Coordination polymers containing 1,3-Phenylenebis-((1H-1,2,4-triazol-1-yl)methanone) ligand: Synthesis and "-caprolactone polymerization behavior

Article abstract of DOI:10.3390/molecules22111860

The reaction of isophthaloyl dichloride with 1H-1,2,4-triazole afforded the new ligand 1,3-phenylenebis(1,2,4-triazole-1-yl)methanone (1). A series of Co(II), Cu(II), Zn(II) and Ni(II) complexes were synthesized using 1 and then characterized by melting p

Full text of DOI:10.3390/molecules22111860

molecules
Article
Coordination Polymers Containing
1
,3-Phenylenebis-((1H-1,2,4-triazol-1-yl)methanone)
Ligand: Synthesis and ε-Caprolactone
Polymerization Behavior
Nestor J. Bello-Vieda , Ricardo A. Murcia , Alvaro Muñoz-Castro 2,3, Mario A. Macías 1 and
John J. Hurtado *
1
1
1
,
ID
1
◦
Department of Chemistry, Universidad de los Andes, Carrera 1 N 18A-12, Bogotá 111711, Colombia;
nj.bello1211@uniandes.edu.co (N.J.B.-V.); ra.murcia@uniandes.edu.co (R.A.M.);
ma.maciasl@uniandes.edu.co (M.A.M.)
2
Grupo de Química Inorgánica y Materiales Moleculares, Universidad Autonoma de Chile, El Llano
Subercaseaux 2801, Santiago 8910060, Chile; aemunozc@gmail.com
Relativistic Molecular Physics (ReMoPh) Group, Universidad Andres Bello, Republica 275, Santiago, Chile
Correspondence: jj.hurtado@uniandes.edu.co; Tel.: +57-1-3394949 (ext. 3468)
3
*
Received: 18 September 2017; Accepted: 26 October 2017; Published: 29 October 2017
Abstract: The reaction of isophthaloyl dichloride with 1H-1,2,4-triazole afforded the new ligand
1,3-phenylenebis(1,2,4-triazole-1-yl)methanone (
1). A series of Co(II), Cu(II), Zn(II) and Ni(II)
complexes were synthesized using and then characterized by melting point analysis, elemental
1
analysis, theoretical calculations, thermogravimetric analysis, X-ray powder diffraction, nuclear
magnetic resonance, infrared and Raman spectroscopy. Experimental and computational studies
predict the formation of coordination polymers (CPs). The cobalt and copper CPs and zinc(II) complex
were found to be good initiators for the ring-opening polymerization of
ε
-caprolactone (CL) under
1
solvent-free conditions. H-NMR analysis showed that the obtained polymers of CL were mainly
linear and had terminal hydroxymethylene groups. Differential scanning calorimetry showed that
the obtained polycaprolactones had high crystallinity, and TGA showed that they had decomposition
◦
temperatures above 400 C. These results provide insight and guidance for the design of metal
complexes with potential applications in the polymerization of CL.
Keywords: triazole ligand; coordination polymers; initiators; ε-caprolactone polymerization
1
. Introduction
Currently, many researchers have focused on the synthesis of biodegradable polymers as there
is great interest in designing environmentally friendly materials [
important polymer used in agricultural, biomedical and environmental fields due to its tunable
properties and biodegradability [ ]. PCL is typically produced by the ring-opening polymerization of
-caprolactone (CL) catalyzed by metal complexes [ ]. One of the first catalysts used in this type of
polymerization was titanium isopropoxide. This catalyst has a number of drawbacks, including high
production costs and sensitivity to normal environmental conditions such as moisture and oxygen [ ].
Other metal catalysts used for the ring-opening polymerization (ROP) of CL require initiators,
which makes polymerization reactions more complex and expensive [ ]. Some catalysts are toxic and
1]. Polycaprolactone (PCL) is an
2,3
ε
4–7
3
8,9
can leave trace metals in the polymers. Additionally, special handling techniques, such as high-vacuum
conditions and all-glass apparatus, are required for these catalysts, and these added difficulties make
them impractical [
6,10,11]. In view of this, it is very important to develop catalysts that are easy to
prepare, are non-toxic and can catalyze the desired reaction under normal atmospheric conditions
Molecules 2017, 22, 1860; doi:10.3390/molecules22111860
www.mdpi.com/journal/molecules

Molecules 2017, 22, 1860
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with adequate catalyst loading and at moderate temperatures. In this context, we have reported the
synthesis, characterization and application of PCL catalysts using zinc and chromium cations. The ROP
was carried out under solvent-free conditions with a monomer-complex ratio of 490:1. The synthesized
◦
PCL was highly crystalline (61%) and had a decomposition temperature above 300 C [12,13].
