Synthesis, characterization, and crystal structure analysis of group IIB coordination compounds containing N,N′-bidentate chelating Schiff-base ligand

Article abstract of DOI:10.1080/00958972.2020.1830072

The solid-state chemistry of coordination complexes has become an actively developing research area of modern inorganic chemistry. Herein, Zn and Hg coordination compounds containing a N,N′-bidentate chelating Schiff-base ligand were synthesized and then

Full text of DOI:10.1080/00958972.2020.1830072

Journal of Coordination Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Synthesis, characterization, and crystal structure
analysis of group IIB coordination compounds
containing N,N′-bidentate chelating Schiff-base
ligand
Taraneh Hajiashrafi , Roghayeh Zekriazadeh & Maciej Kubicki
To cite this article: Taraneh Hajiashrafi , Roghayeh Zekriazadeh & Maciej Kubicki (2020):
Synthesis, characterization, and crystal structure analysis of group IIB coordination compounds
containing N,N′-bidentate chelating Schiff-base ligand, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2020.1830072
To link to this article: https://doi.org/10.1080/00958972.2020.1830072
View supplementary material
Published online: 12 Oct 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/10.1080/00958972.2020.1830072
Synthesis, characterization, and crystal structure analysis
of group IIB coordination compounds containing N,N0-
bidentate chelating Schiff-base ligand
Taraneh Hajiashrafia, Roghayeh Zekriazadeha and Maciej Kubickib
aDepartment of Chemistry, Faculty of Physics and Chemistry, Alzahra University, Tehran, Iran;
bDepartment of Chemistry, Adam Mickiewicz University, Poznan, Poland
ABSTRACT
ARTICLE HISTORY
Received 11 May 2020
Accepted 27 August 2020
The solid-state chemistry of coordination complexes has become an
actively developing research area of modern inorganic chemistry.
Herein, Zn and Hg coordination compounds containing a N,N0-
bidentate chelating Schiff-base ligand were synthesized and then
characterized using spectroscopic techniques and single-crystal X-
ray crystallography. The molecular structures and crystal packing
modes of these complexes, as well as the crystal structures of related
compounds, were investigated thoroughly using geometrical and
Hirshfeld surface analyses, as well as theoretical calculations. It has
been revealed that the supramolecular architecture of these series of
coordination complexes is governed mainly by a combination of
chelateꢀꢀꢀp and pꢀꢀꢀp stacking, and non-classical hydrogen bonding
interactions. This study provides further insight into the understand-
ing of the coordination chemistry of group IIB complexes containing
Schiff-base ligand and the role of weak non-covalent interactions in
the solid-state structure of coordination compounds.
KEYWORDS
Coordination chemistry;
solid-state structure;
theoretical calculations
CONTACT Taraneh Hajiashrafi
t.hajiashrafi@alzahra.ac.ir
Department of Chemistry, Faculty of Physics and
Chemistry, Alzahra University, PO Box 1993891176, Tehran, Iran
Supplemental data for this article can be accessed on the https://doi.org/10.1080/00958972.2020.1830072.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
T. HAJIASHRAFI ET AL.
1. Introduction
The supramolecular chemistry of coordination compounds has attracted considerable
attention due to their versatile structural diversity and their potential applications in dif-
ferent areas from catalysis to photoluminescence and magnetism [1–3]. It is now well-
established that the way in which molecular building blocks are interconnected within
supramolecular structures can severely influence the physical and chemical properties of
crystalline solids [4, 5]. In comparison to organic compounds, one of the major and prob-
ably most important challenges in the design of metal-containing supramolecular struc-
tures is the lack of transferable and robust guidelines for pre-planned synthesis based on
non-covalent interactions [6–8]. The rational design and selection of organic ligands is a
common strategy that chemists use for tuning the supramolecular architecture and func-
tionalities of metal-containing systems [9–13]. These studies revealed that the organic lig-
and not only coordinates the metal ions but also can provide potential interaction sites
to generate desired non-covalent intermolecular contacts, which can program the self-
assembly of molecular building blocks to form extended non-covalent superstructures. It
is now well-known that the variation of the organic ligand’s functionality could provide a
variety of complementary interactions such as hydrogen bonding, pꢀꢀꢀp stacking, and
halogen bonding between discrete molecular units [14–19]. Besides the organic ligands,
the metal ions and the reaction conditions (the metal to ligand ratio [20], counter-ions
[21], reaction solvent [22], reaction temperature [23], time, and pH value [24]) are also
important factors that have been frequently studied and found to control the supra-
molecular architecture of metal-containing species in the solid-state.
Herein, we report the synthesis, characterization, and solid-state X-ray crystal struc-
tures of two new coordination complexes, [ZnL4-OHBr2] (1) and [Hg2(L4-OH)2I4] (2),
where L4-OH is 4-((pyridin-2-ylmethylene)amino)phenol. The crystal structures of these
complexes were studied using geometrical, Hirshfeld surface analyses, and theoretical
calculations. This study has revealed the roles of chelate–p and p–p stacking, as well
as of non-classical hydrogen bonding interactions in directing supramolecular architec-
tures of these coordination compounds.
2. Experimental
2.1. Apparatus and reagents
Starting materials for the synthesis of 1 and 2 were purchased from Aldrich Chemical
Company and used without purification. The Fourier transform infrared spectra were
recorded at room temperature on a Nicolet Fourier Transform IR (Nicolet 100 spectrometer)
from 500 to 4000 cmꢁ1 using KBr pellets. Elemental analyses (carbon, hydrogen, and nitro-
gen) were determined using an ECS 4010 CHN-O made in Costech, Italy. Melting points
were measured by an Electrothermal 9100 melting point apparatus and were corrected.
2.2. Single-crystal diffraction studies
X-Ray diffraction data were collected for 1 at 100(1) K and for 2 at 180(2) K on a Rigaku
four-circle Xcalibur diffractometer with Eos CCD detector and graphite-monochromated

