Syntheses and characterization of mononuclear Zn(II), Cd(II) and Hg(II) complexes of 2-[(3,5-dibromo-2-hydroxy-benzylidene)-amino]-2-hydroxymethyl-propane-1,3-diol: Photoluminescence properties and DFT study

Article abstract of DOI:10.1016/j.ica.2017.11.005

A new Schiff-base ligand HL ((2-[(3,5-dibromo-2-hydroxy-benzylidene)-amino]-2-hydroxymethyl-propane-1,3-diol)) was obtained by the 1:1 condensation of 1,3-dibromo salicylaldehyde and (tris hydroxy methyl) amino methane. Then three new complexes, [Zn(L)

Full text of DOI:10.1016/j.ica.2017.11.005

Accepted Manuscript
Research paper
Syntheses and characterization of mononuclear Zn(II), Cd(II) and Hg(II) com-
plexes of 2-[(3, 5-Dibromo-2-hydroxy-benzylidene)-amino]-2-hydroxymethyl-
propane-1,3-diol: Photoluminescence properties and DFT study
Sourav Chatterjee, Ishani Majumder, Aratrika Chakraborty, Madhulata Shukla,
Tanmay Chattopadhyay
PII:
S0020-1693(17)30979-9
https://doi.org/10.1016/j.ica.2017.11.005
ICA 17975
DOI:
Reference:
Inorganica Chimica Acta
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1 November 2017
3 November 2017
Please cite this article as: S. Chatterjee, I. Majumder, A. Chakraborty, M. Shukla, T. Chattopadhyay, Syntheses and
characterization of mononuclear Zn(II), Cd(II) and Hg(II) complexes of 2-[(3, 5-Dibromo-2-hydroxy-benzylidene)-
amino]-2-hydroxymethyl-propane-1,3-diol: Photoluminescence properties and DFT study, Inorganica Chimica
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Syntheses and characterization of mononuclear Zn(II), Cd(II) and
Hg(II) complexes of 2-[(3, 5-Dibromo-2-hydroxy-benzylidene)-amino]-2-
hydroxymethyl-propane-1,3-diol: Photoluminescence properties and DFT study
Sourav Chatterjee,a Ishani Majumder,b Aratrika Chakrabortyb, Madhulata Shukla*, c, Tanmay
Chattopadhyay*, a
a Department of Chemistry, Panchakot Mahavidyalaya, Sarbari, Purulia, Pin-723121,India,
E-mail:tanmayc2003@gmail.com
b Department of Chemistry,UniversityofCalcutta,92 A. P. C. Road,Kolkata-700009, India.
c Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi, 221005, India.
E-mail address: madhu1.shukla@gmail.com.
Abstract
A new Schiff-base ligand HL ((2-[(3, 5-Dibromo-2-hydroxy-benzylidene)-amino]-2-
hydroxymethyl-propane-1,3-diol)) was obtained by the 1: 1 condensation of 1, 3-dibromo
salicylaldehyde and (tris hydroxy methyl) amino methane. Then three new complexes, [Zn(L)2],
[Cd(L)2] and [Hg(L)2], have been prepared by the reaction of zinc(II), cadmium(II) and mercury(II)
chlorides with the ligand and characterized by routine physicochemical techniques. Complex 1 has
further been characterized by single crystal X-ray structural analyses. The ligands, as well as all
three complexes, are highly fluorescent. For the ligand, the emission band is attributed to a π→π*
transition, whereas for the complexes the emissions may be assigned to ligand-to-metal charge
transfers (LMCT). DFT calculation of all the three complexes has also been done.
Key Words: Schiff base, Zinc complex, Cadmium complex, Mercury complex, Photoluminescence
and DFT study
1. Introduction

Recently, the detection of d10 metal ions is paying attention due to their varieties function on
environment and human body. [1-3] Among d10 metal ions, Zn(II) ions are very much essential for
the human body and are involved in various biological processes whereas Cd(II) and Hg(II), are
highly toxic and carcinogenic metal. [4-7] Cadmium mainly found in electroplated steel, pigments
in plastics, electric batteries and their exposure is connected with increased risks of cardiovascular
diseases, cancer mortality, and damage to liver and kidneys. [8, 9] Mercury is contaminated with
air, water and soil, by many sources such as gold production, coal plants, thermometers,
barometers, caustic soda, and mercury lamps. [10] It also causes strong damage to the central
nervous system, Minamata disease etc. [11] Therefore it is meaningful to develop efficient methods
for the detection of Zn(II), Cd(II) and Hg(II). Fluorescent sensor is widely used for the detection of
these metal ions because of its simplicity, sensitivity and cost. [12] Generally, Schiff base complex
of soft metal ions, like Zn(II), Cd(II) and Hg(II), are used for optoelectronic devices, due their
excellent photoluminescence properties. [13-15] This characteristic property can be used to identify
them because the presence of the d10 electronic configuration obstructs to apply the analytical
techniques such as Mössbauer, EPR spectroscopy and magnetic susceptibility measurements for
their uncovering. But fluorescence spectroscopy can be effectively used because these metal ions
easily change the fluorescence intensity of organic fluorophore. [16] Therefore fluorescence
spectroscopy is most dominant tool to identify these metal ions. [17] Here we report the synthesis
of Zn(II), Cd(II) and Hg(II) complexes with tridentate Schiff-base with metal complexes make us to
design three Schiff base complex namely [Zn(L)2], [Cd(L)2] and [Hg(L)2] where L= 1,3 di bromo 5-
[(tris hydroxy methyl) amino methane]salicyldehyde (Scheme 1) and also shown there
photophysical properties. Finally, to understand the structural and spectral properties of these
complexes, DFT calculations on these three complexes along with the ligand moiety has been

