The use of C1 symmetry imidazole-carboxylate building block and auxiliary acetate co-ligand for assembly of a 2D wave-like zinc(II) coordination polymer: experimental and theoretical study

Article abstract of DOI:10.1080/00958972.2020.1818727

We report the synthesis and characterization of a two-dimensional Zn(II) coordination polymer employing a ligand with a biphenyl core containing imidazole and carboxylate groups in the presence of acetate moieties as bridging molecules. The obtained [ZnLA

Full text of DOI:10.1080/00958972.2020.1818727

Journal of Coordination Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
The use of C1 symmetry imidazole-carboxylate
building block and auxiliary acetate co-ligand for
assembly of a 2D wave-like zinc(II) coordination
polymer: experimental and theoretical study
Dana Bejan , Lucian Gabriel Bahrin , Corneliu Cojocaru , Alexandru Florentin
Trandabat , Narcisa Laura Marangoci , Alexandru Rotaru & Sergiu Shova
To cite this article: Dana Bejan , Lucian Gabriel Bahrin , Corneliu Cojocaru , Alexandru Florentin
Trandabat , Narcisa Laura Marangoci , Alexandru Rotaru & Sergiu Shova (2020): The use of C1
symmetry imidazole-carboxylate building block and auxiliary acetate co-ligand for assembly of a 2D
wave-like zinc(II) coordination polymer: experimental and theoretical study, Journal of Coordination
Chemistry, DOI: 10.1080/00958972.2020.1818727
To link to this article: https://doi.org/10.1080/00958972.2020.1818727
View supplementary material
Published online: 22 Sep 2020.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2020.1818727
The use of C1 symmetry imidazole-carboxylate building
block and auxiliary acetate co-ligand for assembly of a
2D wave-like zinc(II) coordination polymer: experimental
and theoretical study
Dana Bejana, Lucian Gabriel Bahrina, Corneliu Cojocarua, Alexandru Florentin
Trandabatb, Narcisa Laura Marangocia, Alexandru Rotarua and Sergiu Shovaa
a“Petru Poni” Institute of Macromolecular Chemistry, Romanian Academy, Iasi, Romania;
bSC Intelectro Iasi SRL, Iasi, Romania
ABSTRACT
ARTICLE HISTORY
Received 21 April 2020
Accepted 11 August 2020
We report the synthesis and characterization of a two-dimensional
Zn(II) coordination polymer employing a ligand with a biphenyl
core containing imidazole and carboxylate groups in the presence
of acetate moieties as bridging molecules. The obtained [ZnLAc]n
was structurally characterized via X-ray, FTIR, TGA, PXRD, SEM and
EDX analyses. Computer-aided calculations based on density func-
tional theory (DFT) were employed to assess the optimal conform-
ational geometries of both the starting ligand and the Zn(II)
complex. Computational results were compared with the experi-
mental data, disclosing a reasonable agreement. Comparisons
between the single-crystal structures and the calculated optimized
geometries of the molecular entities are discussed. In addition,
the time-dependent DFT method (TD-DFT) was applied to assess
the first excited state of the ligand and complex.
KEYWORDS
Zn coordination polymer;
imidazole derivative; crystal
structure; molecular
geometry optimization; DFT
calculation
1. Introduction
Coordination supramolecular architectures including coordination polymers (CPs) and
the associated metal–organic frameworks have received great scientific attention dur-
ing the last decade [1, 2]. Some of these ordered architectures, built from inorganic
CONTACT Sergiu Shova
shova@icmpp.ro
“Petru Poni” Institute of Macromolecular Chemistry, Romanian
Academy, 700487 Iasi, Romania
Supplemental data for this article is available online at https://doi.org/10.1080/00958972.2020.1818727.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
D. BEJAN ET AL.
metal cations through coordination with functionalized organic ligands, possess
unique properties including porosity [3], luminescence [4], non-linear optics or mag-
netism [5], with subsequent application in gas storage [6], catalysis [7] or sensors [8].
The specific physical and chemical properties of the designed CPs fundamentally
depend on many factors besides the nature of the bridging ligand. Thus, the nature
and coordination properties of metals [9, 10], type of organic building blocks [11, 12],
reaction conditions and stoichiometry [13], and effects of templates or supporting
ligands [14–18] could strongly influence the internal material architecture. Among the
enumerated factors, the type of organic building block is one of the most crucial
ones, giving the possibility of tuning the internal structure due to the possible pres-
ence of multifunctional groups [18, 19]. Among the designed building blocks, mole-
cules containing a biphenyl core with a varying position of carboxylic groups on one
hand, and aromatic nitrogen-containing moieties on the other hand, have recently
attracted special interest [20–22]. For example, building blocks containing both imid-
azole and carboxylate groups have been reported to form coordination compounds
with various transition metals such as Cu, Zn and Cd [20, 23–27], leading to the forma-
tion of interesting 2D and 3D structures. Recently, we have also reported two unsym-
metrical imidazole-biphenyl-carboxylate linkers which were successfully used in the
synthesis of two novel two-dimensional Zn(II) coordination polymers [20]. The struc-
tural investigation of the obtained CPs was performed by single crystal X-ray diffrac-
tion due to the highly crystalline nature of the prepared materials. Interestingly, in the
case of one of the examined linkers, the study of the internal framework formation
also involved the influence of small molecules (particularly acetic acid). It was
observed that two Zn ions within the CP were bridged by two acetate anions in differ-
ent coordination modes, strongly influencing the internal framework. These particular
results on small molecule influence on the CPs internal framework structure, together
with the versatility of Zn(II) metal center and synthetic conditions have stimulated us
not only to continue investigations on formation of new unsymmetrical imidazole-
biphenyl-carboxylate-based Zn(II) CPs in the presence of acetic acid, but also to correl-
ate the obtained X-ray results with computational data on both the starting ligand
and the final CP. Herein, we report the synthetic aspects, spectroscopic data and X-ray
structure of a Zn(II)-based CP, [ZnLAc]n, together with the density functional theory
(DFT) calculation of the optimized geometry for both the starting ligand and the
obtained CP. Quantum chemical calculations using DFT, vibrational frequencies, natural
bond orbitals and HOMO–LUMO have been utilized to perform the geometry opti-
mization. The DFT method was preferred based on its great accuracy and efficiency
[28–30], and due to the fact that the DFT method adequately takes into consideration
electron correlation contributions [31].
2. Materials and methods
2.1. Materials and chemical analysis
All utilized chemicals and solvents were purchased from commercial suppliers as
Sigma-Aldrich (Schnelldorf, Germany) or Carl Roth (Karlsruhe, Germany) and used as
received without purification. The NMR spectra were recorded on a BRUKER AVANCE

