Synthesis, characterization, X-ray crystal structures and antibacterial activities of Schiff base ligands derived from allylamine and their vanadium(IV), cobalt(III), nickel(II), copper(II), zinc(II) and palladium(II) complexes

Article abstract of DOI:10.1016/j.molstruc.2016.06.055

A new Schiff base ligand, HL², and four new Schiff base complexes, NiL¹₂, PdL¹₂, NiL²₂ and ZnL²₂, have been prepared and characterized by elemental analysis

Full text of DOI:10.1016/j.molstruc.2016.06.055

Accepted Manuscript
Synthesis, characterization, X-ray crystal structures and antibacterial activities of
Schiff base ligands derived from allylamine and their Vanadium(IV), Cobalt(III),
Nickel(II), Copper(II), Zinc(II) and Palladium(II) complexes
Hadi Amiri Rudbari, Mohamad Reza Iravani, Vahid Moazam, Banafshe Askari, Mahsa
Khorshidifard, Neda Habibi, Giuseppe Bruno
PII:
S0022-2860(16)30642-1
10.1016/j.molstruc.2016.06.055
MOLSTR 22674
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 30 January 2016
Revised Date: 21 June 2016
Accepted Date: 22 June 2016
Please cite this article as: H.A. Rudbari, M.R. Iravani, V. Moazam, B. Askari, M. Khorshidifard, N. Habibi,
G. Bruno, Synthesis, characterization, X-ray crystal structures and antibacterial activities of Schiff base
ligands derived from allylamine and their Vanadium(IV), Cobalt(III), Nickel(II), Copper(II), Zinc(II) and
Palladium(II) complexes, Journal of Molecular Structure (2016), doi: 10.1016/j.molstruc.2016.06.055.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Synthesis, characterization, X-ray crystal structures and antibacterial activities of
Schiff base ligands derived from allylamine and their Vanadium(IV), Cobalt(III),
Nickel(II), Copper(II), Zinc(II) and Palladium(II) complexes
Hadi Amiri Rudbari,a,* Mohamad Reza Iravani,a,* Vahid Moazam,a Banafshe Askari,a Mahsa
Khorshidifard,a Neda Habibi,b Giuseppe Brunoc
a Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran.
b Department of Biomedical Engineering, College of Engineering, The University of Texas at San
Antonio, One UTSA Circle, San Antonio, TX 78249-0619, USA.
c Department of Chemical Sciences, University of Messina, Via F. Stagno d'Alcontres 31, 98166
Messina, Italy.
* Corresponding author. Tel.: +98 31 37934918.
E-mail address: h.a.rudbari@sci.ui.ac.ir; hamiri1358@gmail.com (H. Amiri Rudbari);
m.r.iravani@sci.ui.ac.ir (M. R. Iravani)
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Abstract
A new Schiff base ligand, HL2, and four new Schiff base complexes, NiL1 , PdL1 , NiL2 and ZnL2 ,
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have been prepared and characterized by elemental analysis (CHN), FT-IR and UV-Vis spectroscopy.
1H and 13C NMR techniques were employed for characterization of the ligand (HL2) and the
diamagnetic complexes (PdL1 and ZnL2 ). The molecular structures of PdL1 , NiL2 and ZnL2
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complexes were determined by the single crystal X-ray diffraction technique. The crystallographic data
reveal that in these complexes the metal centers are four-coordinated by two phenolate oxygen and two
imine nitrogen atoms of two Schiff base ligands. The geometry around the metal center in the PdL1
2
and NiL2 complexes is square-planar and for ZnL2 it is a distorted tetrahedral.
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In the end, five new (HL2, NiL1 , PdL1 , NiL2 and ZnL2 ) and six reported (HL1, VOL1 , CoL1 ,
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CuL1 , ZnL1 and Zn2L1 ) Schiff base compounds were tested for their in vitro antimicrobial activity
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against Staphylococcus aureus and Escherichia coli as examples of Gram-positive and Gram-negative
bacterial strains, respectively, by disc diffusion method.
Keywords: Schiff base, Crystal structure, Antibacterial activity
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1. Introduction
Schiff bases play an important role in inorganic chemistry as they easily form stable complexes with
most transition metal ions [1-7]. The high stability potential of Schiff base complexes with different
oxidation states extended the application of these compounds in a wide range.
The catalytic activity of Schiff base metal complexes has been analyzed critically in various reactions
such as polymerization, oxidation, epoxidation, reduction of ketones, allylic alkylation and Michael
addition reactions [4, 8-17].
Apart from the catalytic applications of Schiff base compounds, they are important class of compounds
in medicinal and pharmaceutical fields. They show potential applications and properties such as
anticancer, anticonvulsant, antitumor, antifungal, antibacterial, antitubercular, antioxidant, antimalarial,
anti-inflammatory and anti-HIV activities [5, 18-28].
Although numerous Schiff base complexes with different structures have been synthesized and
characterized, reports on Schiff base ligands and complexes derived from amines containing terminal
allyl group are scanty [29, 30]. We have recently reported the synthesis and structural properties of a
bidentate Schiff base ligand (HL1) derived from salicylaldehyde and allylamine and its Vanadium(IV),
Cobalt(III), Copper(II) and Zinc(II)) complexes [31]. Also, in another work, a new asymmetric Schiff
base ligand derived from condensation of 2,3-dihydroxybenzaldehyde and allylamine and its Mo(VI)
complex were prepared and characterized by single crystal X-ray analysis that showed special
