Synthesis and characterization of Manganese(II), Cobalt(II) and Copper(II) coordination polymers with a flexible zwitterionic based ligand

Article abstract of DOI:10.1016/j.poly.2021.115419

Four new coordination polymers, formulated as {[MnCl(μ-bipna)](NO₃)?2H₂O}_n (1), {[CoCl₂(μ-bipna)]?2H₂O}_n (2), {[CuCl(μ₄-bipna)]BF₄?2H₂O}_n (3) and {[CuCl(μ₄-bipna)]ClO₄?2H₂O}_n (4) where H₂bipnaBr₂ = 1,1′-(1,1′-biphenyl-4,4′-diylbis(methylene))bis(3-carboxypyridin-1-ium) bromide, were synthesized under solvothermal conditions. Their structures have been characterized by single crystal and powder X-ray diffraction analyses, infrared spectra (IR) and elemental analyses. Complexes 1, 3 and 4 are isostructural and display 3-fold interpenetrated 2D → 2D structures with sql topology and the point symbol 4⁴.6². Complex 2 exhibits a 1D coordination polymer structure, which becomes a stacked 3D supramolecular structure by hydrogen bonding and π???π interactions. The structural diversity of the compounds could be due to the conformation of the flexible zwitterionic ligands. In 2, the bipna ligand displays a cis-conformation, while in the other compounds the ligand shows a trans-conformation. The thermal and optical properties of the compounds were investigated.

Full text of DOI:10.1016/j.poly.2021.115419

Polyhedron 208 (2021) 115419
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and characterization of Manganese(II), Cobalt(II) and Copper(II)
coordination polymers with a flexible zwitterionic based ligand
,
*
Esengül Çiftçia, Mürsel Arıcıa, Mario Wriedtb, Okan Zafer Yes¸ilela
a Department of Chemistry, Faculty of Science and Letters, Eskis¸ehir Osmangazi University, 26040 Eskis¸ehir, Turkey
b Department of Chemistry & Biomolecular Science, Clarkson University, Potsdam, NY 13699, USA
A R T I C L E I N F O
A B S T R A C T
Keywords:
Four new coordination polymers, formulated as {[MnCl(µ-bipna)](NO3)⋅2H2O}n (1), {[CoCl2(µ-bipna)]⋅2H2O}n
(2), {[CuCl(µ4-bipna)]BF4⋅2H2O}n (3) and {[CuCl(µ4-bipna)]ClO4⋅2H2O}n (4) where H2bipnaBr2 = 1,1′-(1,1′-
biphenyl-4,4′-diylbis(methylene))bis(3-carboxypyridin-1-ium) bromide, were synthesized under solvothermal
conditions. Their structures have been characterized by single crystal and powder X-ray diffraction analyses,
infrared spectra (IR) and elemental analyses. Complexes 1, 3 and 4 are isostructural and display 3-fold inter-
penetrated 2D → 2D structures with sql topology and the point symbol 44.62. Complex 2 exhibits a 1D coordi-
Coordination polymers
1,1′-(1,1′-biphenyl-4,4′-diylbis(methylene))bis
(3-carboxypyridin-1-ium) bromide complexes
1D/2D complexes
nation polymer structure, which becomes a stacked 3D supramolecular structure by hydrogen bonding and π⋅⋅⋅π
interactions. The structural diversity of the compounds could be due to the conformation of the flexible zwit-
terionic ligands. In 2, the bipna ligand displays a cis-conformation, while in the other compounds the ligand
shows a trans-conformation. The thermal and optical properties of the compounds were investigated.
