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M.Kr. Paul et al. / Journal of Molecular Structure 1081 (2015) 316–328
The synthetic routes used for the preparation of ligands and their
Zn(II) complexes
appropriate amount of 4-n-alkyloxy-2-hydroxybenzaldehyde. The
yield of Schiff base ligand, spectroscopic and analytical data are
presented below:
The synthetic route for the preparation of salicylaldiminato
Schiff base ligands and their zinc(II) complexes are shown in
scheme 1.
2,3-Bis-((E)-(4-(n-dodecyloxy)-2-hydroxybenzylidene)amino)-
maleonitrile (2a): Yellow solid. Yield: 0.68 g (84%). IR (mmax in
cmꢁ1, KBr): 3199 m(OAH) H-bonded, 2920, 2850 m(CAH) of CH3 and
CH2, 2360 m(CAN) cyano, 1629 m(C@N) imine, 1587, 1508, m(C@C) aro-
Synthesis of 4-n-octadecyloxy-2-hydroxybenzaldehyde (1c)
matic, 1261m(CAO).
1H NMR (CDCl3, 300 MHz): (dH) 12.01 (s, 2H,
4-n-alkoxy-2-hydroxybenzaldehydes were prepared by follow-
ing the earlier reported procedure [45]. 2,4-Dihydroxybenzalde-
hyde (2.1 g, 14.5 mmol), 1-bromooctadecane (4.9 mL, 15 mmol),
KHCO3(1.5 g, 15 mmol) and catalytic amount of KI were mixed in
dry acetone (100 mL) and the mixture was refluxed for 48 h. It
was then filtered hot to remove the insoluble solid. The warm solu-
tion was neutralized by adding dilute HCl and extracted twice with
CHCl3 (100 mL). The combined extracts were concentrated to give
a purple solid. The product was purified by column chromatogra-
phy using silica gel (60–120 mesh) eluting with a mixture of chlo-
roform and hexane (v/v 1:1) followed by evaporation of solvent to
yield white solid. Yield: 4.4 g (78%). IR (mmax in cmꢁ1, KBr): 3449
AOH), 8.64 (s, 2H, ACH@N), 7.26 (d, 2H, J = 8.7 Hz, ArH), 6.49 (d,
4H, J = 8.7 Hz, ArH), 3.98 (t, 4H, J = 8.4 Hz, AOCH2A), 1.72–1.21
(m, 40H, A(CH2)10A), 0.83 (t, 6H, J = 6.6 Hz, ACH3). Molar conduc-
tivity (Km, in DMF): 2.5 ohmꢁ1 cm2 molꢁ1. Elemental analysis cal-
culated for C42H60N4O4: C, 73.65; H, 8.83; N, 8.18 %, Found: C,
73.69; H, 8.91; N, 8.22%.
2,3-Bis-((E)-(4-(n-hexadecyloxy)-2-hydroxybenzylidene)amino)-
maleonitrile (2b): Yellow solid. Yield: 0.60 g (73%). IR (mmax in cmꢁ1
,
KBr): 3199 m(OAH) H-bonded, 2920, 2850 m(CAH) of CH3 and CH2,
2360 m(CAN) cyano, 1629 m(C@N) imine, 1587, 1508, m(C@C) aromatic,
1264 m(CAO).
1H NMR (CDCl3, 300 MHz): (dH) 12.00 (s, 2H, AOH),
8.63 (s, 2H, ACH@NA), 7.27 (d, 2H, J = 9.0 Hz, ArH), 6.49 (d, 4H,
J = 9.0 Hz, ArH), 3.97 (t, 4H, J = 8.7 Hz, AOCH2A), 1.80–1.19 (m, 56H,
(
mOAH, H-bonded), 1666 (mC@O,
aldehyde); 1H NMR (CDCl3,
300 MHz): (dH)11.41 (s, 1H, AOH); 9.66 (s, 1H, ACH@O); 7.40 (d,
1H, J = 8.8 Hz, ArH); 6.51 (d, 1H, J = 8.9 Hz, ArH); 6.61 (d, 1H,
J = 8.7 Hz, ArH); 4.03 (t, 2H, J = 7.8 Hz, AOACH2A); 1.68–1.20 (m,
32H, A(CH2)16A); 0.88 (t, 3H, J = 6.6 Hz, ACH3).