geometry called pseudo-scorpionate due to hydrogen interaction in terminal allyl group of the ligands
[32-36]. In continuation of these studies, herein we report the synthesis, characterization and X-ray
crystal structures of four new complexes, NiL1 , PdL1 , NiL2 and ZnL2 , of the reported (HL1) and
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new (bidentate Schiff base ligands (Schemes 1 and 2). In continuation, the antibacterial activities of
Schiff base ligands, HL1 and HL2, and its mononuclear complexes, VOL1 , CoL1 , CuL1 , ZnL1 ,
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NiL1 , PdL1 , NiL2 and ZnL2 , and also a related binuclear Zn(II) complex, Zn2L1 , have been
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investigated for their in vitro antimicrobial activity against Staphylococcus aureus (ATCC 29737) and
Pseudomonas aeroginosa (PTTC 1570) as examples of Gram-positive and Gram-negative bacterial
strains, respectively, by disc diffusion method. The diffusion method is simple, yet is routinely used in
hospital laboratories; it requires commercial disks, the medium used is Mueller-Hinton agar with 2% of
glucose, and the diameter of the zone of inhibition is visually read 24 h after incubation at 37 °C.
Antibacterial activity was estimated on the basis of the size of the zone of inhibition formed around the
paper disks on the seeded agar plates.
2. Experimental section
2.1. Chemicals and instrumentation
All the chemicals were purchased from Merck Co. and used without further purification. The FT-IR
spectrum was recorded on a JASCO, FT/IR-6300 spectrometer (4000–400 cm-1) in KBr pellets. The
elemental analysis was performed on Leco, CHNS-932 and Perkin-Elmer 7300 DV elemental
analyzers. VOL1 , CoL1 , CuL1 , ZnL1 and Zn2L1 were prepared according to literature methods
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[29, 31].
2.2. Crystal structure determination
X-ray data for PdL1 , NiL2 and ZnL2 complexes were collected on a STOE IPDS-II diffractometer
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with graphite monochromated Mo-Kα radiation. For NiL2 the crystals were green and for PdL1 and
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ZnL2 complexes, the crystals were yellow. A high-quality piece of crystal was chosen in each case
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using a polarizing microscope and they were mounted on a glass fiber, then used for data collection.
Cell constants and an orientation matrix for data collection were obtained by least-squares refinement.
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Data were collected at a temperature of 298(2) in a series of ω scans in 1° oscillations and integrated
using the Stöe X-AREA [37] software package. A numerical absorption correction was applied using
the X-RED [38] and X-SHAPE [39] software’s. The data were corrected for Lorentz and Polarizing
effects. The structures were solved by direct methods using SIR2004 [40]. The non-hydrogen atoms
were refined anisotropically by the full matrix least squares method on F2 using SHELXL [41]. All
hydrogen atoms were added at ideal positions and constrained to ride on their parent atoms.
Crystallographic data for complexes are listed in Table 1. Selected bond distances and angles are
summarized in Table 2.
2.3. Synthesis of Schiff-base ligand (HL2)
Allylamine (10 mmol) was dissolved in 30 ml of absolute methanol or chloroform and added slowly to
a stirred solution 2-hydroxy-5-methylbenzaldehyde (10 mmol) in 30 ml of absolute methanol or
chloroform at ambient temperature. The color immediately changed to yellow. The mixture was then
stirred for 2h at ambient temperature before removal of solvent under vacuum. The result was yellow
oil. Anal. Calc. for C11H13ON: C, 75.40; H, 7.48; N, 7.99. Found: C, 75.33; H, 7.43; N, 8.04. Selected
IR data (KBr,cm-1): 1631(νC=N), 1328 (νC-O).
2.4. Preparation of complexes (NiL1 , NiL2 , ZnL2 and PdL1 )
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A MeOH (or EtOH) solution (20 ml) of allylamine (6 mmol) was added dropwise to a MeOH solution
(20 ml) of the salicylaldehyde (for preparation of NiL1 and PdL1 ) or 2-hydroxy-5-
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2
methylbenzaldehyde (for preparation of NiL2 and ZnL2 ) (6 mmol). The yellow solution was stirred
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for 2h at ambient temperature. Then a solution of triethylamine (8 mmol) in absolute MeOH (5 ml) was
added to the solution. The solution was essentially dark yellow at this time. The mixture was stirred for
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10 min, and then a solution of appropriate metal salt (3 mmol Zn(NO3)2.6H2O , NiCl2.6H2O or
Pd(OAc)2) in absolute MeOH (20 ml) was added dropwise.
NiL1 : Upon addition of NiCl2, the color of solution changed to green. The resulting solution was
2
stirred for 12h at ambient temperature. After concentration at room temperature, the green precipitate
was collected by filtration. The typical yield was 93%. Anal. calc. for C20H20N2O2Ni: C: 63.37, H:
5.32, N: 7.39. Found: C: 63.36, H: 5.35, N: 7.37. Selected IR data (KBr, cm-1): 1609 (νC=N), 1326
(νC-O).
NiL2 : Upon addition of NiCl2, the color of solution changed to green. The resulting solution was
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stirred for 12h at ambient temperature. The green solution was slowly evaporated to dryness at room