1. Introduction
constructed from a rarely reported flexible zwitterionic dicarboxylic
acid, 1,1′-biphenyl-4,4′-diylbis(methylene)bis(3-carboxypyridin-1-ium)
The design and synthesis of coordination polymers (CPs) have
attracted considerable attention due to the structural diversities and
topologies and the potential for innovative applications in storage,
separation, electrical conductivity, catalysis, luminescence, drug de-
livery, magnetism and other similar arenas [1–8]. As a result, many
coordination polymers have been synthesized. However, there are
several factors that influence the resulting structures, such as ligands,
metal ions, counter anions, solvents, pH etc. [9–11 ] To obtain the
desired CP structures, a variety of ligands [e.g. rigid or flexible poly-
carboxylic acids and N-donor ligands] or a combination of ligands have
been utilized [12]. Flexible dicarboxylic acids, containing aliphatic
–CH2-groups on their skeletons, are interesting because they exhibit
diverse conformations in the final structures of the newly constructed
CPs [13,14]. Flexible linkers can rotate around the –CH2– groups and
connect easily to metal ions. These rotations around the –CH2– groups
can affect the dimensionality, resulting in unpredictable CP architec-
tures [15,16].
dibromide (Scheme 1, Figure 4 H2bipnaBr2) [23,24]. Due to the posi-
tively charged pyridinium units and negatively charged carboxylate
units within this ligand’s compounds, the functionally the ligand can be
neutral. Counter ions balance the charge of the metal ions in bipna
compounds. The bipna ligand has four carboxylate oxygen atoms to
connect to metal ions and can adopt diverse coordination modes in its
resulting compounds. In this context, four coordination polymers,
formulated as {[MnCl(µ-bipna)]NO3⋅2H2O}n (1), {[CoCl2(µ-bipna)]⋅
2H2O}n (2), {[CuCl(µ4-bipna)]BF4⋅2H2O}n (3) and {[CuCl(µ4-bipna)]
ClO4⋅2H2O}n (4), were prepared with diverse metal ions in the presence
of H2bipnaBr2. They were characterized by elemental analysis, IR
spectroscopy, single crystal and powder X-ray diffraction and thermal
analysis techniques. The diffuse reflectance spectra of the compounds
were recorded and the related band-gaps were calculated using the
Kubelka-Munk function .
2. Materials and physical measurements
Zwitterionic CPs with charged organic surfaces are very interesting
because of their unique adsorption properties and their magnetic and
photochromic behaviors [17–22]. In this study, the CPs were
All materials and solvents were commercially available and used
without further purification. IR spectra were recorded with a Bruker
* Corresponding authors.
E-mail address: yesilel@ogu.edu.tr (O.Z. Yes¸ilel).
https://doi.org/10.1016/j.poly.2021.115419
Received 26 May 2021; Accepted 4 August 2021
Available online 11 August 2021
0277-5387/© 2021 Elsevier Ltd. All rights reserved.

E. Çiftçi et al.
Polyhedron 208 (2021) 115419
Tensor 27 FT–IR spectrometer with KBr pellets in the range 400–4000
cmꢀ 1. Elemental analyses (CHN) were performed on a Perkin-Elmer
2400C Elemental Analyzer. Powder X-ray diffraction (PXRD) patterns
3435 (m), 3122 (w), 3061 (s), 3001 (w), 2925 (w), 1724 (vs), 1666 (vs),
1629 (s), 1494 (m), 1442 (m), 1381 (m), 1178 (m), 1122 (m), 896 (w),
800 (w), 761 (m), 680 (m), 561 (w) (Fig. S1). 1H NMR (500 MHz, D2O) δ,
ppm: 9.05 (d, J = 6.8 Hz, 4H), 8.78 (d, J = 6.7 Hz, 4H), 7.78 (d, J = 8.3
Hz, 4H), 7.59 (d, J = 8.3 Hz, 4H), 5.92 (s, 4H).
