Synthesis, characterization and coordination chemistry of N, N′-bis(3-pyridylmethyl)benzene-1,4-dicarboxamide with palladium and ruthenium salts

Article abstract of DOI:10.14233/ajchem.2017.20518

N, N′ -bis(3-pyridylmethyl)benzene-1,4-dicarboxamide (L) is a diamide bridging ligand. Utilization of bridging ligand such as L that exhibits amide moieties has greater potential to encapsulate anion via N-H hydrogen bonding donor groups and form metal ligand interaction via its pendant group containing pyridine-N atom. The complexes derived from this ligand also capable to form metallosupramolecular assemblies with the presence of the respective moieties. N, N′-bis(3-pyridylmethyl)benzene-1,4-dicarboxamide is synthesized from reaction between terephthaloyl chloride and 3-pyridylmethylamine in basic solution. The coordination chemistry between ligand L and two metal salts, palladium chloride and ruthenium chloride were attempted. Based on the combination of spectroscopic techniques such as CHNS, FTIR, NMR, TGA and cyclic voltammetry analysis, the molecular formula of the complexes may be suggested as: [Pd₂(L)Cl₄] and [Ru₂(L)Cl₆(H₂O)₄ · 2H₂O].

Full text of DOI:10.14233/ajchem.2017.20518

Asian Journal of Chemistry; Vol. 29, No. 7 (2017), 1459-1462
ASIAN JOURNAL OF CHEMISTRY
https://doi.org/10.14233/ajchem.2017.20518
Synthesis, Characterization and Coordination Chemistry of
N,N'-bis(3-pyridylmethyl)benzene-1,4-dicarboxamide with Palladium and Ruthenium Salts
1
1,*
NURULJANNAH SUHAIDA BINTI IDRIS , MAISARA ABDUL KADIR2,* and MOHAMMAD MONERUZZAMAN KHANDAKER
1School of Agriculture Science & Biotechnology, Faculty of Bioresources and Food Industry, Universiti Sultan Zainal Abidin, Besut Campus,
22200 Besut, Terengganu, Malaysia
2School of Fundamental Science, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia
*Corresponding authors: E-mail: maisara@umt.edu.my; moneruzzaman@unisza.edu.my
Received: 17 January 2017;
Accepted: 17 March 2017;
Published online: 13 May 2017;
AJC-18373
N,N’-bis(3-pyridylmethyl)benzene-1,4-dicarboxamide (L) is a diamide bridging ligand. Utilization of bridging ligand such as L that
exhibits amide moieties has greater potential to encapsulate anion via N-H hydrogen bonding donor groups and form metal ligand
interaction via its pendant group containing pyridine-N atom. The complexes derived from this ligand also capable to form
metallosupramolecular assemblies with the presence of the respective moieties. N,N’-bis(3-pyridylmethyl)benzene-1,4-dicarboxamide is
synthesized from reaction between terephthaloyl chloride and 3-pyridylmethylamine in basic solution. The coordination chemistry between
ligand L and two metal salts, palladium chloride and ruthenium chloride were attempted. Based on the combination of spectroscopic
