Tetradentate Schiff base ligands of 3,4-diaminobenzophenone: Synthesis, characterization and thermodynamics of complex formation with Ni(II), Cu(II) and Zn(II) metal ions

Article abstract of DOI:10.2298/JSC100104004A

Some new symmetrical diimino tetradentate Schiff base ligands were synthesized by the reaction of 3,4-diaminobenzophenone with salicylaldehyde derivatives, such as [3,4-bis(((2-hydroxy-4-methoxyphenyl)methylene)amino)- phenyl]phenylmethanone (L¹), [3,4-bis(((2-hydroxy-5-methoxyphenyl) methylene)amino)phenyl]phenylmethanone (L²), [3,4-bis(((5-bromo-2- hydroxyphenyl)methylene)amino)phenyl]phenylmethanone (L³) and [3,4-bis(((2-hydroxy-5-nitrophenyl)methylene)amino)phenyl]phenylmethanone (L⁴). Additionally, a tetradentate Schiff base ligand [3,4-bis(((2-hydroxy-3-methoxyphenyl)methylene)amino)phenyl]phenylmethanone (L⁵) was synthesized. All the Schiff bases and their Ni(II), Cu(II) and Zn(II) complexes were characterized using elemental analysis and infrared, electronic, mass and ¹H-NMR spectroscopy. The formation constants of the complexes were measured using UV-Vis spectroscopic titration at constant ionic strength 0.10 M (NaClO₄), at 25 °C in dimethylformamide (DMF) as solvent.

Full text of DOI:10.2298/JSC100104004A

J. Serb. Chem. Soc. 76 (1) 63–74 (2011)
UDC 542.913+542.9+547.571+547.551+
JSCS–4100
546.792’562’47+54–71–034:547.415.1’631.6
Original scientific paper
Tetradentate Schiff base ligands of 3,4-diaminobenzophenone:
Synthesis, characterization and thermodynamics of complex
formation with Ni(II), Cu(II) and Zn(II) metal ions
1
1
2
*
MOZAFFAR ASADI , HAJAR SEPEHRPOUR and KHOSRO MOHAMMADI
1Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454 and 2Chemistry
Department, Faculty of Sciences, Persian Gulf University, Bushehr 75169, I. R. Iran
(Received 4 January , revised 12 July 2010)
Abstract: Some new symmetrical diimino tetradentate Schiff base ligands were
synthesized by the reaction of 3,4-diaminobenzophenone with salicylaldehyde
derivatives, such as [3,4-bis(((2-hydroxy-4-methoxyphenyl)methylene)amino)-
phenyl]phenylmethanone (L1), [3,4-bis(((2-hydroxy-5-methoxyphenyl)methyl-
ene)amino)phenyl]phenylmethanone (L2), [3,4-bis(((5-bromo-2-hydroxyphe-
nyl)methylene)amino)phenyl]phenylmethanone (L3) and [3,4-bis(((2-hydroxy-
-5-nitrophenyl)methylene)amino)phenyl]phenylmethanone (L4). Additionally, a
tetradentate Schiff base ligand [3,4-bis(((2-hydroxy-3-methoxyphenyl)methyl-
ene)amino)phenyl]phenylmethanone (L5) was synthesized. All the Schiff bases
and their Ni(II), Cu(II) and Zn(II) complexes were characterized using elemen-
1
tal analysis and infrared, electronic, mass and H-NMR spectroscopy. The for-
mation constants of the complexes were measured using UV–Vis spectroscopic
titration at constant ionic strength 0.10 M (NaClO4), at 25 °C in dimethylform-
amide (DMF) as solvent.
Keywords: synthesis; tetradentate Schiff base; metal complex; diaminobenzo-
phenone; formation constant.
INTRODUCTION
Tetradentate Schiff base ligands were synthesized by the reaction of diami-
nes with the corresponding salicylaldehyde derivative. These reactions are impor-
tant due to the great number of molecules that can be generated and the well-
-known ability of these tetradentate ligands to form stable complexes with dif-
1
ferent metal cations.
