Multi-dimensional copper(I) and silver (I) coordination polymers assembled with a pyridyl bis-urea macrocyclic ligand

Article abstract of DOI:10.1016/j.poly.2021.115170

We report the synthesis of a new flexible multimodal macrocyclic ligand, protected pyridyl bis-urea macrocycle 1, and two of its coordination polymers Cu₂I₂(1)₂·(CH₃CN)_1.63 (2) and [Ag(1)](NO₃).(H₂O)_2.49 (3). The ligand possesses conformational flexibility and adopts different conformations and binding modes depending on the metal ions. The crystal structure of 2 shows a 2D coordination network constructed from rhomboidal Cu₂I₂ dimer units and 1 as a bridging ligand binding through the pyridyl N atoms. 3 forms a sophisticated 3D structure with 1D chains formed by N-Ag-N links between pyridyl N atoms of two adjacent macrocyclic ligands and Ag(I) ions. These chains form 2D layers through longer Ag-O interactions and the chains are linked together into a 3D network by hydrogen bonding involving interstitial water molecules. These results indicate the potential of ligand 1 in the self-assembly of coordination polymers with diverse topology and functional applications.

Full text of DOI:10.1016/j.poly.2021.115170

Polyhedron 201 (2021) 115170
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Multi-dimensional copper(I) and silver (I) coordination polymers
assembled with a pyridyl bis-urea macrocyclic ligand
Bozumeh Som a,b, Mark D. Smith b, Linda S. Shimizu b,
⇑
a Department of Chemistry, University of Ghana, P. O. Box LG 56, Legon, Accra, Ghana
b Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the synthesis of a new flexible multimodal macrocyclic ligand, protected pyridyl bis-urea
macrocycle 1, and two of its coordination polymers Cu2I2(1)2Á(CH3CN)1.63 (2) and [Ag(1)](NO3).
(H2O)2.49 (3). The ligand possesses conformational flexibility and adopts different conformations and
binding modes depending on the metal ions. The crystal structure of 2 shows a 2D coordination network
constructed from rhomboidal Cu2I2 dimer units and 1 as a bridging ligand binding through the pyridyl N
atoms. 3 forms a sophisticated 3D structure with 1D chains formed by N-Ag-N links between pyridyl N
atoms of two adjacent macrocyclic ligands and Ag(I) ions. These chains form 2D layers through longer Ag-
O interactions and the chains are linked together into a 3D network by hydrogen bonding involving inter-
stitial water molecules. These results indicate the potential of ligand 1 in the self-assembly of coordina-
tion polymers with diverse topology and functional applications.
Received 2 February 2021
Accepted 18 March 2021
Available online 24 March 2021
Keywords:
Pyridyl bis-urea macrocycle
Self-assembly
Coordination polymer
Ó 2021 Elsevier Ltd. All rights reserved.
1. Introduction
Especially in metal–organic frameworks, linear organic polycar-
boxylates (O-donors) and pyridines (N-donors) are among the
The design and synthesis of coordination polymers (CPs) have
attracted much attention due to their intriguing topological fea-
tures and functional properties [1,2]. These complex materials
have potential applications for gas storage/separation, [3,4] cataly-
sis, [5] molecular magnetism, [6] and luminescent materials [7,8].
By employing several assembly motifs, scientist have synthesized
CPs with emergent properties. For example, the judicious choice
of organic ligands and metal ions that have specific directionality
gives rise to CPs with diverse solid-state structures (1D, 2D or
3D) and properties [9,10]. Other factors that influence the struc-
tural outcome of CPs include temperature, solvents, pH value,
and reactants ratio. Each of these factors may influence structural
diversity and lead to unpredicted structures [11,12]. In addition
to the above-mentioned factors the design of CPs is centered pri-
marily on the ligand type, position of the donor atoms, as well as
the length and its flexibility [13]. A suitable metal with a rigid
bridging ligand will therefore generate either discrete macro-
cyclic/cage-like architectures or continuous metal–organic frame-
work materials [9]. On the other hand, bridging ligands with
more flexibility give mixtures of coordination polymers due to
the lack of control on the outcome of the self-assembly process.
most used ligands [9,14]. Tuning the flexibility of such ligands
can be achieved by introducing groups such as -O-, –CH2-, and -
O-CH2-, enabling free rotation around these groups to fit the coor-
dination geometry of the metal ions in the assembly process.
