1D, 2D and 3D coordination polymers of 1,3-phenylene diisonicotinate with Cu(i)/Cu(ii): Cu2I2 building block, anion influence and guest inclusions

Article abstract of DOI:10.1039/c4ce00123k

The reactions of a flexible bidentate ligand 1,3-phenylene diisonicotinate (L) with Cu(i/ii) salts afforded coordination polymers with varied dimensionalities and guest inclusion capabilities. Complexation of L with CuI resulted in a 2D-network with (4,4) topology and inclusion of guest molecules such as CHCl₃, bromobenzene, nitrobenzene and benzonitrile. The treatment of L with Cu(PF₆)₂ and Cu(ClO₄) ₂ resulted in a one-dimensional network containing M ₂L₂ macrocycles and a 4-fold interpenetrated three dimensional network having quartz topology, respectively. The 1D-networks included CHCl₃ as guests and the interpenetrated 3D-network includes tetrahedral water clusters.

Full text of DOI:10.1039/c4ce00123k

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1D, 2D and 3D coordination polymers
of 1,3-phenylene diisonicotinate with
Cite this: CrystEngComm, 2014, 16,
Cu(I)/Cu(II): Cu2I2 building block, anion
influence and guest inclusions†
4701
Received 17th January 2014,
Accepted 5th February 2014
*
Gargi Mukherjee and Kumar Biradha
DOI: 10.1039/c4ce00123k
www.rsc.org/crystengcomm
The reactions of
a
flexible bidentate ligand 1,3-phenylene
modes). On the other hand, the ligands with phenyl, hexyl or
octyl spacers have consistently formed 2D-networks which are
further linked by amide-to-amide hydrogen bonds.
diisonicotinate (L) with Cu(I/II) salts afforded coordination polymers
with varied dimensionalities and guest inclusion capabilities.
Complexation of L with CuI resulted in a 2D-network with (4,4)
topology and inclusion of guest molecules such as CHCl3, bromo-
benzene, nitrobenzene and benzonitrile. The treatment of L with
Cu(PF6)2 and Cu(ClO4)2 resulted in a one-dimensional network
containing M2L2 macrocycles and a 4-fold interpenetrated three
dimensional network having quartz topology, respectively. The
1D-networks included CHCl3 as guests and the interpenetrated
3D-network includes tetrahedral water clusters.
Fromm's group and others have explored the network
geometries of ethanediyl bis(isonicotinate) with Cu(I) halides
and AgNO3.7,8 It was observed that diverse types of 1D-chains
were afforded depending on the solvents used. Further, M(II)
halide (Zn, Hg, Co) complexes of the same ligand were
also reported to yield iso-structural metallamacrocycles
with inclusion of guest molecules.9 Furthermore, the role of
spacers containing ester groups which anchor bis-pyridyl
moieties in tailoring the network geometries and properties
was demonstrated by Hosseini's group.10 A set of ester–
pyridine ligands containing various spacers (hexaethylene
glycol, 1,1′-spirobi(indane), dibromofluorene, isomannide,
(R)-6,6′-dibromo-1,1′-binaphthyl) were synthesized and their
combination with different metal salts produced a variety
of novel networks including double stranded interwound
linear networks,10a double stranded interwoven,10b triple
stranded10c and quadruple-stranded helices.10d In this paper,
we wish to present our studies on CPs of an angular bis-
pyridyl ligand (L) containing m-phenylene and ester function-
alities as a backbone. We note here that the corresponding
amide based derivative of L was explored to form CPs
and CP based gels, to the best of our knowledge to date
no CPs of L are explored. Generally, angular or V-shaped
ligands are known to form helical coordination networks
with transition metal ions. Studies on CPs derived from
N,N′-bis(4-pyridinecarboxamide)-1,3-benzene and its reverse
analogue N,N′-bis-(4-pyridyl)isophthalamide with transition
metal salts (e.g., Cu(II) and Zn(II)) revealed to yield mainly
1D-networks.11,12
Coordination polymers (CPs) are being studied extensively due
to their intriguing structures and applicative aspects such as gas
sorption, separation, catalysis, gels and photoluminescence.1,2
The synthesis of new ligands and exploration of their
coordination abilities to form coordination polymers has
developed as an active area of research during the past decade
as there is a direct correlation between structures and
properties. A large amount of CPs reported to date corresponds
to bis(pyridyl) or bis-carboxylate ligands.3,4 Although the coor-
dinating groups, pyridine and carboxylate, play a major role in
the formation of CPs, the backbone that connects these
functional groups plays a more significant role in tailoring the
network topologies and geometries and nature of the cavities
of the CPs.5 We have recently initiated studies on CPs of the
bis(pyridyl) ligand containing secondary amides and phenyl or
alkyl groups –(CH2)n– as a backbone.6 These studies revealed
that CPs containing ligands with shorter spacers such as
–(CH2)2– or –(CH2)4– exhibit versatility in producing 1D chains
containing cavities, open 2D-networks, chiral 2D-networks and
interpenetrated 2D-networks (both parallel and perpendicular
Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India.