carried out, because of its accuracy and relative fastness in analyzing the electronic structure of
large molecules of transition metal complexes. [18] Various density functional such as SVWN5,
B3LYP, B3P86, and B1LYP are used to study the structural characteristics of complexes containing
heavier metal ions, however DFT method with B3LYP functional found to provide the most precise
information about the structure and energy. Along with DFT calculation, time dependent DFT
(TD-DFT) is also being used widely to establish the nature of orbitals involved in transition
processes and also to correlate the structural parameters with the spectroscopic properties of the
complexes. [19]
Br
Br
HO
Br
Ethanol,
Reflux
N
NH2
HO
Br
MCl2
O
+
Br
OH
M
OH
OH
OH
N
OH
HO
HO
M = Zn(II),
Cd(II), Hg(II)
Br
OH
O
OH
OH
O
OH
OH
N
Br
Br
Scheme 1. Synthetic route of complexes 1-3.
2. Experimental
2.1. Instruments and materials
Elemental analyses (C, H and N) were carried out using a PerkineElmer 240C elemental analyzer.
Infrared spectra (4000-500 cm-1) were obtained at 27°C using a Perkine Elmer RXI FT-IR
spectrometer with KBr pellets. UV-visible spectra were recorded with a Shimadzu UV-2450PC
spectrophotometer equipped with multiple cell-holders and thermostat. Fluorescence spectra of the
ligands and complexes were recorded in DMSO solution with a Perkin-Elmer model LS 50B
Luminescence spectrometer. Quantum yields of the ligands as well as the complexes were

determined at room temperature by a relative method using anthracene as the standard [17a]. A
Systronics 304 conductivity meter was used to measure the molar conductance. The cell constant
was calibrated with 0.02 M KCl solution. 1H NMR was recorded at ambient temperature with a
Bruker Advance 300. Zinc chloride, cadmium chloride and mercuric chloride were purchased from
merck (india) and 1, 3-dibromo salicyldehyde and tris-(hydroxyl methyl) amino methane were
purchased from sigma-aldrich (Kolkata, India).
2.2. Computational Method
The energies of the complexes studied in the non-covalent interactions study were computed at the
BP86-D3/def2-TZVP level of theory. The geometries have been fully optimized unless otherwise
noted. For instance to evaluate the noncovalent interactions observed in the solid state, we have
used the crystallographic coordinates. The calculations have been performed using the program
TURBOMOLE version 6.5. For the calculations we have used the BP86 functional with the latest
available correction for dispersion (D3). The basis set superposition error for the calculation of the
interaction energies has been corrected using the counterpoise method. For the spectroscopic
studies, the geometries of the singlet ground state (S0) and the lowest triplet excited state (T1) for
complexes 1, 2 and 3 were optimized using the hybrid functional B3LYP in combination with the
6-31G* basis set for all atoms. Relativistic effects were included for the Zn atom using the ECP-10-
mdf Stuttgart/Dresden pseudo potential. The nature of the stationary points was confirmed by
computing the Hessian at the same level of theory. The Gaussian 03 program [20] ref in last]
package is employed for the DFT calculations at the Becke’s three parameter functional and Lee-
Yang-Parr hybrid functional (B3LYP) level [21, 22] of calculation and using LANL2DZ basis set
for Zn, Cd and Hg atoms and 6-31++G(d,p) basis set for C, H, N, O and Br atoms. Initially, DFT
calculations were carried out on single crystal X-ray diffraction structures (SCXRD) of ligand and
complexes in gas phase to fully optimize the ground state structure. The spectroscopic and