temperature to yield a green solid which was purified by washing with 50 ml of cold methanol and the
obtained green precipitate was dried in air. Appropriate single crystals for X-ray crystallography were
obtained directly from the reaction mixture. The typical yield was 89%. Anal. calc. for C22H24N2O2Ni:
C: 64.90, H: 5.94, N: 6.88. Found: C: 64.86, H: 5.91, N: 6.90. Selected IR data (KBr,cm-1):
1617(νC=N), 1329 (νC-O).
ZnL2 :
2
After adding of Zn(NO3)2.6H2O, the resulting solution was stirred for 12h at ambient temperature. The
yellow solution was slowly evaporated to dryness at room temperature to yield a yellow solid which
was purified by washing with 50 ml of cold methanol. Appropriate single crystals for X-ray
crystallography were obtained directly from the reaction mixture. The typical yield was 84%. Anal.
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calc. for C22H24N2O2Zn: C: 63.85, H: 5.85, N: 6.77. Found: C: 63.88, H: 5.83, N: 6.76. Selected IR data
(KBr,cm-1): 1619 (νC=N), 1322 (νC-O).
PdL1 : Prepared in a similar manner to NiL1 but the resulting green solution after adding Pd(OAc)2 (3
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mmol) was refluxed for 12h. After concentration at room temperature, green precipitate was collected
by filtration and purified by washing with cold methanol. Recrystallization from CH2Cl2 yielded single
crystals of PdL1 suitable for X-ray crystallography. The typical yield was 82%. Anal. calc. for
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C20H20N2O2Pd: C: 56.28, H: 4.72, N: 6.56. Found: C: 56.35, H: 4.73, N: 6.62. Selected IR data
(KBr,cm-1): 1622 (νC=N), 1320 (νC-O).
2.5. Antibacterial studies
The antibacterial activity of compounds were tested on Staphylococcus aureus ATTC 29737 and
Pseudomonas aeroginosa PTTC 1570 (Persian type culture collection) by comparison based on
diameter of inhibition zone using the standard Kirby–Bauer disc diffusion assay (KBDD method). The
bacterial species (Staphylococcus aureus and Pseudomonas aeroginosa) were stored in a refrigerator.
Nutrient agar powder (1.8 g) was dissolved in 50 ml of water, sterilized by autoclaving at 115 °C for 20
min, cooled in a disinfected laminar hood and 100 ꢀl of culture of each organism was seeded in agar
plates using the pour plate technique. The compound was placed on top of the agar and the plates and
incubated at 37 °C overnight. The zones around each disc were measured with a ruler.
3. Results and discussion
3.1. IR spectra
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The formation of Schiff base ligand, HL2, is evidenced by the presence of a strong IR band at 1631 cm-
1 due to ν(C=N), while no bands attributable to ν(C=O) or to ν(NH2) have been detected [31, 42].
A comparison of the spectra of the free ligands, HL1 [31] and HL2, and its Ni(II), Zn(II) and Pd(II)
complexes, NiL1 , PdL1 , NiL2 and ZnL2 , indicated that the ligands were coordinated to the metal
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centers. Coordination of the azomethine nitrogen to the metals was suggested by the shift of the C=N
band to lower frequencies in the IR spectra of the zinc, nickel and palladium complexes compared with
the Schiff base ligands. Formation of M–N bonds leading to weakening of C=N band and this can be
explained by the donation of electrons from the nitrogen atom to the empty d-orbitals of the metal atom
[4]. Additional support for the formation of the Ni(II) Zn(II) and Pd(II) complexes were provided by
the existence of weak intensity bands at ~ 480 cm-1 attributed to the formation of M—N and M—O
bonds [14].
3.2. NMR study
The 1H NMR and 13C NMR spectra of the Schiff base ligand, HL2, and diamagnetic complexes, PdL1
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and ZnL2 , were measured in CDCl3, with TMS as internal standard. The data is depicted in Figs. 1 and
2
2 and spectra in Figs. S1-S7. The 1H and 13C NMR were run immediately after dissolving in CDCl3 and
gave the expected simple spectra, indicating the integrity of Schiff base ligand and complexes. The
spectra for ligand and complexes obtained after 12, 24, 48 and 120 h were similar to the initial spectra
indicating that Pd(II) and Zn(II) complexes are stable in deuterated chloroform.
The 1H NMR spectrum of HL2 shows one singlet peak at 8.31 ppm corresponding to the imine proton
1
(CH=N), and an almost broad O-H signal at 13.22 ppm. The H NMR spectra of the complexes are
almost similar to that of the ligands with slight shift to lower fields. The signal for the imine proton in
the Pd(II) and Zn(II) complexes appears at 7.56 and 8.12, respectively, and this is shifted upfield with
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respect to the corresponding signal in the free ligand, indicating that the metal–nitrogen bond is
retained in solution. Phenolic-OH signals of Schiff base ligands, (HL1:11.1 ppm and HL2:13.2 ppm)
disappears in spectra of their complexes, indicating that OH protons are removed completely upon
coordination.
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The C NMR spectra of Schiff base ligand, Pd(II) and Zn(II) complexes, show one peak at 165.7,
162.6 and 171.3 ppm corresponding to the imine carbon atom of HL2, PdL1 and ZnL2 , respectively.
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3.3. X-Ray diffraction studies
3.3.1. Structure description of PdL1 and NiL2
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The molecular structure of PdL1 and NiL2 are shown in Figures 3 and 4, respectively. The
