Synthesis, reactivity, thermal, electrochemical and magnetic studies on iron(III) complexes of tetradentate Schiff base ligands

Article abstract of DOI:10.1016/j.ica.2011.12.056

Cationic iron(III) complexes of the type [FeLⁿ(H ₂O)₂]NO₃ (n = 1 or 2) were accessed from the interaction of Fe(NO₃)₃·9H₂O with [N₂O₂] donor Schiff base (L) in 1:1 molar ratio. The Schiff base ligands were prepared from condensation of 2-hydroxy-1- naphthaldehyde with o-phenylenediamine or ethylenediamine in 2:1 molar ratio. Reaction of the aquated complexes with neutral N-donor molecules (X) viz. imidazole, benzimidazole and pyridine led to substitution of weakly held axial aquo groups affording new mixed ligand complexes, [FeLⁿX ₂]NO₃. The compounds were characterized by elemental analyses, FT-IR, UV-Vis, solution electrical conductivity, FAB mass, ¹H and ¹³C NMR (ligands only) spectroscopy. The thermal study provided unambiguous evidence for the occurrence of coordinated water in the complexes. Room temperature magnetic susceptibility measurements are consistent with high spin octahedral iron(III) complexes. Cyclic voltammetry revealed a quasi-reversible one electron redox response (ΔE_p > 100 mV) assignable to Fe(III)/Fe(II) couple with negative half wave potential. The ground state geometries of the aquo complex, [FeL ²(H₂O)₂]NO₃ and pyridine complex, [FeL²(Py)₂]NO₃ were ascertained by density functional theory using dmol3 program with BLYP functional.

Full text of DOI:10.1016/j.ica.2011.12.056

Inorganica Chimica Acta 387 (2012) 86–92
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, reactivity, thermal, electrochemical and magnetic studies on iron(III)
complexes of tetradentate Schiff base ligands
b
a
Chira R. Bhattacharjee a, , Pankaj Goswami , Paritosh Mondal
⇑
a Department of Chemistry, Assam University, Silchar 788011, Assam, India
b Department of Chemistry, Silchar Polytechnic, Silchar 788015, Assam, India
a r t i c l e i n f o
a b s t r a c t
Cationic iron(III) complexes of the type [FeLn(H2O)2]NO3 (n = 1 or 2) were accessed from the interaction of
Fe(NO3)3ꢀ9H2O with [N2O2] donor Schiff base (L) in 1:1 molar ratio. The Schiff base ligands were prepared
from condensation of 2-hydroxy-1-naphthaldehyde with o-phenylenediamine or ethylenediamine in 2:1
molar ratio. Reaction of the aquated complexes with neutral N-donor molecules (X) viz. imidazole, benz-
imidazole and pyridine led to substitution of weakly held axial aquo groups affording new mixed ligand
complexes, [FeLnX2]NO3. The compounds were characterized by elemental analyses, FT-IR, UV–Vis, solu-
tion electrical conductivity, FAB mass, 1H and 13C NMR (ligands only) spectroscopy. The thermal study
provided unambiguous evidence for the occurrence of coordinated water in the complexes. Room tem-
perature magnetic susceptibility measurements are consistent with high spin octahedral iron(III) com-
Article history:
Received 24 September 2011
Received in revised form 22 December 2011
Accepted 29 December 2011
Available online 9 January 2012
Keywords:
Schiff base
2-Hydroxy-1-naphthaldehyde
Ethylenediamine
o-Phenylenediamine
Iron(III) complexes
DFT
plexes. Cyclic voltammetry revealed a quasi-reversible one electron redox response (DEp > 100 mV)
assignable to Fe(III)/Fe(II) couple with negative half wave potential. The ground state geometries of the
aquo complex, [FeL2(H2O)2]NO3 and pyridine complex, [FeL2(Py)2]NO3 were ascertained by density func-
tional theory using DMOL3 program with BLYP functional.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
have been employed as efficient catalysts for the oxidation of
sulfides to sulfoxides by urea hydrogen peroxide [32].