electronic properties of these optimized complexes have also been computed by TD-DFT
calculation at the same B3LYP level and using conductor like polarisable continuum model
(CPCM) and DMSO as a solvent. The absence of any imaginary frequency in the calculated
vibrational frequencies ensures that the optimized geometry corresponds to true energy minimum.
2.3. Synthesis of HL
A methanolic solution of tris-(hydroxymethyl)amino methane (1mmol, 91 µL) was added to a
methanolic solution of 3, 5-Dibromo-2-hydroxy benzaldehyde (1 mmol, 0.279 gm) in a drop wise
method. This mixture was stirred for 6 hr. After that the solvent was evaporated under rotary
evaporator. Then it was extracted several times by brine water along with diethyl ether for
purification and dried with anhydrous MgSO4 for removal of the of water. The pure solid ligand
was obtained after slow evaporation of the crude which was dissolved in ethanol. Anal. calcd for
C11H13N1O4Br2: C (34.46%); H (3.39%); N (3.65%); found C (34.16%); H (3.33%); N (3.59%); 1H
NMR (300 MHz, d6DMSO3, 25°C): δ= 3.53 (s, 6H; CH2-OH), 5.69(s, 3H; CH2-OH), 7.98 (s, H;
Ar), 7.78 (s, H; Ar), 8.42 (s, H; CH=N), 14.651 (s, H; Ph-OH); IR (KBr plate): ν(C=N) = 1641 cm-
1; ν (skeletal vibration) 1508 cm-1. UV/vis (DMSO): λmax(ε)= 313 (3426 L mol-1 cm-1); 417 (1473 L
mol-1 cm-1).
2.4. Syntheses of the complexes
2.4.1. [Zn(L)2] (1)
An ethanolic solution (5 mL) of 1, 3-dibromo salicylaldehyde (0.280 g, 1 mmol) was added to a
ethanolic solution (10 mL) of tris-(hydroxyl methyl) amino methane (0.121 g, 1 mmol) and the
resultant mixture was stirred for 2 h. Then a ethanolic solution of zinc(II) chloride (0.204 g, 1.5
mmol) was added to it and the solution was allowed to stir for an additional 3 h. After that the
resulting solution was filtered and the filtrate was kept in a CaCl2 desiccator. Yellow colored single

crystals suitable for X-ray data collection were obtained from the filtrate after two days. Yield:
84%. Anal. Calcd for [Zn(L)2] (1): C, 31.90; H, 2.90; N, 3.38. Found: C, 31.83; H, 2.80; N, 3.29.
Ω (ohm-1 cm2 mol-1): 12.1. Selected IR data on KBr (ν/cm-1): 1649, 1503, 1462. UV/vis (DMSO):
λmax(ε)= 260 (3362 L mol-1 cm-1); 420(1463 L mol-1 cm-1). 1H NMR (300 MHz, d6DMSO3, 25°C):
δ= 3.52 (s, 6H; CH2-OH), 5.09(s, 3H; CH2-OH), 7.78 (s, H; Ar), 7.63 (s, H; Ar), 8.21(s, H; CH=N).
2.3.2. [Cd(L)2] (2)
The complex was synthesized following the similar procedure as we stated above. Here we only
changed zinc(II) chloride with cadmium(II) chloride (0.275g, 1.5 mmol). After a few days, we
obtained yellow colored crystalline product from the filtrate on keeping it in room temperature.
Yield: 86%. Anal. Calcd for [Cd(L)2] (1): C, 30.12; H, 2.73; N, 3.19. Found: C, 30.03; H, 2.68; N,
3.09. Ω (ohm-1 cm2 mol-1): 11.9. Selected IR data on KBr (ν/cm-1): 1644, 1497, 1402. UV/vis
(DMSO): λmax(ε)= 265 (3370 L mol-1 cm-1); 425 (1480 L mol-1 cm-1). 1H NMR (300 MHz,
d6DMSO3, 25°C): δ= 3.53 (s, 6H; CH2-OH), 4.09(s, 3H; CH2-OH), 7.65 (s, H; Ar), 7.63 (s, H; Ar),
8.39(s, H; CH=N).
2.3.3. [Hg(L)2] (3)
The complex was synthesized following the similar procedure as we described above. Here we used
mercuric (II) chloride (0.365g, 1.5 mmol) instead of zinc(II) chloride. After a few days, we got
yellow colored crystalline product from the filtrate on keeping it in room temperature. Yield: 83%.
Anal. Calcd for [Hg(L)2] (1): C, 23.36; H, 2.48; N, 2.90. Found: C, 23.30; H, 2.41; N, 2.84. Ω
(ohm-1 cm2 mol-1): 11.7. Selected IR data on KBr (ν/cm-1): 1640, 1488, 1401. UV/vis (DMSO):
λmax(ε)= 263 (3400 L mol-1 cm-1); 422 (1503 L mol-1 cm-1). 1H NMR (300 MHz, d6DMSO3, 25°C):
δ= 3.58 (s, 6H; CH2-OH), 4.17 (s, 3H; CH2-OH), 7.59 (s, H; Ar), 7.72 (s, H; Ar), 8.36 (s, H;
CH=N).