A(CH2)14A), 0.89 (t, 6H, J = 6.6 Hz, ACH3). Molar conductivity (Km
in DMF): 2.4 ohmꢁ1 cm2 molꢁ1. Elemental analysis calculated for
50H76N4O4: C, 75.33; H, 9.61; N, 7.03%, Found: C, 75.39; H, 9.73; N,
,
C
7.21%.
4-n-dodecyloxy and 4-n-hexadecyloxy-2-hydroxybenzalde-
hyde (n = 12, 16) were prepared following the above procedure
with appropriate amount of 4-n-alkyl bromides. The yield of 4-n-
alkoxy-2-hydroxybenzaldehyde, spectroscopic data are presented
below.
Synthesis of complexes (3a–c)
The Zn(II) complexes (3a–3c) were prepared by the same proce-
dure using different aldehydes (4-n-dodecyloxy, 4-n-hexadecyloxy
and 4-n-octadecyloxy-2-hydroxybenzaldehyde). For example,
[2,3-((E)-4-(n-octadecyloxy)-2-hydroxybenzylideneamino)maleo-
nitrilato]Zn(II) (3c) was synthesized as follows.
4-n-dodecyloxy-2-hydroxybenzaldehyde (1a): White solid.
Yield: 3.5 g (76%). IR (mmax in cmꢁ1, KBr): 3448 (
m
OAH, H-bonded),
1668 (
m
C@O, aldehyde); 1H NMR (CDCl3, 300 MHz): (dH)11.40 (s,
A
solution of zinc acetate dihydrate, Zn(CH3COO)2ꢂ2H2O
1H, AOH); 9.67 (s, 1H, ACH@O); 7.41 (d, 1H, J = 8.8 Hz, ArH);
6.52 (d, 1H, J = 8.9 Hz, ArH); 6.60 (d, 1H, J = 8.7 Hz, ArH); 4.01 (t,
2H, J = 7.8 Hz, AOACH2A); 1.69–1.23 (m, 20H, A(CH2)10A); 0.89
(t, 3H, J = 6.6 Hz, ACH3).
(0.136 g, 1.0 mmol) dissolved in ethanol (20 mL), DAMN (0.108 g,
1.0 mmol) in 20 mL absolute ethanol and (0.780 g, 2.0 mmol) of
4-n-octadecyloxy-2-hydroxybenzaldehyde in 20 mL absolute etha-
nol was prepared separately. The solution of Zn(CH3COO)2ꢂ2H2O
was added to the DAMN solution with stirring and the reaction
mixture was refluxed for 2 h. Then, the solution of 4-n-octadecyl-
oxy-2-hydroxybenzaldehyde was added. The reaction mixture
was refluxed for 48 h at 50 °C. A red color precipitate was formed.
It was filtered hot, washed with ethanol:choloform (3:1 v/v) and
dried in vacuum. Finally, reddish brown solid was obtained. Yield:
4-n-hexadecyloxy-2-hydroxybenzaldehyde (1b): White solid.
Yield: 4.1 g (74%). IR (mmax in cmꢁ1, KBr): 3449 (
m
OAH, H-bonded),
1668 (
m
C@O, aldehyde); 1H NMR (CDCl3, 300 MHz): (dH)11.41 (s,
1H, AOH); 9.67 (s, 1H, ACH@O); 7.43 (d, 1H, J = 8.8 Hz, ArH);
6.50 (d, 1H, J = 8.9 Hz, ArH); 6.61 (d, 1H, J = 8.7 Hz, ArH); 4.03 (t,
2H, J = 7.8 Hz, AOACH2A); 1.67–1.21 (m, 28H, A(CH2)14A); 0.90
(t, 3H, J = 6.6 Hz, ACH3).