The literature clearly shows that the study of Schiff base ligand systems is
2–4
linked with many of the key advances made in inorganic chemistry.
They
5
played a seminal role in the development of modern coordination chemistry. Se-
*Corresponding author. E-mail: asadi@susc.ac.ir
doi: 10.2298/JSC100104004A
63
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64
ASADI, SEPEHRPOUR and MOHAMMADI
veral metal chelates of the ONNO donor class of Schiff bases were studied as
oxygen carrier and they were found to be useful models for bioinorganic pro-
6,7
cesses. Schiff bases are effective inhibitors and could be adsorbed on the sur-
8
face of metals. Symmetric tetradentate Schiff base complexes have been exten-
9
sively used as macrocycle models. These compounds have received consider-
10–14
able attention because of their potential use as catalysts,
and their antibac-
5,15,16
17
18,19
20
terial,
antifungal, antitumour
and herbicidal activities.
The main goals of this study were the synthesis and characterization of some
new tetradentate Schiff bases and their complexation with Ni(II), Cu(II) and
Zn(II) metals. These compounds were characterized by elemental analysis, and
1
FT–IR, H-NMR, mass and UV–Vis techniques. In addition, the formation cons-
tants, K , were determined spectrophotometrically and the free energy changes,
f
ΔG , at 25 °C, were calculated for the complexes. The effects of the electronic
and steric nature of substituents on the Schiff base type ligands on the formation
constants and free energy changes resulting from complex formation were studied.
EXPERIMENTAL
Materials and instruments
The materials, 3,4-diaminobenzophenone, 3-methoxysalicylaldehyde, 4-methoxysalicyl-
aldehyde, 5-methoxysalicylaldehyde, 5-bromosalicylaldehyde, 5-nitrosalicylaldehyde, dime-
thylformamide, methanol, chloroform, nickel acetate tetrahydrate, zinc acetate dihydrate and
copper acetate monohydrate were purchased from Merck and Fluka, Germany. Spectrograde
solvents were used for the spectral measurements.
C, H, N analysis data were obtained using a Thermo Finningan Flash EA-1112 elemental
analysis instrument. Melting points were measured in capillary tubes using a Buchi 535 melt-
ing point apparatus. The infrared spectra were recorded on a Shimadzu FTIR-8300 spectro-
photometer using the KBr pellet technique. The UV–Vis spectra were obtained in DMF on a
Perkin Elmer Lambda 2-UV/Vis spectrophotometer. The 1H-NMR spectra were recorded on a
Bruker Avance DPX-250 MHz spectrometer with TMS as internal standard and the mass spe-
ctra were obtained on a Perkin-Elmer R MU-6E instrument.
Synthesis of the Schiff base ligands and their complexes
All the new tetradentate Schiff base ligands (L1–L4) were prepared by condensation of a
derivative of salicylaldehyde (2 mmol) with 3,4-diaminobenzophenone (1 mmol) by refluxing
in MeOH (30 cm3) for 2 h. The final products were analytically pure solids after recrystalli-
zation from 1:1 chloroform/methanol mixed solvent for L1, L2 and L3, and dimethyl-
formamide/methanol mixture (1:1) for L4. The products were dried at 50 °C under vacuum for
24 h. The L5 Schiff base ligand was prepared according to a previously published method.21
Ni(II), Cu(II) and Zn(II) complexes of L1, L2 and L3 were prepared by the addition of 1.5
mmol of the appropriate metal acetate hydrates dissolved in 10 cm3 of methanol to a hot mix-
ture of methanol (20 cm3) and chloroform (15 cm3) containing 1 mmol of the required Schiff
base ligand. The mixture was then refluxed for 3 h for L1, L2 and L3. The precipitated solids
were recrystallized from methanol and dried under vacuum. The Ni(II), Cu(II) and Zn(II)
complexes of L4 were prepared in a similar way but the Schiff base ligand was dissolved in a
hot mixture of methanol (15 cm3) and DMF (20 cm3). The same metal complexes of L5 were
also prepared by a similar method but dissolved in methanol at room temperature (Scheme 1).