JOURNAL OF COORDINATION CHEMISTRY
3
1
III 400 instrument operating at 400.1 MHz for H. Scanning Electron Microscopy (SEM)
analyses were performed on samples immobilized on aluminum supports using a SEM
type Quanta 200 operating at 20 kV with secondary electrons in low vacuum mode
(GSED detector). The Quanta 200 microscope is equipped with an Energy Dispersive X-
Ray (EDX) system for qualitative and quantitative analysis and elemental mapping.
Infra-red spectra were recorded on a BRUKER VERTEX 70 FTIR spectrometer (Bruker
R
V
Optics, Germany). The measurements were performed in ATR Golden Gate
(Attenuated Total Reflectance) mode in the 600–4000 cmꢀ1 range at room tempera-
ture with a resolution of 4 cmꢀ1 and accumulation of 64 scans. Thermo–analytical
measurements were performed with a STA 449 F1 JUPITER (Netzsch, Germany) device.
About 8 mg of solid sample was weighed and placed in alumina pans for TG measure-
ments. The temperature rangeꢀu1sed for measurements was between 30 and 700 ꢁC
with a heating rate of 5 ꢁC min under an atmosphere of dry nitrogen at a flow rate
of 50 mL minꢀ1. The data were processed with the NETZSCH PROTENS 4.2 software.
Powder X-ray diffraction (PXRD) patterns were collected on a Bruker AXS D8 Phaser
powder diffractometer with monochromated Cu-Ka (k ¼ 1.5418 Å) radiation in Bragg-
Brentano arrangement, with a scan speed of 4 s/step and a step size of 0.02ꢁ (2h) at
RT in the range of 2h ¼ 3.5–50ꢁ. Simulated PXRD patterns were calculated with the
CCDC Mercury 4.1 program using the single-crystal data of the compounds.
2.2. Synthesis of poly[m2-acetato-m-4-(4-(1-pyrazolyl)phenyl)benzoato(-
)zinc(II) ([ZnLAc]n)
In a 30 mL culture tube Zn(NO3)2ꢂ6H2O (0.23 g, 0.76 mmol) and HL (0.11 g, 0.41 mmol,
synthesised according to a previously reported method [20]) were dissolved under
mild stirring in DMF (2 mL) at room temperature. Then, acetic anhydride (0.34 g,
3.3 mmol) was slowly added and the reaction mixture was kept under static conditions
for 3 days at 120 ꢁC. The obtained yellow crystalline product was collected by centrifu-
gation and washed with DMF (4 mL) and then ethanol (5 mL). Finally, the crystals were
dried at room temperature (7 mg, Yield 32%). IR (ATR): m (cmꢀ1) ¼ 4064 w, 3118 m,
2928 w, 2886 w, 1902 w, 1658 m, 1612s, 1531 vs, 1458s, 1404s, 1348 vs, 1317s,
1244 m, 1199 w, 1176 w, 1128s, 1070s, 1026 m, 1009 m, 966 m, 948 m, 869 w, 833 vs,
779 vs, 727 m, 698 s, 655 s, 619 w.
2.3. X-ray crystallography
X-ray diffraction measurements were carried out with a Rigaku Oxford-Diffraction
XCALIBUR E CCD diffractometer equipped with graphite-monochromated MoKa radi-
ation. Single crystals were positioned at 40 mm from the detector and 442 frames
were measured each for 30 s over 1ꢁ scan width. The unit cell determination and data
integration were carried out using the CrysAlis package of Oxford Diffraction [32]. The
absorption correction was applied using a Scale3 Abspack multi-scan method [32]. The
structures were solved by Intrinsic Phasing using Olex2 [33] software with the SHELXT
[34] structure solution program and refined by full-matrix least-squares on F2 with
SHELXL-2015 [34] using an anisotropic model for non-hydrogen atoms. All hydrogens

