Two new 1D zigzag Hg(II) nanostructure coordination polymers: Sonochemical synthesis, thermal study, crystal structure and Hirshfeld surface analysis

Article abstract of DOI:10.1016/j.ica.2016.01.001

Reaction of mercury(II) chloride and bromide with a Schiff base ligand based on isonicotinohydrazide (L) yielded two new 1D zigzag coordination polymers; [Hg(μ-L)Cl₂]_n (1) and [Hg(μ-L)Br₂]_n (2). The Schiff base

Full text of DOI:10.1016/j.ica.2016.01.001

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Two new 1D zigzag Hg(II) nanostucture coordination polymers: Sonochemical
synthesis, thermal study, crystal structure and Hirshfeld surface analysis
M. Montazerozohori, A. Masoudiasl, Th. Doert
PII:
S0020-1693(16)00002-5
http://dx.doi.org/10.1016/j.ica.2016.01.001
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Inorganica Chimica Acta
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Please cite this article as: M. Montazerozohori, A. Masoudiasl, Th. Doert, Two new 1D zigzag Hg(II) nanostucture
coordination polymers: Sonochemical synthesis, thermal study, crystal structure and Hirshfeld surface analysis,
Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.01.001
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Two new 1D zigzag Hg(II) nanostucture coordination polymers:
Sonochemical synthesis, thermal study, crystal structure and Hirshfeld
surface analysis
M. Montazerozohori*1, A. Masoudiasl1, Th. Doert2
1Department of Chemistry, Yasouj University, Yasouj 7591874831 Iran.
2Department of Chemistry and Food Chemistry, TechnischeUniversität Dresden, 01062 Dresden,
Germany.
*Corresponding author E-mail: mmzohori@yu.ac.ir
ABSTRACT
Reaction of mercury(II) chloride and bromide with a Schiff base ligand based on
isonicotinohydrazide (L) yielded two new 1D zigzag coordination polymers; [Hg(µ-L)Cl2]n (1)
and [Hg(µ-L)Br2]n (2). The Schiff base ligand and its Hg(II) complexes have been characterized
1
13
by FT-IR, UV--Vis, H and CNMR spectroscopy. The structures of the complexes were
determined by single crystal X-ray diffraction. Structural data show that the two new mercury
complexes have similar structures. In both complexes, Hg(II) ion is five-coordinated by three
atoms of Schiff base ligand and two halide anions. The ligand (L) acts as N2O-donor and
connects neighboring Hg ion centers to form infinite 1D zigzag chain. This 1D chain is stabilized
as 3D supramolecular network by intermolecular interactions of π…π stacking and X–H…Cl (X
=N and C) in 1 and C–H···π, π…π stacking and X–H…Br (X=N and C) in 2. Hirshfeld surface
analysis and 2D fingerprint plots of asymmetric units of two complexes indicated differences and
similarities between crystal packing of compounds. TG/DTG analyses show that compounds 1
and 2 decompose completely during three or four thermal steps, respectively. Nanostructure
forms of the titled coordination polymers have been also synthesized by sonochemical method
and confirmed by X-ray powder diffraction (XRD), and scanning electron microscopy (SEM).
Keywords: Mercury, Coordination, Polymer, X-ray, XRD, Nanostructure, supramolecular.
1. Introduction
In the last decades, synthesis and design of coordination polymers have attracted high interest
because of their potential applications in adsorption and storage of gases [1,2], sensing [3],
1

catalysis [4,5], ion exchange [6], magnetism [7] and extraction of metal ions [8]. Crystal
engineering of coordination polymers is influenced by judicious design or choice of molecular
building blocks and suitable synthetic conditions [9]. Design of organic building blocks having
particular functional groups and appropriate coordination sites for specified geometries facilitates
rational construction of desired structures and functions by the aid of appropriate metal ions [10-
14]. Indeed, the selection of an appropriate organic ligand leads to a particular coordination
polymer with intriguing structure and unique properties. On the other hand, the self-assembly
processes are sensitive to diverse synthetic conditions and in some cases, change of reaction
conditions such as the solvent, pH, counter ion, and temperature for a given set of metal ions and
organic ligands can cause various structural topologies [15-19]. Moreover the extraordinary
growth of crystal engineering investigations for supramolecular architectures has been
accompanied by an increasing interest in the identification and understanding of non-covalent
intermolecular interactions. These nonbonding forces control the structures and properties of
molecular assemblies such as liquids, molecular crystals and biological molecules [20-22].
Classical and strong hydrogen bonds, and other weaker non-covalent interactions such as
C−H···X (X = Hal, O, N), π···π stacking, C− H···π, or halogen bonding have attracted some
attentions due to stabilization and directionality that they induce to the final structures of
crystalline coordination compounds. [23-28]. Among different metal ions, the spherical d10
configuration of Hg(II) is associated with a flexible coordination environment, thus the
geometries of the mercury complexes can vary from linear to octahedral or even distorted
hexagonal bipyramidal geometries, and severe distortions from ideal coordination polyhedral
structure occur easily [29]. In contrast to nano-scale inorganic materials, little attention has been
paid to nano-structures of coordination compounds. However, recently, the sonochemical
process as a fast, convenient, and economical method has been widely used to produce this type
of materials [30-32]. In this synthetic method, molecules undergo a reaction due to the
application of powerful ultrasound radiation (10 kHz – 20 MHz) [33]. In the present study, we
describe the sonochemical synthesis, spectroscopic studies, thermal study, crystal structures and
Hirschfield surfaces analysis of two novel nanostructured coordination polymers; [Hg(µ-L)Cl2]n
(1) and [Hg(µ-L)Br2]n (2).
2.1. Materials and measurements
2

