D-covalent polymers in a SCSC fashion.
exhibits a square planar geometry with the coordination of two
In those studies, it was found that the formation of the N–HꢀꢀꢀO pyridyl N-atoms and two O-atoms of perchlorate ions. The cross-
hydrogen bonding layer is an essential requirement for such linking of 1D chains of Agꢀ1a takes place such that the linked Ag(I)
polymerization reactions. The hydrogen bonding layer was retained atoms (inter-chain) are separated by perchlorate ions by 5.634 Å
before and after the reaction by changing the angles between the (Fig. 1). The Agꢀ1a chains are further interlinked by N–HꢀꢀꢀO
hydrogen bonded amide groups which was attributed to the shock hydrogen bonding layers between the molecules of 1a. Such a
absorbing nature of the layer. Therefore, we thought that the hydrogen bonding layer was described by us earlier as a self-
synthesis of CPs of derivatives of 1 containing such hydrogen templating polymerization layer, which allows facile transformation
to polymerization in a single crystal to crystal manner due to the
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Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India.
shock absorbing nature of hydrogen bonds. The double bonds in 2
were found to be placed in reactive orientations as required (3.714 Å
and CQCꢀꢀꢀCQC torsion angle 01). Accordingly, the single crystals
E-mail: kbiradha@chem.iitkgp.ernet.in; Tel: +91-3222-283346
†
Electronic Supplementary Information (ESI) available: Experimental details and
1
characterization of the compounds by H-NMR spectroscopy, FTIR spectroscopy,
PXRD analysis, MALDI-TOF mass spectroscopy and thermal analysis, and crystal-
lographic data and refinement details. CCDC 965790–965796. For ESI and crystal-
lographic data in CIF or other electronic format see DOI: 10.1039/c4cc00625a
0
of 2 were irradiated with sunlight to obtain single crystals of 2 .
The crystal structure analysis of 2 reveals that the polymerization
occurred to yield crystals of a CP of an organic polymer (CPOP) with
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of N–C–C–N (1801 in 2 and 1801 and 1731 in 2 ). Significant
0
differences in ClO
4
ions between 2 and 2 were observed: in 2,
disordered ClO ions are coordinated to Ag(I) with a distance as
4
0
short as 2.497 Å, whereas in 2 they are ordered and coordinated
with longer distances of 2.797, 2.979 and 3.007 Å and the cross-
linked Ag atoms exhibit the Agꢀ ꢀ ꢀAg distances of 4.851 and
5.505 Å (5.634 Å in 2).
The polymerization occurred between the CP chains but
within the hydrogen bonding layers. As a result, 1D-CPs are
converted into 2D-CPs (Fig. 2a). The layers contain rectangular
grids of dimensions 10.3 ꢁ 13 Å in which two of the edges are
formed by organic polymers and two of the edges are formed by
coordination polymers. Two of such layers are interpenetrated
(
inclined mode) via amide-to-amide hydrogen bonds to result
Fig. 1 Illustration of the crystal structure of 2: (a) cross packing of 1D-
chains (green and red) via N–Hꢀ ꢀ ꢀO hydrogen bonding; (b) 2D-hydrogen
bonding network that serves as a self-template for polymerization, notice
double-headed arrows showing the reactive sites.
in an overall 3D-network (Fig. 2b). It was also found that the
organic polymer can be isolated from the CPOP by an acid–base
workup. The H NMR of separated material in D
1
2
O with a drop
of HCl reveals the presence of cyclobutane protons at d = 4.40
and 3.92 ppm and the absence of olefinic protons indicating
the quantitative conversion to a polymer (Fig. 3).
Furthermore, the longer ligand containing the butyl spacer
was also found to form crystals of iso-structural complex 3,
4 n 4
[Ag(1b)(ClO )] , when reacted with AgClO in the above-
mentioned manner. The irradiation of these crystals resulted
0
in the single crystals of complex 3 . The crystal structure
0
analysis reveals that the content of the asymmetric unit of 3
3
is four times that of 3 (unit cell volume 2212 versus 4352 Å ) due
to the doubling of the cell and change in the space group (C2/c
to C2) with an overall compression of 1.6% of crystal volume.