were collected with a Rikagu Smartlab X-ray diffractometer using Cu-K
α
radiation (λ = 1.5406 nm), operating at 40 kV and 30 mA, in the 2θ
range 5–40 ◦. Thermal analyses were carried out on a Perkin Elmer
Diamond TG/DTA Thermal Analyzer with a heating rate of 10 ◦C/min in
a dry air atmosphere. Diffuse reflectance spectra (DRS) in the wave-
length range 200–800 nm were taken on a Shimadzu UV-2600 spec-
trophotometer using BaSO4 as a reference. The 1H NMR spectrum of
H2bipnaBr2 was recorded on a Jeol ECZ 500R spectrometer at room
temperature. Topological analyses were performed using ToposPro
software [25]. Diffraction data of complexes 1–4 were collected on a
2.3. Synthesis of complexes 1–4
2.3.1. [MnCl(µ-bipna)]NO3⋅2H2On (1)
A mixture of H2bipnaBr2 (0.040 g, 0.068 mmol) and Mn(NO3)2⋅6H2O
(0.036 g, 0.30 mmol) was sonicated at room temperature for 30 min in a
mixture of DMF-ethanol (1:1, v:v) in the presence of two drops of 6 M
HCl. The resulting mixture was transferred into a 5 mL closed capped
glass bottle and heated at 60 ◦C for one day to obtain crystals. The
crystals were washed with a DMF-ethanol mixture and dried at room
temperature. Yield: 58% (based on H2bipnaBr2). Anal. Calcd. for
C26H24N3O9ClMn: C, 50.95; H, 3.95; N, 6.86 %. Found: C, 50.11; H,
3.90; N, 6.22 %. FT-IR (KBr, cmꢀ 1): 3423 (m), 3057 (w), 2929 (w), 1670
(vs), 1404 (vs), 1385 (vs), 1198 (m), 1128 (m), 835 (m), 768 (m), 687
(m), 555 (m), 433 (m) (Fig. S2).
Bruker Smart Apex II CCD equipped with MoKα radiation (λ = 0.71073
Å). The structures were solved by SHELT and refined by full-matrix
least-squares on all F2 data using SHELXL in conjunction with the
OLEX2 graphical user interface [26,27]. The solvent masking protocol
inside OLEX2 was applied to remove the diffraction contribution from
highly disordered solvent molecules using a void probe radius of 1.2 Å. A
solvent mask was calculated and 196 electrons in a volume of 1032 Å3
for 1, 212 electrons in a volume of 3010 Å3 for 2, and 236 electrons in a
volume of 1080 Å3 for 3 were found in a void per unit cell. These results
are consistent with the presence of approximately two water molecules
per unit cell. The number of solvent molecules seemed to be higher due
to the disorder. According to TG and elemental analysis, the compounds
contained about two water molecules. For all complexes, the anisotropic
thermal parameters were refined for non-hydrogen atoms and hydrogen
atoms were calculated and refined with a riding model. Molecule
drawings were developed with the Mercury program [28].
2.3.2. [CoCl2(µ-bipna)]n⋅2H2On (2)
The synthetic procedure for 2 was similar to that for 1, except Co
(NO3)2 6H2O (0.060 g, 0.30 mmol) was used instead of Mn(NO3)2⋅6H2O
Yield: 93% (based on H2bipnaBr2). Anal. Calcd. for C26H24N2O6Cl2Co: C,
52.90; H, 4.10; N, 4.75 %. Found: C, 52.98; H, 4.53; N, 7.23%. FT-IR
(KBr, cmꢀ 1): 3426 (m), 3065 (w), 2928 (w), 1653 (vs), 1616 (vs),
1497 (w), 1373 (s), 1186 (m), 1094 (m), 766 (m), 691 (m), 551 (m) 422
(m) (Fig. S3).
2.3.3. [CuCl(µ -bipna)]BF42H2On (3)
2.1. Synthesis of 4,4′-bis(bromomethyl)biphenyl
4
The synthetic procedure for 3 was similar to that for 1, except Cu
(BF4)2 xH2O (0.036 g, 0.30 mmol) was used instead of Mn(NO3)2⋅6H2O
4,4′-Dimethylbiphenyl (1.82 g, 10 mmol), N-bromosuccinimide
(3.54 g, 20 mmol) and benzoyl peroxide (0.06 g, 0.25 mmol) were
dissolved in 20 mL of benzene and refluxed at 95 ◦C for 12 h. The re-
action mixture was filtered and the solution was cooled to room tem-
perature. The resulting precipitates were collected by filtration, washed
with an ethanol/hexane mixture and dried under vacuum, resulting in
4,4′-bis(bromomethyl)biphenyl as a white powder (54% yield) (Scheme
S1).
Yield:
51%
(based
on
H2bipnaBr2).
Anal.