Metal–Schiff base complexes have continued to enjoy extensive
interest owing to their structural diversity and potential applica-
tions in pharmacology and catalysis. The design, synthesis, and
characterization of iron complexes with Schiff-base ligands play
a vital role in the coordination chemistry of iron due to their
importance as biomimetic models for iron-containing enzymes
[1,2], oxidation catalysts [3–5], and molecular materials based on
temperature, pressure, or light-induced spin crossover behavior
[6–9]. Attention has been devoted in recent years to the mixed-
ligand complexes of transition metals containing nitrogen donors
[10–12] with potential applications as separation materials, cata-
lysts, precursors, models for understanding enzyme catalysis
[13–16] and interesting structures [17–19]. Mixed-ligand com-
plexes containing N, O, and/or S donors are important owing to
their antifungal, antibacterial, and anticancer activities [20]. Use
of iron–Schiff-base complexes in different catalytic reactions have
been documented [21–24]. Although a large number of metal–
[N2O2] compounds exist [25–28], reports on corresponding Fe(III)
complexes are scarce. Mostly divalent metal ions have been used
for the complexation with diprotic Schiff base ligands having
[N2O2] core [29–31]. Iron(III) tridentate Schiff-base complexes
Recently, we have reported aquated iron(III) complex of a quad-
ridentate [N2O2] donor Schiff base and its ligand (aquo) exchange
reactions with different inorganic donor anions yielding new
mixed-ligand complexes [33] and some mixed-ligand mono- and
dinuclear iron(III) and oxovanadium(IV) complexes with tridentate
[ONO] donor Schiff base ligand [34]. Substitution of weakly bound
ethanol at the axial site of iron(III) Schiff base complexes by neutral
N-donor ligands producing new mixed ligand complexes have
been reported by us very recently [35].
Accordingly we intend to report here the synthesis, thermal,
electrochemical and magnetic studies of iron(III) complexes with
the [N2O2] donor Schiff bases derived from the condensation of
2-hydroxy-1-naphthaldehyde with o-phenylenediamine or ethy-
lenediamine. Reactivity studies of the complexes with neutral
N-donor molecules viz. imidazole, benzimidazole and pyridine as
an access to new mixed ligand Schiff base complexes have also
been incorporated.
2. Experimental
2.1. Physical measurements
⇑
Microanalytical (CHN) data were obtained with a Perkin Elmer
model 240C elemental analyzer. Solid state infrared spectra were
Corresponding author. Tel.: +91 9435175671; fax: +91 3842270803.
E-mail address: crbhattacharjee@rediffmail.com (C.R. Bhattacharjee).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.12.056

C.R. Bhattacharjee et al. / Inorganica Chimica Acta 387 (2012) 86–92
87
recorded with a Perkin Elmer/spectrum BX series FT-IR spectropho-
tometer using KBr pellets in the range 4000–400 cmꢁ1. Electronic
spectra were recorded in dichloromethane solution on a Shimadzu
1600 PC UV–Vis spectrophotometer in 200–800 nm range. NMR
spectra were acquired from Bruker Advance 300 MHz FT NMR spec-
trophotometer using CDCl3 as solvent and TMS as internal standard.
FAB mass spectra were recorded on JEOL SX-102 Mass spectrome-
ter. TGA/DTA was carried out on a PYRIS DIAMOND thermal
analyzer under a dynamic flow of nitrogen (100 ml/min) and heat-
ing rate of 10 °C/min from ambient temperature to 1000 °C. Molar
conductances of the Schiff base complexes were measured on
Systronics direct reading conductivity meter type CM-82. Magnetic
susceptibilities of the complexes were measured at room tempera-
ture on a Lakeshore 7407 Vibrating Sample Magnetometer in
the range ꢁ20000 to +20000 gauss and diamagnetic corrections
were made using Pascal’s constants. Electrochemical behavior of
the complexes were examined by cyclic voltammetry at room tem-
perature in acetonitrile solution (ca. 10ꢁ3) M using TBAP as sup-
porting electrolyte under dry N2 atmosphere on a PC controlled
CHI model 660C electrochemical workstation. A Pt disk, a Pt-wire
auxiliary electrode and an aqueous SCE were used in a three elec-
trode configuration.
9.46 (s, 1H, –HC@N); 6.83–8.44 (m, 16H, phenyl proton); 13C
NMR (CDCl3, TMS, d ppm): 39.21, 39.49, 39.77, 40.04, 40.35,
118.79, 121.51, 123.30, 127.14, 127.79, 128.98, 136.25, 155.96,
168.48. MS (FAB, m/z): 416[M]+.
Ligand H2L2: Yield: 73%. Anal. Calc. for C24H20N2O2: C, 78.26; H,
5.43; N, 7.61. Found: C, 78.46; H, 5.62; N, 7.61%. FT-IR (KBr, cmꢁ1):
m
(C–O) = 1327, m(C@N) = 1617, m(O–H) = 3428. UV–Vis, kmax (nm) [emax
(Mꢁ1 cmꢁ1)] (CH2Cl2): 404 (11100), 350 (12800), 313 (17000),
241 (49700). MS (FAB, m/z): 368[M]+.