Recently, the use of ligands with nitrogen and oxygen with different types of metals has been
explored to drive the polymerization of caprolactone [14]. Magnesium and calcium complexes with
◦
mixed ligands showed low activity, with conversions between 5% and 40% after 12 h at 60 C with a
monomer-complex ratio of 200:1 [15]. Scorpionate ligands with azolic rings have been studied with
very promising results. Complexes using these types of ligands with magnesium produce polymers
with conversions of 98% at room temperature at a monomer-complex ratio of 500:1 [16]. As far as
we know, there are very few reports of transition metal complexes with triazole ligands being used
for CL polymerization [
characterized a series of new neutral Co(II), Cu(II), Zn(II) and Ni(II) coordination polymers containing
,3-phenylenebis(1,2,4-triazol-1-yl)methanone ligands and their behavior as catalysts to polymerize
7,17]. In our search for related polymerization catalysts, we synthesized and
1
CL. The polymers of PLC obtained were highly crystalline and had decomposition temperatures
◦
above 400 C.
2
. Discussion
2
.1. Synthesis of 1,3-Phenylenebis(1,2,4-triazol-1-yl)methanone (1)
Initially, we attempted to synthesize the compound through the addition of isophthaloyl
dichloride and 1H-1,2,4-triazole with anhydrous tetrahydrofuran and toluene as co-solvents.
This procedure did afford some ligand, but the yield was very low. It was then decided to first
synthesize the sodium salt of the triazole using a reported method [18]. This method consisted of
reacting the triazole and a stoichiometric amount of NaOH in methanol for 4 h at room temperature.
◦
Then, the reaction mixture was cooled to
−
15 C, and the salt was obtained as a hygroscopic white solid.
The solid was isolated by filtration and washed with cold methanol and ethyl ether. This salt was
later used as precursor for the reaction and did not require an exogenous base. However, the yield
remained low. Finally, the ligand was obtained by the reaction of 1H-1,2,4-triazole and isophthaloyl
chloride in anhydrous toluene and trimethylamine (Scheme 1).
N-
N Na+
THF
O
O
low yield
low yield
N
reflux, 12 h
Cl
O
Cl
toluene
reflux, 48 h
H
N
O
N
N
O
O
Cl
Cl
Triethylamine
reflux, 36 h
N
N
N
N
53.7%
N
N
Scheme 1. Synthesis of ligand 1.
The ligand was isolated as an air stable white solid at room temperature, and it was soluble in
non-polar solvents such as dichloromethane and chloroform. Mass spectrometry and NMR, FTIR, and
Raman spectroscopy analyses were used to characterize the isolated compound. The electrospray mass
spectrum in acetonitrile showed the molecular ion peak at 291.062 m/z, which matched the calculated
+
value for [(C H N O )Na] (Figure S4 in the Supplementary Materials). NMR spectroscopy confirmed
12
8
6
2

Molecules 2017, 22, 1860
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the formation of the ligand. The H- and 13C-NMR spectrum chemical shifts were assigned with the
aid of a heteronuclear single quantum coherence (HSQC) experiment. (Figures S1–S3 in Supplementary
Materials). The solid-state IR spectra from a KBr pellet (Figure S5 in Supplementary Materials) showed
1
−
1
−1
bands attributable to C=O (1710 cm ) [19] and C=C (1525 cm ) [20]. Raman analysis showed 532 nm
was the optimum wavelength for obtaining Raman dispersion information from the sample. There are
−
1
four vibrational modes in the region of 250 to 1000 cm . These modes correspond to symmetric
vibrations and are characteristic of the synthesized ligand.
2
.2. Synthesis and Characterization of Coordination Polymers (CPs)
The coordination polymers (CPs) were obtained using simple methods of synthesis and purification.
In the synthesis of
as the ligand was poorly soluble in pure acetone. The CP
solid and was stable in air at room temperature. In the case of the zinc complex (
and computational studies predict the formation of mononuclear complex, it was poorly soluble
in common organic solvents, which facilitated purification. The solubility of in DMSO and DMF
allowed its characterization by NMR, which confirmed the formation of the ligand and the zinc CP.