The Shimizu research group has demonstrated the use of pyri-
dyl/bipyridyl urea macrocycles in the synthesis of coordination
complexes in previous reports [15,16]. These functionalized
macrocycles showed remarkable flexibility where the macrocycle
can rotate to access different binding conformations in which
metal ions could be in the interior of the macrocycle (endo) or on
its exterior (exo) [15–17]. The protected pyridyl/bipyridyl urea
macrocycles have displayed diverse coordination modes with
alkali and transition metal ions using both oxygen and nitrogen
donor atoms. Our primary task in the current study was to investi-
gate the flexibility and coordination modes of macrocyclic ligand 1
that was anticipated to bind metal ion(s) through the exterior pyr-
idyl nitrogen(s). Herein, we report the syntheses and characteriza-
tion of this new pyridyl bis-urea macrocycle 1 and, its Cu(I) and Ag
(I) coordination complexes where the pyridyl Ns are key in deter-
mining the architecture of the CPs (Fig. 1).
⇑
Corresponding author.
E-mail address: deposite@ccdc.cam.ac.uk (L.S. Shimizu).
https://doi.org/10.1016/j.poly.2021.115170
0277-5387/Ó 2021 Elsevier Ltd. All rights reserved.

B. Som, M.D. Smith and L.S. Shimizu
Polyhedron 201 (2021) 115170
250 mL round bottom flask and 48% HBr (15 mL) was added slowly
and carefully. The reaction mixture was stirred and heated at 125ꢀC
for 6 h. The reaction mixture was cooled to room temperature, and
40 mL H2O added slowly then adjusted the pH to 8 with saturated
NaHCO3. The resulting whitish precipitate was collected by suction
filtration and washed with H2O (10 mL). This crude product was
dried under vacuum overnight (1.56 g, 55.86% yield). 1H NMR
(300 MHz, CDCl3): d = 8.56 (d, J = 2.0 Hz, 2H), 7.77 (t, J = 2.0 Hz,
1H), 4.47 (s, 4H).
Macrocyclic ligand, 1. An oven dried 500 mL round bottom flask
was filled with a suspension of triazinanone (0.30 g, 1.88 mmol)
and NaH (0.39 g, 9.76 mmol) in dry THF (100 mL) and refluxed
for 2 h under nitrogen then cooled to room temperature. To this
cooled mixture a solution of 3,5-bis(bromomethyl)pyridine hydro-
bromide (0.65 g, 1.88 mmol) in THF (50 mL) was added in one por-
tion (Scheme 1). The reaction mixture stirred and heated to reflux
under nitrogen for 48 h while monitoring the reaction with silica
gel TLC. Upon completion (based on TLC monitoring), the reaction
mixture was cooled to room temperature and quenched with
water (100 mL). The volume of the resulting solution was reduced
by rotary evaporation to a minimum and extracted with dichloro-
methane (DCM) (3 Â 100 mL). The DCM layers were combined,
washed with brine, dried over anhydrous MgSO4 and the solvent
removed under reduced pressure to give a yellow solid. Purifica-
tion of the crude material (wet loaded) by silica gel chromatogra-
phy with CHCl3/MeOH (9:1) afforded macrocyclic ligand 1 as a
dimer (0.15 g, 30.64%). X-ray quality single crystals of this macro-
cycle were grown by slow evaporation from toluene (3 mg / 1 mL).
Macrocyclic ligand 1; 1H NMR (400 MHz, TCE) d 8.40 (s, 2H), 7.98
(s, 1H), 4.64 (s, 4H), 4.26 (s, 4H), 1.14 (s, 9H).; 13C NMR
(101 MHz, CD3CN) d = 156.58, 148.67, 135.86, 62.92, 54.78,
46.16, 28.50: Melting point 268–271ꢀC. HRMS (ES) calculated for
Fig. 1. Schematic structure of flexible macrocyclic ligand 1 used for the synthesis of
CPs.