2.4.
X ray crystal structure analysis
A Bruker Smart CCD diffractometer equipped with graphite-monochromated Mo-Kα radiation
(λ=0.71073 Å) at room temperature were used for data collection. Cell refinement, indexing and
scaling of the data set were performed by Bruker Smart Apex and Bruker Saint packages [23]. The
structure was solved by direct methods and subsequent Fourier analyses [24] and refined by the
full-matrix least-squares method based on F2 with all observed reflections [25]. All the calculations
were carried out using the WinGX System, Ver 1.80.05 [25].
3.
Results and discussion
3.1. Synthesis and characterization
The ligand (HL) was synthesized by simple condensation method and characterized by routine
physiochemical technique. (see SI Fig S1-S3 in Supporting information). The complexes 1-3 were
prepared by in-situ reaction: the ethanolic solution of ZnCl2, CdCl2 and HgCl2 are treated with the
ligand L formed in situ via condensation of 1, 3-dibromo salicylaldehyde and tris-(hydroxyl
methyl) amino methane. The compositions and the structures of the complexes are determined by
the routine physico-chemical techniques as well as single crystal X-ray analysis (in those cases
when suitable single crystals were obtained). Electronic spectra of the complexes (1-3) were
recorded in DMSO medium. All the three complexes show band near 420 nm (see SI Fig S4 in
Supporting information). This band is originated due to ligand to FT-IR spectral study reveals that
all the complexes exhibit bands in the range 1635-1660 cm-1 due to a C=N stretch and in the range
1535-1600 cm-1 due to skeletal vibrations. Here we did not found any bands for the free carbonyl or
primary amine. The result is suggested that complete condensation has occurred (see SI Figs S5-S7
in Supporting information). Molar conductivity measurements of the complexes in DMSO suggest
that all the complexes are non-electrolytes (Experimental section), indicating that chloride is not

present in complexes. The NMR studies of synthesized complexes (1-3) are entirely reliable with
their structures (see SI Figs S8-S10 in Supporting information). Here, each spectrum of the
complexes resembles that of the corresponding ligand except the phenolic OH groups which finds
deprotonated during complexation.
3.2. Structure description of complex 1
The X-ray structural analysis of complex 1 indicates that it crystallizes in monoclinic space group
P21/c with uncoordinated solvent molecules of DMSO and water (Fig. 1). A summary of the details
of the crystal data, data collection and refinement details is given in Table 1. The coordination
geometry of the metal centre can be best described as rougly octahedral,being the zinc meridional
coordinated by two ligands through the phenolate oxygen, the imine nitrogen and an alcoholic
oxygen atoms. Selected bond lengths and bond angles are listed in Table 2. Thus the bond distances
between the trans located nitrogen atoms with Zn are 2.101 Å(Zn1-N1) and 2.112 Å (Zn1-N2). The
Zn-O(phenoxo) bond lengths are of 2.009(3) Å (Zn1-O1), and 2.010(4) Å (Zn1-O5) relatively
longer than the Zn-O bond length between metal centre and the alcoholic groups (Zn1-O6,
2.202(4) Å and Zn1-O2 2.197(4),Å) which are comparable to other literature reports of this type of
systems (Table S1, see Supporting information). The lattice diagram shows that each molecular
unit is connected to adjacent molecular units via intermolecular hydrogen bonds (O2-H2...O4,
2.638 Å and O6-H6…O7, 2.644 Å) to form a 1D polymer (Fig 2). For this 1D propagation water
molecules play an important role by forming weak intermolecular H-bonding hydrogen bonds with
two molecular units (C20-H20B…O9, 3.544 Å and C10-H10A…O9,3.353 Å . Another solvent
molecule that is DMSO connects three molecular units of three aforesaid 1D polymer through
several types of weak hydrogen bonds (O7-H7…O10, 2.721 Å; O8-H8…O10, 2.725 Å; C2AA-

H2AC…O3, 3.349 Å; C1AA-H1AB…O5, 3.457 Å and O3-H3A…S1,3.392 Å, Fig 3, Table 3) to
form a 3D supramolecular structure.
Fig. 1.
Fig. 2.
Fig. 3.
Table 1
Table 2
3.3. Solution studies: Mass spectrometry
To determine the composition of the complexes in solution phase ESI-MS study has been done in
DMSO-ACN mixture. All of the complexes behave similarly in solution phase under the soft
ionization process. The dinuclear complexes dissociate into mononuclear monopositive species as
evident from the mass spectra (SI Figs S11-S13 in Supporting information). The complex 1 (Zn
complex) gives a sharp peak at m/z 447.8503 amu (cal. 447.4053 amu) due to the formation of
[Zn(L)]+ species. Similarly complex 2 and 3 gives another two sharp peaks at m/z 494.7844 amu
(cal. 494.4363 amu) and 582.8447 amu (cal. 582.6153) respectively which corroborates well with
the mononuclear monopositive complex cations [M(L)]+ (where M= Cd for 2 and M= Hg for 3).
However, in all of the cases the base peak at around ῀383 amu is due to the original ligand which
appears in the spectrum due to the dissociation of the d10 metal ions from the complex in solution
phase.
3.4. Absorption and fluorescence properties of ligand and complexes
The ligand in DMSO medium shows two absorption bands maxima at 317 and 413 nm, which may
be attributed to π-π* and n-π* transitions respectively. Interestingly, on excitation at 317 and 413 nm
same emission occurs at 400 nm. The UV-vis spectra of complexes 1 shows two bands at 260 nm