E-mail: kbiradha@chem.iitkgp.ernet.in; Fax: +91 3222 282252; Tel: +91 3222 283346
† Electronic supplementary information (ESI) available: Details of synthesis
procedures and characterization of complexes by IR spectra, XRPD and TGA
data. CCDC 981869–981874. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c4ce00123k
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The ligand 1,3-phenylene diisonicotinate (L) was synthe-
sized by reacting resorcinol with isonicotinic acid in chloro-
form in the presence of dicyclohexylcarbodiimide (DCC).13
The Cu(I) and Cu(II) metal salts were considered for complex-
ation with L as we have shown earlier that related amide
containing ligands have more propensity to form crystalline
complexes with these salts. The diffusion of a CH3CN
solution of CuI into a MeOH solution containing ligand
L and a liquid aromatic guest resulted in bright orange
coloured crystals of complexes {(Cu2I2)(L)2·2(guest)}n, 1–4,
containing CHCl3 (1), nitrobenzene (2), benzonitrile (3) and
bromobenzene (4), respectively, as guests. The single crystal
X-ray diffraction analyses revealed that all contain 2D-networks,
and 1 crystallized in P2(1)/c while 2–4 crystallized in P2(1)/n
space group (Fig. 1). All the asymmetric units contain one unit
each of Cu(I), iodide, ligand L, and guest molecules. The Cu(I)
and I− form Cu2I2 SBU in which each Cu(I) adopts a tetrahedral
geometry as two L and two I are coordinated to it. The
isonicotinyl planes of ligand L are nearly perpendicular to
its central C6-ring in all of the four complexes (74.96, 83.74;
67.55, 83.66; 70.55, 82.62; 66.69, 86.20°). However, the position
of CO groups differs, they point in opposite directions in
1 while they are on the same side in 2–4 (Fig. 2a).
Fig. 2 Comparisons of the crystal structures of 1 & 2–4: geometry of L
in (a) 1; (b) 2–4, notice the difference in ester group orientations.
Interior environment remains the same through interdigitation of
layers in (c) 1 & (d) 2–4. Interdigitation through aromatic and OC⋯O
interactions in (e) 1 & (f) 2–4.
Interestingly, the Cu–Cu distance in Cu2I2 SBU was found
to be much shorter (2.634 Å) in 1 than the other three
(2.854, 2.776 & 2.822 Å) complexes.14 Nevertheless, in all of
the structures, the Cu2I2 SBU acts as a four connected planar
node with four units of L linked to it and results in a 2D
network of (4,4) topology containing rhomboidal cavities of
dimension 12.6 × 32.8 Å2. The layers are found to be highly
corrugated such that there exist continuous channels within
the layers. In other words, the 2D-layer can also be described
as the joining of 1D-helices which run along the b-axis
(Fig. 1e). These helices contain elliptical channels that are
occupied by a column of guest molecules (Fig. 1d). Chloroform
molecules were not located in 1; however, aromatic guest
molecules in 2, 3 and 4 were located and found to form a
dimeric column along the b-axis via C–H⋯O (2.799, 3.283 Å),
C–H⋯N (3.566 Å), and C–H⋯Br (3.838, 3.974 Å), respectively
(Fig. 1f). In 1, the Cu(I) SBUs are joined by the ligand with a
distance of 16.716 Å.