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SCHIFF BASE LIGANDS OF 3,4-DIAMINOBENZOPHENONE
65
Scheme 1. A structural representation of the
Schiff base complexes.
Thermodynamic studies
The formation constants, Kf, were determined by UV–Vis absorption spectroscopy through
titration of a fixed concentration (3×10-5 M) of the ligands with various concentrations of the
metal ions (10-4–10-5 M) at constant ionic strength (0.1 M NaClO4) and at 25 °C. The inter-
action of NaClO4 with the ligands in dimethylformamide was negligible. The absorption mea-
surements were performed at various wavelengths, where the difference in the absorption was the
maximum after equilibrium. The formed product exhibited different absorptions from those of
the free ligand, while the metal ion solution showed no absorption at these wavelengths.
RESULTS AND DISCUSSION
The elemental analyses and some physical properties of the synthesized
ligands and their complexes are collected in Table I.
TABLE I. The analytical and the physical data of the ligands and their complexes
Empirical
formula
C29H24N2O5
Formula Yield
Found (Calcd.), %
M.p.
°C
Compound
L1
Colour
Yellow
weight
%
C
H
N
480.62
78
127 72.71 5.17 5.75
(72.49) (5.03) (5.83)
152 72.79 5.18 5.62
(72.49) (5.03) (5.83)
169 55.74 3.16 4.99
(56.08) (3.14) (4.84)
237 63.60 3.73 11.03
(63.53) (3.55) (10.98)
L2
C29H24N2O5
480.62
578.36
510.63
542.15
70
80
83
70
Yellow
Yellow
Yellow
Brown
L3
C27H18N2Br2O3
C27H18N4O7
L4
CuL1
C29H22N2O5Cu
>250 64.35 4.12 5.15
(64.26) (4.09) (5.17)
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66
ASADI, SEPEHRPOUR and MOHAMMADI
TABLE I. Continued
Found (Calcd.), %
Empirical
formula
C29H22N2O5Cu
Formula Yield
Colour
M.p.
°C
Compound
CuL2
weight
542.15
%
C
H
N
70
Brownish >250 64.21 3.95 5.12
red
Brown
(64.26) (4.09) (5.17)
>250 50.58 2.53 4.32
(50.69) (2.52) (4.38)
>250 56.65 2.84 9.85
(56.70) (2.82) (9.80)
CuL3
CuL4
CuL5
NiL1
NiL2
NiL3
NiL4
NiL5
ZnL1
ZnL2
ZnL3
ZnL4
ZnL5
C27H16N2Br2O3Cu 639.88
54
45
53
45
71
50
55
58
37
70
45
72
40
C27H16N4O7Cu
C29H22N2O5Cu
C29H22N2O5Ni
C29H22N2O5Ni
572.15
542.15
537.30
537.30
Green
Brown
>250 64.10 4.14 5.20
(64.26) (4.09 (5.17)
Brownish >250 64.71 4.18 5.04
red (64.84) (4.13) (5.21)
Brownish >250 64.53 4.02 4.90
red (64.84) (4.13) (5.21)
Brownish >250 50.80 2.45 4.44
red (51.07) (2.54) (4.41)
Brownish >250 57.25 2.72 9.62
red (57.18) (2.84) (9.76)
Brownish >250 64.62 4.23 5.11
C27H16N2Br2O3Ni 635.03
C27H16N4O7Ni
C29H22N2O5Ni
C29H22N2O5Zn
C29H22N2O5Zn
567.30
537.30
543.99
543.99
red
Yellow
(64.84) (4.13) (5.21)
>250 64.12 4.06 5.24
(64.04) (4.08) (5.15)
>250 64.14 4.10 4.29
(64.04) (4.08) (5.15)
>250 56.42 2.46 4.29
(56.51) (2.51) (4.37)
>250 62.15 2.78 9.62
(62.19) (2.81) (9.76)
Red
Orange
Yellow
Red
C27H16N2Br2O3Zn 641.72
C27H16N4O7Zn
C29H22N2O5Zn
573.99
543.99
245 64.15 4.02 4.95
(64.04) (4.08) (5.15)
Spectral characterization
1
1
H-NMR spectra. The H-NMR spectra of the compounds were obtained in
DMSO-d and CDCl at room temperature using TMS as the internal standard.