2.4. Synthesis of iron(III) complexes, [FeLn(H2O)2]NO3, n = 1, 2 (1 and
2)
Fe(NO3)3ꢀ9H2O (2 mmol, 0.808 g) solution in methanol (20 mL)
was added to a solution of the corresponding Schiff base H2L1
(2 mmol, 0.832 g) or H2L2 (2 mmol, 0.736 g) in 20 mL methanol
and the reaction mixture was stirred for 4 h. On cooling, dark
brown microcrystalline solid formed was filtered, washed with
cold ethanol, recrystallized from ethanol and dried in vacuum over
anhydrous CaCl2 (Scheme 2).
Complex 1: Yield: 67%. Anal. Calc. for FeC28H22N3O7: C, 59.15; H,
3.87; N, 7.39. Found: C, 58.95; H, 3.78; N, 7.68%. FT-IR (KBr, cmꢁ1):
m
(Fe–O) = 499,
m
(Fe–N) = 553,
q
wagg (H2O) = 617,
q
rock (H2O) = 853, m(C–
2.2. Materials
O) = 1338, m(N–O) (free NO3ꢁ) = 1385,
m(C@N) = 1597, m(O–H)
(H2O) = 3418. UV–Vis, kmax (nm) [emax (Mꢁ1 cmꢁ1)] (CH2Cl2): 513
(1500), 342 (8200), 248 (11800). MS (FAB, m/z): 568[M]+, 532
Solvents used were purified by standard methods described in
the literature [36,37]. Commercially available pure samples of
2-hydroxy-1-naphthaldehyde, o-phenylenediamine and ethylene-
diamine were obtained from Fluka A.G., Switzerland and used as
received. Metal salts were procured from Fisher Scientific Chemi-
cals, India and used as received.
[Mꢁ2H2O]+, 470. Km(DMSO,
X leff (B.M.): 5.94.
ꢁ1 cm2 molꢁ1): 53.4.
Complex 2: Yield: 62%. Anal. Calc. for FeC24H22N3O7: C, 55.38; H,
4.23; N, 8.07. Found: C, 55.24; H, 4.38; N, 8.18%. FT-IR (KBr, cmꢁ1):
m
(Fe–O) = 515,
m
(Fe–N) = 565,
q
wagg (H2O) = 604,
qrock (H2O) = 869, m(C–
O) = 1339, m(N–O) (free NO3ꢁ) = 1384,
m(C@N) = 1605, m(O–H)
(H2O) = 3434. UV–Vis, kmax (nm) [emax (Mꢁ1 cmꢁ1)] (CH2Cl2): 517
(400), 473 (420), 359 (8130), 319 (12060), 244 (21110). MS
(FAB, m/z): 520[M]+, 484 [Mꢁ2H2O]+, 422. Km (DMSO,
2.3. Synthesis of Schiff base ligands (H2L1 and H2L2)
ꢁ1 cm2 molꢁ1): 51.8. leff (B.M.): 5.91.
The Schiff base ligands were synthesized by refluxing methano-
lic solution of o-phenylenediamine (10 mmol, 1.08 g) or ethylene-
diamine (10 mmol, 0.60 g) with 2-hydroxy-1-naphthaldehyde
(20 mmol, 3.44 g) in 30 mL methanol in presence of few drops of
acetic acid. On cooling, the orange (H2L1) or yellow (H2L2) crystals
formed were filtered and washed with ether. Recrystallization
from ethanol afforded pure Schiff bases (Scheme 1).
X
2.5. Reactivity studies
The complex, [FeLn(H2O)2]NO3 (1 mmol) was dissolved in etha-
nol (20 mL) and was added to an ethanolic solution (20 mL) of
imidazole, benzimidazole or pyridine (2 mmol) separately. The
reaction mixture was stirred on a water bath for 45 min. The
resulting brown micro crystalline solid was filtered, washed with
cold ethanol, recrystallized from methanol-dichloromethane and
dried in vacuum over anhydrous CaCl2 (Scheme 3).
Ligand H2L1: Yield: 78%. Anal. Calc. for C28H20N2O2: C, 80.76; H,
4.81; N, 6.73. Found: C, 80.24; H, 4.78; N, 6.38%. FT-IR (KBr, cmꢁ1):
m
(C–O) = 1319, m(C@N) = 1629, m(O–H) = 3428. UV–Vis, kmax (nm) [emax
(Mꢁ1 cmꢁ1)] (CH2Cl2): 454 (11320), 376 (18700), 322 (17820),
244 (43580). 1H NMR (CDCl3, TMS, d ppm): 15.05 (s, 1H, –OH);
H
H
H
C
O
MeOH, H+
reflux, 3h
C
N
N
C
+
OH
OH
HO
H2N
NH2
H2L1
2-Hydroxy-
o-Phenylenediamine
1-naphthaldehyde
H
H
H2C CH2
H
C
O
MeOH, H+
reflux, 3h
C
N
N
C
H2C
H2N
CH2
NH2
+
OH
OH
HO
Ethylenediamine
2-Hydroxy-
1-naphthaldehyde
H2L2
Scheme 1. Synthesis of Schiff base ligands.