NMR spectra of and the free ligand ( ) showed similar signals. This is likely because complexation
with the metal center does not affect the magnetic environments of the hydrogens in the ligand.
2
, it was necessary to dissolve the ligand in a 1:1 mixture of acetone and ethanol
was obtained as a non-hygroscopic blue
), experimental
2
4
4
4
1
2
.2.1. Infrared Spectroscopy
A comparison of the vibrational bands of the ligand with those of the corresponding CPs showed
that coordination of the ligand to the metal causes some bands to shift or disappear altogether (Table 1).
−
1
In the free ligand, a band at 1710 cm was observed and was attributed to the carbonyl group [21],
and this (C=O) band was shifted in the spectrum of the CPs because the ligand was coordinated to
the metal. In all cases, we observed a shift in the (C=O) band to lower wavenumbers. Those results
indicate the lower rigidity of the (C=O) bonds in the CPs (Table 1).
Table 1. Infrared spectral bands for ligand 1 and its CPs.
−
1
Wavenumber ν/cm
Compound
ν(C–H)
ν(C=O)
ν(N–N)
ν(C–N)
ν(M–N)
1
2
3
4
5
3121 s
3126 s
3135 s
3118 s
3134 s
1710 vs
1700 m
1708 vs
1691 vs
1629 m
1429 m
1427 m
1422 m
1418 m
1427 m
1217 m
1211 m
1215 m
1223 w
1132 m
–
419 w
417 w
420 w
309 m
w: weak; m: medium; s: strong; vs: very strong.
2
.2.2. Thermal Analysis
The stages of decomposition, temperature ranges and decomposition products as well as the
weight loss percentages of the CPs are shown in Table 2. The fragments listed in Table 2 are proposed
based on the mass losses because detection of the actual fragments was not possible. We propose all the
complexes studied here loose HCl and CO molecules. In addition, for 2 and 4, we observed an initial
loss that generated an unstable compound that rapidly degraded to a compound of greater stability,
◦
which was stable to approximately 100 C, and then, we observed final losses of the corresponding
metal residue. For
compounds of greater stability, so slow decays are observed in the mass percentage with respect
to temperature. In contrast, five losses were observed for , which are probably due to the formation
5, three losses were observed, which are probably due to the formation of
3
of compounds of low stability, so fast decays are observed in the mass percentage with respect
to temperature.

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Table 2. Thermoanalytical results (TGA and DTG) for the CPs.
Mass Loss
Total Mass Loss
Compound
◦
Metallic
Residue
◦
TG Range/ C
DTGmax/ C
n
Assignment
loss of C2H2N3
loss of C6H4 + CO + HCl
loss of C2NH3
(
Formula)
Estimated (calcd.)/%
2
5–319
226
395, 432, 444
631
1
3
1
29.46 (30.53)
30.59 (32.34)
18.84 (15.42)
2
3
5
19–500
00–695
78.95 (78.29)
87.07 (84.22)
CoCl
(
(
C
12
12
H
8
8
Cl
2
CoN
6
O
2
)
)
2
5–216
16–368
68–697
190
287, 312, 320
598
1
3
1
13.83 (15.76)
53.15 (52.06)
20.09 (16.40)
loss of HCl + CO
loss of C9H7N3O + HCl
loss of C2N3
3
2
3
Cu
Zn
C
H
Cl
2
6 2
CuN O
2
1–221
211
281
403
476
1
1
1
1
26.49 (24.70)
31.62 (35.64)
14.77 (13.60)
15.64 (9.90)
loss of 2HCl + CO
loss of C HN + C H
2 3 6 5
4
221-300
300–436
88.52 (83.84)
(
(
C
12
12
H
8
8
Cl
2
N
6
O
2
Zn)
loss of C HN O
2
2
4
36–495
loss of CN2
3
7–411
11–545
45–695
291
345
111
1
1
1
34.24 (36.04)
22.52 (22.99)
14.22 (16.05)
loss of C6H4 + CO + HCl
loss of C2H2N3 + CO
loss of C2HN3
5
4
5
71.95 (74.95)
NiCl
C
H
Cl
2
6 2
NiN O )
TG: thermogravimetric analysis; DTG: derivative thermogravimetric; n: number of decomposition steps.