4
D. BEJAN ET AL.
Table 1. Crystal data and details of data collection for [ZnLAc]n.
Empirical formula
C18H14ZnN2O4
Fw
387.68
Space group
a [Å]
b [Å]
P21/c
7.1894(3)
25.2636(9)
9.0208(3)
90
104.602(4)
90
1585.53(11)
4
1.624
c [Å]
ꢁ
ꢁ
ꢁ
[ꢁ]
[ꢁ]
[ꢁ]
V [Å3]
Z
rcalcd [g cm-3]
Crystal size [mm]
T [K]
0.30 ꢄ 0.15 ꢄ 0.03
180
m [mm-1]
1.575
2H range
3.224 to 50.05
12970
2807 [Rint ¼ 0.0327]
2807/0/138
0.0714
0.1813
1.071
Reflections collected
Independent reflections
Data / restraints / parameters
[a]
R1
[b]
wR2
GOF[c]
Largest diff. peak/hole [e Å-3]
1.46/ꢀ0.76
aR1 ¼ RjjFoj ꢀ jFcjj/RjFoj.
bwR2 ¼ fR[w(Fo ꢀ Fc ) ]/R[w(Fo2)2]g
.
2
2 2
1/2
2
2 2
cGOF ¼ fR[w(Fo ꢀ Fc ) ]/(n ꢀ p)g1/2, where n is the number of reflections and p is
the total number of parameters refined.
were introduced in idealized positions (dCH ¼ 0.96 Å) using the riding model with their
isotropic displacement parameters fixed at 120% of their riding atom. As it turned out,
the coordinated ligand is disordered with equal probability over two resolvable posi-
tions. The positional parameters of these atoms were refined using available tools
(PART, DFIX, and SADI) of SHELXL-2015 and the combined anisotropic/isotropic refine-
ment was applied for non-hydrogen atoms. The molecular plots were obtained using
the Olex2 program. The crystallographic data and refinement details are quoted in
Table 1, while bond lengths and angles are summarized in Table S1 in the
Supplementary Information (SI). CCDC ꢀ 1982187 contains the supplementary crystal-
lographic data for this contribution. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (þ44) 1223–336-033 or
E-mail: deposit@ccdc.ca.ac.uk).
2.4. Computation protocol
HPC cluster using the Gaussian09 package [35] has been utilized for computer-aided
simulations for electronic structure calculations. The obtained computational data
were analyzed in GaussView5 graphical-interface software [36] on a Dell Precision
workstation T7910. Density functional theory (DFT) was applied to optimize molecular
geometries using the B3LYP method and double-zeta split-valence basis set
ꢃꢃ
(6–31 G ). For computation of ([ZnLAc]), a dispersion correction (Grimme, DFT-D3BJ)
was applied for the density functional to improve the estimation of the non-covalent
interactions. The crystal structures (CIF-file) were adopted as input conformation for

JOURNAL OF COORDINATION CHEMISTRY
5
the geometry optimization of the isolated molecule (in gas phase) and the merged
model of two disordered components was considered as a starting geometry for cal-
culation. The optimized geometries disclosed no imaginary frequencies confirming the
energetically-minimum structures. YASARA-Structure software [37, 38] was utilized for
conformational goodness-of-fit analysis, together with the MOPAC program in the case
of some descriptors at the level of PM7 [39].
3. Results and discussion
We have previously observed that various synthesis parameters, including the pres-
ence of small molecules [20], can influence the structure and the yield of the final CP.
Thus, the reported results revealed that in the system Zn(NO3)2ꢂ6H2O and 40-(1H-ben-
zo[d]imidazol-1-yl)biphenyl-4-carboxylic acid (L2), the presence of the acetic acid led
to the formation of a new 2D CP [ZnL2Ac]n, while in the case of Zn(NO3)2ꢂ6H2O and
HL without acetic acid residues, the reaction led to the formation of a [ZnL2]n type of
interpenetrated 2D frameworks of a completely different internal organization under
the same reaction conditions. In the current report we have investigated the presence
of acetic acid moieties in the reaction mixture containing Zn(NO3)2ꢂ6H2O and HL, and
performed computational investigations over the structure of both the starting ligand
HL and the structure of the new [ZnLAc]n coordination framework. The synthesis of
the zinc CP with HL followed similar conditions as previously reported [20], by reaction
of a solution of HL and zinc nitrate hexahydrate in a 1:2 ratio (L:M), in DMF as pre-
sented in Scheme 1, but with the addition of an excess of acetic anhydride as a modu-
lating agent. These reaction conditions led to the formation and isolation of suitable
single crystals of a new [ZnLAc]n coordination framework.
3.1. FT-IR spectroscopy
The FT-IR spectrum of [ZnLAc]n CP confirms the presence of the deprotonated HL lig-
and, containing imidazole and phenyl units, used in the CP synthesis (Figure S1 in
Supporting Information). The moderate bands between 3118 cmꢀ1 and 2886 cmꢀ1
may be assigned to the C-H stretching of the aromatic aryl and imidazole rings and
acetate ions (Supporting Information Figure S1). The strong bands at 1531 and
1348 cmꢀ1 can be associated with asymmetric/symmetric vibrations of the carboxylate
group. The presence of aromatic rings in the complex was observed by the oscillations
at 1128–1070 cmꢀ1, as well as the metal–ligand stretching vibrations at 698 cmꢀ1
.
3.2. Thermal analysis
The TGA curve (Figure S2 in Supporting Information) shows that the complex is stable
up to 260 ꢁC, followed by a weight loss between 260 and 400 ꢁC that amounts to
ꢅ27.6%, which can be attributed to the loss of a coordinated acetate group and lig-
and decomposition. Further weight loss between 400 and 700 ꢁC is attributed to the
breakdown of the ligand framework. The residual weight of 35.7% at 700 ꢁC is attrib-
uted to decomposition products.