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crystallographic data and selected bond lengths and angles are collected in Tables 1 and 2. In the solid
state, PdL1 and NiL2 are placed in a crystallographic center of symmetry that is right in the middle
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point of the M(II) in a planar-transoid conformation (Figs. 3 and 4). The molecular unit is
centrosymmetric and is made up of equivalent halves. The crystallographic data reveal that the Ni(II)
and Pd(II) complexes are four-coordinated by two phenolate oxygen and two imine nitrogen atoms of
two Schiff base ligands. The Schiff base ligands are arranged with respect to each other in a trans
orientation such that one allyl substituent lies above the [MO2N2] plane and the other below (Fig. S8.).
In NiL2 complex, the chelate rings have the envelope form and the structure is the step configuration,
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while the configuration in PdL1 complex is planar [4]. The C=N bond distance is 1.284(4) (N1=C7)
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for PdL1 and 1.285(5)Å (N1=C7) for NiL2 , which are consistent with a slight elongation of the C—N
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double bond when coordinated to a metal center [31]. Examination of the main metal–ligand distances
in Ni(II) and Pd(II) complexes shows that the M···N distance [1.928(3) Å for NiL2 , 2.017(2) Å for
2
PdL1 ] is longer than the M···O distance [1.837(3) Å for NiL2 , 1.981(2) Å for PdL1 ]. The bond
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angles O–M–N [O(1)–M(1)–N(1) = 92.53(12)° [NiL2 ] and 91.90(10)° [PdL1 ]; O(1)—M(1)–N(1A) =
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87.47(12)° [NiL2 ] and 88.10(10)° [PdL1 ] are close to 90°. These distances and angles are similar to
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those seen in related complexes [4, 31]. The C=C distance [1.278(8) Å for NiL2 and 1.294(2) Å for
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PdL1 ] is well within the range expected for double bonds found in allyl derivatives [29, 31].
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Although there are no classical hydrogen bonds in structure of PdL1 and NiL2 , but two intramolecular
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C–H…O contacts are observed in the solid state (Figs. 3, 4; Table 3). Also, there are intermolecular C–
H…π interactions in NiL2 complex (Fig. 5). Special structures of molecular assemblies can be formed
2
and controlled by various kinds of hydrogen bonding, even by C–H…π interactions that are
considerably weaker than classical H bonding. These C–H/π interactions also play notable structure-
stabilizing roles in structures. Here C–H…π edge-to-face interactions are present between CH groups
with H…π distance of 2.96 Å for C(5)—H(5) …Cg(1) and 2.90 Å for C(10)—H(10B)…Cg(1) [Cg(1)
is centroid for C(1)/C(6) ring].
3.3.2. Structure description of ZnL2
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An ORTEP view of ZnL2 with the atom-numbering scheme is presented in Fig. 6 and the
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crystallographic data and selected bond lengths and angles are collected in Tables 1 and 2. The
asymmetric unit of ZnL2 consists of two independent Schiff base complexes with slightly different
bond lengths and angles. The crystallographic data reveal that the metal center is four-coordinated by
two phenolate oxygen and two imine nitrogen atoms of two Schiff base ligands. The geometry around
the metal center is distorted tetrahedral, with P21/c, space group. The ligands coordinate to the metal
center in cis geometry with respect to each other.
The C=N bond distances for two independent molecules are 1.276(6) Å (N1=C7), 1.287(6) Å
(N2=C18), 1.286(8) Å (N3=C29) and 1.302(8) Å (N4=C40) which are consistent with a slight
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elongation of the C—N double bond when coordinated to a metal center [29,31]. The C–O bond
distance exhibit values between 1.313(7) until 1.328(6) Å [(C(1)-(O1): 1.314(6): (C(12)-(O2): 1.328(6)
; (C(23)-(O3): 1.321(7); (C(34)-(O4): 1.313(7)] in ZnL2 complex, which is nearer to a C–O single
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bond than to a C–O double bond distance. These distances prove that the ligand coordinates to the
Zn(II) in enolate form [29,31].
Surprisingly, we can see the big difference in geometry around Zn(II) in ZnL1 and ZnL2 complexes.
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As depicted in Fig. 6, The geometry around the Zn(II) center in ZnL2 complex is distorted tetrahedral.
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But, as previously reported by our group [31], the geometry around the Zn(II) center for ZnL1
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complex is square planer. The only difference between ZnL1 complex and ZnL2 complex is use of 2-
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hydroxy-5-methylbenzaldehyde instead of salicylaldehyde in synthesis of ZnL2 complex. In order to
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justify such structures, the investigating of steric and electronic factors in these two complexes is
necessary. As shown in Fig. 6, the methyl group of HL2 Schiff base ligand is very far from Zn(II)