The layers pack via the interdigitation of adjacent helices
which occurs through aromatic interactions between the
pyridyl moieties and the central phenyl rings (4.299,
4.180 Å) and OC⋯O interactions (Fig. 2). Although the
geometry of the ligand is different in 1 and 2–4, the interior
environment of the channel remains similar given the
interdigitation of the layers. The solvent accessible volumes
amount to 31.7%, 29.7%, 31.8% and 31.5%, respectively,
in 1–4. We note here that previously the amide analogue
of 1 which contains –HN–C2H4–NH– in place of –O–C6H4–O– in
1 was shown to form a similar type of 2D-layers with Cu2I2
SBU.6a Those layers were found to include only CHCl3/CHBr3
Fig.
1 Illustrations of the crystal structure of 2: 2D layer of
(4,4)-topology: (a) top view, guest molecules were not shown; (b) side
view along the b-axis, guest molecules were shown in space filling
mode; (c) helical nature of the layer; (d) packing of layers via aromatic
and ester–ester interactions; (e) dimeric column of C–H⋯O hydrogen
bonded nitrobenzene molecules in 2.
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molecules as guests across the layers but not within
the layer.
reactions with other guest molecules failed to produce
crystalline materials.
The reactions of L with Cu(II) metal salts such as Cu(PF6)2
and Cu(ClO4)2 are also investigated to study the network
geometries of the resulted materials, guest inclusion proper-
ties, anion influence and also to understand the difference
between SBU based and non-SBU based complexes. The reac-
tion of L with Cu(PF6)2 and Cu(ClO4)2 resulted in the crystals
of complexes {[Cu(L)2(H2O)2)]·2(PF6)·(CHCl3)}n, 5, and
Complex 6 crystallizes in C2 space group (Fig. 4) and
the asymmetric unit is constituted by two Cu(II) ions with
occupancies of 1 and 0.5, three units of L, anions and water
molecules. The Cu(II) centres exhibit two coordination modes:
square pyramidal (Cu1) and distorted octahedral geometry
(Cu2). The Cu1 and coordinated H2O (Cu–O: 2.267(10) Å)
lie on the glide plane and connected to four units of L in
equatorial positions (Cu–N: 1.984(7), 2.032(7) Å). Whereas,
the Cu2 exhibits distorted octahedral geometry with two water
molecules at axial sites, one of which exhibited a very weak
interaction (2.649 Å) and was removed during final refine-
ment, due to very high thermal motion, using the PLATON
squeeze option. The three ligands almost have similar confor-
mational geometries with an overall length (N-atom to N-atom)
of 13 Å. Although the metal centre has square planar coordina-
tion with respect to pyridyl groups, the angular nature of the
ligand results in a tetrahedral building block. The depiction of
Cu(II) centres as nodes and ligands as node-connections reveals
that the network has quartz-type topology and the voids of each
network are filled by 4-fold interpenetration of such networks.