6
3
1
The H-NMR assignments of the compounds are presented in Table II. The
chemical shift observed for the OH protons in the ligands (12.27–13.88 ppm)
were not observed in any of the complexes. This confirms the bonding of the
oxygen atoms to the metal ions (C–O–M).The presence of a sharp singlet for the
–C(H)=N proton in the Schiff bases (7.99–9.15 ppm) clearly indicates that the
magnetic environments for all such protons were similar, suggesting the presence
22
of a planar ligand in these complexes. The multiplets of the aromatic protons
1
2
5
appeared within the range 6.15–8.63 ppm. In ligands L , L , L and their com-
plexes, the protons peak of O–CH appeared in 3.69–3.86 ppm region.
3
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SCHIFF BASE LIGANDS OF 3,4-DIAMINOBENZOPHENONE
67
TABLE II. 1H-NMR data of the Schiff bases and their complexes (δ / ppm)
Compounds
OH
12.27
13.37
12.75
H–C=N
Ar–H
OMe
L1a
8.63
7.99
8.61
9.01
8.14
8.95
8.46
9.15
9.15
8.91
9.08
8.25
8.96
9.04
6.45–7.77
6.96–7.77
6.92–7.76
6.82–8.25
6.31–7.80
6.82–8.50
6.77–8.10
6.53–8.52
6.53–8.50
6.15–8.16
6.63–8.25
6.63–7.97
6.73–8.63
6.40–8.21
3.81
3.79
–
L2a
L3a
L4b
13.88
–
NiL1b
NiL2b
NiL3b
NiL4b
NiL5a
ZnL1b
ZnL2b
ZnL3b
ZnL4b
ZnL5b
–
–
–
–
–
–
–
–
–
–
3.80
3.71
–
–
3.75
3.73
3.69
–
–
3.73
aCDCl3; bDMSO-d6
IR spectra. The IR spectra provided valuable information regarding the
nature of the functional groups attached to the metal atom. The main infrared
bands and their assignments are listed in Table III. The strong broad band in the
–1
IR spectra of the ligands in the range 3375–3463 cm is assigned to O–H
stretching vibrations, which is affected by the intramolecular hydrogen bond to
the azomethine group (O–H⋅⋅⋅N=C). These bands disappeared through com-
23
–1
plexation with the metal ions. The weak bands at 2823–3062 cm are related
–1
to (C–H) vibrations. The band in the region 1643–1666 cm is attributed to
(ν
). The spectra of the ligands showed two different (–C=N) bands in the
C=O
–1
region 1527–1620 cm , which were shifted to lower frequencies in the spectra
of all the complexes, indicating the involvement of the –C=N nitrogen in the
24
coordination to the metal ions.
The ring skeletal vibrations (C=C) were ob-
–1
served in the region 1427–1546 cm . The phenolic C–O stretching vibrations
appeared in the region 1188–1292 cm . The assignment of the proposed coordi-
nation sites was further supported by the appearance of bands at 489–574 cm
and 412–493 cm , which could be attributed to ν
–1
–1
–1
and ν
, respectively.
N–M
O–M
All the IR data suggest that the metal was bonded to the Schiff bases through the
25
phenolic oxygen and the imino nitrogen.
1–3
5
Electronic spectra. The electronic spectra of the free ligands L
and L
show a weak band, as a shoulder in the region of 415–485 nm, which is assigned
*
to n→π transition involving molecular orbitals of the C=N chromophore and the
26–29
4
benzene ring.