88
C.R. Bhattacharjee et al. / Inorganica Chimica Acta 387 (2012) 86–92
+
H
H
H
H
OH2
C
N
O
N C
C
N
N C
MeOH
NO3
Fe
+
+
Fe(NO3).9H2O
stirred,
O
OH HO
4h
OH2
H2L1
[Fe(L1)(H2O)2]NO3 (1)
+
OH2
H
H2C CH2
N
H
H
H
C
N C
C
N
O
N
C
MeOH
Fe(NO3).9H2O
NO3
Fe
stirred,
OH HO
O
4h
OH2
Scheme 2. Synthesis of complexes.
NH
N
[Fe(Ln)(Im)2]NO3
+
EtOH, Stirr, w.b. 40 min
OH2
(n=1; 3 or n=2; 4)
H
N
H
H
C
N
O
N
O
C
[Fe(Ln)(BIm)2]NO3
N
NO3
Fe
EtOH, Stirr, w.b. 40 min
(n=1; 5 or n=2; 6)
OH2
N
[Fe(Ln)(Py)2]NO3
[Fe(Ln)(H2O)2]NO3
EtOH, Stirr, w.b. 40 min
(n=1; 7 or n=2; 8)
(n=1 or 2) Scheme 3. Reactivity of the complexes, 1 and 2.
bands at ca. 610 and 860 cmꢁ1 attributable to wagging and rocking
3. Results and discussion
modes of coordinated water, respectively [40]. A strong band
around 1385 cmꢁ1 assignable to
nated nitrate [41].
mN–O(asy) is typical of uncoordi-
The ligands and complexes including those accessed through
reactivity studies, are stable to air and moisture. Though ionic in
character, the compounds are soluble in dichloromethane, chloro-
form as well as in acetonitrile, DMF, DMSO and ethanol. We
presume that such solubility behavior arises due to higher hydrocar-
bon content (>75%) of the compounds. The Schiff base ligand H2L2,
however, was very poorly soluble in these solvents. The analytical
data are in good agreement with the proposed formulae of the Schiff
base ligands and their complexes. Two molecules of water were
found to coordinate to the metal center in the complexes. Efforts
to obtain diffraction quality single crystal by using slow evaporation
in different solvents, solvent diffusion method or replacing the
counter anion by BF4ꢁ or ClO4ꢁ did not prove successful.
3.2. UV–Vis spectra
The electronic spectra of the ligands and the complexes recorded
in dichloromethane exhibited high intensity bands in the range
244–359 nm attributed to intra-ligand
tions [42]. Very low intensity bands in the range 473–517 nm in
the complexes are anticipated to arise from partly allowed d–d
transition (6A1 ? excited states) confirming the occurrence of high
spin octahedral Fe(III) center [43].
p ?
p⁄ and n ? p⁄ transi-
3.3. NMR spectra
3.1. Infrared spectra
The NMR spectra of Schiff base ligand H2L1 were recorded in
CDCl3 at room temperature. The 1H NMR spectral data (vide infra)
of the ligand H2L1 showed a sharp singlet at 9.46 ppm assignable to
protons of the azomethine group (–CH@N–). Multiplet in the range
6.83–8.44 ppm is due to protons of the benzene ring. A sharp sin-
glet in the downfield region at 15.05 ppm is attributed to hydroxyl
protons. The 13C NMR spectra of the ligand is concordant with
different types of magnetically non-equivalent carbons. The peak
at 168.48 ppm is due to azomethine carbon (–CH@N–). NMR spec-
tra of the ligand H2L2 could not be recorded due to very poor
solubility of the compound in CDCl3 as well as DMSO.
The free ligands showed stretching modes attributed to C@N,
C–O and O–H at ca. 1620, 1320 and 3428 cmꢁ1, respectively.
On complexation, the C@N band shifts to lower wave number, indi-
cating coordination through the azomethine nitrogen [38]. The
participation of phenolic oxygen and azomethine nitrogen in the
complexes is further supported by prominent IR peaks for
and
(M–N) in the ranges 499–515 and 553–565 cmꢁ1, respectively
[39]. Presence of coordinated water in the complexes were con-
firmed by a broad band at ca. 3425 cmꢁ1 for
(O–H) with two weak
m(M–O)
m
m

C.R. Bhattacharjee et al. / Inorganica Chimica Acta 387 (2012) 86–92
89
Table 1
TGA data of the complex 2.