JOURNAL OF COORDINATION CHEMISTRY
3
Table 1. Structural data and refinement parameters for 1 and 2.
1
2
Formula
fw
k/Å
T/K
C12H10Br2N2OZn
423.41
0.71073
100(1)
C26H28Hg2I4N4O4
1369.30
0.71073
180(2)
Crystal system
Space group
Monoclinic
P21/c
Triclinic
Pi
ꢀ
a/Å
b/Å
7.52894(18)
9.9216(2)
18.4609(5)
90
94.847(2)
90
7.6074(6)
9.6379(8)
12.2028(10)
107.732(7)
93.641(7)
98.987(7)
835.85(12)
2.720
c/Å
a/ꢂ
b/ꢂ
c/ꢂ
V/Å3
1374.08(6)
2.047
Dcalc/Mgꢀmꢁ3
Z
4
1
l (mmꢁ1
F(000)
)
7.591
816
52.8
12.902
616
53.2
2h (ꢂ)
R (int)
0.0536
1.050
0.0365
0.0901
1994939
0.0293
1.079
0.0431
0.1137dd
GOOF
a
R1 (I > 2r(I))
b
wR2 (I > 2r(I))
CCDC No.
1994940
aR1 ¼ RjjFoj ꢁ jFcjj/RjFoj.
1
bwR2 ¼ [R(w(Fo ꢁ Fc ) )/Rw(Fo )2] .
2
2 2
2
=
2
MoKa radiation (k ¼ 0.71069 Å) [25]. The data were corrected for Lorentz-polarization as
well as for absorption effects [26]. Precise unit-cell parameters were determined by a
least-squares fit of 5438 (1) and 3130 (2) reflections of the highest intensity, chosen
from the whole experiment. The structures were solved with SIR 92 [27] and refined
with the full-matrix least-squares procedure on F2 by SHELXL-2013 [28]. All non-hydro-
gen atoms were refined anisotropically; hydrogens were placed in idealized positions
and refined using a “riding model” with isotropic displacement parameters set at 1.2
(1.5 for hydroxyl groups) times Ueq of the appropriate carrier atoms. The crystallographic
information is listed in Table 1.
Hirshfeld surfaces and two-dimensional fingerprint plots were calculated by using
Crystal Explorer 3.1 software [29]. These surfaces visually show the spatial arrangement
and relevance of intermolecular contacts by their color code.
2.3. Theoretical methods
Density functional theory (DFT) and time-dependent density functional theory (TD-
DFT) calculations of the non-covalent interactions were carried out using the ORCA
quantum chemistry suite [30]. The BLYP exchange-correlation functional [31] with the
recent D3 empirical dispersion correction (BLYP-D3) was used to evaluate the binding
energies [32]. The basis set superposition error (BSSE) is not taken into consideration
because small BSSE effects are assumed to be absorbed by the D3 empirical potential
[33]. The decomposition of the interaction binding energy was also computed at
BLYP-D3/TZ2P. To evaluate the interactions in the solid-state, we used the crystallo-
graphic coordinates. This procedure and level of the theory have been successfully
used to evaluate similar interactions [18, 34, 35]. An all-electron triple-zeta basis-set