2
.2.3. X-ray Diffraction Studies
The XRD patterns for the Co, Cu and Ni-CPs are shown in Figure 1. The diffractograms were
successfully indexed on a monoclinic unit cell using the DICVOL06 and Jana-2006 programs [22
,
23
]
◦
with an absolute error of
±
0.05 (2
θ
) in the calculations (Table 3). In all cases, an analysis of the patterns
was performed using the Le Bail method [24]. The refinements were performed using a pseudo-Voigt
profile function for the peak shape and a calculated background using a linear interpolation between
a set of fixed points. Table 3 shows the refined unit cell parameters and the most likely space group
estimated using Jana software [22].
Table 3. Refined unit cell parameters obtained from the Le Bail method for CPs.
Complex
Co
Cu
Ni
a (Å)
b (Å)
c (Å)
14.236 (19)
3.629 (4)
12.250 (16)
94.36 (9)
631 (1)
14.171 (2)
3.6617 (5)
12.232 (2)
94.21 (2)
633.0 (2)
7.180 (2)
3.5372 (5)
9.950 (3)
90.65 (2)
252.71 (15)
P2/m
◦
β ( )
3
V (Å )
Space Group
Rp
P2 /m
P2 /m
1
1
2.76
3.62
1.02
4.56
5.97
1.19
3.88
5.04
1.13
wRp
GOF
In all cases, the formation of a single phase was confirmed through the X-ray analyses since no
additional peaks from secondary phases have been identified after the Le Bail analysis. From Table 4,
it is possible to imagine that the Co and Cu CPs. have similar crystal structures. However, the
presence of Ni in the CPs breaks the two-fold rotoinversion axis observed in the Cu and Co CPs, and
a two-fold screw axis in the [010] direction is present instead. The consequence of these changes in
the symmetry is still under investigation due to difficulties in obtaining single crystals of adequate
size. An approximation of the crystallite size (the size of the coherently diffracting domain) of the
CPs was calculated using the Scherrer equation, D = (Kλ)/(βcosθ), using K as 0.89 [25]. The apparent
crystallite sizes of the Co, Cu and Ni CPs are 17.0, 24.6 and 24.1 nm, respectively, which are consistent
with the width and low intensity of the peaks. These peaks are more prominent in the case of the
Co CP. A similar X-ray diffraction study was planned in the case of the Zn CP; however, it was not
possible to find a solution that could explain the complete diffractogram (not shown), which suggests
fast degradation of the CP even during the measurement.

Molecules 2017, 22, 1860
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Ni-L
Cu-L
Co-L
10
20
30
40
50
2θ (°)
Figure 1. XRD patterns for Co, Cu and Ni CPs showing some of the hkl indices.
2
.2.4. Molecular Modeling
In order to evaluate probable structures for all the complexes, molecular modeling calculations
were performed preliminary by semi-empirical methods (PM6), and followed by DFT calculations.
Owing to the different coordinating sites provided by ligand , different coordination modes
1
were studied. The results are shown in Figure 2. Vibrational frequencies were calculated to determine
the global minimum in the surface potential, owing to the absence of imaginary frequencies.
Figure 2. Representative structures for both ligand and metallic complexes. (
metal is coordinated only via N,N of the triazolyl ligand; ( ) The metal is coordinated via a C=O and
a N from the triazolyl ligand moiety; ( ) Two metals are coordinated via the C=O and N moieties of the
triazolyl ligand. Calculations were done by using DFT TZ2P/BP86-D3 level of theory.
a) Free ligand (1); (b) The
c
d

Molecules 2017, 22, 1860
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Because we observed shifts in the C=O band to lower wavenumbers (relative to the free ligand) in
the experimental IR experimental spectra, we decided to computationally simulate the infrared spectra
for the possible complexes and study the shift of the C=O band. The results are presented in Figure 3.
Figure 3. Simulated infrared spectra of the possible complexes. The letters (a–d) corresponds to the
molecules in Figure 2, with M = Zn.
In general, the simulated IR patterns corresponded to those obtained experimentally for all metal
complexes. In the computational study, we observed that the (C=O) band in is at higher energy when
4
the metal is coordinated only via the N,N from the triazoly ligand (Figure 2b). This result contradicts
what was observed in the experimental IR spectra.