All reagents used for the syntheses and analysis were commercially available and applied as
received. The FT-IR spectra of the compounds were recorded on JASCO-680 spectrophotometer
in the range 4000–400 cm-1 using the KBr disk technique. Melting points or decomposition
1
13
temperatures of the compounds were measured on a Kruss instrument. The H and C NMR
spectra of compounds were recorded by a Bruker DPX FT/NMR-400 spectrometer. A Perkin–
Elmer lambda 25 spectrometer has been used for measurement of UV–Visible spectra in
dichloromethane solvent in the range of 200–800 nm. X-ray powder diffraction (XRD)
measurements were performed using a STOE type STADI-MP-Germany X-ray diffractometer
with Cu Kα radiation (λ = 1.5418 Å). The simulated XRD powder patterns based on single
crystal data were prepared using Mercury software [34]. Single crystal diffraction data were
collected on a Bruker Kappa APEX II diffractometer with CCD detector (Mo Kα graphite-
monochromatic radiation, λ = 0.71073 Å) controlled by the APEX2 software package [35]. A
semi-empirical, absorption correction (multi-scan) was applied with SADABS [36]. The
structures were solved by direct methods, SHELXS-97 [37] and refined by full-matrix least-
squares refinement cycles on F2 using SHELXL-97 [38, 39] Details of crystal data, collection
and refinement for the two mercury complexes are listed in Table 1. The record of scanning
electron microscopy (SEM) images was carried out by KYKY-EM 3200 field emission scanning
electron microscope using Ac voltage of 25 kV. The thermal stabilities for 1 and 2 were
investigated by a Perkin-Elmer Pyris model instrument with a heating rate of 10 ˚C/ min under
nitrogen atmosphere.
2.2. Synthesis of N'-(4-(dimethylamino)benzylidene)isonicotinohydrazide ligand (L)
Schiff base ligand (L) was prepared according to literature procedure [40-43]. A mixture of 4-
(dimethylamino)benzaldehyde (1 mmol, 149.2 mg) and isonicotinic acid hydrazide (1 mmol,
137.1 mg) in ethanol (50 mL) was refluxed for about 24 h. After cooling to room temperature, a
yellow precipitate was filtered off and washed twice with ethanol to give the product L as a
yellow solid that was stable in air. Yield: 85%. M.p.: 201-203 ˚C. UV--Vis, CH2Cl2 [λ , nm]:
max
258, 361. Selected FT-IR data (KBr, cm-1): 527(w), 582(w), 686(m), 817(s), 1051(m), 1182(m),
1
1310(m), 1367(s), 1524(s), 1593(s), 1664(s), 2845(m), 2972(w), 3080(w), 3192(m). HNMR
(DMSO-d6); δ: 11.78(s, 1He), 8.77(d, 2Hgg', J=4.4 Hz), 8.33(s, 1Hd), 7.81(d, 2Hff', J=4.16 Hz),
13
7.56(d, 2Hcc', J=7.6 Hz), 6.76(d, 2Hbb', J=7.6 Hz), 2.99(s, 6Haa') ppm. CNMR (DMSO-d6); δ:
3

161.01(C7), 151.67(C2), 150.23(C10,10'), 145.60(C6), 140.80(C8), 128.63(C4,4'), 123.16(C5),
121.43(C9,9'), 111.75(C3,3'), 39.90(C1) ppm.
2.2. Synthesis of mercury (II) complexes
2.2.1. [Hg(µ-L)Cl2]n (1)
Crystals of 1 were obtained by slow diffusion in a branched tube [44]. Mercury(II) chloride (101
mg, 0.37 mmol) and Schiff base ligand (L) (100mg, 0.37 mmol) were placed in the main arm of
a branched tube and methanol solvent was carefully added to fill the arms. The tube was sealed
and the arm containing the reagents immersed in an oil bath at 60 ˚C while the other arm was
kept at ambient temperature. After one week, crystals of 1 were deposited in the cooler arm,
which were washed with acetone and ether and analyzed after separation. Yield: 45%. M.p.: 220-
222˚C. UV--Vis, CH2Cl2 [λ , nm]: 256, 358. Selected FT-IR data (KBr, cm-1): 451(w), 509(w),
max
572(w), 692(s), 804(m), 1061(m), 1180(s), 1376(s), 1533(m), 1585(s), 1639(s), 2821(m),
1
2902(w), 3081(w), 3263(m). HNMR (DMSO-d6); δ: 11.81(s, 1He), 8.78(d, 2Hgg'), 8.33(s, 1Hd),
7.86(d, 2Hff', J=4.00 Hz), 7.56(d, 2Hcc', J=7.6 Hz), 6.76(d, 2Hbb', J=7.6 Hz), 2.99(s, 6Haa') ppm.
13CNMR (DMSO-d6); δ: 160.85(C7), 151.69(C2), 149.95(C10,10'), 145.61(C6), 141.31(C8),
128.66(C4,4'), 123.63(C5), 121.74(C9,9'), 111.76(C3,3'), 39.87(C1) ppm.
2.2.1. [Hg(µ-L)Br2]n (2)
Crystals of 2 were prepared by a similar manner as complex 1 except that mercury(II) chloride
was replaced by mercury(II) bromide. Yield: 53%. M.p.: 246-248˚C. UV--Vis, CH2Cl2 [λ , nm]:
max
261, 353. Selected FT-IR data (KBr, cm-1): 453(w), 509(w), 559(w), 692(s), 804(m), 1061(m),
1
1189(s), 1375(s), 1533(m), 1583(s), 1633(s), 2821(m), 2908(w), 3077(w), 3272(m). HNMR
(DMSO-d6); δ: 11.80(s, 1He), 8.77(d, 2Hgg', J=6.00 Hz), 8.33(s, 1Hd), 7.85(d, 2Hff', J=7.60 Hz),
13
7.56(d, 2Hcc', J=8.80 Hz), 6.60(d, 2Hbb', J=8.80 Hz), 2.99(s, 6Haa') ppm. CNMR (DMSO-d6); δ:
160.75(C7), 151.69(C2), 150.04(C10,10'), 145.60(C6), 141.28(C8), 128.65(C4,4'), 123.60(C5),
121.74(C9,9'), 111.75(C3,3'), 39.89(C1) ppm..
2.3. Synthesis of nanostructure mercury compounds [Hg(µ-L)X2]n (X = Cl for 1 and X = Br
for 2)
4