Calcd.
for
C
26H24BN2O6F4ClCu, 48.32; H, 3.74; N, 4.11 %. Found: C, 47.75; H,
3.70; N, 4.34 %. FT-IR (KBr, cmꢀ 1): 3426 (m), 3101 (w), 3065 (w), 2934
(w), 1660 (vs), 1499 (w), 1414 (s), 1207 (m), 1074 (s), 835 (w), 766 (m),
688 (m), 486 (m) (Fig. S4).
2.3.4. {[CuCl(µ4-bipna)]ClO4‧2H2On (4)
The synthetic procedure for 4 was similar to that for 3, except Cu
(ClO4)26H2O (0.060 g, 0.30 mmol) was used of Cu(BF4)2 xH2O. Yield:
91% (based on H2bipnaBr2). Anal. Calcd. for C26H24N2O10Cl2Cu, 47.39;
H, 3.67; N, 4.25 %. Found: C, 47.06; H, 3.74; N, 4.79 %. FT-IR (KBr,
cmꢀ 1): 3419 (m), 3140 (w), 3096 (w), 3063 (w), 2935 (w), 1661 (vs),
1499 (w), 1414 (w), 1207 (s), 1115 (s), 1092 (s), 833 (w), 766 (m), 688
(m), 623 (m), 484 (m) (Fig. S5).
2.2. Synthesis of 1,1′-biphenyl-4,4′-diylbis(methylene)bis(3-
carboxypyridin-1-ium) dibromide (H2bipnaBr2)
A solution of 4,4′-bis(bromomethyl)biphenyl (0.68 g, 2.0 mmol) in
DMF (5 mL) was added dropwise to a solution of nicotinic acid (0.49 g,
4.0 mmol) in DMF (20 mL). After the mixture had been stirred at 70 ◦C
for 6 h, the resulting precipitates were collected by filtration, washed
with DMF and diethyl ether, and then dried in vacuum, resulting in
H2bipna as a white powder (52% yield) (Scheme S1). IR (KBr, cmꢀ 1):
Scheme 1. Molecular structure of 1,1′-([1,1′-biphenyl]-4,4′-diylbis(methylene))bis(3-carboxypyridin-1-ium) bromide (H2bipnaBr2).
2

E. Çiftçi et al.
Polyhedron 208 (2021) 115419
– –
bond interactions and C– H⋅⋅⋅π interactions. There are C– H⋅⋅⋅O weak
3. Results and discussion
hydrogen bond interactions between the C4–H4/C5-H5/C7–H7B and
O3, O4 and O5 atoms from nitrate ions, with D⋅⋅⋅A distances ranging
3.1. Synthesis and characterization
–
from 3.385 to 3.598 Å. The 2D layers are further linked via C– H⋯Cl
Four new coordination polymers were synthesized with a zwitter-
ionic ligand in a mixture of DMF:ethanol at 60 ◦C in one day. The
complexes were characterized by elemental analysis, IR spectroscopy
and single crystal X-ray diffraction techniques. The elemental analysis
results are consistent with the assigned formulations. In the IR spectra of
hydrogen bonding interactions between the Cl1 ligand and the C6 atom
of the pyridinium group with C6⋅⋅⋅Cl1 = 3.573 Å and C6-H6⋅⋅⋅Cl1 =
◦
–
144.75 . Furthermore, there is a C– H···
π interaction between
C12ꢀ H12 and the pyridine ring (C12⋅⋅⋅Cg1 = 3.6500(3) Å and C12-
H12⋅⋅⋅Cg1 = 143◦, Cg1 = N1-C2-C3-C4-C5-C6). Topological analysis
shows that complex 1 has 44.62 point symbol with sql topology (Fig. 1c).