2. Experimental
Materials and methods. Unless otherwise specified, all chemi-
cals were purchased from commercial sources (Sigma-Aldrich, Alfa
Aesar, TCI or VWR) and used without further purification. Dimethyl
pyridine-3,5-dicarboxylate, 3,5-bis(hydroxymethyl)pyridine and
3,5-bis(bromomethyl)pyridine hydrobromide were prepared
according to published literature procedures respectively [18–
20]. Triazinanone was prepared as previously described [21]. 1H
NMR and 13C NMR were recorded on Varian Mercury/VX 400
NMR spectrometer. FT-IR spectra were obtained with a Perkin
Elmer Spectrum 100 FT-IR Spectrometer over the range 4000–
650 cmÀ1 with 2 cmÀ1 resolution and 32 scans per sample.
C
28H40N8O2: [M + H], 521.3347. Observed m/z 521.3351. IR (neat
ATR) 2969, 1630, 1503, 1427, 1362, 1302, 1202, 1156, 1025, 955,
893, 793, 752, 707 cmÀ1
.
Coordination polymer Cu2I2(1)2Á(CH3CN)1.63, (2). The pro-
tected pyridyl macrocyclic ligand 1 (10 mg, 0.0192 mmol) was dis-
solved in DCM (1 mL) and was added to an acetonitrile solution of
CuI (3.65 mg, 0.0192 mmol in 1.0 mL). The mixture was then stir-
red at room temperature for an hour. This resulted in a white pow-
der that was collected by filtration, washed with diethyl ether-
acetonitrile mixture and chloroform then dried under vacuum.
Yield: 10.4 mg (76%). X-ray quality single crystals were grown by
dissolving 3 mg of the powder obtained from the above synthesis
3. Ligand synthesis
Dimethyl pyridine-3,5-dicarboxylate. Thionyl chloride (1.3 mL,
17.94 mmol) was added dropwise to a stirring solution of pyri-
dine-3,5-dicarboxylic acid (1.0 g, 5.98 mmol) in dry methanol
(10 mL) at 0 °C. The reaction was heated at reflux (3 h) after which
the mixture was cooled to room temperature then concentrated in
vacuo. The residue was diluted with water (100 mL) and extracted
with ethyl acetate (100 mL). The aqueous layer was neutralized
with 8 M NaOH solution and extracted with ethyl acetate again
(100 mL). The combined organic layers were washed with satu-
rated NaHCO3 solution and brine, dried over anhydrous Na2SO4.
Finally, the solvent was removed under reduced pressure to give
a white solid material (0.8 g, 68% yield).1H NMR (300 MHz, CDCl3):
d = 9.37 (d, J = 2.0 Hz, 2H), 8.87 (t, J = 2.1 Hz, 1H), 3.99 (s, 6H).
3,5-Bis(hydroxymethyl)pyridine. Dimethyl pyridine-3,5-dicar-
boxylate (2.10 g, 10.76 mmol) was dissolved in dry THF (150 mL)
and added dropwise to a suspension of LiAlH4 (1.02 g, 26.90 mmol
in 150 mL of THF) in an ice/acetone bath (0ꢀC) under nitrogen. After
addition, the resulting yellow mixture could warm gradually to r.t.
then left stirring overnight. Upon completion, the reaction mixture
was quenched by sequentially adding H2O (1 mL), 10% NaOH
(2 mL) and H2O (3 mL). The mixture was suction filtered, and the
yellow filtrate dried over anhydrous MgSO4. Removal of the solvent
under reduced pressure followed by drying under vacuum gave a
yellow solid crude (1.12 g, 75% yield). The product was used
directly for the next reaction without any further purification.