Complex
TG plateau (°C)
DTG (°C)
Mass loss (%)
Expl.
Process
Calc.
[Fe(L2)(H2O)2]NO3
135–164
164–252
252–664
147
244
643
6.88
11.87
28.75
6.92
11.92
–
loss of two molecules of coordinated water
loss of NO3
partial decomposition of the ligand
Table 2
DTA data of the complex 2.
Complex
Temperature
range (°C)
DTA
peak
(°C)
D
H (J/g)
Process
[Fe(L2)(H2O)2]NO3 100–185
226–287
150 exo
166.28
64.25
partial
decomposition
partial
254 exo
decomposition
Fig. 2. Cyclic voltammogram of the complex [Fe(L2)(H2O)2]NO3.
plexes. Further the peak observed at m/z 470 and 422 for the iron
(III) complexes (1 and 2) is attributed to the species [Fe(L1)]+ and
ꢁ
[Fe(L2)]+, respectively, arising from the loss of NO3 counter ion.
Thus the mass spectrometric fragmentation patterns are consistent
with the proposed formulae of the aquated complexes 1 and 2.
3.5. Thermal study
Fig. 1. Magnetization vs. magnetic field curve of the complex [Fe(L2)(H2O)2]NO3.
Thermal analysis of one of the complexes, [Fe(L2)(H2O)2]NO3 was
carried out by TG and DTA technique as a representative case.
Thermal data of the complexes are presented in Tables 1 and 2.
The complex underwent three-step decomposition. The first step
(135–164 °C) with DTG peak at 147 °C showed a weight loss of
6.88% that corresponds to the loss of two molecules of coordinated
water. The second (164–252 °C) and the third step (242–664 °C)
with DTG. peak at 244 and 643 °C, respectively, corresponds to loss
of nitrate ion and partial decomposition of the ligand moiety.
The exothermic changes in the temperature ranges 100–185
and 226–287 °C with DTA peak at 150 and 254 °C, respectively, is
related to the decomposition of the ligand molecule.
Table 3
Electrochemical data of complexes 1 and 2.
a
c
Compounds
Ep (V)
Ep (V)
D
Ep (V)
E1/2 (V)
[Fe(L1)(H2O)2]NO3
[Fe(L2)(H2O)2]NO3
ꢁ0.404
ꢁ0.326
ꢁ0.763
ꢁ0.687
0.359
0.361
ꢁ0.583
ꢁ0.506
3.4. Mass spectra
The mass spectra of the compounds were recorded in FAB ion-
ization mode. The molecular ion peak of the ligands H2L1and H2L2
at m/z 416 and 368, respectively, and other fragments observed
were in good agreement with the proposed formula. The molecular
formula [Fe(L1)(H2O)2]NO3 and [Fe(L2)(H2O)2]NO3 suggested for
the complexes were confirmed by the observed molecular ion peak
in the FAB mass spectra at m/z 568 and 520, respectively. The first
fragmentation step for the complexes correspond to the loss of
water molecules resulting in formation of the fragment ions
{[Fe(L1)]NO3}+ and {[Fe(L2)]NO3}+ at m/z 532 and 484, respectively
corroborating the occurrence of coordinated water in the com-
3.6. Molar conductance
The solution electrical molar conductance of the complexes
[Fe(L1)(H2O)2]NO3 and [Fe(L2)(H2O)2]NO3 in DMSO (10ꢁ3 M) were
53.4 and 51.8
X
ꢁ1 cm2 molꢁ1, respectively, suggesting 1:1 electro-
lytic nature of the complexes [44].
3.7. Magnetic susceptibility
The magnetization versus magnetic field variation were exam-
ined in the range ꢁ20000 to +20000 Gauss and the hysteresis

90
C.R. Bhattacharjee et al. / Inorganica Chimica Acta 387 (2012) 86–92
Table 4
Analytical data and physical properties of complexes 3–8.
Complexes
Color
Yield (%)
Elemental analysisa (%)
K
(X
ꢁ1 cm2 molꢁ1
)
leff (B.M.)