However, if the metal is coordinated via the C=O and one nitrogen of the triazole moiety
(
Figure 2c), a split carbonyl signal is produced since the free C=O vibration is different than the vibration
for C=O coordinated to the metal (C=O–M). Finally, if the metals are symmetrically coordinated to the
ligand via the C=O and N moieties (Figure 2d), the bands shift to lower wavenumbers as was found in
the experimental IR spectrum.
The favored coordination modes provided by structures Figure 2b,c, were evaluated for Co(II),
Ni(II), Cu(II) and Zn(II) at the DFT TZ2P/BP86-D3 level of theory. Interestingly, for Co(II) and Ni(II),
the more stable structure is given by the coordination mode involving a C=O and a N from the triazolyl
ligand moiety (Figure 2b and Figure 4i). In contrast, for Cu(II) and Zn(II), the metal is coordinated
preferably only via N,N of the triazolyl ligand (Figure 3c and Figure 4ii).
Figure 4. Probable structure for coordination polymers (i) 2 and 5; (ii) for 3.

Molecules 2017, 22, 1860
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Although mononuclear, binuclear and coordination polymers have been obtained using related
bis(azolyl) ligands [26 30], in our case, the isolation of non-soluble compounds indicates the probable
formation of a polymeric species for and . This assumption is supported by the results from both
experimental and computational studies, and it was possible to propose structures of metal complexes
coordination polymers) as shown in Figure 4. Where for Co(II) and Ni(II), polymeric arrangement
–
2,
3
5
(
polymer (i) from Figure 4 is expected, and polymer (ii) is anticipated for Cu(II).
On the other hand, the elemental analysis results showed a (metal: ligand) of 2:1 ratio for 2, 3
and
and its infrared spectrum showed no effect on the intensity of the C=O band. Based on the observed is
proposed for a mononuclear structure, where the metal is coordinated preferably only via N,N of the
triazolyl ligand.
5, corresponding to L(MCl ) . Finally for the zinc complex 4, the metal:ligand ratio found was 1:1
2 2
4
2
.2.5. ε-Caprolactone Polymerization
Other metal complexes have been studied as catalysts for CL polymerization [1,3,6,11,31,32].
However, some of them require special handling techniques such as high vacuum conditions and
all-glass apparatus, which makes them difficult to use in a practical sense. Recently, we have been
interested in catalysts for ROP that can be easily synthesized [12]. The behaviors of CPs
2–
5
as
initiators for polymerization of CL were tested. The solvent-free polymerization of
conducted at 110 C for 72 h using a [monomer]:[CPs] molar ratio of 490:1. This ratio was selected
ε-caprolactone was
◦
because it represents the minimum catalyst loading relative to the monomer. Initiator
5 did not
produce the desired PCL under the conditions studied. We think that this result may be due to its low
solubility in the reaction medium or because the active species was not generated [
5
,
12]. The polymers
1
of PCL were obtained as white powders and were characterized by DSC, TGA, FTIR and H-NMR
spectroscopy (Figures S20–S27 in Supplementary Materials). Table 4 shows the yield and DSC and
TGA characterization data of the obtained PCL.
Table 4. Yield and characterization of the obtained PCL by DCS and TGA.
Melting point a ( C) Crystallization T ( C)
◦
◦
Crystallinity b (%) Decomposition T ( C)
◦
Initiator (%) Yield
2
3
4
57
56
50
59.0
59.8
59.6
37.24
37.09
38.33
67
68
63
435
440
445
◦
All the materials were synthesized with a [monomer]/[CPs] mass ratio of 490:1 at 110 C for 72 h. [a] The value
correspond to the first heating ramp. [b] Calculated using a 100% crystalline -PCL enthalpy of fusion equal to
36 J/g [3].
ε
1
The results showed that the CPs and
4 were active in the ring opening polymerization
of
percent conversion. The activities of the CPs and
reaction medium. The products all have melting points of 59 C (Figures S22–S27 in the Supplementary
ε-caprolactone, and the yields were 50–57%. Longer reaction times did not increase the
4
seem to be governed by their solubility in the
◦
Materials), which is characteristic of PCL [3], and high crystallinities (63–68%). The crystallinities were
higher than that of commercial PCL (31% according to manufacturer’s report), which may be beneficial
for applications in films. It has been reported that changes in the orientation and crystallization of
the polymers can improve their barrier properties [32]. The obtained polymers showed crystallinity
values similar to those of the PCL produced using a zinc catalyst or the chromium complexes we have
reported [12,13].