For the synthesis of nanostructure mercury(II) complexes, an ethanol/dichloromethane (10:1,
v/v) solution of Schiff base ligand (1 mmol) was positioned under ultrasonic irradiation. Then, an
ethanolic solution of mercury(II) halide (1 mmol) was drop wisely added. The reaction mixture
was kept in the ultrasonic bath for about 60 min. The obtained precipitates were filtered and
washed with ethanol several times and then dried at 70 ˚C.
2.4. Hirshfeld surfaces calculations
Molecular Hirshfeld surface analyses were carried out by using the CrystalExplorer computer
program [45]. Hirshfeld surfaces are mapped using the normalized contact distance (dnorm),
which is calculated using the following equation:
ꢀꢆ −ꢅꢇꢈꢉꢊ
ꢀꢋ −ꢅꢇꢈꢉꢊ
ꢋ
ꢆ
ꢀꢁꢂꢃꢄ =ꢅ
+ꢅ
ꢇꢈꢉꢊ
ꢇꢈꢉꢊ
ꢋ
ꢆ
Where de is the distance from the Hirshfeld surface to the nearest atom outside the surface, di is
the distance from the Hirshfeld surface to the nearest atom inside the surface and dnorm is defined
in terms of de and di and the van der Waals (vdW) radii of atoms. Three-dimensional (3D)
Hirshfeld surface maps are generated with dnorm using a red–white–blue color scheme, indicating
shorter contacts, vdW contacts, and longer contacts, respectively, and two dimensional (2D)
fingerprint plots generated using de and di.
3. Results and discussion
3.1. Spectroscopic studies
A schematic representation of Schiff base ligand (L) and its coordination mode to Hg(II) center
is illustrated in Scheme 1. Data related to FT-IR, NMR and UV-Vis spectra of ligand and its
mercury(II) complexes have been described in Section 2. In the FT-IR spectrum of the ligand,
the absorption peak around 3192 cm-1 is attributed to N–H stretching frequency. After
complexation, this absorption peak shifted to higher frequencies (3263 cm-1 in 1 and 3272 cm-1
in 2). The C=O stretching frequency of ligand appeared around 1664 cm-1 as sharp peak shifts to
a lower wavenumbers in the spectra of complexes (1639 cm-1 in 1 and 1633 cm-1 in 2). Also the
absorption peak at 1593 cm-1 related to C=N stretching vibration of ligand shifts to lower
5

frequencies in the complexes spectra (1585 cm-1 in 1 and 1583 cm-1 in 2). These signal shifts
confirm the participation of the imine nitrogen and carbonyl oxygen of the ligand in binding to
the mercury center. Moreover, the presence of new peaks in the IR spectra of the synthesized
complexes at 450 – 510 cm-1 can be assigned to ν(M–N) vibrations that may be as an evidence
for the coordination of nitrogen atom to the metal center [46].
The UV-Visible spectra of free ligand exhibits two bands, one as a shoulder at 258 nm assigned
to π→π* transitions due to π-system of pyridine and phenyl rings and carbonyl and azomethine
bonds and the second one as intense bond at 361 nm assigned to n→π* transitions of C=O and
C=N groups [47]. The red and blue shifts of the these bands in the complexes spectra with
respect to the free ligand indicate the coordination of the ligand to the Hg(II) ion. In
continuation, NMR spectra of ligand and its mercury complexes were also recorded to confirm
the suggested structures. In the ligand spectrum, imidic hydrogen (He) appears as a singlet peak
at 11.78 ppm.Olefinic hydrogen of Hd appears as a singlet signal at 8.33 ppm. Aromatic
hydrogens of Hgg', Hff', Hcc' and Hbb' are found as doublet signals at 8.77, 7.81, 7.56 and 6.76 ppm
respectively. Finally, aliphatic hydrogens of 6 Haa' resonate at 2.99 ppm. After coordination,
chemical shifts of the hydrogens are unchanged or downfielded. In 13C NMR spectrum of ligand,
carbon signals of (C7), (C2), (C10,10'), (C6), (C8), (C4,4'), (C5), (C9,9'), (C3,3') and (C1) appear at 161.01,
151.67, 150.23, 145.60, 140.80, 128.63, 123.16, 121.43, 111.75 and 39.90 ppm respectively.
After binding of ligand to mercury center, the carbon signals are appeared as downfielded or
upfielded signals as detailed in experimental section.
Scheme 1
3.2. Crystal structures description
Crystal structure of ligand has been previously reported [40-43]. Tables of 1 and 2 show the X-
ray structure determination details, selected bond lengths and bond angles of the compounds(1
and 2), respectively. The intermolecular interactions of compounds are listed in Table 3.
3.2.1. [Hg(µ-L)Cl2]n (1)
6