3,5-Bis(bromomethyl)pyridine Hydrobromide. The crude 3,5-bis
(hydroxymethyl)pyridine (1.12 g, 8.05 mmol) was added to a
Scheme 1. Synthesis of pyridyl bis-urea macrocyclic ligand
1
aReagents and
conditions: (a) triazinanone (in THF), NaH, refluxed for 1 h, cooling, followed by
addition of 3,5-bis(bromomethyl)pyridine hydrobromide in THF, then refluxed for
48 h.
2

B. Som, M.D. Smith and L.S. Shimizu
Polyhedron 201 (2021) 115170
in 10 mL acetonitrile and allowed to slowly evaporate over 5 days.
IR (neat ATR): 3479, 2973, 1638, 1511, 1436, 1366, 1304, 1234,
form-d and 4.20 ppm in acetonitrile d3. The broadening and only
one signal observed for these sixteen methylene protons in the
room temperature 1H NMR suggest the presence of two or more
conformations slowly interconverting on the NMR time scale. So,
we turned to high temperature 1H NMR (variable temperature
NMR) to observe the chemical shift of these methylene groups.
Upon running the experiment in a high boiling NMR solvent
(1,1,2,2-Tetrachloroethane-d2) at higher temperature (125ꢀC) two
sets of signals were obtained (at d = 4.64 ppm and 4.26 ppm) for
these sixteen methylene protons (Fig. S2). Integration of these
peaks gave a ratio of 1:1 representing eight benzylic protons
(d = 4.64 ppm) and eight protons from the heterocyclic ring methy-
lene groups (d = 4.26 ppm). The 13C NMR spectrum of macrocycle 1
exhibits the requisite number of signals at both room temperature
and high temperature (125ꢀC). Fig. S3 shows 13C NMR spectrum of
macrocycle 1 in acetonitrile d3 at room temperature. X-ray quality
single crystals 1 were crystallized from toluene (3 mg / 1 mL) by
slow evaporation to give good solvent-free colorless rhombic
plates. The macrocycle (1) crystallizes in the triclinic space group
P-1 (No. 2) as confirmed by structure solution. The asymmetric
unit consists of one complete macrocyclic ligand 1 molecule and
half each of two additional ligand 1 molecules, both of which are
located on crystallographic inversion centers. There are three crys-
tallographically independent molecules, two of which are cen-
trosymmetric (Fig. 2). All the three molecules of 1 adopted the
1,2-alternate conformation in the crystal structure. The pyridyl N
atoms in the structure are poised on the exterior and pointing in
opposite directions whilst the urea carbonyl groups and triazi-
nanone rings are antiparallel to each other. Packing structure of 1
in the solid state revealed that the molecules are layered on top
each other. There are two layers; one made of molecule A and
the other made of alternating molecule B and molecule C (Fig. 3).
Macrocyclic ligand 1 and its constitutional isomer (4) [27] as
depicted in Fig. 4, can be considered as analogues of calix[4]arenes,
which are of special interest due to their ability to adopt well-
defined three-dimensional structures. Calix[4]arenes are com-
monly discussed in terms of four basic conformations: cone, partial
cone, 1,2- and 1,3-alternate [28,29]. Prior reports of pyridyl bis-
urea macrocycle 4 showed that it adopted two conformations in
1197, 1143, 1029, 959, 894, 795,752, 703 cmÀ1
.
Coordination polymer [Ag(1)](NO3)Á(H2O)2.49, (3). Ligand 1
(3.0 mg, 5.76 Â 10-3 mmol) and AgNO3 (1.95 mg, 11.5 Â 10-3 mmol)
were each dissolved in hot acetonitrile (1.0 mL). The solutions were
mixed thoroughly and filtered through a Millipore filter, cooled,
and allowed to slowly evaporate over 2–3 days. A cluster of color-
less block crystals formed that were suitable for single crystal X-
ray diffraction. Yield was 70% (2.96 mg). IR (neat ATR): 3409,
2969, 1632, 1513,1420, 1304,1199, 1156, 1031, 960, 932, 900,
796, 757, 701 cmÀ1
.