1–4, the broad bands observed at 3426–3423 cmꢀ 1 are due to
ν(OH)
stretching vibrations of water molecules. The weak bands observed in
the ranges 3140–3063 and 2928–2860 cmꢀ 1 are attributed to aromatic
3.2.2. [CoCl2(µ-bipna)]2 H2On (2)
and aliphatic
ν
(CH) stretching vibrations, respectively. The bands
The molecular structure and atom numbering scheme of 2 is shown
in Fig. 2. Single-crystal X-ray diffraction analysis indicates that complex
2 crystallizes in the orthorhombic crystal system with the Cmce space
group. As shown in Fig. 2a, the asymmetric unit of 2 consists of half a Co
(II) ion, half a bipna ligand and one chloride ligand. The Co(II) ion
adopts a tetrahedral coordination geometry, coordinating to two
carboxylate oxygen atoms from two different bipna ligands and two
chloride ligands. The bipna ligand acts with the bis-monodentate coor-
dination mode to bridge adjacent Co(II) ions, forming a 1D chain
(Fig. 2b). The crystal packing is mainly stabilized by hydrogen bonding
observed at 1724, 1666 and 1381 cmꢀ 1 are due to asymmetric and
symmetric stretching vibrations of the carboxylate groups of the free
H2bipnaBr2 ligand. The asymmetric vibration at 1724 cmꢀ 1 of H2bip-
naBr2 disappeared after conversion to complexes 1–4, indicating full
deprotonation of the carboxylate groups of H2bipnaBr2. The asymmetric
and symmetric stretching vibrations of the carboxylate groups of
H2bipnaBr2 in 1–4 appeared in the ranges 1653–1670 and 1414–1373
cmꢀ 1, respectively. Further, B-F and Cl-O stretching vibrations were
assigned to peaks observed at 1074 and 642–812 cmꢀ 1, respectively
(Figs. S2-S5).
and
π
⋅
π
interactions. Adjacent chains are further linked by C5–H5⋅⋅⋅Oi
–
and C– H⋅⋅⋅Cl1 hydrogen bonding interactions into a 3D supramolec-
ular network structure (C5⋅⋅⋅Oi = 3.022, C4⋅⋅⋅Cl1 = 3.533, C6⋅⋅⋅Cl1 =
3.711, C7⋅⋅⋅Cl1 = 3.663 and C7⋅⋅⋅Cl1 = 3.683 Å, C5–H5⋅⋅⋅Oi = 162.18,
C4–H4⋅⋅⋅Cl1 = 152.48, C6–H6⋅⋅⋅Cl1 = 142.01, C7–H7A⋅⋅⋅Cl1 = 156.57
3.2. Description of the crystal structures
The crystal data and the refinement details of complexes 1–4 are
listed in Table 1. Selected bond distances and angles are listed in
Tables S1-S4.
and C7–H7B⋅⋅⋅Cl1 = 158.32 ◦). Furthermore, there are
π⋅⋅⋅π interactions
between the pyridine and phenyl rings (Cg(1)⋅⋅⋅Cg(1)i = 3.5389 and Cg
(2)⋅⋅⋅Cg(2)ii = 3.8195(7) Å; Cg1 = N1-C2-C3-C4-C5-C6 and Cg2 = C8-
C9-C10-C11-C12-C13, (i) ½-x, ½-y, -z, (ii) ×, -y, -z) to form a 3D network
(Fig. 2d).
3.2.1. {[MnCl(µ-bipna)0.5](NO3)⋅2H2O}n (1)
The molecular structure of complex 1 is given in Fig. 1a, and the
bond lengths (Å) and bond angles (o) are given in Table S1. The complex
crystallizes in the orthorhombic system with the space group Cmcm. The
asymmetric unit of 1 consists of one Mn(II) ion, one chloride ligna , half
a bipna ligand, one nitrate ion and two crystal water molecules (Fig. 1).
The Mn(II) ion has a distorted square pyramidal geometry, coordinated
by four carboxylate oxygen atoms in the equatorial plane and one
chloride ligand in the axial position (Fig. 1a). The Mn1-O1 and Mn1-O2
bond lengths are 2.123(17) and 2.154(16) Å, respectively. Adjacent Mn
(II) ions are bridged by carboxylate oxygen atoms of four bipna ligands
to form paddlewheel [Mn2(CO2)4] units with a Mn⋅⋅⋅Mn distance of
3.387 Å, forming a 2D network (Fig. 1b). The identical 2D layers
interlock and form an interesting 3-fold parallel-interpenetrated 2D →
2D network (Fig. 1b). The crystal packing in 1 displays weak hydrogen
3.2.3. [CuCl(µ4-bipna)]BF42H2On (3) and {[CuCl(µ4-bipna)]ClO4⋅2H2On
(4)
Single-crystal X-ray diffraction analysis indicates that complexes 3
and 4 are isostructural. The molecular structures of 3 and 4 with the
atom numbering schemes are shown in Fig. 3a and Fig. 4, respectively.