C
H
N
[Fe(L1)(Im)2]NO3 (3)
[Fe(L2)(Im)2]NO3 (4)
[Fe(L1)(BIm)2]NO3 (5)
[Fe(L2)(BIm)2]NO3 (6)
[Fe(L1)(Py)2]NO3 (7)
[Fe(L2)(Py)2]NO3 (8)
brown
brown
brown
brown
pale brown
pale brown
62
60
58
55
63
61
61.35(61.08)
58.29(58.06)
65.39(65.63)
63.23(63.33)
65.85(66.09)
63.74(63.55)
4.05(3.89)
4.01(4.19)
3.81(3.91)
4.30(4.17)
4.17(4.06)
4.53(4.36)
14.41(14.67)
15.98(15.81)
12.90(12.76)
13.49(13.61)
9.98(10.14)
10.71(10.90)
52.8
53.1
55.2
50.9
54.7
57.5
5.88
5.83
5.94
5.92
5.88
5.90
a
Calculated values are given in parenthesis.
Table 5
FT-IR (KBr, cmꢁ1), UV–Vis, kmax (nm) [emax (Mꢁ1 cmꢁ1)] and mass spectral data of complexes 3–8.
Complexes
mN–H
(Im/
BIm)
mC–H
(Py)
mC@N mFe– mFe– Ring modes of
coordinated (Im/BIm/Py)
d–d band
CT band
Mass
peak (m/
z)
N
O
[Fe(L1)(Im)2]NO3 (3)
[Fe(L2)(Im)2]NO3 (4)
3410
3417
–
–
1610 553 506 1540, 1508, 1460, 1342
1612 560 510 1541, 1505, 1435, 1337
503 (890)
519 (860)
346 (5660), 317 (5500), 244 (12620)
310 (23100), 257 (27000), 237
(26800)
361 (9100), 337 (11600), 309 (12400), 768
257 (24200)
340 (13510), 306 (12200), 318
(11900), 295 (10080)
380 (5560), 340 (8700), 320 (6900),
250 (17800), 235 (20200)
668
620
[Fe(L1)(BIm)2]NO3
3414
–
1612 555 493 1510, 1480, 1455, 1441,
495 (700)
508 (770)
498 (980)
496 (840)
(5)
1427
[Fe(L2)(BIm)2]NO3(6) 3403
–
1615 556 502 1522, 1482, 1464,1440,
1422
1610 565 503 1570, 1436, 637, 473
720
690
642
[Fe(L1)(Py)2]NO3 (7)
[Fe(L2)(Py)2]NO3 (8)
–
–
3040
3050
1615 564 512 1576, 1410, 643, 478
340 (6100), 320 (5700), 290 (5530),
257 (20700), 234 (19840)
Fig. 3. DFT (BLYP/DNP) optimized geometry of the complex [Fe(L2)(H2O)2]+.
Fig. 4. DFT (BLYP/DNP) optimized geometry of the complex [Fe(L2)(Py)2]+.

C.R. Bhattacharjee et al. / Inorganica Chimica Acta 387 (2012) 86–92
91
Table 6
Structurally significant geometrical parameters of complexes 1 and 8 as computed from DFT.
Bond distances (Å)
Bond type
Bond angles (°)
[Fe(L2)(H2O)2]+
[Fe(L2)(Py)2]+
Bond type
[Fe(L2)(H2O)2]+
[Fe(L2)(Py)2]+
Fe(1)–N(1)
Fe(1)–N(2)
Fe(1)–O(1)
Fe(1)–O(2)
Fe(1)–O(3)
Fe(1)–O(4)
Fe(1)–N(3)
Fe(1)–N(4)
2.104
2.104
2.004
2.005
2.456
2.465
–
2.148
2.145
2.009
2.013
–
N(1)–Fe(1)–N(2)
N(1)–Fe(1)–O(1)
O(1)–Fe(1)–O(2)
O(2)–Fe(1)–N(2)
O(3)–Fe(1)–O(4)
N(3)–Fe(1)–N(4)
–
80.20
85.21
109.57
85.07
158.20
–
78.79
83.69
113.86
83.79
–
173.15
–
–
–
2.407
2.397
–
–
–
–
curve of the complex [Fe(L2)(H2O)2]NO3 is presented in Fig. 1 as a
representative case. The effective magnetic moment of the com-
plexes are then calculated from the initial slope of the hysteresis
using the relation
3.10. Quantum chemical calculations
Quantum-chemical calculations of two selected compounds viz.