and 420 nm due to intra-ligand charge transfer and LMCT respectively. On excitation at 260 nm, no
fluorescence action is observed. But we have observed fluorescence spectra with emitted band
maxima at 485 nm, when the excitation is done 420 nm. The UV-vis spectrum of complexes 2 and
3 also exhibit two bands at ∼260 nm and ∼420 nm, similar to complex 1. Here we again observed
no fluorescence activity on excitation at ∼260 nm. But interestingly we have again observed
fluorescence activity with emitted band maxima at ∼ 490 nm, when the excitation is done 420 nm.
However, it is interesting to note that the highest emission band for the ligand is observed at 400
nm, whereas the emission band maxima for all the complexes are shifted to higher wavelengths
(Table 4). These red shifts suggest successful complexation between the metal salts and the ligand
in all cases. The fluorescence shows the following trend for complexes: Zn(II) > Cd(II) > Hg(II);
thus the highest efficiency is seen for the Zn(II) complex (Fig. 4.). This can be explained by
considering heavy atom perturbation for which energy dissipation through non-radiative channels
increases, and consequently the fluorescence intensity decreases.
Fig. 4.
Table 4
3.5. Geometry optimization of Ligand and complexes
DFT calculations were carried out on single crystal X-ray diffraction structures (SCXRD) of Ligand
and all the three complexes in gas phase to fully optimize the ground state structure. Fig. 5 (a-d)
depicts the optimized structures of Ligand and Zn, Cd and Hg- complexes respectively. In order to
avoid lengthy paper, we have just shown only the optimized structural parameters of Ligand and Zn
complex, as all the three complexes confirm the similar optimized structural parameters. The DFT
calculated main geometrical parameters were tabulated in Table S2-S3 (see Supporting
information) for complexes. DFT calculated data reports the experimental data very closely. Very

slight differences are observed between XRD and DFT calculated parameters. The calculated Zn-
OH bond length (2.30 Å) varies by 0.1 Å while Zn-N bond length (2.12 Å) varies by just 0.01 Å
from the experimental bond lengths 2.20 and 2.11 Å respectively. Experimental and calculated Zn-
Br bond length remains equal (1.90 Å). Calculated bond angles N-Zn-N (167°) and O-Zn-O (167°)
varies by 7° and 2° from the experimental angles 160 and 165° respectively. Hence the calculated
bond lengths and bond angles are in reasonably good agreement with the experimental values.
Slight inconsistency between the calculated and experimental geometries are practical as the
calculated geometry is in isolated state whereas the experimental geometry is for the atoms packed
in a lattice in which intermolecular interactions play a significant role. Hence, the common trends
observed in the experimental data are well reproduced in the calculations.
Fig. 5 (a-d)
3.6. Electronic spectra and its correlation with spectroscopic transitions
The electronic spectra of complexes (1-3) were recorded in DMSO (see SI Fig S4 in Supporting
information). The spectral features for all the complexes are nearly same. Absorption spectra for all
the three complexes consist of mainly two bands i.e. at 420 and 260 nm. In order to get deeper
understandings of transitions occurring in these complexes, TD-DFT calculations have been
performed. The ground state absorption spectra of complexes, simulated by TD-DFT calculation
using CPCM/B3LYP method in DMSO are shown as vertical lines in Fig. 6. The calculated
absorption bands for complex 1 in the ground state, their oscillator strengths, energies and the band
assignments are present in Table 5. The vertical electronic transitions for complex 1 found at 411,
391, 379, 360, 311, 285, 277, 275,259 and 257nm and are either due to ligand to ligand transition
(i.e. π → π* transitions in benzene or n(Br/O)→π*(benzene) or metal to ligand transition (d(Zn)→
π*(benzene)). Approximately similar transitions were observed for other complexes (2 and 3).