4
T. HAJIASHRAFI ET AL.
with two polarization functions, TZ2P, was used to describe all the atoms. The core
electrons were treated by using a frozen core approximation. The zeroth-order regular
approximation (ZORA) was applied for treating relativistic effect.
2.4. Synthesis
2.4.1. Synthesis of ligand L4-OH
2-Pyridinecarbaldehyde (0.48 mL, 0.0050 mol) was added to a solution of 4-hydroxyani-
line (0.55 g, 0.0050 mol) in methanol (0.0060 L). The resulting solution was stirred at 50 ꢂC
for about 15 min. Experiments were performed in air and ambient pressure. Precipitation
of a yellow solid resulted with a yield of 80%, which was collected by filtration and dried
under reduced pressure.
Ligand L4-OH (yield 80% equal to 0.79 g). FT-IR (KBr, t/cmꢁ1): 3550 (O–H); 3068 (C–H,
aromatic); 1587 (C ¼ N); 1568 (C ¼ C); 1072 (C–O), UV–Vis: k(CH3OH): 238 nm, 285 nm,
345 nm. MS (m/z): [MH]þ ¼ 199.
2.4.2. Synthesis of [ZnL4-OHBr2] (1)
The synthesis of [ZnL4-OHBr2] was reported previously by Ghosh and co-workers, but no
crystal structure determination has been reported [17]. To a solution of (0.00010 mol,
0.023 g) anhydrous ZnBr2 in 0.0050 L methanol, a solution of 4-((pyridin-2-ylmethylene)a-
mino)phenol L4-OH ligand (0.00010 mol, 0.020 g) in 0.0050 L of methanol was added with
stirring. The mixture was heated at 50 ꢂC for about 15 min, followed by reduction of the
solvent volume, resulting in an immediate formation of a bright yellow solid precipitate.
Experiments were performed in air and ambient pressure. The precipitate was collected
by filtration and washed several times with cold methanol, and then dried in vacuo. The
solid was then recrystallized in boiling acetonitrile (0.010 L) and filtered. Slow evaporation
of the filtrate, at room temperature within a week, afforded crystals of 1 for X-ray analysis.
Compound 1 (yield 75% equal to 0.032 g). Anal. calcd for C12H10Br2N2OZn: C, 34.04;
H, 2.38; N, 6.62. Found: C, 34.10 H, 2.42; N, 6.62. FT-IR (KBr, t/cmꢁ1): 3676(w), 3446(m,
broad), 3238(m), 3129(w),1693(s), 1619(s), 1581(s), 839(s), 796(m), 693(s),
672(m),640(m), 549(m). UV–Vis: k(CH3OH): 248 nm, 286 nm, 361 nm. Melting point:
158–160 ꢂC. MS (m/z): 423 [Zn(L)Br2]þ.
2.4.3. Synthesis of [Hg(L4-OH)2I2] (2)
To a solution of (0.00010 mol, 0.045 g) anhydrous HgI2 in 5 mL methanol, a solution of
4-((pyridin-2-ylmethylene)amino)phenol L4-OH ligand (0.00010 mol, 0.020 g) in 0.0050 L
of methanol was added with stirring. The mixture was heated at 50 ꢂC for about
15 min, followed by reduction of the solvent volume, resulting in an immediate forma-
tion of a bright yellow solid precipitate. The precipitate was collected by filtration and
washed several times with cold methanol, and then dried in vacuo. The solid was then
recrystallized in boiling acetonitrile (0.010 L) and filtered. Slow evaporation of the fil-
trate, at room temperature within a week, afforded crystals of 2 for X-ray analysis.
Compound 2 (yield 60% equal to 0.082 g). Anal. calcd for C26H28Hg2I4N4O4: C, 22.81;
H, 2.06; N, 4.09. Found: C, 22.79 H, 2.10; N, 4.11. FT-IR (KBr, t/cmꢁ1): 3676(w), 3420(m,
broad), 3238(m), 3420(w), 1577(s), 837(s), 793(w), 696(w), 643(m). UV–Vis: k(CH3OH):

JOURNAL OF COORDINATION CHEMISTRY
5
Scheme 1. L4-OH ligand and coordination complex syntheses.
238 nm, 280 nm, 345 nm. Melting point: 170–172 ꢂC. MS (m/z): 1369 [Hg(L)2I4]þ;
653 [Hg(L)I2]þ.
3. Results and discussion
3.1. Synthesis and characterization
Schiff-base ligands are easily prepared ligands that can form stable complexes with
metal ions [36, 37]. The substituted-1-(pyridin-4-yl)methanimine ligands are suitable
building blocks for crystal engineering studies of coordination compounds since they
are capable of coordinating to the metal ion in a predictable manner while providing
potential interaction sites to generate self-assembled structures. Compounds [ZnL4-
OHBr2] (1) and [Hg2(L4-OH)2I4] (2) were synthesized by the reaction between 4-((pyridin-
2-ylmethylene)amino)phenol ligand and the corresponding metal halide salts (Scheme
1). It should be noted that other zinc and mercury halide complexes with L4-OH ligand
would have been of interest here, but the solid-structure could not be studied
because no suitable crystals were obtained. These compounds were characterized by
FT-IR spectroscopy and elemental analysis. These data are provided in the Supporting
Information. The FT-IR characteristic frequencies of 1 and 2 are summarized in
Sections 2.4.2 and 2.4.3. The FT-IR spectra of 1 and 2 show m(C ¼ N) stretching fre-
quencies at 1581 and 1577 cmꢁ1, respectively, which are shifted relative to free L4-OH
m(C ¼ N) frequency at 1568 cmꢁ1. The blue shift observed in the frequency of the
stretch of the C ¼ N indicates that the bond order of this bond is slightly increased on
complexation [38]. The O–H stretching frequencies of 1 and 2 appear at 3446 and
3420 cmꢁ1, which are red-shifted relative to the O–H stretching frequency of free L4-OH
(3550 cmꢁ1). The red-shift of the band is an indication of the involvement of the O–H
proton in a weak hydrogen bonding interaction [39]. The relatively weak absorption
bands at around 2900 and 3050 cmꢁ1 are due to the modes of aliphatic and aromatic
C–H groups. The pyridine in-plane ring deformation frequencies of 1 and 2 are
assigned at 640 and 643 cmꢁ1, respectively. Terminal M-X and M-Py stretching fre-
quencies as well as pyridine out of plane ring deformation frequencies are located in
the far IR-spectrum, at lower frequencies than could be observed here. The elemental

6
T. HAJIASHRAFI ET AL.
ꢃ
Figure 1. ORTEP diagram of 1 (a) and 2 (b) (symmetry code for in 1(b) is 1 ꢁ x, 2 ꢁ y, 1 ꢁ z)
drawn at 50% probability ellipsoids.
analyses reveal the metal:ligand stoichiometry in the coordination compound as 1:1,
which is further supported by the single crystal X-ray diffraction (SXRD). The absorb-
ance properties of 1 and 2 as well as free L4-OH are listed in Sections 2.4.2 and 2.4.3.
Interestingly, 1 and 2 have similar absorbance bands to that of free L4-OH, which can
be assigned to p–p and n–p transition belonging to free L4-OH, according to the TD-
DFT calculation. The predicted electronic spectrum at bands between 200 and 400 nm
is assigned to the electronic transitions from the HOMO and lower occupied MOs to
ꢃ
ꢃ
the LUMO of free L4-OH
.
3.2. Crystal structure analysis
X-Ray analysis reveals that [ZnL4-OHBr2] (1) and [Hg2(L4-OH)2I4] (2) crystallize in mono-
ꢀ
clinic P21/c and triclinic Pi space groups, respectively. ORTEP drawings of 1 and 2,
which are drawn at 50% ellipsoid probability level, are shown in Figure 1. Selected
bond distances and angles are listed in Table 2. The asymmetric unit of 1 consists of
one crystallographically independent Zn ion, two bromide ions, and one L4-OH ligand,
while 2 is Ci-symmetrical; the Hg ion lies across the inversion center in the space