[Fe(L2) (H2O)2]+ and [Fe(L2)(Py)2]+ were studied using DMOL3 soft-
ware package [48]. Generalized Gradient approximation and DNP
(Double Numerical Plus Polarization) basis set with BLYP functional
were adopted in density functional theory (DFT) calculations. The
sextet (s = 5/2) spin state was found to be energetically more stable
than the doublet (s = 1/2) state, attesting the high-spin configura-
tion of Fe3+ (d5) as is also suggested by magnetic susceptibility mea-
surements. The energy optimized structures of the complexes
(Figs. 3 and 4) and the geometrical parameters (Table 6) suggest a
distorted octahedral structure. The iron–oxygen (aquo) bond length
(ꢃ2.4 Å) in [Fe(L2)(H2O)2]+ is quite longer than the iron–oxygen
(Schiff base) bond length (ꢃ2.0 Å) validating the labile nature of
metal-aquo linkages. The geometry of the complex [Fe(L2)(H2O)2]+
remains almost unaffected upon substitution of axial aquo groups.
The HOMO and LUMO energies of the complex [Fe(L2)(H2O)2]+
p
leff ¼ 2:827 ꢂ
ð
v0m ꢂ TÞ; v0m
¼
vm
¼
vdia
;
where vdia is diamagnetic correction.
The diamagnetic corrections are calculated by summing the
contributions from the atoms, ions and bonds of the molecule
using Pascal’s constants.
The magnetic moment values of the complexes [Fe(L1)(H2O)2]-
NO3 and [Fe(L2)(H2O)2]NO3 at room temperature were found to
be 5.94 and 5.91 B.M., respectively, in conformity with octahedral
high spin (s = 5/2, d5) configuration for the complexes.
3.8. Cyclic voltammetry
are found to be ꢁ3.692 and ꢁ2.566 eV (
DE = 1.126 eV), respec-
tively, while that for the complex [Fe(L2)(Py)2]+ are ꢁ3.473 and
Electrochemical behavior of the complexes (1 and 2) were exam-
ined by cyclic voltammetry in anhydrous acetonitrile solution
(10ꢁ3 M) containing 0.1 M tetrabutyl ammonium perchlorate
(TBAP) as supporting electrolyte in the potential range 1.2 to
ꢁ1.2 V versus SCE at 100 mV sꢁ1 scan rate (Table 3). The free ligands
did not show any responses in the potential range scanned implying
their redox innocent behavior. The complexes exhibited quasi-
ꢁ2.203 eV (DE = 1.270 eV), respectively. The HOMO–LUMO energy
gap increases slightly on substitution of axial aquo groups in the
complex [Fe(L2)(H2O)2]+ reflecting relatively higher stability of
the substituted product.
reversible one electron response (DEp > 100 mV) corresponding to
Fe(III)/Fe(II) couple with half wave potential (E1/2), being negative.
A relatively low E1/2 values suggest easy redox susceptibility of
the complexes. A representative voltammogram of the complex is
displayed in Fig. 2. Our previous work on iron(III) complexes con-
taining tetradentate [N2O2] donor Schiff base ligand also showed
quasi-reversible electrochemical behavior under identical condi-
4. Conclusion
Aquated iron(III)–Schiff base complexes of the type [Fe(Ln)
(H2O)2]NO3 have been synthesized from the reaction of [N2O2]
donor tetradentate Schiff bases (L1 or L2) with Fe(NO3)3ꢀ9H2O and
characterized by spectroscopic methods. The weakly bound water
molecules at the axial coordination site of iron are readily replaced
by neutral donor molecules leading to new mixed-ligand iron(III)
complexes. Magnetic measurements and conductivity studies
support a high spin (d5) 1:1 electrolytic nature of the complexes.
The complexes revealed quasi-reversible redox behavior with peak
tions with similar
DEp values and negative half wave potential
[33]. Pertinent here is to mention that quasi-reversible electro-
chemical behavior of iron(III) complexes containing Schiff bases
are well documented [45–47]. Our recent publication also ad-
dressed quasi-reversible electrochemical nature of iron(III) com-
plexes containing [ONO] donor tridentate Schiff base ligand [35].
separation,
DEp > 100 mV. The TGA–DTA analysis data are consis-
tent with the proposed structures and provided unambiguous evi-
dence for coordinated water in the complexes. The synthetic
strategy adopted is anticipated to open up new vistas for accessing
vast array of new mixed-ligand complexes.
3.9. Reactivity of the complexes
Reaction of the iron(III) complexes (1 and 2) with neutral nitro-
gen donor molecule imidazole, benzimidazole and pyridine in 1:2
molar ratio led to substitution of weakly held axial aquo groups
affording new mixed ligand complexes (Scheme 3). Formation of
the complexes (3–8) were confirmed by elemental analysis and
spectroscopic data (Tables 4 and 5). The reactivity pattern thus
provided access to an array of new complexes suggesting that this
approach may be effectively employed involving other neutral or
anionic donor molecules to afford variety of mixed ligand iron(III)
complexes.