The complexes crystallize in the orthorhombic system with the Cmcm
space group. The asymmetric units of 3 and 4 contain half a Cu(II) ion,
half a chloride and half a bipna ligand. In addition, there is a tetra-
fluoroborate ion and two water molecules in the asymmetric unit of 3
and a perchlorate ion and two water molecules in the asymmetric unit of
4. Each Cu(II) ion is coordinated by four carboxylate oxygen atoms from
four different bipna ligands and one chloride ligand to give a distorted
Table 1
Crystal data of complexes 1–4.
Complexes
1
2
3
4
Formula
C
26H24N3O9ClMn
C26H24N2O6Cl2Co
590.32
C26H24BN2O6F4ClCu
646.28
C26H24N2O10Cl2Cu
658.93
MA (gmolꢀ 1
)
612.87
Diffractometer
Rad. / λ (Å)
Temperature (K)
Color
Bruker APEX II CCD
Br Bruker APEX II CCD
Bruker APEX II CCD
Bruker APEX II CCD
Mo-K
α
/ 0.71073
Mo-K
306
α
/ 0.71073
Mo-K
293
α
/ 0.71073
Mo-K
297
α / 0.71073
306
Colorless
Orthorhombic
Cmcm
Blue
Green
Green
Crystal system
Space group
a (Å)
Orthorhombic
Cmce
Orthorhombic
Cmcm
Orthorhombic
Cmcm
26.470(2)
8,5317(7)
25.495(2)
5757.7(8)
8
30.795(5)
16,042(3)
14.922(2)
7372(2)
8
26.274(2)
8.4216(6)
26.417(2)
5845.2(8)
8
26.483(2)
8.5229(7)
26.385(2)
5955.4(9)
8
b (Å)
c (Å)
V (Å3)
Z
d (g cmꢀ 3
θmax. (◦)
Rint.
)
1.331
0.999
1.387
1.331
3.0–15.1
0.098
3.0–25.6
0.153
3.0–24.8
0.127
3.0–24.8
0.151
R[F2 > 2
wR(F2)
S
σ
(F2)]
0.100
0.078
0.094
0.086
0.258
0.271
0.220
0.279
1.07
1.02
1.05
1.02
3

E. Çiftçi et al.
Polyhedron 208 (2021) 115419
Fig. 1. (a) Molecular structure of complex 1, (b) three-layer supramolecular structure, (i) -x + 1, y, z; (ii) -x + 1, -y, -z + 1; (iii) ×, -y, -z + 1; (iv) ×, y, -z + 3/2; (v) -x
+ 3/2, -y + 3/2, -z + 1; (vi) + x, 1,5-y, 1-z; (vii) ½ + x, 1.5 + y, z. (c) Topological structure of complex 1.
square pyramidal geometry. Two crystallographically independent Cu
(II) ions are bridged by four different bipna ligands adopting a bis
(monodentate) coordination mode to form a paddlewheel unit,
Cu2(COO)4, with Cu⋅⋅⋅Cu distances of 2.774 Å for 3 and 2.824 Å for 4
(Fig. 3b). These dinuclear clusters are connected by bipna ligands to
generate a 2D layer network (Fig. 3b). Adjacent 2D single layers are
interlocked with each other to form a 3-fold parallel-interpenetrated 2D
→ 2D architecture.
interpenetrated 2D networks extend into a 3D supramolecular network
–
–
by C– H⋅⋅⋅F for 3 and C– H⋅⋅⋅O for 4 hydrogen bonding interactions
(Fig. 3c). In 3, the C3⋅⋅⋅Cl1 distance is 3.639 Å and the C⋅⋅⋅F distances are
in the range 3.035–3.339 Å. In 4, the C6⋅⋅⋅Cl1 distance is 3.617 Å and the
–
C⋅⋅⋅O distances are in the range 3.095–3.440 Å. C– H⋅⋅⋅Cl1 interactions
between two neighboring 2D networks further stabilize the structures.