JOURNAL OF COORDINATION CHEMISTRY
7
Table 2. Selected bond distances (Å) and angles (ꢂ) for 1 and 2.
1
2
Bond distance
M1-N1
M1-N8
M1-X1
M1-X2
2.042(3)
2.082(3)
2.3424(6)
2.3481(6)
2.340(6)
2.519(9)
2.6535(8)
2.7395(8)
2.340(6)
M1-X2
3.2550(9)a
107.19(6)
129.33(2)
105.77(5)
104.00(5)
105.18(5)
103.87(5)
Bond angle
N1-M1-N8
X1-M1-X2
N1-M1-X1
N1-M1-X2
N8-M1-X2
N8-M1-X2
81.3(1)
115.68(2)
111.20(8)
117.75(8)
113.12(8)
113.17(8)
a1 ꢁ x, 2 ꢁ y, 1 ꢁ z.
group P21/c, and therefore the asymmetric unit of 2 contains one half of Hg ion, two
iodide ions, one L4-OH ligand and one solvent (methanol) molecule. The molecular
structures of 1 and 2 exhibit, therefore, different kinds of species: discrete neutral
mononuclear four-coordinate zinc and binuclear five-coordinate mercury units,
respectively. The coordination environment around Zn is defined by two nitrogens
from pyridyl and imine groups and by two terminal bromide ions. In 1, the Zn1-Br1
and Zn1-Br2 bond distances are 2.3424(6) Å and 2.3481(6) Å, the Zn1-N1 bond dis-
tance is 2.042(3) Å, and the Zn1-N8 bond distance is 2.082(3) Å. The bond distances
are in close agreement with those previously determined for [ZnL4-HBr2] complex,
where L is N-phenyl-1-(pyridin-2-yl)methanimine (Ref code: QIRJOS) [40]. Based on the
four-coordinate geometry index (s4), defined by Houser [33], the four-coordinate
geometry around the Zn center in 1 can be described as distorted trigonal pyramidal
with a s4 value of 0.897. The index of trigonality (s5), as defined by Addison and
Reedijk, is 0.55 for the Hg ion in 2, which implies that the coordination geometry can
be described as an intermediate between trigonal pyramidal and square-pyramidal
formed by the pyridyl nitrogen atom, terminal and bridging iodide ions (Hg1-
I2 ¼ 2.7395(8) Å and Hg1-I2 ¼ 3.2550(9) Å) and imine nitrogen atom. The average Hg-I
and Hg-N distances in this complex are in good agreement with the values obtained
for [HgL4-HI2] (Ref code: LEKSAX) [40]. Notably, there has been no reported crystal
structure on a binuclear mercury iodide complex based on N-phenyl-1-(pyridin-2-
yl)methanimine derivatives. The dihedral angle between the planes of phenyl and pyr-
idyl rings of free L4-OH has been reported as 49.94ꢂ [41]. For 1 and 2, these dihedral
angles between the two aromatic rings of L4-OH are 3.87ꢂ and 5.15ꢂ, respectively, thus
the ligand adopts a much more planar conformation in order to adjust itself to meet
the requirement of a N,N0-bidentate chelating coordination geometry of the metal
atom and the optimal inter-atomic distances in the crystal structure.
The crystal packing analysis of 1 reveals that discrete neutral units of [ZnL4-OH Br2]
are connected to each other along the crystallographic a-direction via pyridylpꢀꢀꢀpphenyl
stacking interaction (Table 3 and Figure 2). These units are further linked to each other
through O–HꢀꢀꢀBr and C–HꢀꢀꢀBr non-classical hydrogen bonding interactions in the bc-
plane (Table 4). In the crystal structure of 2, adjacent binuclear units of [Hg2(L4-OH)2I4]
are linked to each other through a combination of p-interactions, chelatepꢀꢀꢀppyridyl and
pyridylpꢀꢀꢀpphenyl, in the crystallographic a-direction (Table 3 and Figure 3(a)). Recent