6
D. BEJAN ET AL.
Scheme 1. Synthetic pathway for the preparation of HL and its Zn(II) coordination polymer.
3.3. Single crystal X-ray diffraction
According to X-ray crystallography the studied compound is a neutral two-dimensional
coordination polymer built-up from Zn(II) cations, deprotonated ligands L- and acetate
anions in 1:1:1 ratio (Figure 1). As shown in Figure 1a, the Zn ion exhibits an NO3 coordin-
ation environment in a slightly distorted tetrahedral geometry provided by three carb-
oxylate oxygen atoms and nitrogen atom from an imidazole ring. 40-(1H-Imidazol-1-
yl)biphenyl-4-carboxylate linkers (L-) coordinate two Zn ions, separated at 16.3060(9) Å,
through the nitrogen atom of the imidazole ring (Zn(1) – N2’(2 – x, ꢀ0.5 þ y, 1.5 – z) ¼
2.024(5) Å) and oxygen atom of the monocoordinated carboxylate group at Zn(1) –
O1 ¼ 1.93(2) Å distance. The coordination polyhedron is completed by two acetate
anions acting as l2-r2O:O’ bridging ligands. The acetate ligand holds the neighboring
zinc ions at a Zn1ꢂꢂꢂZn1’(x, 0.5 – y, ꢀ0.5 þ z) distance of 4.5644(3) Å. The self-assembly of
the asymmetric units that occurs through two bridging ligands (CH3COO- and L-) gener-
ates a 2D wave-like coordination polymer parallel to the 011 plane, which is illustrated
by Figure 1b. A view of the coordination polymers along the b-axis is shown in Figure 1c.
The main crystal structure motif (Figure 1d) essentially results from a dense parallel pack-
ing of 2D networks. Notably, this arrangement is likely to be driven by the weak C-HꢂꢂꢂO
interlayer interactions involving imidazole rings as donors and non-coordinated

JOURNAL OF COORDINATION CHEMISTRY
7
Figure 1. (a) Extended asymmetric unit and the coordination environment of Zn2þ with atom
labelling scheme and thermal ellipsoids at the 40% probability level. Symmetry generated atoms
i
ii
iii
are shown with faded colors. Symmetry codes: 2 – x, ꢀ0.5 – y, 1.5 – z; 2 – x, 0.5 – y, 1.5 – z; x,
0.5 – y, 0.5 þ z. (b) 2D coordination polymer, viewed along the a axis. (c) Space filling representa-
tion of 2D network. (d) Partial view of the crystal structure along the c axis. H-bonds are shown as
dashed lines. Hydrogens are omitted for clarity.
carboxylate oxygen atoms of the L- as acceptors: C14-HꢂꢂꢂO1 [C14-H 0.93 Å, HꢂꢂꢂO1 2,19 Å,
C14ꢂꢂꢂO2(1 ꢀ x, 1 ꢀ y, 1 – z) 3,07(2) Å, /C14HO2 157.4ꢁ].
The bulk purity of the product was confirmed by powder X-ray diffraction (PXRD).
As shown in Figure S3 (Supporting Information), the pattern of the simulated diffracto-
gram based on the single-crystal X-ray data closely matches that obtained from pow-
der diffraction measurements. The observed and calculated diffraction data as well as
hkl indices are presented in Table S2 (Supporting Information).
The SEM images (Supporting Information Figure S4) of [ZnLAc]n showed the morph-
ology of agglomerated irregularly shaped micrometer-scale sheets of different sizes.
The investigated aggregated sheets have predominantly sharp edges, indicating the
crystalline structure of the examined coordination polymer. The chemical composition
of these micrometer-scale crystalline sheets was further investigated by energy-disper-
sion X-ray (EDX) spectroscopy (Supporting Information Figure S5) and the analysis con-
firmed the presence of Zn, C, N and O.
3.4. Molecular modeling of HL and [ZnLAc]
Computational studies using density functional theory (DFT) calculations were carried
out for HL and [ZnLAc]. The latter ([ZnLAc]) represents the truncated model of the