center. For this reason, we don’t have any steric hindrance on behalf of methyl group in ZnL2 complex
2
for changing of the structure of square planar to distorted tetrahedral. Then, the only effective
parameter for this change is electronic factor.
3.4. Electronic spectra
Electronic spectra of the free Schiff base ligands and their complexes were recorded in a MeOH
solution and are shown in Fig. 7. Based on literature data recorded for benzene [43] and similar
Schiff bases in different solvents [44], all UV spectra of Schiff bases and their complexes exhibit
two main bands. The first intense and lower wavelength bands in the 215–270 nm region have molar
extinction coefficient values greater than one thousand and are attributed to intra-ring π→π* transitions
of the phenolic ring that in the complexes are significantly shifted relative to the free ligand as a result
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of the coordination of the heavy metal core. The second bands at the 270–400 nm range involve the
azomethine π→π* and n→π* transitions that for HL2 and its complexes shift to lower wavelengths.
In the Ni(II) and Pd(II) complexes, the band around 400 nm may be due to LMCT (O/N(p)→M(d))
transition. In these two complexes with d8 square planar structure, it is expected to show three
1
spin-allowed d–d transition bands corresponding to 1A1g → 1A2g, 1A1g → 1B1g and A1g → 1Eg, while
the tailing of CT bands that appeared at ~ 400 nm toward the visible region cause the
disappearance of these bands [4, 45].
3.5. Antibacterial results
Schiff base ligand and its metal complexes were evaluated for their in vitro antibacterial activity
against Staphylococcus aureus and Escherichia coli as examples of Gram-positive bacteria and
Gram-negative bacteria, respectively. The disk- diffusion method was carried out to evaluate the
antibacterial activity of compounds (Fig. S9). All compounds were used as powder in antibacterial
activity test except the Schiff base ligands that were used as oil. The results of the antimicrobial activity
of the Schiff base ligand and complexes against tested bacteria are shown in Table 4. From the results,
we can conclude that:
1. On comparing the activity of the tested complexes with Schiff base ligands, the obtained data
indicated that the activity of HL1 is less than its complexes, while the activity of HL2 is partly more
than its complexes.
2. All the tested compounds, except CoL13, CuL1 and PdL1 are found to have biological activity
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against E. coli.
3. All the tested compounds, except CoL1 and PdL1 are found to have biological activity against S.
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aureus.
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4. Ni(II) complex, NiL1 , appears to have a higher activity than all the other metal complexes.
2
5. There are not lack of growth of S. aureus and E. coli around the VOL1 complex, but 15 mm after
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the VOL1 complex, we can see a zone with very weak growth of bacteria (Fig. S9).
2
6. Although monometallic and bimetallic Zn(II) complexes prepared from HL1 ligand, ZnL1 and
2
Zn2L1 , are found to have no biological activity against S. aureus until 20 mm of samples, but 20
4
mm after the samples another zone can be seen that the growth of bacteria is greatly reduced (Fig.
S9).
7. The tested ligands and complexes have almost similar inhibitory against Gram-positive and Gram-
negative bacteria.
4. Conclusion
In this study, a new Schiff base ligand, HL2, and four new Schiff base complexes, NiL1 , PdL1 , NiL2
2
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2
and ZnL2 , have been prepared and characterized. The molecular structures of PdL1 , NiL2 and ZnL2
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2
complexes were determined by the single crystal X-ray diffraction technique. The crystallographic data
reveal that in all the complexes the metal centers are four-coordinated by two phenolate oxygen and
two imine nitrogen atoms of two Schiff base ligands. The geometry around the metal center in the
PdL1 and NiL2 complexes is square-planar and for ZnL2 it is a distorted tetrahedral.
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2
The new synthesized Schiff base ligand and complexes, HL2, NiL1 , PdL1 , NiL2 and ZnL2 , along
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with reported Schiff base ligand and complexes, HL1, VOL1 , CoL1 , CuL1 , ZnL1 , Zn2L1 , were
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assayed for their in vitro antibacterial activity against Staphylococcus aureus and Escherichia coli as
examples of Gram-positive and Gram-negative bacterial strains, respectively, by using disc diffusion
method.
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Acknowledgement
The authors are grateful to the Research Council of the University of Isfahan for financial support of
this work.
Appendix A. Supplementary data
Crystallographic data for the structures in this paper have been deposited with the Cambridge
Crystallographic Data Centre as the supplementary publication no. CCDC 1449477, 1449478 and
1449479 for NiL2 , PdL1 and ZnL2 , respectively. Copies of the data can be obtained, free of charge,
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on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (Fax: +44 1223 336033 or e-mail:
deposit@ccdc.cam.ac.uk).
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17