8
T. HAJIASHRAFI ET AL.

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 2. Representation of the self-assembly of 1 showing the association of discrete molecular
units through pyridylpꢀꢀꢀpphenyl stacking interaction along the a-axis. These units are further linked to
each other through O–HꢀꢀꢀBr and C–HꢀꢀꢀBr hydrogen bonding interactions in the bc-plane.
studies have revealed that aromaticity might not be the key feature of stacking inter-
actions and those nonaromatic cyclic systems such as chelate rings with delocalized
p-bonds can form stacking interactions [42]. The methanol molecules of crystallization
link discrete molecular units, in the bc-plane, via O–HꢀꢀꢀO hydrogen bonding interac-
tions, which is further assisted by imineC–HꢀꢀꢀI and C–HꢀꢀꢀO interactions to generate the
three-dimensional 3D crystal network (Table 4 and Figure 3(b)).
A search in the Cambridge Structural Database (CSD) revealed that no crystal struc-
ture had been reported on any group IIB coordination compounds containing L4-OH
[43]. However, several group IIB halide coordination complexes have been synthesized
based on different para-substituted derivatives of N-phenyl-1-(pyridin-2-yl)methani-
mine ligands, such as para-halophenyl and para-tolyl, which are listed in Table 5. The
molecular structure analysis of these compounds reveals that group IIB metal centers
are bound to the bidendate para-substituted derivatives of N-phenyl-1-(pyridin-2-
yl)methanimine ligand, resulting in both mononuclear and binuclear complexes. All
the mononuclear complexes are four-coordinate (similar to 1), while the binuclear
complexes are halogen-bridged, five-coordinate (similar to 2). The study reveals that
the ligand para-substituent is not involved in metal coordination but contributes to
intermolecular interactions. In the crystal structure of mononuclear complexes, there is
a subtle interplay between p-interactions and non-classical hydrogen bonding interac-
ꢀ
tions. The majority of these complexes crystallized in the triclinic Pi space group with
extended alternative pyridylp … pphenyl and chelatep … pphenyl/pyridyl interactions, while
extended head-to-tail pyridylp–pphenyl interactions are observed in the crystal structures
of mononuclear complexes which crystallize in monoclinic space groups. For the sake
of comparison, the p-stacking interactions of Ref code OTEFEZ were analyzed and the
parameters are listed in Tables 3 and 5. The presence of the bulky t-Bu substituent
results in weaker p-stacking interactions compared with 1. The C–HꢀꢀꢀX and C–HꢀꢀꢀO,

10
T. HAJIASHRAFI ET AL.

JOURNAL OF COORDINATION CHEMISTRY
11
Figure 3. A representation of the crystal structure of 2: adjacent binuclear units of [Hg2(L4-OH)2I4]
are linked to each other through a combination of chelatepꢀꢀꢀppyridyl and pyridylpꢀꢀꢀpphenyl interactions
along the a-direction (a) the methanol molecules of crystallization link discrete molecular units in
the bc-plane via O–HꢀꢀꢀO hydrogen bonding interactions, which is further assisted by imineC–HꢀꢀꢀI
and C–HꢀꢀꢀO interactions (b).
where there is an oxygen-containing pendant group, are also contributing to the for-
mation of 3D crystal packing. The schematic representation of common p-stacking
synthons in these structures is presented in Table S1. In the cases of binuclear com-
plexes, the coordination complexes based on non-substituted ligands crystallize in tri-
ꢀ
clinic Pi space groups (Ref codes EHUJEX, LEKRUQ and NOCCOZ) with alternative
pyridylp–pphenyl and chelatep–pphenyl/pyridyl interactions, which is the same as what is
observed about 2 (Tables S1 and 5). The parameters for the p-stacking interactions of
Ref code LEKRUQ are also listed in Table 3. The p-stacking interactions in this complex
are comparable to that of 2. Contrary to these structures, those of other complexes in
monoclinic space groups represent crystal structures in which only one aromatic ring
of each ligand is involved in p–p stacking interaction and the para-substitution con-
tributes more actively in the process of self-assembly and is involved in C–HꢀꢀꢀX/O/p
hydrogen bonds, highlighting the intriguing interplay between weak intermolecular
interactions. For example, in a nitro-substituted ligand (Ref codes OBUMOQ and
ULAMEA), the nitro group participates in C–HꢀꢀꢀOnitro hydrogen bonds and weak
p-stacking interactions are observed. Interestingly, cadmium bromide and cadmium
iodide complexes containing N-(4-methoxyphenyl)-1-(pyridin-2-yl)methanimine (Ref
ꢀ
codes NOCBOY and NOBZOV) crystallize in the triclinic Pi and monoclinic P21/c space
groups, respectively, indicating a close competition between weak p-stacking and
non-classical hydrogen bonds. It might be also noted that all above-mentioned exam-
ples of binuclear complexes are Ci-symmetrical, like 2.

12
T. HAJIASHRAFI ET AL.
Figure 4. Relative contributions of various non-covalent contacts to the Hirshfeld surface area in 1
and 2.
3.3. Hirshfeld surface analysis and theoretical study
Hirshfeld surface analyses were carried out to obtain additional insight into the inter-
molecular interactions present in the crystal packing of 1 and 2. Hirshfeld surface ana-
lysis is a powerful graphical tool for obtaining additional intuition into the
intermolecular contacts in crystalline systems [29]. Hirshfeld surfaces of 1 and 2 are
mapped with dnorm, shape index (ꢁ1.0 (red) and þ1.0 (blue)) and curvedness
(between ꢁ4.0 (red) and þ0.4 (blue), Figure S1. Distinctive features can be identified
on the shape index and curvedness plots of 1 and 2, leading to patterns of intermo-
lecular interactions. The red regions on the dnorm surface in Figure S1 represent both
donors and acceptors of hydrogen bonding interactions listed in Table 4. The pattern
of red and blue triangles on the same region of the shape index surface and the pres-
ence of a large flat green surface on the curvedness surface indicate the pꢀꢀꢀp stacking
interactions (Table 3). A bar chart of percentage contributions of the different types of
intermolecular contacts and the (2D) fingerprint plots of the coordination compounds
are shown in Figures 4 and S2, and Table S1. The Hirshfeld surface analysis and associ-
ated fingerprint plots reveal that the crystal packing of 1 and 2 are supported by
C–HꢀꢀꢀX, HꢀꢀꢀH, C–Hꢀꢀꢀp, C–HꢀꢀꢀO, and pꢀꢀꢀp stacking interactions (Figures S1 and S2). The
C–HꢀꢀꢀX and HꢀꢀꢀH intermolecular contacts are the most abundant contacts and play
important roles in forming the crystal packing and pꢀꢀꢀp, C–Hꢀꢀꢀp, C–HꢀꢀꢀO and C–HꢀꢀꢀN
interactions are the next priorities, respectively. In the crystal structure of 1, the pꢀꢀꢀp
interaction is dominant to the C–Hꢀꢀꢀp interaction, while this is vice versa for 2. The
small contributions from the other interatomic contacts, Nꢀꢀꢀp and Xꢀꢀꢀp to the
Hirshfeld surface of 1 and 2, listed in Table S2, show negligible influence upon the for-
mation of crystal packing. The large contribution for the van der Waals HꢀꢀꢀH