8
D. BEJAN ET AL.
Figure 2. Molecular structure of HL: (a) optimized geometry calculated at the level of DFT/B3LYP/
ꢃꢃ
6-31G theory along with full atomic numbering and dipole moment orientation (1.921 Debye);
(b) distribution of partial atomic charges (Mulliken) calculated by DFT method.
coordination complex (i.e. the main motif of the coordination polymer). Hence, the lig-
and and the main motif of the coordination complex were fully optimized in the
ground state to compare the modelled geometries with the structures observed from
ꢃꢃ
X-ray single-crystal analysis. In this study, we applied DFT with the B3LYP/6-31G
functional/basis set for geometry optimization of HL and [ZnLAc]. The optimized
geometry of the ligand is shown in Figure 2 along with full atomic numbering, dipole
moment orientation and partial atomic charges distribution (Mulliken). Similarly, the
optimized conformation of the complex is illustrated in Figure 3. When comparing
data from Figures 2 and 3 (ligand vs. complex), one may note the change of the
dipole moment orientation and its value, i.e. from 1.921 Debye (in ligand) to 3.013
Debye (in complex). Likewise, the partial atomic charges in carboxyl group of the lig-
and were evidently changed after ligand complexation with Zn(II). In addition, we
have performed the Natural Bond Orbital analysis to determine the natural atomic
charges (Supporting Information Figure S6). Even though the results are different in
magnitude than Mulliken charges, the trends seem to be similar because the dipole
moment orientations are the same.
The selected structural parameters (bond lengths, valence and torsion angles) calcu-
lated from the optimized geometries of HL and [ZnLAc] are reported in Tables 2 and
3, respectively. Additionally, these tables present a comparison between similar data
extracted from the X-ray crystal data and predicted geometries given by DFT. From
the data given in Tables 2 and 3, one may discern a reasonable agreement between

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 3. Molecular structure of [ZnLAc]: (a) optimized geometry calculated at the level of DFT/
ꢃꢃ
B3LYP/6-31G theory along with full atomic numbering and dipole moment orientation (3.013
Debye); (b) distribution of partial atomic charges (Mulliken) calculated by DFT method.
experimental and theoretical values of the structural parameters. Note that the calcu-
lated N-C bond length (phenylimidazole moiety) is equal to 1.417 Å and 1.415 Å for HL
and [ZnLAc], respectively. As regards the carboxylic group, the calculated bond lengths
for C-O and C ¼ O (in HL) are equal to 1.357 Å and 1.215 Å, respectively (Table 2).
Instead, for [ZnLAc], these bonds turn out as equivalent, i.e. 1.274 Å (Table 3). This is
because the negative charge is delocalized on both oxygen atoms, giving the carb-
oxylate anion stabilized by resonance. The calculated valence angle (O-C-O) for HL is
equal to 122.02ꢁ, whereas for the complex this value is smaller, 118.67ꢁ. Such behavior
also might be attributed to the resonance effect in the carboxylate anion. According
to DFT computations, the distance of Zn-O is greater than 2 Å (see Table 3), suggest-
ing the nature of the coordination bond. Regarding the torsion angle (dihedral) C-N-C-
C associated to the phenylimidazole moiety, the calculated values are equal to
ꢀ143.77ꢁ and 141.05ꢁ for HL and [ZnLAc], respectively (Tables 2 and 3). Hence, in
terms of absolute values these dihedrals are similar, but they are of opposite clockwise
directions.
In order to better understand the comparison between the obtained theoretical
and experimental structural values, the DFT optimized structures were compared with
X-ray crystal data in terms of root-mean-square-deviation (RMSD). This estimator (RMSD)
is a measure of resemblance between observed crystal structure and predicted geom-
etry of a molecule in terms of atomic positions. The smaller the RMSD value, the better
is the match between the experimental (X-ray) structure and predicted (DFT) geom-
etry. The explicit mathematical relationship employed to compute the RMSD estimator
is given the in Supplementary Information (Equation S1). Comparison of the single-
crystal structures and the optimized molecular geometries calculated by DFT method
is shown in Figure 4a (HL) and Figure 4b ([ZnLAc]).