Fig. 6.
Table 5.
Hence TD-DFT calculation produces a better correlation with experimentally observed electronic
spectrum. The strongest band for complex 1 in absorption spectrum appears in the region of 250-
300 nm (λmax = 275 nm), which is predominantly due to π(benzene)/dZn/N(Br) →π*(benzene/C=N)
charge transfer and 350-475 nm (λmax = 420 nm) which is due to π(benzene)/dZn/n(N)→
π*(benzene/C=N) charge transfer, with a small contribution from metal to ligand charge transfer
(MLCT). Molecular Orbital (MO) 202, is the Highest Occupied Molecular Orbital (HOMO) and
MO 203, is the Lowest Unoccupied Molecular Orbital (LUMO). Assignment of calculated
transitions was based on the contour plots and relative energy of HOMOs and LUMOs involved in
electronic transitions. Assignment of electronic transitions at molecular level are carried out
generally through Frontier molecular orbital (FMO) involved in transition as shown in Fig. 7.
Fig. 7.
3.7. Calculated vibrational spectra and assignment of bands
IR spectrums of all complexes have been recorded in the range 4000-400cm-1 and have been shown
in Fig. S5-S7 (see Supporting information). The experimental results are interpreted and
rationalized in the light of the theoretical investigation based upon the DFT calculation. The
calculated IR bands with the corresponding assignments are presented in Table 6 for zinc complex.
Vibrational frequencies corresponding to different vibrational motions such as stretching,
scissoring, twisting, in plane bending, rocking, ring breathing etc. were assigned based on the
predominant motion of the atoms and magnitude of the displacement vector associated with the
atoms involved in concerned vibration and are also included in the tables. Band at 3678 cm-1
corresponds to O-H stretching which is quite wide in experimental spectra as shown in Fig. 8.

Peaks at 3132 and 3051 cm-1 correspond to asymmetric and symmetric C-H stretching in CH2
group. Most intense peak at 1659 cm-1 corresponds to C=N stretching which differ by just 10 cm-1
from the experimental frequency. Peaks at 1537 and 1535 cm-1 corresponds to C=C stretching in
benzene ring and C=C stretching in benzene ring coupled with C-H in plane bending respectively.
Other vibration motions are shown in Table 6. The calculated IR bands (see SI Figs S14-S15 in
Supporting information) with the corresponding assignments are presented in Table S4 for
cadmium and mercury complexes.
Fig. 8.
4. Conclusion
A Schiff base ligand, HL, has been synthesized by 1: 1 condensation of 1, 3-dibromo
salicylaldehyde and (tris hydroxy methyl) amino methane. The structure of ligand has been
evaluated in solution phase. The ligand shows excellent fluorescent property due to
π→π* transition. The reaction of zinc or cadmium or mercury halide (MX2) with this ligand yields
mononuclear complexes of the general formulation [ML2]. The fluorescence intensity increases
upon complexation, most likely due to the increasing rigidity of the molecule. The structures of
complexes were studied in solution phase as well as in solid phase. The molecular structure of
complex 1 has been determined by single crystal X-ray diffraction. DFT and TD-DFT calculation
of all the three complexes have also been performed to determine the origine of the spectral
behavior of the complexes.
Acknowledgement: MLS thanks Computer Centre, BHU for providing the computational facility
and SERB-India for providing financial support (PDF/2017/002589).
Supplementary material

CCDC 1555947 contains the supplementary crystallographic data for complex 1. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated with this article can be
found, in the online version,
References
[1]
[2]
[3]
[4]
[5]
[6]
Y. Yang, Q. Zaho, W. Feng, F. Li, Chem. Rev. 113 (2012) 192.
X. Li, X. Gao, W. Shi, H. Ma, Chem. Rev. 114 (2013) 590.
Z. Liu, W. He, Z. Guo, Chem. Soc. Rev. 42 (2013) 1568.
B.L. Vallee, D.S. Auld, Biochemistry 29 (1990) 5647.
J.M. Berg, Y. Shi, Science 271 (1996) 1081.
A. Voegelin, S. Pfister, A.C. Scheinost, M.A. Marcus, R. Kretzschmar, Environ. Sci.
Technol. 39 (2005) 6616.
[7]
[8]
[9]
R. R. Lauwerys, A. M. Bernard, H. A. Reels and J.-P. Buchet, Clin. Chem. (Washington, D.
C.) 40 (1994) 1391.
G. F. Nordberg, R. F. M. Herber and L. Alessio, Cadmium in the Human Environment,
Oxford University Press, Oxford, UK, 1992.
C. N. McFarland, L. I. Bendell-Young, C. Guglielmo and T. D. Williams, J. Environ. Monit.
4 (2002) 791.
[10] F. Di Natale, A. Lancia, A. Molino, M. Di Natale, D. Karatza and D. Musmarra, J. Hazard.
Mater. 132 (2006) 220.
[11] C. M. L. Carvalho, E.-H. Chew, S. I. Hashemy, J. Lu and A. Holmgren, J. Biol. Chem.,
283 (2008) 11913.