X-ray Crystal Structure Determination. Diffraction data of
ligand 1 and the coordination polymers (2 and 3) were collected
at 100(2) K using a Bruker D8 QUEST diffractometer equipped with
a PHOTON-100 CMOS area detector and an Incoatec microfocus
source (Mo Ka radiation, k = 0.71073 Å). The raw area detector data
frames were reduced and corrected for absorption effects using the
Bruker APEX3, SAINT + and SADABS programs [22,23]. Final unit
cell parameters were determined by least-squares refinement of
large sets of reflections taken from the data sets. All structures
were solved with SHELXT [24,25]. Subsequent difference Fourier
calculations and full-matrix least-squares refinement against F2
were performed with SHELXL-2017 [24,25] using OLEX2 [26]. A
summary of the crystallographic data and structure refinements
are given here in Table 1 and further details in the supporting
information.
4. Results AND DISCUSSION
Ligand Design and Synthesis. The new pyridyl bis-urea macro-
cyclic ligand (1) was synthesized following a previously reported
procedure [27] to give a yield of 30.6%. The proton NMR of 1 was
first recorded at room temperature in chloroform-d then in ace-
tonitrile d3(Fig. S1). However, in both cases we were missing the
peak associated with the methylene group in between the pyridyl
rings and the protected urea groups. In both spectra of 1, the six-
teen methylene protons are broad signals at d 4.22 ppm in chloro-
Table 1
Crystallographic data and structure refinement parameters of macrocyclic ligand 1, and Cu2I2(1)2Á(CH3CN)1.63 (2) and [Ag(1)](NO3).(H2O)2.49 (3).
1
Cu2I2(1)2Á(CH3CN)1.63 (2)
[Ag(1)](NO3).(H2O)2.49 (3)
Empirical formula
C
28H40N8O2
C59.26H84.89Cu2I2N17.63O4
C28H44.98AgN9O4.49
Formula weight
520.68
1489.15
735.42
T/K
100(2)
100(2)
100(2)
Crystal system
triclinic
triclinic
triclinic
Space group
P-1
P-1
P1
a/Å
b/Å
c/Å
10.6246(5)
11.0831(5)
22.5999(11)
8.6693(4)
13.1139(7)
15.1067(8)
8.9880(3)
9.1999(3)
10.5400(4)
a
/°
b/°
/°
90.020(2)
90.197(2)
94.120(2)
2654.3(2)
96.502(2)
97.650(2)
93.897(2)
1685.20(15)
70.9060(10)
88.585(2)
76.0530(10)
797.92(5)
c
Volume/Å3
Z
4
1
1
q
l
calcg/cm3
1.303
0.086
1.467
1.604
1.530
0.693
/mmÀ1
F(000)
1120.0
760.0
383.0
Crystal size/mm3
2h range/°
0.26 Â 0.2 Â 0.18
0.2 Â 0.14 Â 0.04
4.414 to 58.256
66,300
9060 [Rint = 0.0433, Rsigma = 0.0324]
9060/200
0.16 Â 0.1 Â 0.04
4.678 to 60.342
48,759
9401 [Rint = 0.0344, Rsigma = 0.0319]
9401/107
5.13 to 60.344
Reflections collected
Independent reflections
Data/restraints
Parameters
146,413
15,682 [Rint = 0.0483, Rsigma = 0.0352]
15682/0
699
1.036
491
1.060
489
1.037
GoF on F2
Final R indexes [I>=2
Final R indexes [all data]
qmax./min. (e ÅÀ3
r
(I)]
R1 = 0.0449, wR2 = 0.1090
R1 = 0.0635, wR2 = 0.1183
0.42/À0.24
R1 = 0.0344, wR2 = 0.0703
R1 = 0.0524, wR2 = 0.0773
1.04/À0.73
R1 = 0.0276, wR2 = 0.0509
R1 = 0.0329, wR2 = 0.0525
0.32/À0.38
D
)
3

B. Som, M.D. Smith and L.S. Shimizu
Polyhedron 201 (2021) 115170
Fig. 2. Components of the structure of macrocyclic ligand 1. a) Structure of component B. b) Three crystallographically independent, chemically similar molecules. Molecules
B and C are located on crystallographic inversion centers. Superscripts denote symmetry-equivalent atoms. Displacement ellipsoids drawn at the 60% probability level.