ACCEPTED MANUSCRIPT
OH
OH
MeOH or CHCl3
NH2
+
25 °C
N
CHO
HL2
Scheme 1. Synthesis of Schiff base ligand (HL2)
R
O
N
N
O
M
R
O
R= H, M : Zn, Cu and Pd
R= CH3, M : Zn and Ni
N
O
N
Co
O
N
R
c
b
R
a
+
NH2
CHO
OH
N
d
OH
e
R= H, HL1
R= CH3, HL2
O
N
a: MeOH, 25°C
N
Zn
O
b: MX2: Zn(NO3)2.6H2O, CuCl2.2H2O, NiCl2.6H2O, PdCl2, NEt3, 25°C
c: CoCl2.6H2O, NEt3, 25°C
O
N
Zn
d: Zn(OAc)2, , NEt3, Reflux
e: VO(acac)2, NEt3, 25°C
O
V
O
N
N
N
O
O
Scheme 2. Synthetic routes for the preparation of Schiff base ligands and complexes
18

ACCEPTED MANUSCRIPT
Fig. 1. 1H NMR and 13C NMR data for PdL1
2
H10b
H8b
H10a
H8a
H7
C3
C2
C1
N
O
H9
Pd
H5
C4
C5
O
C6
C7
H4
N
C8
C9
C10
H2
H3
1HNMR
13CNMR
H7
7.56(s)
C7
C8
162.59
59.48
164.52, 136.10,
134.67, 134.16,
120.35, 120.31,
H3
H5
H2
H4
7.27(d of t)
7.20(d of d)
6.91(d)
C9, C10, Car
6.59(t)
H9
6.12 (m)
116.85, 115.00
H10b, H10a
5.29(d of t),
5.19 (d of d)
4.40(d)
H8a,H8b
s, singlet; d, doublet; t, triplet; m, multiplet
19