–
Furthermore, there is a C– H···π interaction between C12–H12 and the
pyridine ring in 3 (C12⋅⋅⋅Cg1 = 3.7791(3) Å and C12-H12⋅⋅⋅Cg1 = 144◦,
–
Cg1 = N1-C3-C2-C6-C5-C4). All these hydrogen bonds and C– H···π
The crystal structures are mainly stabilized by intermolecular
–
–
C– H⋅⋅⋅Cl and C– H⋅⋅⋅F hydrogen bonding interactions. The adjacent
interactions enhance the stability of the compounds. Topological
4

E. Çiftçi et al.
Polyhedron 208 (2021) 115419
Fig. 2. (a) Molecular structure of complex 2, (b) 1D structure, (c)
ꢀ x + 1, y, z.
π
⋅⋅⋅π
interactions (d) Three dimensional supramolecular structure, (i) ꢀ x + 3/2, y, ꢀ z + 1/2; (ii)
analyses show that complexes 3 and 4 have sql topology with the point
symbol 44⋅62.
stabilities of the complexes (Figs. S10-S13). The first stage for 1 shows a
weight loss of 4.91% between 35 and 148 ◦C, which corresponds to the
loss of two crystal water molecules (calc. 5.88%). In the temperature
◦
range 148–578 C, a weight loss of 82.54% is observed which corre-
3.3. Powder X-ray diffraction and thermal analysis results
sponds to the loss of the bipna and chloride ligands, and the nitrate ion
(Calcd. 84.70%). The final product of 1, with a weight of 11.21%, is
MnO (calc.: 11.57%).
The purities of the bulk materials 1–4 were confirmed by powder X-
ray diffraction (PXRD). The simulated PXRD patterns were obtained
using the Mercury CSD software package based on the single-crystal
data. The PXRD patterns of the complexes matched very well with
those of the simulated patterns, indicating that the crystalline products
were in the pure phase (Figs. S6-S9).
The thermal decomposition of 2 occurs in four stages, giving endo-
◦
thermic effects at 143 and 297 C, and exothermic effects at 463 and
496 ◦C (DTG). These four stages of 2 are related to the successive
decomposition of two water molecules, the bipna and chloride ligands.
In the last stage, a strong exothermic peak (DTGmax. = 497 ◦C) is
Thermal analyses were carried out in order to determine the thermal
5

E. Çiftçi et al.
Polyhedron 208 (2021) 115419
Fig. 3. (a) Molecular structure of complex 3 (b) Paddlewheel unit and single layer structure for complex 3 (c) 3D structure for complex 3 ((i) -x + 1, -y, - z + 1; (ii)
×, -y, -z + 1; (iii) -x + 1, y, z; (iv) -x + 3/2, -y + 3/2, -z + 1; (v) + x, 1,5 + y, z).
associated with the burning of the organic residue, leading finally to
Co3O4. The endothermic peak at 901 ◦C is related to the conversion of
Co3O4 to CoO (found: 11.19%, calc.: 12.32 % for 2).
Thermal decomposition of 3 proceeds in four stages. The first
endothermic peak in the temperature range 35–122 ◦C corresponds to
the loss of water molecules. The anhydrous complex is stable up to
196 ◦C. The following stages, in the temperature range 196–618 ◦C, are
related to the consecutive decomposition of bipna and the chloride li-
gands, and the BF4 ion. The final decomposition product consists of
metallic copper (found: 6.37%, calc.: 9.56 %).
Complex 4 exhibits a weight loss of 5.33% between 30 and 144 ◦C
which corresponds to the loss of two lattice water molecules (calc.
5.47%). The following exothermic stages are related to the consecutive
decomposition of bipna and the chloride ligands, and a ClO4 ion. The
decomposition product of 4, with the weight of 10.09 %, is metallic Cu
(calc.: 9.64 %).