techniques such as CHNS, FTIR, NMR, TGA and cyclic voltammetry analysis, the molecular formula of the complexes may be suggested
as: [Pd2(L)Cl4] and [Ru2(L)Cl6(H2O)4·2H2O].
Keywords: Amide ligand, Coordination chemistry, Metal complexes.
prepared and its coordination chemistry was studied. The
ligand reacted with palladium(II) chloride and ruthenium(III)
chloride to form metal complexes.
INTRODUCTION
Supramolecular chemistry is the aggregates small subunit
to larger unit via weak intermolecular forces [1]. The importance
of weak intermolecular interactions are polar interaction,
hydrogen bonding interaction, metal coordination and hydro-
phobic and hydrophilic interaction [2]. The interaction of hydro-
gen bonding can be occurred when partially positive hydrogen
atom donate it’s proton to the partially negative atom. Among
others, amide group has great ability to increase the strength
of intermolecular interaction from its hydrogen bonding
interaction and also metal coordination via N-H bonding donor
group. It has also been reported that N–H bonding donor group
can act as an effective neutral anion receptor because it ability
to bind anion via its hydrogen bond. Ligand contains nitrogen
as a donor atom was also reported stable, convenient to synthesis
and has unique properties useful in many applications [3-6].
Amide ligand is versatile ligand because its bombastic structure
can act as good anion receptor and also form metallosupra-
molecule when it interacts with metal centre. Realising the
special properties and great benefits ligand incorporate amide
moieties, hence, it has driven ours effort to investigate the
compound derivate from amide group. In this study, the ligand
N,N’-bis(3-pyridylmethyl)benzene-1,4-dicarboxamide was
EXPERIMENTAL
Infrared spectra were carried out on FTIR, Perkin-Elmer
spectrum 100 by using KBr disks. CHNS elemental analysis
1
was recorded by using a Flash EA 1112 Series. The H and
13C NMR were recorded on a BrukerAdvance III 400 spectro-
meter with DMSO-d6 as a solvent. For thermogravimetric
analysis, it was carried out by using TGA/SDTA 851e analyzer
METTLER TOLEDO. Melting points were measured from
Stuart Scientific Melting Point Apparatus SMP3. The redox
reaction was interpreted by using cyclic voltammetry (CV).
N,N’-bis(3-Pyridylmethyl)benzene-1,4-dicarboxamide,
(L): Terephthaloyl chloride (2.03 g, 10.1 mmol) was dissolved
in dichloromethane (20 mL). 3-pyridylmethylamine (2.1 mL,
20.6 mmol) and triethylamine (2.9 mL, 20.9 mmol) were
dissolved in dichloromethane (20 mL) and added slowly. The
resulting solution was stirred for 48 h to give the diamide
compound as a yellowish solid (3.78 g, 92 %). m.p.: 172-174 °C.
Palladium complex in ratio 1:1, 2:1 and 4:1 (metal-to-
ligand ratio), (complex 1-3, respectively): Palladium chloride
(0.040 g, 0.23 mmol; 0.042 g, 0.24 mmol; 0.041 g, 0.24 mmol)