Single-crystal X-ray diffraction analysis revealed that 1 crystallizes in the orthorhombic space
group Pbca. Crystal structure and asymmetric unit of 1 are shown in Fig. 1. The asymmetric unit
is composed of one Hg(II) ion, one Schiff base ligand (L), and two chloride anions. The Hg(II)
ion is five-coordinated by three atoms of Schiff base ligand (imine nitrogen, pyridine nitrogen
and carbonyl oxygen) and two Cl atoms. The Schiff base ligand (L) acts as N2O-donor (Scheme
1), and connects to neighboring Hg centers to form an infinite 1D zigzag chain (Fig. 3).
According to equation defined by Addison et all [48] for five coordinated compounds, the value
of τ5 parameter is 0.24, indicating a distorted square pyramidal (SP) geometry for the mercury
(II) center. In this SP coordination, the equatorial plane contains two nitrogen atoms of two
distinct Schiff base ligands (imine nitrogen from one and pyridine nitrogen from other) and two
terminal chloride anions and the apical position is occupied by carbonyl oxygen atom of ligand.
The Hg, Cl1 and Cl2 atoms lie out of the mean plane defined by N1N3HgCl1Cl2 by a distance
of 0.154, 0.674 and 0.780 Å to the opposite side of apical oxygen (O1), while the pyridine
nitrogen(N1) and imine nitrogen(N3) are displaced toward apical position by distances of 0.867
and 0.740 Å, respectively. The Hg–Npyridin bond length (2.547 Å) is significantly shorter than the
Hg–Nimine bond length (2.80 Å), and the Hg–Ocarbonyl bond length is shorter than these two bonds.
In a reported pyrrole hydrazone mercury complex [49], this order changes as following: Hg–
Nimine < Hg–Npyridin< Hg–Ocarbonyl. The average Hg–Cl distance (2.354 Å) is comparable with its
average value in mercury complexes containing HgN2OCl2 chromophore [49, 50]. The angles
around the Hg center is ranging from 62.16(4)º to 151.76(16)˚. The Schiff base ligand form a
five-membered chelate ring with bite angle of about 62.16˚ that is close to its value (60.35˚) in
pyrrole hydrazone mercury complex [49].
As shown in Fig. 3, the Hg(II) atoms are connected through bridging Schiff base ligand(L) that
results in 1D zigzag chain. The crystal packing analyses shows that 1D chains are further
arranged in the crystal lattice by π…π stacking and X–H…Cl (X = N and C) intermolecular
interactions. The Cl1 atom participates in hydrogen bonding with hydrogen atom (H14C) of the
methyl group of substituent on phenyl ring. This C–H…Cl non-covalent interaction leads to 2D
expansion of crystal network (Fig. 4(left)). The polymeric chains are also embraced through
intermolecular π…π stacking interactions between pyridine rings of Schiff base ligand with a
centroid-to-centroid distance of 3.733 Å and symmetry code (-1/2+x, y, 1/2-z) for Cg1…Cg1
(Cg1: N1, C1, C2, C3, C4, C5). These chains are further embraced through intermolecular N–H
7

…Cl hydrogen bonds between Cl2 atom and amide hydrogen (H2A) of Schiff base ligand. These
two last interactions induce consecutive layers of polymeric chains (Fig. 4(right)). The dihedral
angle between planes of two adjacent polymeric chains is 10.3˚ indicating these chains are
almost parallel.
3.2.2. [Hg(µ-L)Br2]n (2)
X-ray single crystal diffraction analysis and vibrational spectroscopic studies reveal that the two
mercury(II) coordination polymers have similar structures. The asymmetric unit of 2 is shown in
Fig. 2. This compound consists of 1D polymeric chains of µ-L-connected square pyramidal (SP)
complexes (Fig. 3). In the distorted square pyramidal geometry (τ5 = 0.07) of the mercury(II)
center, the equatorial positions are occupied by pyridine nitrogen(N1), imine nitrogen(N3) and
two bromide anions (Br1 and Br2) while the carbonyl oxygen atom (O1) is at the apical position.
The distance of Hg1 from the mean plane defined by N1N3HgBr1Br2 is 0.056 Å. The bonds of
the central atom to the coordinating ligand atoms have almost identical lengths (∆Hg–Npyridine
=
0.005 Å, ∆Hg–Nimine = 0.04 Å and ∆Hg–Ocarbonyl = 0.011 Å). In both complexes, the Hg–Nimine
bond distance is longer than the range previously reported for five-coordinated mercury
complexes involving ligation by imine nitrogen atom [49-52]. However, Hg–N bonds longer
than 2.76 Å have been reported in several Hg(II) compounds [53-54].
In the crystal packing of 2, distinct C–H···π interactions are accompanied by π-π stacking and
X–H…Br (X = N and C) interactions (Table 3). Edge-to-face C14–H14c···Cg2 (Cg2: C8-C13)
interactions are formed between hydrogen atom (H14C) of the methyl group from one polymeric
chain with phenyl ring from the next polymeric chain. These interactions expand the chains to a
2D network (Fig. 5(left)). Also, these layers of polymeric chains are embraced inside this 2D
network through π-π stacking interactions and X–H…Br hydrogen bonds. Intermolecular π…π
stacking interactions exhibit two types of pairwise embrace. One embrace involves π…π
interactions between pyridine rings, while the other involves π…π interactions between phenyl
rings. Interacting pyridine planes [Cg1···Cg1 (Cg1: N1, C1, C2, C3, C4, C5 and symmetry code:
-1/2+x,1/2-y,z)] are approximately parallel (dihedral angle: 2.678˚) with a centroid–centroid
distance of 3.769 Å. The interaction between phenyl rings [Cg2···Cg2, (Cg2: C8-C13 and
symmetry code: 1-x, 1-y, z)] is weaker with a centroid–centroid distance of 3.919 Å and a
dihedral angle of 6.824˚, respectively. On the other hand, adjacent layers are further embraced by
8