320–404 nm for L
L shows a sharp peak at 428 nm. The band in the range of
1–3
5
and L is assigned to π→π* type transition, which involves
molecular orbitals essentially localized on the C=N group and the benzene ring;
thus, the transition involves the azomethine group. This type of transition in L is
4
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68
ASADI, SEPEHRPOUR and MOHAMMADI
4
a sharp peak at 375 nm. These differences in shape and position of the band in L
are probably due to the presence of the NO chromophore in the ligand (See
2
Table IV).
TABLE III. The IR bands of the ligands and their complexes, cm-1 (s – strong, m – medium,
w – weak)
Compounds
L1
νO–H
3444 3047(w) 1647(s) 1612(s) 1546(s) 1234(m)
2927(w) 1584(s) 1508(s)
3463 3209(w) 1647(s) 1604(s) 1488(s) 1269(m)
2823(w) 1577(s) 1461(s)
3402 3047(w) 1643(s) 1620(s) 1469(s) 1276(m)
2927(w) 1554(s) 1446(s)
3382 3055(w) 1647(s) 1620(s) 1533(s) 1292(m)
2850(w) 1589(s) 1481(s)
2935(w) 1647(s) 1612(s) 1515(s) 1199(m) 516(w) 439(w)
2835(w) 1573(s) 1461(s)
2931(w) 1654(s) 1600(s) 1523(s) 1215(m) 505(w) 451(w)
2835(w) 1581(s) 1465(s)
3047(w) 1643(s) 1608(s) 1504(s) 1242(m) 516(w) 443(w)
2912(w) 1577(s) 1454(s)
2912(w) 1666(s) 1608(s) 1542(s) 1272(m) 524(w) 443(w)
3058(w) 1581(s) 1492(s)
2927(w) 1658(s) 1620(s) 1537(s) 1238(m) 520(w) 443(w)
2835(w) 1600(s) 1475(s)
2935(w) 1647(s) 1612(s) 1504(s) 1207(m) 528(w) 435(w)
2835(w) 1573(s) 1431(s)
2835(w) 1654(s) 1577(s) 1461(s) 1215(m) 509(w) 451(w)
2827(w) 1527(s) 1427(s)
3058(w) 1654(s) 1608(s) 1512(s) 1245(m) 516(w) 412(w)
2908(w) 1577(s) 1446(s)
3062(w) 1658(s) 1604(s) 1542(s) 1276(m) 516(w) 455(w)
2923(w) 1581(s) 1504(s)
3000(w) 1647(s) 1608(s) 1539(s) 1242(m) 574(w) 493(w)
2920(w) 1581(s) 1461(s)
2923(w) 1647(s) 1608(s) 1519(s) 1188(m) 509(w) 466(w)
2854(w) 1577(s) 1427(s)
2890(w) 1649(s) 1604(s) 1527(s) 1211(m) 489(w) 443(w)
2831(w) 1581(s) 1469(s)
3047(w) 1651(s) 1612(s) 1515(s) 1245(m) 547(w) 497(w)
2908(w) 1581(s) 1461(s)
2997(w) 1654(s) 1612(s) 1546(s) 1272(m) 505(w) 439(w)
2923(w) 1585(s) 1485(s)
2997(w) 1647(s) 1608(s) 1539(s) 1230(m) 501(w) 439(w)
2920(w) 1577(s) 1465(s)
νC–H
νC=O
νC=N
νC=C
νC–O
νN–M
–
νO–M
–
L2
–
–
–
–
–
–
L3
L4
CuL1
CuL2
CuL3
CuL4
CuL5
NiL1
NiL2
NiL3
NiL4
NiL5
ZnL1
ZnL2
ZnL3
ZnL4
ZnL5
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
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SCHIFF BASE LIGANDS OF 3,4-DIAMINOBENZOPHENONE
69
Shifts were observed in the visible spectra of the metal complexes when
compared with those of the corresponding free ligands. The formation of the me-
tal–nitrogen bond stabilizes the electron pair on the nitrogen atom, i.e., the
energy of the non-bonding orbital is lowered and the transition occurs at a lower
wavelength. This band is obscured by a strong band which can be assigned to
30,31
π→π* type transitions involving the metal–ligand bonds.