Analyzing the results of TGA (Figures S28–S30 in the Supplementary Materials), the materials
◦
show decomposition temperatures above 400 C, which suggest they are stable at high temperatures.
The decomposition temperature of the PCL obtained when using
4 as the initiator was higher than
that of the PCL produced using zinc complexes derived from coumarin, salen and Schiff base
ligands [12,32,33]. The TGA and DSC results from the PCL product showed that these materials
have potential applications in the design of biodegradable packaging.

Molecules 2017, 22, 1860
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3
. Materials and Methods
3
.1. General Information
All manipulations were routinely performed in an inert atmosphere (nitrogen) using standard
Schlenk-tube techniques. All reagent-grade solvents were dried, distilled, and stored under a
nitrogen atmosphere. Commercial PCL (reference No. 440744) was purchased from Sigma-Aldrich
(St. Louis, MO, USA). Elemental analyses (C, H and N) were carried out on a Thermo Scientific™
FLASH 2000 CHNS/O Analyzer (Thermo Fisher Scientific, Waltham, MA, USA). Fourier transform
infrared (FTIR) spectra were recorded on a Thermo Nicolet NEXUS FTIR spectrophotometer using KBr
pellets or on a Thermo Scientific Nicolet 380 spectrophotometer. Nuclear magnetic resonance (NMR)
spectra were recorded on a Bruker 400 spectrometer. Chemical shifts are reported in ppm relative to
1
a SiMe ( H) internal standard. The mass spectra of the new ligand was obtained on a Micromass
4
®
Quattro Q-TOF LC/. Melting points were determined on a Mel-Temp 1101D apparatus in open
capillary tubes, and they are uncorrected. Thermogravimetric analyses (TGA) of the complexes and
polymers (PCL) were obtained on a NETZSCH STA 409 PC/PG from 8 to 10 mg of the complexes in
◦
nitrogen media. The samples were subjected to dynamic heating over a temperature range of 30–700 C
◦
−1
with a heating rate of 10 C min . The TG curves were analyzed to determine the percentage of
mass lost as a function of temperature. Raman spectroscopy was performed in an RIBA Yovin-Ivon
spectrometer using different laser wavelengths (532, 638, and 786 nm).
The molecular modeling calculations were performed by semi-empirical methods (PM6) with
MOPAC2012 software, version 15.152 W [34,35], and Gabedit, version 2.3.8 [36]. Density Functional
Theory (DFT) calculations, were done by using the ADF2016 package [37], with the dispersion
corrected BP86 GGA exchange-correlation functional (BP86-D3) [38] in conjunction to all electron TZ2P
basis set [39].
After synthesis, phase analysis was performed by X-ray diffraction (XRD) at room temperature
using a Miniflex-Rigaku X-ray diffractometer working in Bragg-Brentano geometry with Cu-K 1
α
,2
wavelengths (1.54051 and 1.54433 Å). The diffractometer was operated over the angular range of
◦
◦
◦
2
θ = 10 –70 using a step size of 0.02 (2θ) and an acquisition time of 4 s per step.
Differential scanning calorimetry (DSC) analysis of the PCL was performed with a TA Instruments
−
1
DSC Q200 instrument in a nitrogen atmosphere (50 mL min ). An 8–10 mg sample was heated from
◦
◦
◦
◦
−1
3
0 to 150 C, cooled from 150 to
−
90 C and heated from
−
90 to 90 C at a heating rate of 5 C min .
The crystallinity was determined using the formula:
∆
Hexp
Xc =
0
∆
H
u
where ∆Hexp is the area of the melting peak and ∆H u0 is the melting enthalpy of 100% crystalline PCL
(
136.08 J g 1) [40].
−
3
.2. Synthesis of 1,3-Phenylenebis(1,2,4-triazole-1-yl)methanone (1)
To a Schlenk tube equipped with a reflux condenser was added isophthaloyl dichloride (2.46 mmol;
4
99.5 mg), 1H-1,2,4-triazole (4.98 mmol; 345.0 mg), triethylamine (0.8 mL) and toluene (20 mL), and the
mixture was refluxed for 36 h. The hot mixture was filtered, and the filtrate was evaporated to dryness.