formation of X–H…Br hydrogen bonds. Br2 atom from one polymeric chain interacts with
amide hydrogen (H2a) and aromatic hydrogen (H5) on pyridine ring from its neighbor chain by
the formation of N–H…Br and C–H…Br hydrogen bonds, respectively (Table 3). These
intermolecular interactions expand 1D chains to a 3D supramolecular architecture (Fig. 5(right)).
In this complex, the dihedral angle between two adjacent layers is 23.32˚.
Table 1
Table 2
Table 3
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
3.3. Molecular Hirshfeld surfaces
The Hirshfeld surface analyses of two Hg(II) coordination polymers have been performed on
their asymmetric unit. The Hirshfeld surfaces mapped over dnorm (-0.335 to 1.229 Å) are
displayed in Figs. 6 and 7 as transparent to permit visualization of the respective molecules. The
most obvious red spots on the dnorm surface of both complexes (one near to the Hg atom and
another on the pyridine nitrogen atom) are due to the Hg…N interactions. Two remaining visible
red regions on dnorm surface of 1 refer to X–H…Cl (X = N and C) interactions. The dnorm surface
of 2 contains several large red regions. Some of them are invisible on dnorm surface of 1. Two
doublet red spots are due to H…C contacts (C–H···π interactions). Also, H…H interactions are
observed as two small light red spots around the hydrogen atoms on the phenyl rings. The
interactions of Br atom with various hydrogen atoms (H…Br interactions) are visible as small
light red regions. The 2D fingerprint plots are used for identification and separation of
intermolecular interactions and relative contribution of these interactions can be obtained from
the area of the surfaces [55]. The 2D fingerprint plots of compounds, displayed by the standard
view, are shown in Fig. 8. The comparison of the relative contributions of different interactions
9

(Fig. 9) indicates the more or less identical contribution of interactions in these two mercury
complexes due to their structural similarity. H···H (29.4%) and X–H···Br (29.7%) contacts have
the highest share of Hirshfeld surface in 1 and 2, respectively. H···H interactions appeared as a
very distinct spike on the diagonal of the plots .They have the lowest value of de + di in both
complexes (≈ 2.2 Å in 1 and 2.1 Å in 2). The interaction of the hydrogens with the coordinated
halogens (H···Halogen interaction) comprises a high share of the Hirshfeld surface (28.8% in 1
and 29.7% in 2) and appear as wings on the top left (H···halogen) and bottom right
(halogen···H) of the 2D fingerprint plots. These contacts are due to N–H···Halogen and C–
H···Halogen intermolecular interactions. C···H/H···C contacts (C–H···π interactions) comprise
15.8% and 14.3% of the surface for each molecule in complex 1 and 2, respectively. In spite of
the high share of C···H/H···C contacts in 1, no significant C–H···π interactions are observed in
this compound, while these interactions are observed as doublet distinct red spots on the dnorm
surface of 2. These interactions manifest as two weak spikes beside H···Cl interactions in the
fingerprint plot of 1, while they are visible as two partly flat spikes in the plot of 2. C···C
contacts (π-Stacking interactions) appear in the central region of the plots and they comprise area
fractions of 4.8% and 5.3% in 1 and 2 complexes, respectively.
Fig. 6
Fig. 7
Fig. 8
Fig. 9
3.4. Thermal analyses
The thermal stability of the coordination polymers were investigated based on thermogravimetric
method at a heating rate of 10 ˚C/min under nitrogen atmosphere. Figures of 10 and 11 present
the TG/DTG plots of the mercury complexes. The thermal analyses data including temperature
range, mass loss (%) and kinetic activation parameters of thermal decomposition steps obtained
from the TG/DTG plots are listed in Table 4. The thermal decomposition processes of 1 and 2
occur in three and four thermal steps, respectively. In both complexes, the first thermal step is
related to the removal of one CH3 group. The second thermal degradation step of 1 happens in
10