Fig. 3. Packing diagram of ligand 1. Layered structure made of two types of layers. Layer 1 (top and bottom) is made of only molecule A, and layer 2 (middle) is made of
alternating molecule B and C. Color coded for the crystallographically independent, chemically similar molecules. Molecules A (green), B (blue) and C (red).
the solid state, a partial cone and 1,3-alternate when crystalized
from two different solvents, o-xylene and DMSO respectively
[27]. In comparison ligand 1 adopted the 1,2-alternate when crys-
tallized from toluene. This suggests that the solvent of crystalliza-
tion has a greater influence on the conformation adopted by these
macrocycles. Elucidation of the solid-state crystal structures of the
two macrocyclic isomers (1 and 4) shows more access to the het-
eroatom binding sites (potential oxygen and pyridine binding
sites) in 1 than 4. This is particularly important for crystal engi-
neering of coordination polymers, as it will lead to the production
of multi-dimensional molecular architectures which is of signifi-
cance in the quest for new functional materials [30].
Crystal structure of Cu2I2(1)2Á(CH3CN)1.63 (2). Coordination
polymer Cu2I2(1)2Á(CH3CN)1.63 (2) crystallizes in a triclinic space
group P-1 (No. 2). The asymmetric unit consists of one Cu and
one I atom, half each of two (1) ligands and two acetonitrile mole-
cules (Fig. 5). There are two crystallographically independent
macrocyclic ligands. One of the macrocyclic ligands is disordered
across an inversion center over two orientations and there is some
acetonitrile mixed among the disordered ligand atoms. Only the
protected urea part is disordered; the CH2(pyridyl)CH2 linker is
common to both. The disorder components each have an occu-
pancy of 50%. The single crystal X-ray diffraction analysis reveals
that Cu2I2(1)2Á(CH3CN)1.63 (2) is a 2D sheet coordination polymer
where the macrocyclic ligands link Cu2I2 units through pyridyl N
atoms into infinite 2D layers parallel to the crystallographic (1–
1–1) plane (Fig. 6). The Cu2I2 group forms a rhombus. Each Cu(I)
center is further coordinated by two pyridyl N atoms of the ligands
creating a tetrahedral coordination geometry around the Cu(I) cen-
ter (d(Cu–N) = 2.070(2) Å (Cu1-N4) and 2.074(2) Å (Cu1-N8)). Cu-I
bond lengths are 2.6051(4) and 2.6294(4) Å. The CuÁÁÁÁCu distance
is 2.5989(6) Å as a diagonal of the Cu2I2 rhombus repeating motif.
This CuÁÁÁÁCu distance is shorter than the sum of the van der Waals
radii of two Cu atoms (2.80 Å) [31] and remarkably close to that in
copper metal (2.56 Å), suggesting strong cuprophillic interaction
that may significantly affect the photophysical properties [32,33].
In this structure, ligand 1 acted as a bidentate-bridging ligand
coordinating the Cu(I) centers with both pyridyl N atoms.