The d–d band was
not observed, as it was masked by the metal to ligand charge transfer (MLCT)
band.
TABLE IV. The electronic spectral data of the Schiff bases and their complexes (nm) in DMF
Compounds
π–π*
n–π*
450(sh)
485(sh)
477(sh)
428
415(sh)
Charge transfer transition
L1
393
338
344
375
331
390
390
386
323
395
395
382
330
330
330
404
380
320
325
371
–
–
–
–
L2
L3
L4
L5
–
NiL1
NiL2
NiL3
NiL4
NiL5
ZnL1
ZnL2
ZnL3
ZnL4
ZnL5
CuL1
CuL2
CuL3
CuL4
CuL5
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
452
478
484
392
467
454
481
420
390
431
462
494
427
390
475
In the compounds, bands of the ligands were observed in the 331–393 nm
and 415–485 nm ranges, as shoulders. In their complexes, the bands were shifted
to lower energy. The spectral changes were observed in DMF solution when up
2
to 3.5 equivalents of Ni(OAc) were added relative to L . In the absence of the
2
2
metal ion, the L solution showed absorption bands at 338 and 485 nm as
shoulders. As the metal ion solution was added, the signals of L decreased and
those of the new complex, NiL , at 390 and 478 nm increased in intensity with
2
2
isosbestic points at 370 and 700 nm. After the addition of 3.5 equivalents of the
2
metal ion, the solution showed only the signals for NiL . The same was valid for
the other systems.
The electronic spectra of the complexes formed during the titration were the
same as those of the separately synthesized complexes. The UV–Vis spectra of
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70
ASADI, SEPEHRPOUR and MOHAMMADI
2
2
2
L , NiL from the titration and the synthesized NiL product are shown in Fig. 1.
The data show that the synthesized complex and the product of the titration are
same. The results were same for the other systems.
Fig. 1. UV–Vis spectra of the ligand L2 (1), the end point of the titration of the ligand
with Ni2+ (2), and the synthesized NiL2 (3) in DMF.
Mass spectra. The mass spectra of the ligands and complexes show intense
+
+
molecular ion peaks m/z M /(M+H) . In addition to these peaks, they show some
peaks due to elimination of phenyl or benzyl derivative species from the molecu-
lar ion. The mass spectra of the compounds also show some prominent peaks
+
+
+
+
+
corresponding to m/z (M–Ar) , (M–Ar–CH) , (Ar) , (Ar–CH) and (PhCO) (Tab-
2
le V). The fragmentation of the mass spectrum of the L ligand is: 480 (M+, 9.9),
344 (C H COC H N=CHC H OHOMeN, 70.6), 239 (C H N=CHC H OHOMeN,
6
5
6
3
6
3
6
3
6 3
4.6), 221 (C H COC H N=CHN, 5.0), 180 (C H COC H , 3.2), 123
6
5
6
3
6
5
6 3
(C H OHOMe, 11.5), 105 (C H CO, 95.0), 77(C H , 100.0) (Table V).
6
3
6
5
6 5
The formation constants
Complexes were obtained from the reaction of the metals with the Schiff
base donors according to Eq. (1):
x
x
H L + M(OAc)
[ML ] + 2HOAc
(1)
2
2
The formation constants were determined by UV–Vis absorption spectros-
copy through titration of the ligands with various concentrations of the metal ions
at a constant ionic strength 0.1 M (NaClO ) at 25 °C. The complex formation
4
32
constants, K , were calculated using the SQUAD computer program, designed
f
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SCHIFF BASE LIGANDS OF 3,4-DIAMINOBENZOPHENONE
71
to calculate the best values for formation constants by employing a non-linear,
least squares approach. The free energy change ΔG of the formed complexes
were calculated from ΔG = –RT ln K at 25 °C, where K is the complex for-
f
f
mation constant, R the gas constant and T the thermodynamic temperature (Table
VI).