1460 Idris et al.
Asian J. Chem.
represented to complexes 1-3, respectively were dissolved in
2 M hydrochloric acid. These solution were added dropwise
to a solution of L (0.081 g, 0.23 mmol; 0.042 g, 0.12 mmol;
0.021 g, 0.06 mmol) in methanol (20, 15 and 10 mL) for
complexes 1-3, respectively.A yellow precipitate formed after
being stirred overnight, collected by filtration, washed with
ethanol and dried to give pale yellow solid (0.71 g, 66 %),
m.p. 106-255 °C; yellow solid (0.07 g, 86 %), m.p: 252-299
°C and dark yellow solid (0.01 g, 24 %), m.p: 268-295 °C
represented to complex 1-3, respectively.
FTIR spectrum of L showed five absorption bands due to
NH stretch (3191 cm-1), C=O stretch (1639 cm-1), C=C stretch
(1594 cm-1), NH bend (1543 cm-1) and CN stretch (1318 cm-1).
From the comparison between the FTIR spectra of L and the
literature compound which is the analogue of the ligand namely
N,N’-2,6-bis(4-pyridylmethyl)pyridinedicarboxamide [7]
(Table-1), it has been confirmed that the expected ligand was
amide derivatives compound.
TABLE-1
COMPARISON BETWEEN THE FTIR SPECTRA BETWEEN N,N’-
BIS(3-PYRIDYLMETHYL)BENZENE-1,4-DICARBOXAMIDE (L)
AND THE LITERATURE LIGAND (N,N’-2,6-BIS(4-
PYRIDYLMETHYL)PYRIDINEDICARBOXAMIDE)
Ruthenium complex in ratio 4:1 (metal-to-ligand ratio)
(complex 4): Ruthenium(III) chloride (0.25 g, 1 × 10-6 mmol)
was dissolved in methanol (25 mL). The solution was heated
under reflux for 5 h until the solution turned green. The N,N’-
bis(3-pyridylmethyl)benzene-1,4-dicarboxamide (0.1 g, 2.7 ×
10-7 mmol) was added to the solution. The mixture was refluxed
for 2 h. The dark green precipitate was filtered and dried under
vacuum. Then, the product was recrystallized with methanol
to give dark green solid (0.046 g, 46 %). m.p.: 400-430 °C.
Literature compound (cm-1)
L (cm-1)
3191
Bands
N-H stretch
C=O
3062
1640
1600
1540
1639
C=C stretch
N-H bend
1594
1543
1H NMR spectra of L can be observed at δH 8.0 ppm belongs
to phenyl aromatic proton. The inducing ring current of
aromatic π electron is affected the downfield position of this
peak. NH moieties can be assigned at δH 9.3 ppm. The higher
chemical shift of this molecule due to its position is closer to
the stronger electronegativity oxygen atom; so, proton will be
decrease the electron density around it [10]. The signal range
of δH 7.4-8.7 ppm were indicated the H atom for pyridine ring.
For methylene linker, the signal of proton appears at δH 4.5
ppm.The 13C NMR spectrum showed the carbon resonance
for the –CH2 peaks at δc 9 ppm. The resonance observed at δc
167 ppm belongs to the C atom of C=O amide group. The
DMSO-d6 peak appears at δc 40 ppm. The carbon resonance
for C (aromatic ring) can be observed at δc 135 ppm. Lastly,
peak of –CN for pyridine was indicated at δc 46 ppm.
RESULTS AND DISCUSSION
N,N'-bis(3-Pyridylmethyl)benzene-1,4-dicarboxamide,
(L): The ligand, L was synthesised based on the literature
procedures [7]. It was reacted with terephthaloyl chloride, 3-
pyridylamine and triethylamine. Triethylamine acts as a base
[8,9] to increase the effectiveness of nucleophilic substitution
of the amines. The mechanism of the reaction is suggested in
Scheme-I.
O
Cl
Cl
H2N
NH
2O
N
Palladium complexes 1-3: Three different ratios of palla-
dium(II) chloride, complexes 1-3 have been attempted in order
to find the most efficient method for coordination polymer.All of
three palladium complexes show similar FTIR spectra (Table-2)
which represented to palladium complexes with general formula
of [Pd2(L)Cl4]. The complex based on palladium transiton-metal
currently interest because its properties suitable for catalytic
applications [11].Vouti [12] stated the interaction between ligand
and metal centre influence the chemical behaviour of a metal
ion and its properties as a metal complex.
N
O
Cl
N
NH
H2
Cl
N
N
O
O
H
N
H
N
H
N
H
TABLE-2
COMPARISON OF IR SPECTRA BETWEEN
THREE PALLADIUM COMPLEXES
N
Cl
O
O
Complex 1
(cm-1)
Complex 2
(cm-1)
Complex 3
(cm-1)
Bands
Cl
N(CH2CH3
)
3
N-H stretch
C=O
3324.80
1642.51
1537.81
1293.76
3326.12
1643.05
1537.51
1293.65
3325.67
1643.38
1537.75
1293.74
N-H bend
C-N stretch
N
Meanwhile, the special band was detected at 499.77 cm-1
for complex 3. It shows that palladium was attached on ligand
via nitrogen atom. The previous studies stated the appearance of
band at the range 509-467 cm-1 showed the confirmations of metal
coordinate on the respective ligand via nitrogen atom [13].
N
H
+
-
+
(CH2CH3)3NH Cl
H
N
N
O
Scheme-I: Mechanism of L (N,N’-bis(3-pyridylmethyl)benzene-1,4-
dicarboxamide)