[12]
[13]
[14]
Z. Xu, J. Yoon, D.R. Spring, Chem. Soc. Rev. 39 (2010) 1996.
W. Huang, H.-B. Zhu, S.-H. Gou, Coord. Chem. Rev. 250 (2006) 414.
A. Morsali, M.Y. Masoomi, Coord. Chem. Rev. 253 (2009) 1882.
[15] J. Otsuky, T. Akasaka, K. Araki, Coord. Chem. Rev. 252 (2008) 32.
[16] P. Jiang, Z. Guo, Coord. Chem. Rev. 248 (2004) 205.
[17] (a) T. Chattopadhyay, M. Mukherjee, K. S. Banu, A. Banerjee, E. Suresh, E. Zangrando, D.
Das, J. Coord. Chem., 6 (2009) 967. (b) A. Guha, R. Sanyal, T. Chattopadhyay, YG Han, T.
K. Mondal, D. Das, J. Mol. Struct. 1042 (2013) 104. (c) M. Khorshidifard, H. Amiri
Rudbari, Z. Kazemi-Delikani, V. Mirkhani, R. Azadbakht, J. Mol. Struct. 1081 (2015) 494.
(d) S. Shit, A Sasmal, P. Dhal, C. Rizzoli, S. Mitra, J. Mol. Struct. 1108 (2016) 475. (e)
S. Roy, B. N. Sarkar, K. Bhar, S. Satapathi, P. Mitra, B. K. Ghosh, J. Mol. Struct. 1037
(2013) 160. (f) R. Golbedaghi, M. Rezaeivala, L. Albeheshti, J. Mol. Struct. 1076 (2014)
673.
[18] A. Ahmedova, P. Marinova, K. Paradowska, M. Marinov, I. Wawer, M. Mitewa,
Polyhedron 29 (2010) 1639.
[19] M. Shukla, B. Kharediya, N. Srivastava, S. Saha, S. Sunkari, Polyhedron 54 (2013) 164.
[20] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J.
A. Montgomery, Jr.; , T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima,
Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, 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, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J.

J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D.
K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G.
Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I.
Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C.
Gonzalez, J. A. Pople. Gaussian, Inc. Wallingford, CT, 2004.
[21] A. D. Becke, J. Chem. Phys. 98 (1993) 5648.
[22] C. Lee, W. Yang, R. G. Parr, Phys. Rev. B, 37(1988)785.
[23] Bruker, APEX 2, v. 2.0-2; Bruker (2005) SAINT v. 7.23; Bruker AXS Inc., Madison,
Wisconsin, USA, 2006.;
[24] G.M. Sheldrick, SADABS v. 2. University of Goettingen, Germany, 2001.
[25] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.

Fig. 1. Perspective view (50% probability ellipsoids) of complex 1
H2O
DMSO
Fig. 2. 1D polymer through different types of intermolecular H-bonding interactions

Fig. 3. Different types of intermolecular H-bonding interactions between DMSO and complex 1
Fig. 4. Fluorescence spectra of complexes (1-3) in DMSO at 298 K, (λex = 420 nm).

(b) Complex 1
(a) Ligand
(d) Complex 3
(c) Complex 2
Fig. 5. Optimized structure of Ligand and the Zn, Cd and Hg-complexes.
Fig. 6. Experimental (curve line) and TD-DFT calculated (vertical lines) absorption spectra of
complex 1 in DMSO.

209
204
203
203
259nm
391nm
411nm
275nm
202
202
202
198
Wavelengh/nm
Fig. 7. The frontier molecular orbital (FMO) pictures of Zinc complex involved in electronic
transitions.

Fig. 8. IR spectrum of Zn-complex (curved line in blue) and DFT calculated frequency (vertical line
in black)

Table 1. Crystallographic Data and Details of Refinements for complex 1.
Complex 1
Emperical Formula
Formula Weight
Crystal System
Space group
a/(Å)
C24 H32 Br4 N2 O10 S Zn
925.58
Monoclinic
P21/c
14.181(3)
12.993(2)
21.334(5)
90
b/(Å)
c/(Å)
α(o)
β(o)
γ(o)
100.064(11)
90
V(Å3)
3870.4(14)
4
Z
Dcalc (g/cm-3)
1.588
µ (mm)
4.863
F(000)
1824
Theta range
3.1-27.5
Total Data
33876
8763
Unique Data
Rint
0.058
Observed data (I > 2σ(I)
Radiation (Å)
Parameters
7359
0.71075
382
a
R1
0.0553
0.1415
1.041
wR2 (I > 2σ (I))a
GOF on F2
Residuals ( e A-3 )
-2.74,2.40
½
[a]R1 = ΣFo–Fc / ΣFo, wR2 = [Σw (Fo2 – Fc 2) 2/ Σw (Fo2) 2 ]