Crystal structure of [Ag(1)](NO3).(H2O)2.49 (3). The crystal
structure of [Ag(1)](NO3).(H2O)2.49 (3) was confirmed by single
crystal X-ray diffraction. It crystallizes in the triclinic system with
the acentric group P1 (No. 1). Structural analysis revealed that the
Ag(I) center adopts a distorted tetrahedral coordination geometry,
bonded to two pyridyl N donors, one carbonyl O donor from ligand
1, and the O atom of a nitrate anion (Fig. 7). In this structure the
macrocyclic ligand 1 adopted a flattened cone conformation with
the carbonyl groups on the same side. The Ag-N bond distances
were 2.167(2) and 2.166(2) Å, while the Ag-O bond distances are
2.517(2) and 2.529(14) Å. There are 1D chains formed by N-Ag-N
links (angle 154ꢀ) between pyridyl N atoms of two adjacent macro-
cyclic ligands and the Ag(I) ion (Fig. 8). A further Ag-O interaction
of 2.517(2) Å links the Ag centers to a carbonyl oxygen atom O2 of
neighboring chain, forming 2D layers (Fig. 9). Furthermore, OH-N
hydrogen bonding between the interstitial water molecules and a
4

B. Som, M.D. Smith and L.S. Shimizu
Polyhedron 201 (2021) 115170
Fig. 4. Comparison of the triazinanone protected pyridyl bis-urea macrocycles 1
and 4. (a) Macrocycle 1 adopted a 1,2-alternate conformation when crystallized
from toluene. (b) Comparison of conformers of 4 obtained under three crystalliza-
tion conditions: (i) partial cone conformation from o-xylene, (ii) 1,3-alternate
conformation from DMSO and (iii) A 1:1 mixture of partial cone/1,3-alternate
conformations from benzene.[27] Hydrogen atoms in crystal structures are omitted
for clarity.
Fig. 5. Components of the crystal structure of Cu2I2(1)2Á(CH3CN)1.63 (2) expanded
by symmetry. One ligand is disordered about a crystallographic inversion center
along with acetonitrile. Displacement ellipsoids drawn at the 50% probability level.
Superscripts denote symmetry-equivalent atoms.
protecting group N atom forms a 3D structure. The nitrate anions
are located near Ag but are disordered over three sites (Ag1-O3A/
B/C ranging from 2.53 to 2.65 Å). The interstitial water molecules
are disordered but occupy closely separated split sites, allowing
for location of their hydrogen atoms.
FT-IR spectroscopy. Further investigation on different function-
alities present in the ligand structure and the change in electronic
states upon complexation are analyzed using FT-IR. Comparison of
the solid-state infrared (IR) spectra of the synthesized ligand 1 and
coordination polymers is shown in (Fig. 10). The results were con-
sistent with the single crystal X-ray diffraction structural results in
terms of the key dominant vibrational modes of the coordinated
ligand observed in the 650–4000 cmÀ1 range. The IR spectrum of
ligand 1 exhibited a strong band at 1631 cmÀ1 which is attributed
to the carbonyl (C@O) group. Upon coordination the intensity of
this band decreased in both Cu2I2(1)2Á(CH3CN)1.63 (2) and [Ag(1)]
(NO3).(H2O)2.49 (3). In coordination polymer Cu2I2(1)2Á(CH3CN)1.63
(2) the band is split in two at 1615 and 1638 cmÀ1, indicating
two different carbonyl groups are present in the complex. This
agrees with the single crystal X-ray structure of Cu2I2(1)2Á(CH3-
CN)1.63 (2) which displays two crystallographically independent
macrocyclic ligands of 1. A similar splitting of the carbonyl group
was observed in the spectrum of [Ag(1)](NO3).(H2O)2.49 (3) at
1615 and 1632 cmÀ1 corresponding to a coordinating carbonyl
group (C@O-Ag) and an uncoordinated carbonyl group (C@O)
respectively. Another key functional group in the structure of
ligand 1 is the C@N (pyridine) group. The absorption band of this
group has shifted to higher wavenumbers (by 7–10 cmÀ1) in the
coordination polymers. Broad bands are observed at 3479 cmÀ1
for Cu2I2(1)2Á(CH3CN)1.63 (2) and 3409 cmÀ1 for [Ag(1)](NO3).
Fig. 6. Coordination network of Cu2I2(1)2Á(CH3CN)1.63 (2) with disorder component
B. Macrocyclic ligands link Cu2I2 units through pyridyl N atoms into infinite 2D
layers. Solvent molecules are omitted for clarity.
(H2O)2.49 (3), which are absent in the spectrum of ligand 1. These
bands are attributed to the interstitial solvent molecules (CH3CN
and H2O) present in the structures of Cu2I2(1)2Á(CH3CN)1.63 (2)
and [Ag(1)](NO3).(H2O)2.49 (3) respectively.