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Fig. 2. 1H NMR and 13C NMR data for HL2 and ZnL2
2
H10b
H8b
C10
H10a
H8a
C8
C9
H7
C6
C2
C7
H9
H5
C4
H3
N
C5
C3
H11
C1
H11
C11
OH
H11
H2
1HNMR
13CNMR
HL2
HL2
ZnL2
ZnL2
2
2
H7
H3
H5
H2
H9
8.31 (s)
7.14 (d of d)
7.07 (d)
6.92 (d)
6.05 (m)
8.12 (s)
7.14 (d of d)
6.88 (d)
6.78 (d)
5.86 (m)
C7
C8
C11
165.7
61.4
20.4
171.3
62.7
20.2
C9, C10, Car 158.9, 134.9, 165.6, 136.5,
133.1, 131.4, 134.9, 133.4,
H10b, H10a 5.28, 5.23,
5.18, 5.13,
127.6, 118.5, 133.1, 131.3,
5.21, 5.19 (4q) 5.11, 5.08 (4q)
116.8, 116.4
122.9, 119.4
H8a,H8b
H11
OH
4.25, 4.23(2d)
2.32(s)
13.22(s)
4.14(d)
2.25(s)
-----
s, singlet; d, doublet; q, quartet; m, multiplet
20

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Fig. 3. ORTEP representation of PdL1 . Displacement ellipsoids are drawn at the 30% probability level
2
and H atoms are shown as small spheres of arbitrary radii. Hydrogen bonds are shown as dashed lines.
Fig. 4. ORTEP representation of NiL2 . Displacement ellipsoids are drawn at the 50% probability level
2
and H atoms are shown as small spheres of arbitrary radii. Hydrogen bonds are shown as dashed lines.
21

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X—H(I)…Cg(J)*
C(5)—H(5) …Cg(1)
C(10)—H(10B) …Cg(1)
H…Cg
2.96
2.90
X…Cg
3.670(4)
3.681(7)
X—H…Cg
134
142
Symmetry codes
-X,-1/2+Y,1/2-Z
1+X,Y,Z
*Cg(1): C(1)/C(6) ring
Fig. 5. Illustration of C—H…π interactions in molecular structure of NiL2
2
22

ACCEPTED MANUSCRIPT
Fig. 6. ORTEP representation of ZnL2 . Displacement ellipsoids are drawn at the 30% probability level
2
and H atoms are shown as small spheres of arbitrary radii.
23

ACCEPTED MANUSCRIPT
Fig. 7. Electronic spectra of Schiff base ligands and complexes (A: HL1 B: VOL1 , C: CoL1 , D:
,
2
3
NiL1 , E: ZnL1 , F: CuL1 , G: PdL1 H: HL2, I: NiL2 and J: ZnL2 )
2
2
2
2,
2
2
24

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Table 1 Crystal data and structure refinement details of PdL1 , ZnL2 and NiL2 .
2
2
2
PdL1
C20H20N2O2Pd
426.78
ZnL2
C22H24N2O2Zn
413.80
NiL2
2
C22H24N2O2Ni
407.14
2
2
Empirical formula
Formula weight
Temperature (K)
298(2)
298(2)
298(2)
Wavelength (Å)
Crystal system
Space group
0.71073
Monoclinic
P21/c
0.71073
Monoclinic
P21/c
0.71073
Monoclinic
P21/c
Unit cell (Å, °)
a
b
c
β
9.1663(9)
5.3797(5)
18.5168(18)
90.995(5)
912.96(15)
2
13.830(3)
13.282(3)
23.576(5)
102.39(3)
4229.7(17)
8
8.7116(17)
5.8886(12)
19.249(4)
93.67(3)
985.4(3)
2
Volume (Å3)
Z
Calculated density (Mg/m3)
1.552
1.300
1.179
1.372
1.003
Absorption coefficient (mm-1) 1.031
F(000)
432
1728
428
2.20 to 27.10
-11≤ h ≤11
-6≤ k ≤6
23≤ l ≤23
13167
2.56 to 27.00
-15≤ h ≤17
-16≤ k ≤16
-30≤ l ≤30
28537
3.06 to 25.00
-8≤ h ≤10
-7≤ k ≤7
-22≤ l ≤22
5191
θ range for data collection (°)
Index ranges
Reflections collected
Independent reflections
Data Completeness (%)
Refinement method
13167 [R(int) = 0.0465]
99.5
9222 [R(int) = 0.1613]
99.9
1704 [R(int) = 0.1445]
98.6
Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares
on F2
on F2
on F2
Data / restraints / parameters
Goodness-of-fit on F2
2002 / 1 / 115
1.072
9222 / 6 / 500
0.806
1704 / 0 / 125
1.047
Final R indices [I>2σ (I)]
R1 = 0.0326
wR2 = 0.0788
R1 = 0.0505
wR2 = 0.0886
0.625 and -0.433
R1 = 0.0688
wR2 = 0.1576
R1 = 0.1481
wR2 = 0.1813
1.132 and -1.321
R1 = 0.0711
wR2 = 0.1815
R1 = 0.0775
wR2 = 0.1890
1.221 and -1.564
R indices (all data)
Largest diff. peak and hole
(e.Å-3)
25