Table 2. Coordination Bond Lengths (Å) and Angles (deg) for complex 1.
Zn1-O1
Zn1-O2
Zn1-O5
Zn1-O6
Zn1-N1
2.009(3)
2.197(4)
2.010(4)
2.202(4)
2.101(4)
O1-Zn1-O2
O1-Zn1-O6
O1-Zn1-O5
O1-Zn1-N1
O1-Zn1-N2
O2-Zn1-O5
O2-Zn1-O6
O2-Zn1-N1
O2-Zn1-N2
O5-Zn1-O6
O5-Zn1-N1
O5-Zn1-N2
O6-Zn1-N1
O6-Zn1-N2
N1-Zn1-N2
165.61(14)
91.66(13)
97.90(15)
89.69(15)
102.57(15)
89.19(16)
84.34(14)
76.42(15)
89.98(15)
164.37(14)
103.93(16)
89.14(15)
88.39(14)
76.67(14)
160.79(15)
Table 3. Different types of H-bonding interactions in 1 (* D is donor and A is acceptor).
D-H…A
D-H
H…A
1.782
1.793
2.578
3.001
1.911
1.922
2.649
2.542
2.677
D…A
2.638
2.644
3.554
3.353
2.721
2.725
3.349
3.457
3.392
O2-H2...O4
0.873
0.894
0.990
0.990
0.842
0.841
0.978
0.980
0.840
O6-H6…O7
C20-H20B…O9
C10-H10A…O9
O7-H7…O10
O8-H8…O10
C2AA-H2AC…O3
C1AA-H1AB…O5
O3-H3A…S1

Table 4. Absorption, steady state fluorescence and quantum yield data at 298 K for complex 1 in
DMSO.
Ligand/Complex
Excitation Wavelength
λ (nm)
Emission Wavelength
Quantum
Yield
λ (nm)
415
HL
375, 415
0.089
Complex 1
Complex 2
Complex 3
260, 420
420
0.160
255, 422
420
0.145
252, 419
420
0.141
Table 5. The calculated absorption bands, oscillator strengths, energies and the transition for
complex 1 in the ground state.
Wavelength Oscillato Energ Transition Transitions Assigned
/nm
411
391
379
360
311
285
277
275
259
257
r strength y/eV
occurring
0.1071
0.0578
0.0361
0.0058
0.0040
0.0115
0.0925
0.1799
0.0248
0.0381
3.019 202 →203 π(benzene)/dZn/n(N)→ π*(benzene/C=N)
3.170 202 →204 π(benzene)/dZn/n(N)→ π*(benzene)
3.269 201 →203 π(benzene)/dZn/n(Br)→ π*(benzene/C=N)
3.441 201 →204 π(benzene)/dZn/n(Br)→ π*(benzene)
3.981 199 →204 dZn/n(Br/O)→ π*(benzene)
4.347 199 →203 dZn/n(Br/O)→ π*(benzene/C=N)
4.460 200 →204 π(benzene)/dZn/n(Br)→π*(benzene)
4.495 198 →203 π(benzene)/dZn/N(Br)→π*(benzene/C=N)
4.781 202 →209 π(benzene)/dZn/n(N)→ σ*(C-Br/O-H)
4.805 201 →206 π(benzene)/dZn/n(Br)→ σ*(C-Br)

Table 6. Selected IR frequencies obtained from DFT calculation for Zn complexes in gas phase.
Frequency/cm-1 Intensity
Assignment
3678
3200
3132
3051
1659
1537
1535
219
12
O-H stretching
C-H stretching of benzene ring
Asymmetric C-H stretching in CH2
Symmetric C-H stretching in CH2
C=N stretching
16
66
751
140
172
C=C stretching in benzene ring
C=C stretching in benzene ring coupled with C-H
in plane bending
1507
1495
1443
1424
1415
1406
15
230
53
29
22
25
H-C-H scissoring in CH2 group.
H-C-H scissoring in CH2 group.
C-H wagging in CH2 group
C-H scissoring in N-C(H)-C-C(H)
C-H twisting in CH2 group
C-H wagging in CH2 group coupled with C-C
stretching
1312
1218
1147
15
C-H twisting in CH2 group coupled with O-H in
plane bending
81
C-H twisting in CH2 group coupled with O-H
inplane bending
136
C-C stretching coupled with H-C-H rocking in
CH2 group and C-Br stretching

1056
722
196
120
15
C-OH stretching
C-Br stretching and ring breathing
C-N stretching coupled with ring breathing
692

Highlights
• Three new complexes have been prepared by the reaction of zinc(II), cadmium(II) and
mercury(II) chlorides with a new Schiff-base ligand HL ((2-[(3, 5-Dibromo-2-hydroxy-
benzylidene)-amino]-2-hydroxymethyl-propane-1,3-diol)).
• All the complexes have been characterized by UV-Vis, FT-IR, ESI-MS and 1HNMR
techniques. Complex 1 has further been characterized by single crystal X-ray structural
analyses.
• The fluorescent properties of the ligand as well as all three complexes have been
investigated.
• DFT study has been performed to rationalize the spectral behavior of UV-Vis and FT-IR.