The solid residue was treated with water (25 mL) and extracted with dichloromethane (2 30 mL).
×
The organic layer was separated and dried with magnesium sulfate, and the solvent was evaporated
◦
to dryness. The resulting white solid was washed with n-pentane and dried at 80 C for 6 h. Yield:
◦
−1
355.0 mg (54%). M.p.: 322–323 C. IR (KBr)
ν/cm : 3120, 2925, 2809, 2625, 1710, 1525, 1377, 1272,
1
121, 955, 723, 665, and 518. Atom numbering for 1 is as follows:

Molecules 2017, 22, 1860
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1
H-NMR (400 MHz, DMSO-d ):
δ
9.48 (s, 2H), 8.75 (t, 1H, J 1.7), 8.42 (dd, 4H, J 8.1 and 1.8 Hz), and
6
.85 (t, 1H, J 7.9 Hz). 13C { H}:
1
δ
164.36 (C5, C5’), 154.22 (C7, C7’), 147.59 (C2, C2’), 136.86 (C6, C6’),
7
1
3
34.38 (C4), 131.25 (C3, C3’), and 129.32 (C1) Anal. calcd. for C H N O : C, 53.73; H, 3.01; and N,
12 8 6 2
1.33; found: C, 53.57; H, 3.04; and N, 29.65%. MS (FTMS + IT) m/z, calcd. for [M + Na] : 291.062;
+
found: 291.062.
3
.3. Synthesis of Catena-Poly[chlorocobalt-di-µ-chloro-cobalt-µ-[1,3-Phenylenebis(1,2,3-triazole-1-yl)-
methanone-O:N,O’:N’]] (2)
A solution of (0.38 mmol; 101 mg) in a 1:1mixture of acetone:ethanol (4 mL) was added to
1
a solution of cobalt(II) chloride (0.38 mmol; 49.5 mg) in acetone (5 mL). The reaction mixture was
stirred at room temperature (rt) for 1 h. The resulting light blue solid was filtered off, washed
◦
◦
with acetone and ethanol, and dried at 80 C for 12 h. Yield: 97.0 mg (65%). M.p.: >400 C
(
−
1
decomposition); IR (KBr) ν/cm : 3126, 3017, 2912, 2827, 2361, 1700, 1521, 1422, 1312, 1064, 884,
6
18, and 419. Anal. calcd. for C H Cl Co N O : C, 27.28; H, 1.52; and N, 15.91; found: C, 27.08; H,
12
8
4
2
6
2
1
.51; and N, 15.20%.
3
.4. Synthesis of Catena-Poly[chlorocopper-di-µ-chloro-copper-µ-[1,3-Phenylenebis(1,2,3-triazole-1-yl)-
methanone-O:N,O’:N’]] (3)
A solution of
1 (0.74 mmol; 198.0 mg) in acetone (3 mL) was added to a solution of copper(II)
chloride (0.75 mmol; 100.7 mg) in acetone (3 mL). The reaction mixture was stirred for 5 h at rt.
The resulting blue solid was filtered off; washed with acetone, dichloromethane and diethyl ether; and
◦
◦
−1
:
dried at 80 C for 12 h. Yield: 146.0 mg (49%). M.p.: 340 C (decomposition). IR (KBr)
448, 3135, 3024, 2926, 1708, 1519, 1427, 1373, 1215, 1079, 955, 876, 717, and 620. Anal. calcd.
for C H Cl Cu N O : C, 26.81; H, 1.49; and N, 15.64; found: C, 26.61; H, 1.50; and N, 15.67%.
ν
/cm
3
12
8
4
2
6
2
3
.5. Synthesis of Catena-Poly[chlorozinc-di-
µ-chloro-zinc-µ-[1,3-Phenylenebis(1,2,3-triazole-1-yl)-methanone-
O:N,O’:N’]] (4)
A solution of
1 (0.188 mmol; 50.5 mg) in acetone (2 mL) was added to a solution of zinc(II)
chloride (0.19 mmol; 26.5 mg) in acetone (1 mL). The reaction mixture was stirred for 1 h at rt.
The resulting white solid was filtered off, washed with acetone and ethanol, and dried under a vacuum.
◦
−1
Yield: 31.0 mg (40%). M.p.: >400 C (decomposition); IR (KBr)
H NMR (400 MHz, DMSO-d6):
ν
/cm : 3118, 1691, 1418, 1223, and 420.