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Table 2 Selected bond distances (Å) and angles (°) for PdL1 , NiL2 and ZnL2
2
2
2
NiL2
PdL1
ZnL2
2
2
2
M(1)*—O(1)
M(1)—N(1)
N(1)-C(7)
1.837(3)
1.928(3)
1.285(5)
1.278(8)
1.981(2)
2.017(2)
1.284(4)
1.294(2)
Zn(1)-O(1)
Zn(1)-O(2)
Zn(1)-N(1)
Zn(1)-N(2)
Zn(2)-O(3)
1.911(4)
1.921(4)
1.995(4)
2.011(4)
1.916(4)
1.921(4)
2.004(5)
2.007(5)
1.276(6)
1.287(6)
1.286(8)
1.302(8)
C(9)-C(10)
O(1)-M(1)-O(1A) 180.00(10) 180.000(1) Zn(2)-O(4)
O(1)-M(1)-N(1) 92.53(12) 91.90(10) Zn(2)-N(4)
N(1)-M(1)-N(1A) 180.00(17) 180.00(13) Zn(2)-N(3)
C(1)-O(1)-M(1)
C(7)-N(1)-M(1)
C(8)-N(1)-M(1)
128.4(2)
124.3(2)
120.6(2)
126.4(2)
123.3(2)
119.7(2)
88.10(10)
N(1)-C(7)
N(2)-C(18)
N(3)-C(29)
N(4)-C(40)
O(1)-M(1)-N(1A) 87.47(12)
O(1)-Zn(1)-O(2)
O(1)-Zn(1)-N(1)
O(2)-Zn(1)-N(1)
O(1)-Zn(1)-N(2)
O(2)-Zn(1)-N(2)
N(1)-Zn(1)-N(2)
O(3)-Zn(2)-O(4)
O(3)-Zn(2)-N(4)
O(4)-Zn(2)-N(4)
O(3)-Zn(2)-N(3)
112.99(15)
97.01(16)
120.20(18)
117.48(18)
96.83(15)
113.78(17)
111.58(17)
121.38(19)
96.1(2)
96.2(2)
O(4)-Zn(2)-N(3)
N(4)-Zn(2)-N(3)
123.3(2)
110.3(2)
* M = Ni for NiL22 and Pd for PdL1 . Symmetry transformations used to generate equivalent atoms: 1
2
-x+2,-y,- z+2 (for NiL2 ) and 1 -x+1,-y+2,-z+2 (for PdL1 )
2
2
Table 3. Intramolecular hydrogen bond geometries (Å,°) for PdL1 and NiL2
2
2
D—H...A
D—H
H...A
D...A
D—H...A
Symmetry
codes
PdL1
NiL2
C(8)—H(8A)...O(1A)
C(8)—H(8B)...O(1A)
0.97
0.97
2.28
2.20
2.792(5)
2.712(5)
112
112
1-x,-y,-z
-x,2-y,-z
2
2
26

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Table 4 Antimicrobial activities of Schiff base ligands and complexes
HL1
NiL1
PdL12
one drop
620
27
15
0
2
VOL1
2000
0
There are not lack of growth of bacteria around the complex, but 15 mm
after the complex, we can see a zone with very weak growth of bacteria.
2
CoL1
ZnL12
580
380
460
0
10
4
CuL13
There are not lack of growth of bacteria around the complex, but 20 mm
after the complex, we can see a zone with very weak growth of bacteria.
There are not lack of growth of bacteria around the complex, but 20 mm
after the complex, we can see a zone with very weak growth of bacteria.
2
Zn2L1
700
11
4
HL2
NiL2
ZnL22
2
7
2.5
38
10
0
2
HL1
NiL2
PdL1
one drop
800
2
VOL1
2500
0
There are not lack of growth of bacteria around the complex, but 20 mm
after the complex, we can see a zone with very weak growth of bacteria.
2
CoL1
560
330
960
820
0
0
6
CuL13
ZnL12
2
Zn2L1
3
4
HL2
NiL2
ZnL22
2.5
12
4
2
27

ACCEPTED MANUSCRIPT
Highlights:
•
•
•
Synthesis and characterization of a new bidentate Schiff base ligand (HL2) and four new
Schiff base complexes (NiL1 , PdL1 , NiL2 and ZnL2 ).
2
2
2
2
Determination of molecular structures of PdL1 , NiL2 and ZnL2 complexes by the
2
2
2
single crystal X-ray diffraction technique.
Investigation of antimicrobial activity of reported (HL1, VOL1 , CoL1 , CuL1 , ZnL1
2
2
3
2
and Zn2L1 ) and new (HL2, NiL1 , PdL1 , NiL2 and ZnL2 ) Schiff base compounds.
4
2
2
2
2