JOURNAL OF COORDINATION CHEMISTRY
13

14
T. HAJIASHRAFI ET AL.

JOURNAL OF COORDINATION CHEMISTRY
15
Figure 5. QAIM analysis of the self-assembled dimers retrieved from the X-ray structure of 2. Bond
and ring critical points (CPs) are represented by red and green spheres, respectively.
interactions is typical of organic molecules and is consistent with the presence of CH
groups along the ligand backbone [44].
Theoretical calculations are employed to get another viewpoint for analyzing the
non-covalent interactions that direct the self-assembly of 1 and 2 in the solid-state.
We have focused our attention to the most important interactions, C–HꢀꢀꢀX/O hydro-
gen bonding and pꢀꢀꢀp stacking interactions. The binding energies obtained from the
BLYP-D3 calculation on two relative fragments provide us with an opportunity to
evaluate the intermolecular contacts between [MLX2] molecular units (Tables 3 and 4).
The selected fragments were cut out directly from the CIF file and are shown in Figure
S2. The energies of intermolecular contacts are in the range of those found for a series
of neutral coordination complexes [35, 45–49]. The O–HꢀꢀꢀBr interaction energy in 1 is
ꢁ9.18 kcal/mol, while that of the O-HꢀꢀꢀO interaction in 2 is ꢁ17.37 kcal/mol. The pꢀꢀꢀp
interaction energies in 1 and 2 are in the range of 20.92–31.61 kcal/mol, which agrees
with the reported values for p-interactions in the crystal structure of molecular solids
(Table 3). Not surprisingly, the interaction energies of fragments containing two hydro-
gen bonds and two p-interactions in 1 and 2 are larger than that of the fragments in
which only hydrogen bonding is present (Tables 3 and 4; Figure S2). To provide add-
itional evidence for the presence of chelatepꢀꢀꢀpphenyl interactions, Bader’s Quantum
Theory of Atoms In Molecules (QTAIM) analysis was carried out for the self-assembled,
p-stacked dimer of 2, retrieved from the X-ray crystal structure [50, 51]. The results of
the AIM analysis are presented in Figure 5. Ring critical points (green sphere) are gen-
erated upon metal complexation due to the formation of the chelate ring. The pres-
ence of chelatepꢀꢀꢀpphenyl interactions between the two fragments can be explored by
the presence of bond critical points in the intermolecular region between the carbon
atoms of chelate and aromatic rings. Furthermore, the analysis reveals the existence of
a critical point and a bond path connecting the hydrogen atom to the halide ion, indi-
cating the formation of C–HꢀꢀꢀI hydrogen bonds.
4. Conclusion
Herein, the crystal structures of two new group IIB coordination compounds containing
N,N0-bidentate chelating Schiff-base ligand, mononuclear [ZnL4-OHBr2] (1) and binuclear
[Hg2(L4-OH)2I4] (2), are reported. The crystal structures of these compounds, as well as the
related structures, were investigated. Geometrical analysis shows the distorted trigonal