Fig. 4. Molecular structure of complex 4 ((i) -x + 1, -y + 2, -z + 1; (ii) × , -y +
3.4. Optical absorption properties
2, -z + 1; (iii) -x + 1, y, z; (iv) × ,y, -z+½; (v) -x+½, -y+½, -z + 1).
The solid state diffuse reflectance spectra of the free ligand and the
6

E. Çiftçi et al.
Polyhedron 208 (2021) 115419
compounds were recorded to show their optical band gaps (Eg) which
4. Conclusion
are related to their conductivity. The Kubelka–Munk function (the curve
of (h
ν
F(R))1/2 versus photon energy) was obtained from the solid state
Four coordination polymers using a flexible zwitterionic ligand in
the presence of diverse metal ions were prepared and characterized by
various techniques. Bipna acted as a neutral ligand in the compounds
and counter ions completed the charge balance of the metal ions. X-ray
analysis results showed that compounds 1, 3 and 4 display 3-fold
interpenetrated 2D → 2D frameworks while compound 2 has a 1D
structure. This was attributed to the ligand conformation. In 1, 3 and 4,
the carboxylate groups of the bipna ligand display a trans-conformation,
while in 2 the carboxylate groups of the bipna ligand display a cis-
conformation. Hence, a lower dimensionality is observed in 2 due to cis-
diffuse reflectance spectra to calculate the Eg value (Fig. 5). An extrap-
olation from the linear portion of the absorption edges gave the Eg value.
The Eg values of the ligand and compounds 1–4, obtained from the plots
of the Kubelka–Munk function, were 3.55, 2.71, 2.94, 2.35 and 2.26 eV,
respectively. The compounds exhibited semi-conductive properties and
higher conductivity than the ligand alone. Moreover, compounds 1, 3
and 4, which have 2D → 2D interpenetrated structures, displayed higher
conductive properties than compound 2, which has a 1D structure.
Fig. 5. The Kubelka-Munk plots as a function of energy for the free ligand and 1–4.
7

E. Çiftçi et al.
Polyhedron 208 (2021) 115419
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CRediT authorship contribution statement
[11] P.K. Yaman, M. Arıcı, H. Erer, O.Z. Yes¸ilel, The Effect of Metal Salts on the
Structures of 2, 2-Dimethylglutarate Complexes with a Flexible 1, 4-bis (imidazol-
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Esengül Çiftçi: Investigation, Formal analysis. Mürsel Arıcı: Vali-
dation, Software, Writing - original draft. Mario Wriedt: Conceptuali-
zation, Writing - review & editing. Okan Zafer Yesilel: Methodology,
¸
Writing - original draft, Supervision.
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¨
Declaration of Competing Interest
[14] G.G. Sezer, M. Arıcı, I. Erucar, O.Z. Yes¸ilel, H.U. Ozel, B.T. Gemici, H. Erer, Zinc(II)
and cadmium(II) coordination polymers containing phenylenediacetate and 4,4′-
azobis (pyridine) ligands: Syntheses, structures, dye adsorption properties and
molecular dynamics simulations, J. Solid State Chem. 255 (2017) 89–96.
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coordination networks based on 1, 2-bis(imidazol-1yl-methyl)benzene, Polyhedron
102 (2015) 1–7.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[16] A.K. Gupta, K. Tomar, P.K. Bharadwaj, Structural diversity of Zn(II) based
coordination polymers constructed from a flexible carboxylate linker and pyridyl
co-linkers: Fluorescence sensing of nitroaromatics, New J. Chem. 41 (2017)
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Acknowledgments
This work has been supported by Eskisehir Osmangazi University
Scientific Research Projects Coordination Unit under grant number
201919019.
[17] D. Aulakh, A.P. Nicoletta, J.R. Varghese, M. Wriedt, The structural diversity and
properties of nine new viologen based zwitterionic metal–organic frameworks,
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[18] D. Aulakh, T. Islamoglu, V.F. Bagundes, J.R. Varghese, K. Duell, M. Joy, S.J. Teat,
O.K. Farha, M. Wriedt, Rational Design of Pore Size and Functionality in a Series of
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Tetrazolate, and Carboxylate Cobridging Magnetic Systems: Ferromagnetic
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8