Vol. 29, No. 7 (2017)
Synthesis of Pd and Ru Complexes with N,N'-bis(3-pyridylmethyl)benzene-1,4-dicarboxamide 1461
Ruthenium(III) complex (4): FTIR spectrum of complex
4 shows four absorptions for (N-H stretch), ν(C=O), ν(N-H
bend) and ν(C-N stretch) at 3430.60, 1637.56, 1542.14 and
1296.47 cm-1, respectively. As comparing the FTIR spectrum
between complex 4 and ligand, the significant changes was
observed on the vibration of (N-H stretch). In the complex,
the frequency of NH stretch was shifted from 3191.00 to
3430.60 cm-1. It shows that ruthenium was attached to ligand
at nitrogen atom.
cyclic voltammetry. The redox behaviour of complex has been
examined in acetonitrile with 1 × 10-5 M of sulphuric acid as a
supporting electrolyte. This complex exhibits metal and ligand-
centred electrochemistry in the potential range -2 to +2 V. One
complete of quasi-reversible for oxidation and reduction process
was shown. The scan rate is set at 0.5 V/s to control the time
scale of this experiment. Based on voltammogram (Fig. 1), the
oxidation process occurs at the initial potential of -2 V where
Ru2+ begins to be oxidized to the Ru3+. The current was increase
as the rate of oxidation increase at more positive potentials. Ru3+
begins to reduce to Ru2+. Then, the scan direction was reversed
at the 2.0 V where the reduction of Ru3+ to Ru2+occurs. In the
process of reduction, the layer of Ru3+ has been depleted and
accumulated the layer of Ru2+. The oxidation and reduction of
half-reaction of ruthenium complex are:
Elemental analysis: The elemental analysis of ligand (L),
Pd(II) and Ru(III) complexes also been analyzed to know the
general formula and expected structure. Table-3 shows the
elemental data of the compounds. All of the results showed
the agreement between the theoretical and experimental data,
with molecular formula suggested in Table-3.
Oxidation: Ru2+ → Ru3++ e
Reduction: Ru3++ e → Ru2+
Thermogravimetric analysis (TGA): The thermal de-
composition of Pd(II) and Ru(III) complexes have been studied.
The temperature used is the range 200-700 °C at the heating
rate of 10 °C/min. Based on the TGA results, it show that the
complexes decomposes stepwise (Table-4).
Eskelinen and co-workers [14]have reported that the oxi-
dation potential of (Ru2+/Ru3+) is positively shifted due to the
strong electron donor properties of the Cl– ligand in ruthenium
complex.
Cyclic voltammetry (CV): The oxidation and reduction
state of the metal centre in the complex 4 was analyses by using
TABLE-3
ELEMENTAL ANALYSIS AND EXPECTED RESULTS OF LIGAND (L), Pd(II) AND Ru(III) COMPLEXES
C (%)
H (%)
N (%)
Sample
Expected structure and molecular formula
Calcd.
55.04
Found
56.99
Calcd.
6.47
Found
6.33
Calcd.
12.84
Found
12.78
O
N
N
H
H
N
Ligand, L
N
O
C20H18N4O2⋅5H2O
Cl
Cl
Pd
N
O
N
H
H
N
Pd(II)
complex
34.26
35.24
2.59
2.87
7.99
7.84
N
O
Pd
Cl
Cl
[Pd2(L)Cl4] (trigonal planar)
O
N
H
H
N
Ru(III)
complex
N
28.52
28.44
3.76
2.93
6.34
6.38
N
Cl
Cl
Cl
Cl
Cl
O
Ru
Ru
H2O
Cl
H2O
(H2O)2
OH2
OH2
[Ru2(L)Cl6(H2O)2⋅4H2O] (octahedral)
TABLE-4
TGA RESULTS OF PALLADIUM AND RUTHENIUM COMPLEXES
Temp. (°C)
Decompo-
sition steps
Weight
loss (%)
Sample
Molecule decomposition
Start
210
250
300
340
300
435
475
555
End
250
300
340
420
435
475
555
655
1st
2nd
3rd
4th
1st
1.6975
17.6470
13.6012
13.2139
1.6975
One lattice water molecule
Elimination of chloro atom and evolution of CO
Two pyridine groups, C10H10N2 from L and liberation of CN gas
Elimination of C8H10N2 from L
Pd(II)
complex
Loss of two lattice water molecule along with six chloro atoms
Loss of four coordinated water
2nd
3rd
4th
5.7926
Ru(III)
complex
12.3699
11.4403
Elimination of the of two pyridine groups, C10H10N2 from L and liberation of CN gas
Loss of C8H10N2 from L

1462 Idris et al.
Asian J. Chem.
0.100x10-7
0.075x10-7
0.050x10-7
0.025x10-7
0
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The authors thank the School of Agriculture Science and
Biotechnology, Faculty of Bioresources and Food Industry,
Universiti Sultan Zainal Abidin and School of Fundamental
Science, Universiti Malaysia Terengganu and Institute Marine
Biotechnology (IMB) and the RMIC, UniSZA for facilities
and publication support.