10
D. BEJAN ET AL.
Table 2. Summary of selected structural parameters: bond lengths (Å), valence angles (ꢁ) and tor-
sion angles (ꢁ) for HL.
ꢃ
ꢃꢃ
Geometry/structural parameter
Experiment (X-ray)
B3LYP/6-31G
b (21N–30C)
b (6C–20C)
b (4C–17C)
b (17C–1O)
1.428(1) Å
1.478(4) Å
1.486(2) Å
1.316(4) Å
1.218(2) Å
1.417 Å
1.483 Å
1.485 Å
1.357 Å
1.215 Å
b (17C–3O)
ꢁ
ꢁ
/ (11C–21N–30C)
/ (24C–6C–20C)
/ (31C–4C–17C)
/ (1O–17C–3O)
s (11C–21N–30C–26C)
s (24C–6C–20C–13C)
s (31C–4C–17C–1O)
ꢃ
125.9(3)
119.5(2)
118.1(3)
123.4(1)
127.16
121.11
118.14
122.02
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢀ143.0(4)
ꢀ143.77
ꢁ
ꢁ
ꢁ
143.9(3)
143.44
179.97
ꢁ
ꢀ179.1(2)
(b – bond); (/ valence angle); (s – torsion angle).
Table 3. Summary of selected structural parameters: bond lengths (Å), valence angles (ꢁ) and tor-
sion angles (ꢁ) for [ZnLAc]n.
ꢃ
ꢃꢃ
Geometry/structural parameter
Experiment (X-ray)
B3LYP/6-31G
b (6N–24C)
b (19C–14C)
b (9C–8C)
b (8C–3O)
b (8C–2O)
d (3O–1Zn)
d (2O–1Zn)
d (4O–1Zn)
d (5O–1Zn)
1.441(2) Å
1.484(1) Å
1.505(2) Å
1.231(2) Å
1.229(3) Å
2.752(2) Å
1.996(3) Å
1.971(3) Å
2.693(2) Å
1.415 Å
1.478 Å
1.475 Å
1.274 Å
1.274 Å
2.031 Å
2.031 Å
2.037 Å
2.028 Å
ꢁ
ꢁ
/ (29C–6N–24C)
/ (27C–19C–14C)
/ (17C–9C–8C)
/ (3O–8C–2O)
s (29C–6N–24C–22C)
s (27C–19C–14C–12C)
s (17C–9C–8C–3O)
ꢃ
127.0(1)
122.0(1)
123.3(2)
119.9(1)
126.77
121.02
120.18
118.67
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
141.3(2)
141.05
ꢁ
ꢁ
ꢁ
ꢁ
ꢀ175.6(3)
ꢀ142.08
ꢀ159.2(3)
ꢀ179.94
(b – bond distance), (d – inter-atomic distance); (/ valence angle); (s– torsion angle).
According to Figure 4a, the RMSD value for HL is small (0.185 Å), revealing a very
good similitude between experimental and theoretical data. By contrast, the RMSD
value for [ZnLAc]n is greater (0.855 Å) disclosing more discrepancy between the
obtained experimental data and DFT model, when compared to HL. The observed
larger difference could be attributed to the fact that computations for the [ZnLAc]
molecule were performed for the gas phase, while the experimental observation (X-ray
structure) was recorded for the crystal phase, where the periodicity or the effect of
the neighboring molecules did matter. Another explanation for the observed differen-
ces could be the fact that the results on geometry optimization strongly depend upon
the calculation method used, leading to significant under- or overestimations in the
case of Zn complexes possessing Zn-O and Zn-N bonds [40]. Similar difficulties in
geometry optimization were typically observed in case of transition metals and some-
times Zn complexes with carbonyl groups [41].
On the basis of atomic charge distribution, the electrostatic potential surfaces (ESP)
surrounding the molecular entities (HL and [ZnLAc]) were calculated by integration
ꢃꢃ
techniques at the level of DFT/B3LYP/6-31G . Figure 5 shows the mapped isosurface

JOURNAL OF COORDINATION CHEMISTRY
11
Figure 4. Comparison between observed (X-ray mono-crystal) and theoretical structures of (a) HL
and (b) [ZnLAc]; overlapping of X-ray structures (blue) and theoretical structures (red) computed by
ꢃꢃ
DFT/B3LYP/6-31G method; (RMSDLigand ¼ 0.185 Å, RMSDComplex ¼ 0.855 Å).
Figure 5. Electrostatic potential (ESP) surface map of (a) HL and (b) [ZnLAc]; computation per-
ꢃꢃ
formed at the level of B3LYP/6-31G theory.
of ESP calculated by DFT for the ligand (Figure 5a) and complex (Figure 5b). In this
illustration, the highest positive ESP region (blue-spot), suggesting the site for nucleo-
philic attack, can be distinguished near the proton of the carboxylic acid group in the
ligand (Figure 5a), and near the coordination center (Zn ion) in the complex (Figure
5b). The highest negative ESP zones (red-spotted regions) are present in both ligand
(Figure 5a) and complex (Figure 5b); these regions are sites of electrophilic attack and
belongs to one of the nitrogen atoms from imidazole and oxygen atom from a
C ¼ O moiety.
The patterns of frontier molecular orbitals (HOMO, LUMO) are given in Figure 6 for
ꢃꢃ
HL. According to the DFT/B3LYP/6-31G
LUMO) is equal to 4.379 eV (for ligand).
method, the band-gap energy (HOMO-
By inspecting the HOMO-LUMO pattern of the ligand, one can discern that this con-
ꢃ
figuration corresponds to a p-p electronic transition. The lobes of the HOMO orbital
are mainly spread over the p-conjugated system of the phenylimidazole moiety, which