the range of 222–395 °C and corresponds to the loss of nonmetallic parts (Schiff base ligand and
chloride anions), accompanied by a weight loss of 61.46% (calculated: 60.0%). The mercury
atom is lost in the final thermal step. Compound 2 loses the pyridine and the substituted phenyl
ring in the second step; the residual parts of the ligand and one of the coordinated bromide
anions in third step and Hg-Br fragment in last step without final residue. Moreover, the kinetic
and thermodynamic parameters for the decomposition processes of Hg(II) coordination polymers
including the activation energy (E*), the enthalpy of activation (∆H*), the entropy of activation
(∆S*) and the free energy of activation (∆G*) were investigated graphically by using the Coats–
Redfern relation [56], the obtained data are tabulated as Table 5. The positive values of
activation energies (E*) in the range of 37.87–588.58 kJ·mol-1 for the thermal decomposition
steps reveals the high stability of the compounds [57, 58]. The higher activation energy of the
first decomposition step for 1 suggests its enhanced thermal stability against decomposition as
compared with 2. Positive values of the activation entropies (∆S*) at the first thermal steps of
both complexes may indicate the dissociation character of the decomposition [57, 59]. The
negative values of ∆S* for other decomposition steps indicate more ordered activated complex
than the reactants or a slower reaction rate than normal degradation processes. The positive
values of the enthalpy of activation (∆H*) in the range of 31.19–584.55 kJ·mol-1 indicates the
endothermic nature of all thermal decomposition steps. Also, the positive values of the Gibbs
free energy of activation (∆G*) reflects the non-spontaneous nature of thermal decomposition
processes. On the other hand, the significant increase of values of ∆G* for consecutive
decomposition steps of both compounds is due to the increase of the values of T∆S* which
overcome the values of ∆H*[59].
Table 4
Fig. 10
Fig. 11
3.5. Characterization of nanostructured mercury complexes
The experimental XRD pattern of both compounds prepared by the sonochemical process in
comparison with simulated ones on the basis of the single crystal X-ray analysis are shown in
Fig. 12. All major peaks of sonochemically prepared compounds match well with those of the
simulated PXRD, indicating their crystalline phase purity. The significant broadening of the
peaks of the sonochemically synthesized compounds indicates that the particles are of nanometer
11

ꢌꢍ
dimensions. The average size of particles was estimated from Scherer's equation (D =ꢎꢏꢂꢐꢅꢑꢅ
,
where D is the average grain size, ꢒ is Blank’s constant (0.891), λ is the X-ray wavelength
(0.15405 nm), θ andꢅꢓ are the diffraction angle and full-width at half maximum of an observed
peak, respectively). The obtained values for 1 and 2 are 40 and 39 nm, respectively. SEM images
have been used for investigation of morphology and size of the coordination polymers prepared
under sonochemical conditions. Fig. 13 illustrates the SEM images of compounds 1 and 2. These
images show spherical morphology with diameters of nano-dimension. In both compounds, the
particles are agglomerated and particle size distribution is almost homogeneous.
Fig. 12
Fig. 13
4. Conclusion
Two new one dimensional zigzag Hg(II) coordination polymers based on N'-(4-
(dimethylamino)benzylidene)isonicotinohydrazide Schiff base ligand (L) were prepared and
identified by different spectroscopic techniques and X-ray crystallography. Structural data
showed that two complexes have similar structure; both crystallize in the orthorhombic system.
In both complexes, the Hg(II) ion is five-coordinated by three atoms of the Schiff base ligand
and two halide anions. The coordination geometry of the complex is a distorted square pyramidal
based on τ5 parameter (0.24 for 1 and 0.07 for 2). The Schiff base ligand (L) acts as N2O-donor
and connects to neighboring Hg centers to form infinite 1D zigzag chain. The crystal packing
analysis of two complexes revealed that 3D supramolecular architectures can produce from one
dimensional coordination chains through π … π stacking and X–H … Cl (X = N and C)
intermolecular interactions in 1 and C–H···π, π···π stacking and X–H…Br (X = N and C)
interactions in 2. Hirshfeld surface analyses exhibited effective role of C–H···π and H···H
contacts in crystal packing of 2. The 2D fingerprint plots indicate the more or less identical
contributions of interactions in the complexes arising from their structural similarity. TG/DTG
diagrams showed that the thermal decomposition process of 1 and 2 occurs in three and four
thermal steps without final residue, respectively. The sonochemical process, as a simple, low
cost and environmentally friendly approach, has been used for synthesis of nanostructure
coordination polymers. Comparing the XRD pattern of two sonochemically prepared compounds
12

with the simulated XRD pattern from single crystal X-ray analysis indicates that the compounds
obtained by two methods are identical except in particle sizes.
Supplementary information: CCDC 1435591 and 1435593 are corresponded to the
supplementary crystallographic data for this paper. These data are available free of charge at
http://www.ccdc.cam.ac.uk/conts/retrieving.html.
Acknowledgement: Partial support of this work by Yasouj University is acknowledged.
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16