16
T. HAJIASHRAFI ET AL.
pyramidal (1) and intermediate between trigonal pyramidal and square-pyramidal (2)
coordination geometry around the metal centers in these structures. It has been revealed
that the L adjusts its conformation to adopt the coordination geometry requirement of
the metal atom and to optimize inter-atomic distances in the supramolecular structure.
The crystal structure analyses revealed that the main interactions governing the supra-
molecular architecture are a combination of chelate–p and p–p stacking, and C/O–HꢀꢀꢀX
(for 1 and 2) and O–HꢀꢀꢀO involving solvent molecule (for 2) hydrogen bonding interac-
tions. The results reported herein are useful for understanding the coordination chemistry
and solid-state structure of group IIB containing Schiff-base ligands.
Acknowledgement
We gratefully acknowledge the financial support from the Research Council of
Alzahra University.
Disclosure statement
No potential conflict of interest was reported by the authors.
References
[1] L.F. Lindoy, K.-M. Park, S.S. Lee. Chem. Soc. Rev., 42, 1713 (2013).
[2] L. Brammer. Chem. Soc. Rev., 33, 476 (2004).
[3] D. Braga. J. Chem. Soc., Dalton Trans., 3705 (2000).
[4] S. Varughese, M. Kiran, U. Ramamurty, G.R. Desiraju. Angew. Chem. Int. Ed. Engl., 52, 2701
(2013).
[5] G.R. Desiraju. J. Am. Chem. Soc., 135, 9952 (2013).
€
[6] A.J. Blake, N.R. Champness, P. Hubberstey, W.-S. Li, M.A. Withersby, M. Schroder. Coord.
Chem. Rev., 183, 117 (1999).
ꢂ
-
ꢁ
€
[7] M. Dakovic, Z. Soldin, B.-M. Kukovec, I. Kodrin, C.B. Aakeroy, N. Baus, T. Rinkovec. IUCrJ, 5,
13 (2018).
[8] N.C. Gianneschi, M.S. Masar, C.A. Mirkin. Acc. Chem. Res., 38, 825 (2005).
ꢁ
[9] Y.E. Alexeev, B. Kharisov, T.H. Garcıa, A. Garnovskii. Coord. Chem. Rev., 254, 794 (2010).
[10] M.W. Hosseini. Chem. Commun., 5825 (2005).
[11] B. Moulton, M.J. Zaworotko. Chem. Rev., 101, 1629 (2001).
€
[12] C.B. Aakeroy. Acta Crystallogr. Sect. B Struct. Sci., 53, 569 (1997).
[13] H. Furukawa, K.E. Cordova, M. O’Keeffe, O.M. Yaghi. Science, 341, 1230444 (2013).
[14] H.R. Khavasi, A.A. Tahrani. CrystEngComm, 15, 5799 (2013).
[15] H.R. Khavasi, A. Azhdari Tehrani. Inorg. Chem., 52, 2891 (2013).
[16] A. Azhdari Tehrani, S. Abedi, A. Morsali. Cryst. Growth Des., 17, 255 (2017).
[17] A.S. Roy, P. Saha, P. Mitra, S.S. Maity, S. Ghosh, P. Ghosh. Dalton Trans., 40, 7375 (2011).
ꢁ
[18] A.A. Tehrani, H. Ghasempour, A. Morsali, A. Bauza, A. Frontera, P. Retailleau.
CrystEngComm, 19, 1974 (2017).
[19] M.T. Allen, A.D. Burrows, M.F. Mahon. J. Chem. Soc., Dalton Trans., 215 (1999).
[20] J.L. Gulbransen, C.M. Fitchett. CrystEngComm, 14, 5394 (2012).
[21] Y. Ikeda, T. Imae, M. Iida, N. Koine, S. Kaizaki. Langmuir, 17, 361 (2001).
[22] Z.-Z. Yuan, F. Luo, Y-m Song, G-m Sun, X-z Tian, H-x Huang, Y. Zhu, X-f Feng, M-b Luo, S-
j Liu, W-y Xu. Dalton Trans., 41, 12670 (2012).
[23] S. Masaoka, D. Tanaka, Y. Nakanishi, S. Kitagawa. Angew. Chem. Int. Ed. Engl., 43, 2530
(2004).

JOURNAL OF COORDINATION CHEMISTRY
17
[24] A.C. Warden, M. Warren, M.T. Hearn, L. Spiccia. Inorg. Chem., 43, 6936 (2004).
[25] P. CrysAlis. Oxford Diffraction Ltd., Yarnton, England (2009)
[26] Agilent Technologies, CrysAlis PRO (Version 1.171.33.36d), Agilent Technologies Ltd.,
2011.
[27] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori, M. Camalli.
J. Appl. Crystallogr., 27, 435 (1994).
[28] G.M. Sheldrick. Acta Crystallogr. Sect. C Struct. Chem., 71, 3 (2015).
[29] M.A. Spackman, D. Jayatilaka. CrystEngComm, 11, 19 (2009).
[30] F. Neese, U. Becker, D. Ganyushin, A. Hansen, D. Liakos, C. Kollmar, S. Kossmann, T.
Petrenko, C. Reimann, C. Riplinger. ORCA, version 2.7. 0, University of Bonn: Bonn,
Germany (2009). There is no corresponding record for this reference.
[31] A.D. Becke. Phys. Rev. A Gen. Phys., 38, 3098 (1988).
[32] S. Grimme, J. Antony, S. Ehrlich, H. Krieg. J. Chem. Phys., 132, 154104 (2010).
[33] L. Yang, D.R. Powell, R.P. Houser. Dalton Trans., 9, 955 (2007).
ꢁ
[34] D. Sadhukhan, M. Maiti, G. Pilet, A. Bauza, A. Frontera, S. Mitra. Eur. J. Inorg. Chem., 2015,
1958 (2015).
ꢁ
[35] P. Chakraborty, S. Purkait, S. Mondal, A. Bauza, A. Frontera, C. Massera, D. Das.
CrystEngComm, 17, 4680 (2015).
[36] S. Arulmurugan, H.P. Kavitha, B. Venkatraman. Rasayan J. Chem, 3, 385 (2010).
[37] N. Raman, S.J. Raja, A. Sakthivel. J. Coord. Chem., 62, 691 (2009).
[38] M.R. Mahmoud, M.T. El-Haty. J. Inorg. Nucl. Chem., 42, 349 (1980).
[39] G.; Nikolic. Fourier Transforms: New Analytical Approaches and FTIR Strategies,
BoD–Books on Demand (2011)
[40] T.S.B. Baul, S. Kundu, A. Linden, N. Raviprakash, S.K. Manna, M.F.C.G. da Silva. Dalton
Trans., 43, 1191 (2014).
[41] K. Heinze, J.D. Bueno Toro. Eur. J. Inorg. Chem., 2004, 3498 (2004).
ꢁ
ꢁ
ꢁ
[42] D.P. Malenov, G.V. Janjic, V.B. Medakovic, M.B. Hall, S.D. Zaric. Coord. Chem. Rev., 345, 318
(2017).
[43] C.R. Groom, I.J. Bruno, M.P. Lightfoot and S.C. Ward. Acta Cryst., B72, 171 (2016).
[44] J.J. McKinnon, D. Jayatilaka, M.A. Spackman. Chem. Commun., 37, 3814 (2007).
[45] H.R. Khavasi, B.M.M. Sadegh. Dalton Trans., 43, 5564 (2014).
[46] B. Cheng, A.A. Tehrani, M.-L. Hu, A. Morsali. CrystEngComm, 16, 9125 (2014).
ꢁ
[47] S. Saha, A. Sasmal, C.R. Choudhury, G. Pilet, A. Bauza, A. Frontera, S. Chakraborty, S. Mitra.
Inorg. Chim. Acta, 425, 211 (2015).
ꢁ
[48] T. Hajiashrafi, R. Zekriazadeh, K.J. Flanagan, F. Kia, A. Bauza, A. Frontera, M.O. Senge. Acta
Crystallogr. Sect. C Struct. Chem., 75, 178 (2019).
ꢁ
[49] T. Hajiashrafi, S. Salehi, M. Kubicki, A. Bauza, A. Frontera, K.J. Flanagan, M.O. Senge.
CrystEngComm, 21, 6301 (2019).
[50] S. Bhattacharya, S. Roy, K. Harms, A. Bauza, A. Frontera, S. Chattopadhyay. Inorg. Chim.
Acta, 442, 16 (2016).
[51] R. Parthasarathi, V. Subramanian. Struct. Chem., 16, 243 (2005).
€
[52] M. Schulz, M. Klopfleisch, H. Gorls, M. Kahnes, M. Westerhausen. Inorg. Chim. Acta, 362,
4706 (2009).
[53] M. Malekshahian, M. Talei Bavil Olyai, B. Notash. Acta Crystallogr. Sect. E Struct. Rep.
Online, 68, m218 (2012).
€
[54] T.S.B. Baul, S. Kundu, S. Mitra, H. Hopfl, E.R. Tiekink, A. Linden. Dalton Trans., 42, 1905
(2013).
[55] T.S. Basu Baul, S. Kundu, S.W. Ng, N. Guchhait, E.R. Tiekink. J. Coord. Chem., 67, 96 (2014).
[56] K. Wurst, M.R. Buchmeiser. Heterocycl. Commun., 5, 37 (1999).
[57] Y.-W. Dong, R.-Q. Fan, X.-M. Wang, P. Wang, H.-J. Zhang, L.-G. Wei, Y. Song, X. Du, W.
Chen, Y.-L. Yang. Eur. J. Inorg. Chem., 2016, 3598 (2016).
€
[58] T.S.B. Baul, S. Kundu, H. Hopfl, E.R. Tiekink, A. Linden. Polyhedron, 55, 270 (2013).
[59] M.R. Talei Bavil Olyai, V. Razzaghi Fard, J. Shakibaii Far, A. Mahmoudi. Z. Kristallogr. New
Cryst. Struct., 225, 169 (2010).