12
D. BEJAN ET AL.
Figure 6. Patterns of frontier molecular orbitals (HOMO–LUMO) and associated band-gap energy
ꢃꢃ
value for the HL molecule; computations done by DFT/B3LYP/6-31G method.
may act as an electron-donor. In turn, the lobes of the unoccupied LUMO orbital are
mainly distributed over the benzoyl moiety that may act as an electron-acceptor
(Figure 6). In the case of [ZnLAc], the HOMO-LUMO pattern also corresponds to the
ꢃ
intraligand p-p electronic configuration, similar to that of the ligand (Figure 7). As
shown in Figure 7, the band-gap energy (HOMO-LUMO) for [ZnLAc] is equal to
4.384 eV, which is close to the value for HL.
In addition, the low-lying excited states of the ligand and the complex were
assessed by the time-dependent (TD-DFT) method performed at the level of CAM-
ꢃꢃ
B3LYP/6-31G
theory. Outcomes of the TD-DFT computations are summarized in
Table S3 (Supporting Information), which is reported in the Supplemental Information
(ESI). Here, we report the first excited-state (S1) data for the ligand, [ZnLAc] complex,
and additionally, for the complex [ZnL2Ac] – comprising two ligand molecules.
According to the computational results (Supporting Information Table S3/ESI), the
highest oscillator strengths (f > 1) were determined for the excited state S1 (in ligand
and complexes). This excited state S1 emerged in the transition wavelength domain of
ꢃ
264–266 nm, and it is associated with a p-p electronic transition. In the case of ligand
and ZnLAc complex, the excited state S1 is mainly assigned to the HOMO!LUMO
electronic configuration (Supporting Information Table S3). In turn, for the complex
[ZnL2Ac], involving two ligand molecules, the excited state S1 is mainly attributed to
the HOMO!LUMO þ 1 electronic pattern (Supporting Information Table S3), which is
also an intraligand configuration (Figure 8).
Additionally, we calculated the molecular and reactivity descriptors for HL and
[ZnLAc] according to the methodology presented elsewhere [42–44]. These results,
related to molecular properties and global reactivity descriptors, are summarized in
Table S4 (Supporting Information). According to Table S4 (Supporting Information),

JOURNAL OF COORDINATION CHEMISTRY
13
Figure 7. Patterns of frontier molecular orbitals (HOMO–LUMO) and associated band-gap energy
ꢃꢃ
value for the [ZnLAc]; computations were done at the level of theory DFT/B3LYP/6-31G (includ-
ing empirical dispersion effect).
Figure 8. Patterns of frontier molecular orbitals (HOMO–LUMO þ 1 involved in the excited state
S1) and associated band-gap energy value for the dimer entity [ZnL2Ac]; computations were done
ꢃꢃ
at the level of theory DFT/B3LYP/6-31G (including empirical dispersion effect).
the chemical softness and electrophilicity index is greater for the [ZnLAc] complex
than for HL, including the electron-donating and electron-accepting powers, data sug-
gesting that the complex has the tendency to be more reactive than HL. In qualitative
terms, this can be described as the ability of the nucleophiles (or bases) to donate
electrons more readily to electrophiles (acids) in order to start the bond forma-
tion reaction.

14
D. BEJAN ET AL.
4. Conclusion
A novel [ZnLAc]n two-dimensional coordination polymer was prepared and structurally
characterized. The presence of an acetate moiety in the reaction mixture strongly
influences the final structure generating a 2D wave like coordination polymer. The
coordination polymer structure was further confirmed by FTIR, TGA, PXRD, SEM and
EDX analyses, supporting the X-ray data. Quantum chemical calculations using DFT, at
ꢃꢃ
the level of B3LYP/6-31G theory, have been utilized to perform the geometry opti-
mization of both HL and the Zn(II) complex, and the results were compared with the
experimental data. The comparison of the single-crystal structures and the optimized
molecular geometries for the molecule (HL) revealed a very good similitude between
experimental and theoretical data providing a low RMSD value equal to 0.185 Å. In the
case of [ZnLAc], a RMSD value of 0.855 Å was obtained, suggesting a reasonable
agreement between experimental data and DFT model. Likewise, TD-DFT calculations
ꢃ
disclosed the intraligand p-p electronic configuration, for the first excited state S1,
occurring in HL and ZnLAc. According to this, the phenylimidazole moiety from the lig-
and might act as electron-donor, whereas the benzoyl moiety might act as elec-
tron-acceptor.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
€
€
[1] S.R. Batten, N.R. Champness, X.M. Chen, J. Garcia-Martinez, S. Kitagawa, L. Ohrstrom, M.
O’Keeffe, M. Paik Suh, J. Reedijk. Pure Appl. Chem, 85, 1715 (2013).
[2] C. Janiak, J.K. Vieth. New J. Chem., 34, 2366 (2010).
[3] S. Kitagawa, R. Kitaura, S.I. Noro. Angew. Chem. Int. Ed. Engl., 43, 2334 (2004).
€
[4] J. Heine, K. Muller-Buschbaum. Chem. Soc. Rev., 42, 9232 (2013).
[5] M. Kurmoo. Chem. Soc. Rev., 38, 1353 (2009).
[6] M.P. Suh, H.J. Park, T.K. Prasad, D.W. Lim. Chem. Rev., 112, 782 (2012).
[7] M. Yoon, R. Srirambalaji, K. Kim. Chem. Rev., 112, 1196 (2012).
[8] L.E. Kreno, K. Leong, O.K. Farha, M. Allendorf, R.P. Van Duyne, J.T. Hupp. Chem. Rev., 112,
1105 (2012).
[9] P.C. Lemaire, D.T. Lee, J. Zhao, G.N. Parsons. ACS Appl. Mater. Interfaces, 9, 22042 (2017).
[10] P. Ji, K. Manna, Z. Lin, A. Urban, F.X. Greene, G. Lan, W. Lin. J. Am. Chem. Soc., 138, 12234
(2016).
ꢀ
[11] S.W. Jaros, M.F.C. Guedes da Silva, M. Florek, M.C. Oliveira, P. Smolenski, A.J.L. Pombeiro,
A.M. Kirillov. Cryst. Growth Des., 14, 5408 (2014).
[12] P. Manna, S.K. Das. Cryst. Growth Des., 15, 1407 (2015).
[13] L.J. Beeching, C.S. Hawes, D.R. Turner, S.R. Batten. CrystEngComm, 16, 6459 (2014).
[14] Y. Kobayashi, K. Honjo, S. Kitagawa, T. Uemura. ACS Appl. Mater. Interfaces, 9, 11373
(2017).
[15] R. Ding, C. Huang, J. Lu, J. Wang, C. Song, J. Wu, H. Hou, Y. Fan. Inorg. Chem., 54, 1405
(2015).
[16] J. Wang, C. Bai, H.M. Hu, F. Yuan, G.-L. Xue. J. Solid State Chem., 249, 87 (2017).
[17] J.Y. Zhang, J.X. Shi, L.Y. Chen, Q.X. Jia, W. Deng, E.Q. Gao. CrystEngComm, 19, 1738 (2017).
[18] J. Gu, M. Wen, X. Liang, Z. Shi, V.M. Kirillova, M.A. Kirillov. Crystals, 8, 83 (2018).