TABLE V. The mass spectra of the ligands and their complexes
Compound
m/z
L1
480
480
578
510
537
537
635
567
537
543
543
641
573
543
542
542
639
572
542
344
344
392
360
401
403
448
418
400
407
406
456
424
407
406
408
453
406
343
239
240
283
253
343
338
393
345
295
343
347
393
344
342
343
302
392
345
330
221
181
220
178
298
280
345
240
238
302
301
351
318
239
303
179
377
301
180
180
105
185
105
239
236
285
183
179
238
243
287
240
180
185
122
169
183
124
105
77
77
L2
L3
124
77
105
57
77
L4
NiL1
NiL2
NiL3
NiL4
NiL5
ZnL1
ZnL2
ZnL3
ZnL4
ZnL5
CuL1
CuL2
CuL3
CuL4
CuL5
183
180
169
137
124
185
180
170
177
123
123
105
105
105
105
122
124
77
105
105
105
77
105
137
77
105
77
105
105
77
77
77
77
77
105
77
77
77
77
77
TABLE VI. The formation constants, log Kf, and the thermodynamic free energy for the com-
plexes of the ligands with the metal ions at 25 °C, in DMF and at I = 0.1 mol dm-3 (NaClO4)
Cu2+
Ni2+
Zn2+
Ligand
log Kf
ΔG / kJ mol-1
log Kf ΔG / kJ mol-1
log Kf ΔG / kJ mol-1
L1
L2
L3
L4
L5
5.42(0.48) –30.92(1.11) 5.63(0.04) –32.10(0.32) 5.33(0.24) –30.39(0.12)
5.84(0.43) –33.30(0.76) 6.13(0.22) –34.96(0.19) 5.11(0.30) –29.14(0.74)
5.31(0.26) –30.28(0.19) 5.41(0.04) –30.85(0.37) 4.14(0.02) –23.61(0.44)
3.67(0.01) –20.93(0.07) 4.85(0.01) –27.66(0.44) 2.42(0.63) –13.80(1.31)
5.60(0.30) –31.93(0.09) 5.79(0.06) –33.02(0.19) 5.20(0.32) –29.65(0.74)
The metal effect
The trend of the complex formation of the metal ions with a given ligand is
2+
2+
2+
as follows: Ni > Cu > Zn .
The crystal field stabilization energy, CFSE, affects the stability of the pro-
2+
duced complexes. Ni has the highest CFSE; hence, it has the highest formation
constant. The coordination around nickel is essentially square planar with a small
33
34
tetrahedral distortion. The molecular structure of [Ni(salen)], [Ni(cd Clsalen)]
5
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2011 Copyright (CC) SCS

72
ASADI, SEPEHRPOUR and MOHAMMADI
35
and [Ni(cdsalen)] were determined previously and may be compared with the
1–5
structure of the present complexes NiL
.
10
Zn(II), with a d configuration, has more potency to take a tetrahedral con-
figuration; hence, it has the smallest formation constant, while Cu(II), with a d
9
configuration, tends to have a distorted square planar geometry because of the
36
Jahn–Teller effect (Table VI).
The electronic effect of para-substituted Schiff base ligands
For studying the electronic effect of para substitution on the Schiff base
ligands, some different substituents were used. In the para-substituted Schiff
base ligands, the formation constants vary as could be expected according to the
electronic effect of the substituents at the para position. Thus, the formation
constants decrease according to the sequence OMe > Br > NO . An electron-with-
2
drawing functional group, such as NO , makes the Schiff base a poorer donor
2
ligand and decreases the formation constant, while an electron-donor group, such
as OMe, increases the formation constant. Therefore, the ligands having Br and
3
4
NO groups, (L ) and (L ), respectively, have the smallest formation constants,
2
37,38
while the ligands with an OMe group have the highest (Table VI).