1
δ 9.49 (s, 2H, 2,2’), 8.76 (t, 1H, J 1.7 Hz), 8.42 (dd, 4H, J 8.1 and 1.8 Hz),
and 7.85 (t, 1H, J 7.9 Hz). Anal. calcd. for C H Cl ZnN O : C, 35.60; H, 1.98; and N, 20.76; found: C,
12
8
2
6
2
3
5.15; H, 1.88; and N, 20.72%.
3
.6. Synthesis of Catena-Poly[chloronickel-di-µ-chloro-nickel-µ-[1,3-Phenylenebis(1,2,3-triazole-1-yl)-
methanone-O:N,O’:N’]] (5)
To a Schlenk tube equipped with a reflux condenser was added nickel(II) chloride (0.39 mmol;
49.8 mg) in methanol (12 mL) and the mixture was refluxed for 30 min. Then, 1 (0.60 mmol; 160.2
mg) was added, and the mixture was refluxed for an additional 72 h. The resulting light violet solid
◦
was filtered off, washed with tetrahydrofuran and diethyl ether, and dried at 80 C for 12 h. Yield:
9
◦ −1
4.0 mg (63%). M.p.: >400 C (decomposition). IR (KBr) ν/cm : 3134, 2907, 1630, 1524, 1427, 1310,

Molecules 2017, 22, 1860
10 of 12
1
132, 1067, and 309. Anal. calcd. for C H Cl Ni N O : C, 27.30; H, 1.52; and N, 15.93; found: C, 27.30;
12 8 4 2 6 2
H, 1.34; and N, 15.89%.
3
.7. Polymerization of ε-Caprolactone
The polymerization of -caprolactone was performed solvent-free in four reaction tubes using
ε
[
ε
monomer]:[initiator] ([M]/[CPs]) ratios of 490:1 with 0.0036 mmol of CP and 0.178 mmol of
-caprolactone. The reactions were carry out at 110 C for 72 h. After the reaction time, the mixtures
◦
were cooled to room temperature. The polymers were purified by dissolving the crude product in
dichloromethane (1 mL), and cold ethanol (7 mL) was added to give a white precipitate. The precipitate
was then isolated by centrifugation, washed with HCl (7 mL, 0.1 M) (to remove traces of the catalyst)
◦
and ethanol (7 mL), and dried under vacuum at 40 C [12
,
40]. The polymers were characterized
−
1
by DSC, TGA, NMR and FTIR spectroscopy. IR (KBr; cm ):
ν 2945(C-H), 1725(C=O ester), 1241,
1
1
185 (C–O–C). H-NMR (400 MHz, CDCl ):
δ
4.09 (t, 2H), 2.38 (t, 2H), 1.72 (m, 4H), 1.41 (m, 2H) ppm.
3
These data suggest that the obtained polymers were linear and have terminal hydroxymethylene
groups [11].
4
. Conclusions
We synthesized and characterized new metal complexes prepared via the reaction of
,3-phenylenebis(1,2,4-triazol-1-yl)methanone with CoCl , CuCl , ZnCl and NiCl . Experimental and
1
2
2
2
2
computational studies predict the formation of coordination polymers (CPs). The prepared cobalt,
copper and zinc CPs were good initiators for the ring-opening polymerization of -caprolactone under
ε
solvent-free conditions and afforded polymers with high crystallinities (63–68%) and decomposition
◦
temperatures above 400 C. The results of TGA and DSC of the PCL showed that these materials have
potential applications in the design of biodegradable packaging.
Supplementary Materials: The following are available online.
Acknowledgments: Thanks to the Department of Chemistry and the School of Science of the Universidad de los
Andes for the financial support. We thank the reviewers and editor for their useful comments. We also thank to
Laura V. Lopez for assistance with IR spectroscopy.
Author Contributions: N.J.B.-V., R.A.M. and J.J.H. carried out the synthesis and characterization of ligand
and metal complexes; N.J.B.-V. and R.A.M. carried out the studies of ε-caprolactone polymerization; M.A.M.
provided the characterization of the complexes by X-ray powder diffraction; A.M.-C. carried out the DFT
computational calculus. All authors contributed with crucial discussions and constructive reviews. J.J.H. is
the corresponding author.
Conflicts of Interest: Authors declares have no conflicts of interest.
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2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).