Scheme, Figures and table captions:
Scheme 1.Atom numbering representation of Schiff base ligand and its coordination mode to
metal center.
Fig. 1. Part of crystal structure of [Hg(µ-L)Cl2]n (1). Hydrogen atoms are omitted for clarity.
(Symmetry transformations used to generate equivalent atoms: #1: -x+1,y+1/2,-z+1/2 and #2: -
x+1,y-1/2,-z+1/2.
Fig. 2. Asymmetric unit of [Hg(µ-L)Br2]n (2), hydrogen atoms are omitted for clarity.
Fig. 3. Polymeric 1D zigzag chain in [top] [Hg(µ-L)Cl2]n (1) and [bottom] [Hg(µ-L)Br2]n (2).
Fig. 4. [left] View of 2D network induced by C–H…Cl interactions and [right] embraced chains
by π…π stacking and N–H…Cl interactions (green dotted lines: π…π stacking and black dotted
lines: N–H…Cl interactions) in crystal packing of 1.
Fig. 5. [left] View of 2D network induced by C–H…π interactions and [right] View of 3D
supramolecular network induced by intermolecular interactions in 2.
Fig. 6. The Hirshfeld surface of [Hg(µ-L)Cl2]n (1) mapped over dnorm
.
Fig. 7. The Hirshfeld surface of [Hg(µ-L)Br2]n (2) mapped over dnorm from two different views.
Fig. 8. 2D fingerprint plots of [left] [Hg(µ-L)Cl2]n (1) and [right] [Hg(µ-L)Br2]n (2).
Fig. 9. Relative contributions to the Hirshfeld surface area for the various intermolecular
contacts in two complexes.
Fig. 10. The TG diagrams of both Hg(II) coordination polymers.
Fig. 11. The DTG diagrams of both Hg(II) coordination polymers.
Fig. 12. XRD patterns of simulated pattern based on single crystal data and nanostructure
prepared by sonochemical process of [A] [Hg(µ-L)Cl2]n (1) and [B] [Hg(µ-L)Br2]n (2).
Fig. 13.SEM images of coordination polymers 1 (A) and 2 (B) prepared by sonochemical
process.
Table 1
Crystal data and structure refinement for [Hg(µ-L)Cl2]n (1), and [Hg(µ-L)Br2]n (2)
Table 2
Bond lengths (Å) and angles (˚) for [Hg(µ-L)Cl2]n (1) and [Hg(µ-L)Br2]n (2)
Table 3
Intermolecular interactions in crystal packing of [Hg(µ-L)Cl2]n (1) and [Hg(µ-L)Br2]n (2)
Table 4
Thermal analysis data including temperature range, mass loss and thermodynamic activation
parameters of decomposition processes of complexes.
17

a,1
b, 3
M
c, 4
O
N
2
f, 9
5
N
a',1'
7
g, 10
N
H
e
8
b', 3'
d, 6
c', 4'
N
f', 9'
M
g', 10'
Scheme 1.Atom numbering representation of Schiff base ligand and its coordination mode to
metal center.
Fig. 1. Part of crystal structure of [Hg(µ-L)Cl2]n (1). Hydrogen atoms are omitted for clarity.
(Symmetry transformations used to generate equivalent atoms: #1: -x+1,y+1/2,-z+1/2 and #2: -
x+1,y-1/2,-z+1/2.
18

Fig. 2. Asymmetric unit of [Hg(µ-L)Br2]n (2), hydrogen atoms are omitted for clarity.
Fig. 3. Polymeric 1D zigzag chain in [top] [Hg(µ-L)Cl2]n (1) and [bottom] [Hg(µ-L)Br2]n (2).
19

Fig. 4. [left] View of 2D network induced by C–H…Cl interactions and [right] embraced chains
by π…π stacking and N–H…Cl interactions (green dotted lines: π…π stacking and black dotted
lines: N–H…Cl interactions) in crystal packing of 1.
Fig. 5. [left] View of 2D network induced by C–H…π interactions and [right] View of 3D
supramolecular network induced by intermolecular interactions in 2.
20

Fig. 6. The Hirshfeld surface of [Hg(µ-L)Cl2]n (1) mapped over dnorm
.
Fig. 7. The Hirshfeld surface of [Hg(µ-L)Br2]n (2) mapped over dnorm from two different views.
Fig. 8. 2D fingerprint plots of [left] [Hg(µ-L)Cl2]n (1) and [right] [Hg(µ-L)Br2]n (2).
21

35
30
25
20
15
10
5
1compound
2compound
0
Interaction type
Fig. 9. Relative contributions to the Hirshfeld surface area for the various intermolecular
contacts in two complexes.
Fig. 10. The TG diagrams of both Hg(II) coordination polymers.
22

Fig. 11. The DTG diagrams of both Hg(II) coordination polymers.
23

A
B
Fig. 12. XRD patterns of simulated pattern based on single crystal data and nanostructure
prepared by sonochemical process of [A] [Hg(µ-L)Cl2]n (1) and [B] [Hg(µ-L)Br2]n (2).
24

A
B
Fig. 13.SEM images of coordination polymers 1 (A) and 2 (B) prepared by sonochemical
process.
25