The cross-linked Ag(I) atoms exhibit Agꢀ ꢀ ꢀAg distances of 6.380 Å
0
(
Ag–O 2.776 Å) in 3 and 6.188 and 6.625 Å in 3 (Ag–O 3.167 Å,
3.073 Å, 2.985 Å). The CPOP layer contains square grids of
dimensions 12.75 and 12.95 Å, which are doubly interpenetrated
via the 2D-hydrogen bonding layer to result in a three-
dimensional structure (Fig. S21, see in the ESI†). We note here
that the hydrogen bonding parameters remain almost similar for
both the structures but several adjustments in the layers were
0
Fig. 2 Illustration of the crystal structure of 2 : (a) two-dimensional layer
of CPOP; (b) the double interpenetration of 2D-networks in inclined mode
(left), hydrogen bonding between the interpenetrated networks (right).
significant changes in the crystal structure (Fig. 2). Although the
space group remains the same, the content of the asymmetric unit of
0
3
2
was increased three times (unit cell volume 1974 versus 5783 Å )
with an overall compression due to polymerization by 2.5% of crystal
volume.
Interestingly, the hydrogen bonding layer remains intact
during the entire course of reaction with albeit minor differences
1
Fig. 3 H NMR spectra in D
2
O + HCl: (a) of 1a, notice the doublets at 7.32
and 6.67 ppm for olefin protons; (b) of the isolated polymer of 1a, notice
in the form of interplanar angles between the H-bonded amide
planes (51 in 2 and 01and 171 in 2 ) and changes in torsion angles protons at 4.40 and 3.92 ppm.
the absence of doublets and the presence of signals for cyclobutane
0
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observed in terms of interplanar angles between the amide quantitative yield, which is evidenced by H NMR and XRPD
0
planes (161 in 3 and 171 and 81 in 3 ) and alkyl chain geometries patterns.
0
0
0 0
(1801 in 3 and 1791, 741 in 3 ). In the case of 2 and 2 , the H-bonded
To determine the molecular weight of these polymers (2 –5 ),
amide planes are parallel to each other before reaction whereas the MALDI-TOF mass spectra were recorded using 2,5-dihydroxy-
0
they become angular after reaction. In the case of 3 and 3 , the benzoic acid (DBH) as a matrix and sodium tri-fluoroacetate as a
H-bonded amide groups are in plane before reaction, which cationizing agent. In all the cases, the molecular weight corres-
become separated into two parallel planes after reaction.
ponding to 7-mer was observed.
To investigate the influence of anions, the reactions of 1a
In summary, four examples of crystalline materials of coordina-
and 1b with AgNO
of NH OH to produce single crystals of 4, [Ag(1a)(NO
Ag(1b)(NO )] , respectively. The crystal structures of 4 (triclinic, ligands in the crystal structure of CPs helps in self-templating the
3
were conducted in MeOH–DCM with a drop tion polymers of organic polymers were produced by [2+2] reaction
4
3 n
)] , and 5, of dienes in a SCSC manner. The 2D-hydrogen bonding layer of the
[
3
n
P1%) and 5 (monoclinic, C /c) were found to contain similar one- reaction and also the layer adjusts itself according to the demands of
2
dimensional chains, which are observed in 2 and 3. The one- structural transformation of the crystal. This reaction serves as a
dimensional chains are interlinked by similar 2D-hydrogen means of producing crystalline CPs of OPs otherwise impossible to
bonding layers, which facilitate polymerization. In the case of produce. Fragment 1 as such is amenable to functionalizations and
4
, the asymmetric unit is constituted by two Ag(I) ions, one and modifications, which provide an opportunity for the creation of
two half units of 1a and two nitrate ions which are disordered. several such CPOPs by extending the similar strategy.
The Ag(I) ion exhibits linear coordination geometry and is We gratefully acknowledge financial support from DST and
connected to two 3-pyridyl units. The zig-zag chains pack in a DST-FIST for single crystal X-ray facility. MG thanks IIT-KGP for
crisscross manner such that the molecules of 1a from adjacent a research fellowship.
networks are linked through N–Hꢀ ꢀ ꢀO hydrogen bonds to form
an anticipated layer. Accordingly, the irradiation of 4 leads to
Notes and references
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0
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3570 | Chem. Commun., 2014, 50, 3568--3570
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