18
T. HAJIASHRAFI ET AL.
€
[60] S. Tushar, B. Baul, S. Kundu, H. Hopfl, E.R.T. Tiekink, A. Linden. J. Coord. Chem., 67, 1061
(2014).
[61] S. Salehzadeh, M. Khalaj, S. Dehghanpour. Acta Crystallogr. Sect. E Struct. Rep. Online, 68,
m1041 (2012).
[62] T.S. Basu Baul, S. Kundu, S.W. Ng, E.R. Tiekink. Acta Crystallogr. Sect. E Struct. Rep. Online,
69, m623 (2013).
[63] K. Marjani, J. Asgarian, M. Mousavi, V. Amani. Z. Anorg. Allg. Chem., 635, 1633 (2009).
[64] Y.-W. Dong, R.-Q. Fan, W. Chen, H.-J. Zhang, Y. Song, X. Du, P. Wang, L.-G. Wei, Y.-L. Yang.
Dalton Trans., 46, 1266 (2017).
[65] S. Salehzadeh, S. Dehghanpour, M. Khalaj, M. Rahimishakiba. Acta Crystallogr. Sect. E
Struct. Rep. Online, 67, m327 (2011).
[66] S. Salehzadeh, M. Khalaj, S. Dehghanpour, I. Tarmoradi. Acta Crystallogr. Sect. E, 67,
m13556 (2011).
[67] J.J. Braymer, J.-S. Choi, A.S. DeToma, C. Wang, K. Nam, J.W. Kampf, A. Ramamoorthy, M.H.
Lim. Inorg. Chem., 50, 10724 (2011).
[68] M.S.H. Faizi, N. Dege, K. Goleva. Acta Crystallogr. Sect. E Crystallogr. Commun., 73, 809
(2017).
[69] M.S.H. Faizi, E.V. Prisyazhnaya. Acta Crystallogr. Sect. E Crystallogr. Commun., 71, m175
(2015).
[70] S. Dehghanpour, A. Mahmoudi. Acta Crystallogr. Sect. E Struct. Rep. Online, 68, m1113
(2012).
[71] A. Mahmoudi, S. Dehghanpour, M. Khalaj, S. Pakravan. Acta Crystallogr. Sect. E Struct. Rep.
Online, 65, m889 (2009).
[72] M. Khalaj, S. Dehghanpour, A. Mahmoudi. Acta Crystallogr. Sect. E Struct. Rep. Online, 64,
m1018 (2008).
[73] S. Dehghanpour, A. Mahmoudi, M. Khalaj, S. Salmanpour, M. Adib. Acta Crystallogr. Sect. E
Struct. Rep. Online, 63, m2841 (2007).
[74] S. Dehghanpour, A. Mahmoudi, M. Khalaj, S. Salmanpour. Acta Crystallogr. Sect. E Struct.
Rep. Online, 63, m2840 (2007).