Table 1
Crystal data and structure refinement for [Hg(µ-L)Cl2]n (1), and [Hg(µ-L)Br2]n (2)
Compound
(1)
(2)
Empirical formula
Formula weight (g/mol)
Temperature (K)
Wavelength (Å)
Crystal system
C15H16Cl2HgN4O
539.81
296(2)
0.71073
Orthorhombic
C15H16Br2HgN4O
628.73
296(2)
0.71073
Orthorhombic
Space group
Pbca
Aba2
Unit cell dimensions
a = 7.4365(16) Å
a = 7.4556(2) Å
b = 12.437(3) Å
c = 37.674(8) Å
3484.4(13)
8
b = 36.8955(11) Å
c = 12.7559(4) Å
3508.87(18)
8
Volume (Å3)
Z
3
2.058
2.380
Calculated density (Mg/m )
Absorption coefficient (mm-1)
F(000)
9.149
2048
13.336
2336
Crystal size (mm)
0.108 x 0.059 x 0.027
0.146 x 0.077 x 0.023
Theta range for data collection (°)
2.162 to 20.823
3.194 to 27.494
Index ranges
-7 ≤ h ≤ 7, -12 ≤ k ≤ 12, -37 ≤ l ≤ 37
-9 ≤ h ≤ 9, -47 ≤ k ≤ 47, -16 ≤ l ≤ 16
Reflections collected
Independent reflections
Rint
23554
1829
0.1152
20527
3959
0.0867
Completeness to theta (%)
Absorption correction
Max. and min. transmission
Refinement method
99.8
99.8
Semi-empirical from equivalents
Semi-empirical from equivalents
0.7446 and 0.4782
0.7461 and 0.5523
Full-matrix least-squares on F2
Full-matrix least-squares on F2
Data/restraints/parameters
1829/0/206
1.238
3959/1/211
1.060
2
Goodness-of-fit on F
R1 = 0.0475, wR2 = 0.1154
R1 = 0.0597, wR2 = 0.1207
1.429 and -0.971
R1 = 0.0358, wR2 = 0.0785
R1 = 0.0426, wR2 = 0.0801
1.863 and -1.769
Final R indices [I>2σ(I)]
R indices (all data)
Largest diff. peak and hole(e.Å-3)
Table 2
Bond lengths (Å) and angles (˚) for [Hg(µ-L)Cl2]n (1) and [Hg(µ-L)Br2]n (2)
(1)
(2)
Bond length (Å)
Bond length
(Å)
Hg–N1#1
2.545(11)
2.800(1)
2.466(10)
2.339(5)
2.369(4)
Hg1–N1#2
Hg1–N3
Hg1–O1
Hg1–Br1
2.550(8)
2.760(8)
2.455(7)
2.4661(13)
2.4733(13)
Hg–N3
Hg–O1
Hg–Cl1
Hg–Cl2
Hg1–Br2
Bond angle (°)
N1#1–Hg–O1
N1#1–Hg–N3
N1#1–Hg–Cl1
N1#1–Hg–Cl2
N3–Hg–O1
N3–Hg–Cl1
N3–Hg–Cl2
O1–Hg–Cl1
O1–Hg–Cl2
Cl1–Hg–Cl2
Bond angle (°)
N1#2–Hg–O1
N1#2–Hg–N3
N1#2–Hg–Br1
N1#2–Hg–Br2
N3–Hg–O1
N3–Hg–Br1
N3–Hg–Br2
O1–Hg–Br1
O1–Hg–Br2
Br1–Hg–Br2
75.9(4)
137.16(3)
96.3(3)
78.2(3)
140.03(2)
94.7(2)
97.11(18)
62.29(2)
100.47(2)
91.75(2)
104.5(2)
111.0(2)
144.23(4)
92.9(3)
62.16(4)
99.40(3)
91.62(3)
100.6(3)
107.5(3)
151.76(16)
Symmetry transformations used to generate equivalent atoms:
#1 -x+1,y+1/2,-z+1/2
#2 -x+1,-y+1/2,z-1/2
26

Table 3
Intermolecular interactions in crystal packing of [Hg(µ-L)Cl2]n (1) and [Hg(µ-L)Br2]n (2)
Interaction
(1)
D–H···A
D–H (Å)
H···A (Å)
D···A (Å)
A···H–D (°)
Symmetry operation
N–H···Cl
C–H···Cl
N2–H2A···Cl2
C14–H14C···Cl1
0.860
0.960
2.703
2.875
3.537
3.638
164
137
1-x,1-y,1-z
1/2-x,1/2+y, z
(2)
N–H···Br
C–H···Br
C–H···π
N2–H2A···Br2
C5–H5···Br2
C14–H14C···Cg2
0.859
0.930
0.961
2.971
3.039
2.743
3.791
3.781
3.558
161
138
143
1/2-x,y,-1/2+z
-1/2+x,1/2-y,z
-x,1-y,z
Ring code: Cg2: C8, C9, C10, C11, C12, C13.
Table 4
Thermal analysis data including temperature range, mass loss and thermodynamic activation
parameters of decomposition processes of complexes.
Compound
Temperature
Mass loss (%)
Proposed
E*
∆S*
∆H*
∆G*
step(˚C)
exp. (cald)
segment
(kJ.mol−1)
(kJ.mol−1)
(kJ.mol−1)
(kJ.mol−1)
202-222
222-395
395-800
2.55(2.77)
61.46(60.00)
35.99(37.22)
CH3
C14H13Cl2N4O
588.58
116.93
158.37
9.23×102
-8.48×101
-1.12×103
584.55
112.41
151.06
1.38×102
1.59×102
1.14×103
[Hg(µ-L)Cl2]n
Hg
-
CH3
C13H15N2
CH2BrN2O
HgBr
196-223
228-300
320-403
403-800
3.29(2.38)
30.62(31.63)
22.66(21.93)
43.61(44.51)
405.34
109.33
39.90
5.44×102
-9.95×101
-2.39×102
-4.01×102
401.31
104.79
34.62
1.37×102
1.59×102
1.86×102
3.54×102
[Hg(µ-L)Br2]n
37.87
31.19
-
27

Graphical abstract (Synopsis)
Two new 1D zigzag coordination polymers; [Hg(µ-L)Cl2]n (1) and [Hg(µ-L)Br2]n (2) were
synthesized and identified by single crystal X-ray diffraction. The ligand (L) acts as N2O-donor.
The 1D zigzag chain is stabilized as 3D supramolecular network by intermolecular interactions
of π…π stacking and X–H…Cl (X =N and C) in 1 and C–H···π, π…π stacking and X–H…Br
(X=N and C) in 2. Hirshfeld surface analysis and 2D fingerprint plots of asymmetric units of two
complexes indicated differences and similarities between crystal packing of compounds.
Nanostructure forms of the titled coordination polymers have been also synthesized.
28

Graphical abstract:
29