5. Conclusion
In summary, the redesigned pyridyl bis-urea macrocyclic ligand
(1) showed several structural differences when compared to its
5

B. Som, M.D. Smith and L.S. Shimizu
Polyhedron 201 (2021) 115170
Fig. 10. FT-IR profiles of ligand 1 and coordination polymers (2–3) in the range
4000–650 cmÀ1
.
ligand 1 adopted the 1,2-alternate conformation when crystallized
from toluene, while 4 adopted the partial cone and the 1,3-alter-
nate conformations when crystallized from o-xylene and DMSO,
respectively. Two coordination polymers Cu2I2(1)2Á(CH3CN)1.63 (2)
and [Ag(1)](NO3).(H2O)2.49 (3), have been synthesized by reacting
macrocyclic ligand 1 with copper(I) iodide and silver(I) nitrate,
respectively. Structural characterization shows that ligand 1 is
flexible and can adopt different coordination modes with different
Fig. 7. Components of the crystal structure of [Ag(1)](NO3).(H2O)2.49 (3). Asym-
metric unit of the crystal structure of 3 with additional atoms to complete Ag and
ligand coordination environments. Only one component each of the disordered
nitrate and water molecules are shown. Hydrogen bonds are dashed lines.
Displacement ellipsoids drawn at the 50% probability level. Superscripts denote
symmetry-equivalent atoms.
Fig. 8. 1D chains showing the side and top views of the coordination environments of [Ag(1)](NO3).(H2O)2.49 (3) along the crystallographic [110] direction. One nitrate
disorder component shown. Solvent molecules and hydrogens are omitted for clarity.
previously reported positional isomer (4)[27]. These dimers (1 and
4) adopted different conformations in the solid state. Macrocyclic
metal ions. In Cu2I2(1)2Á(CH3CN)1.63 (2), ligand 1 is a bidentate
ligand only binding through the pyridyl N atoms. However, ligand
Fig. 9. 2D layers in crystal structure of [Ag(1)](NO3).(H2O)2.49 (3). Ag1-O2 interaction between chains creates 2D layers parallel to the crystallographic (001) plane. Solvent
molecules and nitrate ions are omitted for clarity.
6

B. Som, M.D. Smith and L.S. Shimizu
Polyhedron 201 (2021) 115170
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1 behaved as a tridentate ligand in [Ag(1)](NO3).(H2O)2.49 (3), bind-
ing through the pyridyl N atoms and one carbonyl O atom. These
coordination polymers present extended architectures with inter-
esting dimensionality from 1D to 3D structures. While uncommon,
the coordination complexes characterized do exhibit partial sol-
vent occupancy. Current studies probe the effects of solvent and
crystallization conditions to evaluate if additional crystal forms
with different geometries are readily accessible. Based on these
results, further syntheses, and studies of ligand 1 complexes of
Cu(I) and Ag(I) containing different anions to determine if that is
a structural determinant or has any influence on the luminescence
properties of the complexes.
Synopsis
A new multimodal flexible pyridyl bis-urea macrocyclic ligand
and its Cu(I) and Ag(I) coordination polymers have been synthe-
sized and structurally characterized by single crystal X-ray diffrac-
tion. The coordination polymers displayed extended architectures
with interesting dimensionality from 1D to 3D structures.
Declaration of Competing Interest
The Authors declare that they have no known competing finan-
cial interests of personal relationships that could have appeared to
influence the work reported in this paper.
Appendix A. Supplementary data
CCDC <2060221-2060223> contains the supplementary crystallo-
graphic data for <1-3>. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1eZ, UK; fax: (+44) 1223-336-033; or email:
deposite@ccdc.cam.ac.uk. Supplementary date to this article can
be found online at http://doi.org/10.1016/j.poly.2021.#. Supple-
mentary data to this article can be found online at https://doi.
org/10.1016/j.poly.2021.115170.
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