{[Cu3(L)6(H2O)3)(ClO4)6]·14(H2O)}n, 6, respectively, in
MeOH–H2O–CHCl3 solvent system.
a
The crystal structure analysis of 5 reveals that it crystal-
lized in monoclinic C2/c space group and the asymmetric
unit is constituted by one unit each of Cu(II), L, PF6 ion, half
chloroform and coordinated water molecules (Fig. 3). The
Cu(II) centres adopt an octahedral environment with four
ligand units at equatorial sites and two water molecules at
axial sites. The geometry of the ligand is somewhat similar to
the one observed in complex 1; however, it resulted in the
formation of the 1D-network containing M2L2 macrocycles
which facilitated the angular nature of the ligand. The CHCl3
molecule is situated at the centre of M2L2 macrocycles. The
1D-networks are linked to the 2D-network via O–H⋯O hydro-
gen bonds between coordinated H2O and OC of the ester
group (Fig. 3b). We note here that a similar type of hydrogen
bonding was also observed in the CPs of amide analogues.6f
The layers packed on each other via C–H⋯O and edge-to-face
(3.56 Å) aromatic interactions. It is found that these cavities
in 1D-chain are suitable only for CHCl3, unlike 1–4, as the
Fig.
4 Illustrations of the crystal structure of 6: (a) coordination
geometry around Cu(II) ions; 3D-network with cage-like nature:
(b) cylinder mode, (c) space filling mode; (d) depiction of quartz topology
by designating Cu(II) as nodes and ligands as node connections;
(e) 4-fold interpenetration of networks; (f) tetrahedral water cluster
incorporated in the channels of 4-fold interpenetrated nets.
Fig. 3 Illustrations of the crystal structure of 5: (a) 1D-chain containing
M2L2 macrocycles and rectangular cavities; (b) 2D-layer formed by
the joining of 1D-chains via O–H⋯O hydrogen bonds, (c) side view of
packing of the 2D-layers.
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Despite the 4-fold interpenetration, the structure contains
three types of channels: two channels were filled by water
tetramers and the third one was filled by anions which are
hydrogen bonded to coordinated water. It is interesting to
mention here that the water tetramers are found to exhibit
distorted tetrahedron geometries with O⋯O distances ranging
from 2.2 to 3.2 Å.
Acknowledgements
We acknowledge DST, New Delhi, India, for financial support
and DST-FIST for single crystal X-ray diffraction measurements.
GM thanks CSIR for a research fellowship.
The UV-vis absorption spectra of the free ligand (L) and
complexes 1–3 in the solid state were recorded at room
temperature. The spectrum of L shows peaks at 267 and 300 nm
(Fig. 5a). The spectrum of complex 1 shows broad absorption in
the range 250–550 nm with three intense peaks at 268, 352
and 520 nm. A similar type of absorption behaviour was also
observed for the complexes 2 (256, 350, 507 nm) and 3
(263, 350, 510 nm) with a blue shift in all three peaks com-
pared to 1. The blue shift of absorption edges can be corre-
lated with the longer Cu⋯Cu distances in SBUs of 2 (2.854 Å)
and 3 (2.776 Å) compared to 1 (2.634 Å). A further solid state
luminescence study, at the excitation wavelength of 325 nm,
was carried out on complexes 1–3 at room temperature
(Fig. 5b) to determine if there are any apparent differences in
their emission properties. An emission (reddish yellow) peak
of complex 1 was observed at 637 nm. As for complex 2, it is
blue shifted to 633 nm and becomes sharper compared to 1,
while complex 3 exhibits emission band at 634 nm which is
broader compared to 1. The luminescence emission of these
complexes can be attributed to strong cuprophilic inter-
actions observed in the complexes. At room temperature, all
three complexes show a low-energy (LE) broad emission
centred around 630 nm. Based on the previous reports on the
Cu(I) clusters, the LE emissions are assigned to iodide-
to-copper charge transfer transition (XMCT, X = halogen).15
In conclusion, the exo-bidentate bis-pyridyl ligand L was
shown to form coordination networks of versatile topologies
with Cu(I/II) salts. The networks observed here include a 1D
chain with a cavity occupied by anion and CHCl3 guest
molecules, a two-dimensional (4,4) network with elliptical
channels which are occupied by variety of guest molecules,
and a three-dimensional 4-fold interpenetrated network with
quartz topology which accommodates water tetramers. The
angular nature of the ligand imparted some helicity into the
two-dimensional and three-dimensional networks.
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