0.69 g (67%). IR (
m(CAN) cyano, 1618 m(C@N) imine, 1583, 1525, 1468 m(C@C) aromatic,
m m(CAH) of CH3, 2216
max in cmꢁ1, KBr): 2918, 2848
Synthesis of 2,3-Bis-((E)-(4-(n-octadecyloxy)-2-
hydroxybenzylidene)amino)maleonitrile (2c)
1217 m
(CAO). Molar conductivity (Km in DMF): 1.8 ohmꢁ1 cm2
molꢁ1. Elemental analysis calculated for C54H82N4O4Zn: C, 70.76;
H, 9.02; N, 6.11%, Found: C, 70.83; H, 9.18; N, 6.24%.
An ethanolic solution (20 mL) of 4-n-octadecyloxy-2-hydroxy-
benzaldehyde (0.781 g, 2 mmol) was added to an absolute etha-
nolic solution of DAMN (0.108 g, 1 mmol). The solution was
refluxed with a few drops of mild base, piperidine as catalyst for
3 h to yield the yellow Schiff base ligand (2c). The solution was fil-
tered, when it was hot to avoid the impurity of unreacted reactants
and to yield yellow precipitate of Schiff base which was washed
with cooled ethanol and then, repeatedly, recrystallized from chlo-
roform/ethanol (1:3 v/v) to give a pure compound (2c). Yield:
0.62 g (68%). IR (mmax in cmꢁ1, KBr): 3201 m(OAH) H-bonded, 2920,
2850 m(CAH) CH3 and CH2, 2312 m(C@N) cyano, 1629 m(C@N) imine,
The Zn(II) complexes of Schiff base ligands (2a and 2b) were
prepared following the above procedure. The yield of compounds,
spectroscopic and analytical data are presented below.
[2,3-((E)-4-(n-dodecyloxy)-2-hydroxybenzylideneamino)-
maleonitrilato]Zn(II) (3a): Reddish brown solid. Yield: 0.69 g (80
%). IR (mmax in cmꢁ1, KBr): 2922, 2850 m(CAH) of CH3 and CH2,
2181 m(CAN) cyano, 1618 m(C@N) imine, 1593, 1514, 1435 m(C@C)
aromatic, 1217m(CAO).
1H NMR (CDCl3, 300 MHz): (dH) 8.63(s, 2H,
ACH@NA), 7.27 (d, 2H, J = 8.4 Hz, ArH), 6.49 (d, 4H, J = 8.7 Hz,
ArH), 3.96 (t, 4H, J = 8.4 Hz, AOCH2A), 1.80–1.21 (m, 40H,
A(CH2)10A), 0.83 (t, 6H, J = 6.6 Hz, ACH3). Molar conductivity
1585, 1508, m(C@C) aromatic, 1263m(CAO)
.
1H NMR (CDCl3,
300 MHz): (dH)12.00 (s, 2H, AOH), 8.64(s, 2H, ACH@NA), 7.27 (d,
2H, J = 9.0 Hz, ArH), 6.50 (d, 4H, J = 8.7 Hz, ArH), 3.98 (t, 4H,
J = 8.4 Hz, AOCH2A), 1.78–1.19 (m, 64H, A(CH2)16-), 0.81 (t, 6H,
J = 6.6 Hz, ACH3). Molar conductivity (Km, in DMF): 3.5 ohmꢁ1
(
Km in DMF): 1.6 ohmꢁ1 cm2 molꢁ1. Elemental analysis calculated
for C42H58N4O4Zn: C, 67.41; H, 7.81; N, 7.49%, Found: C, 67.50; H,
7.88; N, 7.67%.
[2,3-((E)-4-(n-hexadecyloxy)-2-hydroxybenzylideneamino)-
maleonitrilato]Zn(II) (3b): Reddish brown solid. Yield: 0.67 g
(69%). IR (mmax in cmꢁ1, KBr): 2922, 2850 m(CAH) of CH3 and CH2,
2181 m(CAN) cyano, 1618 m(C@N) imine, 1593, 1514, 1435 m(C@C)
cm2 molꢁ1
. Elemental analysis calculated for C54H84N4O4: C,
76.01; H, 9.92; N, 6.57%, Found: C, 76.12; H, 10.09; N, 6.81%. The
compound 2a and 2b were prepared following the procedure with