JOURNAL OF COORDINATION CHEMISTRY
15
[19] K.Q. Hu, L.Z. Zhu, C.Z. Wang, L. Mei, Y.H. Liu, Z.Q. Gao, Z.F. Chai, W.Q. Shi. Cryst. Growth
Des., 16, 4886 (2016).
[20] D. Bejan, L.G. Bahrin, S. Shova, M. Sardaru, L. Clima, A. Nicolescu, N. Marangoci, V. Lozan,
C. Janiak. Inorg. Chim. Acta, 482, 275 (2018).
[21] L.Z. Yang, J. Wang, A.M. Kirillov, W. Dou, C. Xu, R. Fang, C.L. Xu, W.S. Liu. CrystEngComm,
18, 6425 (2016).
[22] J.F. Song, Y.Y. Jia, R.S. Zhou, S.Z. Li, X.M. Qiu, J. Liu. RSC Adv., 7, 7217 (2017).
[23] Q. Yu, Y.F. Zeng, J.P. Zhao, Q. Yang, X.H. Bu. Cryst. Growth Des., 10, 1878 (2010).
ꢀ
ꢀ
ꢀ
[24] Y. Akhriff, J. Server-Carrio, A. Sancho, J. Garcıa-Lozano, E. Escriva, J.V. Folgado, L. Soto.
Inorg. Chem., 38, 1174 (1999).
[25] T.L. Hu, W.P. Du, B.W. Hu, J.R. Li, X.H. Bu, R. Cao. CrystEngComm, 10, 1037 (2008).
[26] P. Liu, Y. Zhu, L. Xia, Y.L. Wu, X.Q. Lu, C.K. Xia, J.M. Xie. Polyhedron, 102, 276 (2015).
[27] X. Feng, L. Liu, J.G. Zhou, L.L. Zhou, Z.Q. Shi, L.Y. Wang. Synth. React. Inorg. Met. Org.
Nano Met. Chem., 43, 705 (2013).
[28] V. Karunakaran, V. Balachandran. Spectrochim. Acta A Mol. Biomol. Spectrosc., 98, 229
(2012).
[29] A. Suvitha, S. Periandy, S. Boomadevi, M. Govindarajan. Spectrochim. Acta A Mol. Biomol.
Spectrosc., 117, 216 (2014).
_
[30] M. Karabacak, E. S¸ahin, M. C¸ınar, I. Erol, M. Kurt. J. Mol. Struct., 886, 148 (2008).
_
[31] I. Sıdır, Y.G. Sıdır, M. Kumalar, E. Tas¸al. J. Mol. Struct., 964, 134 (2010).
[32] CrysAlisPro Software system, version 1.171.38.46, Rigaku Corporation: Oxford, UK (2015).
[33] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann. J. Appl.
Crystallogr., 42, 339 (2009).
[34] G.M. Sheldrick. Acta Crystallogr. A Found. Adv., 71, 3 (2015).
[35] G.W. Trucks, M.J. Frisch, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P.
Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J.A. Montgomery, J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N.
Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant,
S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V.
Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R.
Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P.
€
Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J.
Cioslowski, D.J. Fox. GAUSSIAN 09, Revision D.01, Gaussian, Inc., Wallingford, CT (2009).
[36] R. Dennington, T. Keith, J. Millam. GaussView, Version 5, Semichem Inc., Shawnee Mission,
KS (2009).
[37] E. Krieger, G. Vriend. Bioinformatics, 30, 2981 (2014).
[38] E. Krieger, G. Vriend, J. Comput. Chem., 36, 996 (2015).