The effect of the position of the methoxy substituent on the Schiff base
The results show the following trend of complex formation of either nick-
2
5
el(II) and copper(II) with the Schiff bases (Table VI): 5-OMe (L ) > 3-OMe (L ) >
1
> 4-OMe (L ).
2
In the case of L , the methoxy group was situated in the para position to the
phenolic oxygen of the N O backbone, which can release an electron directly to
2
2
1
5
the phenyl ring compared with that of the meta and ortho positions in L and L ,
39
respectively.
2+
The trend of the formation constant for the Zn complexes is as follows: 5-
-OMe (L ) < 3-OMe (L ) < 4-OMe (L ).
It seems, due to the preference of Zn for a tetrahedral geometry, the steric
factor predominates over the electronic factor.
2
5
1
2+
CONCLUSIONS
Some new symmetrical di-imino tetradentate Schiff base ligands and their
complexes with Ni(II), Cu(II) and Zn(II) were synthesized and characterized. The
thermodynamic formation constants, K , were determined spectrophotometrically
f
at 25 °C. By considering the formation constants and the free energy changes, the
following conclusions were drawn.
The complex formation constant for Ni(II) was higher than Cu(II) and Zn(II)
has the smallest formation constant: Ni(II) > Cu(II) > Zn(II).
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2011 Copyright (CC) SCS

SCHIFF BASE LIGANDS OF 3,4-DIAMINOBENZOPHENONE
73
An electron-donor group increases the formation constant, while an electron-
-withdrawing functional group decreases it. The trend of the formation constant
1,2,5
3
4
is as follows: ML
> ML > ML , M = Cu(II), Zn(II) and Ni(II).
Acknowledgements. We are grateful to the Shiraz University Research Council for their
financial support.
И З В О Д
СИНТЕЗА ТЕТРАДЕНТАТНИХ ЛИГАНАДА ТИПА ШИФОВИХ БАЗА ПОЛАЗЕЋИ ОД
3,4-ДИАМИНОБЕНЗОФЕНОНА: СИНТЕЗА, КАРАКТЕРИЗАЦИЈА И ТЕРМОДИНА-
МИЧКЕ КОНСТАНТЕ ФОРМИРАЊА КОМПЛЕКСА Ni(II), Cu(II) И Zn(II)
MOZAFFAR ASADI1, HAJAR SEPEHRPOUR1 и KHOSRO MOHAMMADI2
1Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454 и 2Chemistry Department,
Faculty of Sciences, Persian Gulf University, Bushehr 75169, I. R.. Iran
У реакцији између 3,4-диаминобензофенона и деривата салицилалдехида, као што су
[3,4-бис(((2-хидрокси-4-метоксифенил)метилен)амино)фенил]фенилметанон (L1), [3,4-бис-
(((2-хидрокси-5-метоксифенил)метилен)амино)фенил]фенилметанон (L2), [3,4-бис(((5-бро-
мо-2-хидроксифенил)метилен)амино)фенил]фенилметанон (L3) и [3,4-бис(((2-хидрокси-5-
-нитрофенил)метилен)амино)фенил]фенилметанон (L4), синтетисани су нови тетрадентатни
лиганди типа Шифових база. Поред тога, у овом раду описана је синтеза тетрадентатног
лиганда [3,4-бис(((2-хидрокси-3-метоксифенил)метилен)амино)фенил]фенилметанона (L5),
који такође припада типу Шифових база. Добијени лиганди су употребљени за синтезу одго-
варајућих Ni(II), Cu(II) и Zn(II) комплекса. За карактеризацију ових комплекса употребљени
су елементарна микроанализа, инфра-црвени, електронски, масени спектри. Поред тога, за
1
карактеризацију комплекса, осим за Cu(II) комплексе, употребљени су и њихови H-NMR
спектри. Дате су вредности за константе грађења комплекса, као и вредности за неке термо-
динамичке параметре, који су одређени помоћу UV–Vis спектрофотометрије у 0,10 M NaClO4
на 25 °C у диметилформамиду (DMF) као растварачу.
(Примљено 4. јануара, ревидирано 12. јула 2010)
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