Acknowledgements
The authors thank to SAIF, NEHU, Shillong; SAIF, STIC, Kochi;
CIF, IIT, Guwahati and SAIF, CDRI, Lucknow, India for providing
analytical and spectral results. One of the author, Paritosh Mondal,
thanks Department of Science and Technology, New Delhi for
financial support (SR/FT/CS-86/2010).

92
C.R. Bhattacharjee et al. / Inorganica Chimica Acta 387 (2012) 86–92
[21] P.G. Cozzi, Chem. Soc. Rev. 33 (2004) 410.
Appendix A. Supplementary material
[22] S.K. Edulji, S.T. Nguyen, Organometallics 22 (2003) 3374.
[23] J.A. Miller, W. Jin, S.T. Nguyen, Angew. Chem., Int. Ed. 41 (2002) 2953.
[24] C. Celic, M. Tumer, S. Serin, Synth. React. Inorg. Met.-Org. Chem. 32 (2002)
1839.
[25] M.T. Kaczmarck, I. Pospieszna-Markiewick, W. Radecka-Paryzek, J. Incl.
Phenom. Macro. Chem. 49 (2004) 115.
[26] S. Ilhan, H. Temel, A. Kilic, E. Tas, J. Cord. Chem. 61 (2008) 1443.
[27] S. Chandra, R. Kumar, Synth. React. Inorg. Met.-Org. Chem. 35 (2005) 161.
[28] S. Ilhan, H. Temel, I. Yilmaz, A. Kilic, Trans. Met. Chem. 32 (2007) 344.
[29] S.K. Gupta, P.B. Hitchcock, Y.S. Kushwah, J. Coord. Chem. 55 (2002) 1401.
[30] C.M. Che, J.S. Huang, Coord. Chem. Rev. 242 (2003) 97.
[31] F. Marchetti, C. Pettinary, R. Pettinary, A. Cingolari, D. Leonesi, A. Lorenzotti,
Polyhrdron 18 (1999) 3041.
[32] M. Bagherzadeh, M. Amini, Inorg. Chem. Commun. 12 (2009) 21.
[33] C.R. Bhattacharjee, P. Goswami, P. Mondal, J. Coord. Chem. 63 (2010) 2002.
[34] C.R. Bhattacharjee, P. Goswami, M. Sengupta, J. Coord. Chem. 63 (2010) 3969.
[35] C.R. Bhattacharjee, P. Goswami, H.A.R. Pramanik, P.C. Paul, P. Mondal, Spec.
Chim. Acta. Part A: Mol. Biomol. Spectrosc. 78 (2011) 1408.
[36] D.D. Perrin, W.L.F. Armarego, D.R. Perrin, Purification of Laboratory Chemicals,
second ed., Pergamon Press, 1981.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.12.056.
References
[1] V.K. Subramanian, M. Ganesan, S. Rajagopal, R. Ramaraj, J. Org. Chem. 67
(2002) 1506.
[2] H. Fuijii, T. Kurahashi, M. Sugimoto, K. Oda, T. Ogura, J. Inorg. Biochem. 96
(2003) 133.
[3] R.B. Bedfort, D.W. Bruce, R.M. Frost, J.W. Goodby, M. Hird, Chem. Commun.
(2004) 2822.
[4] K.P. Bryliakov, E.P. Talsi, Angew. Chem., Int. Ed. 43 (2004) 5228.
[5] T. Katsuki, Chem. Soc. Rev. 33 (2004) 437.
[6] M.M. Bhadbhade, D. Srinivas, Polyhedron 17 (1998) 2699.
[7] S. Hayami, K. Inoue, Y. Maeda, Mol. Cryst. Liq. Cryst. 335 (1999) 573.
[8] W. Chiang, D. Vanengan, M.E. Thompson, Polyhedron 15 (1996) 2369.
[9] C.T. Brewer, G. Brewer, G.B. Jameson, P. Kamaras, L. May, M. Rapta, J. Chem.
Soc., Dalton Trans. (1995) 37.
[10] H. Olmez, F. Arslan, H. Icbudak, J. Therm. Anal. Cal. 76 (2004) 793.
[11] D. Czakis-Sulikowska, J. Radwaska-Doczekalska, A. Czylkowska, A.
Gouchowska, J. Therm. Anal. Cal. 78 (2004) 501.
[12] R. Carballo, A. Castineiras, S. Balboa, B. Covelo, J. Niclós, Polyhedron 21 (2002)
2811.
[13] J.B. Vincent, H.L. Tsai, A.G. Blackman, S. Wang, P.D.W. Boyd, K. Folting, J.C.
Huffman, E.B. Lobkovsky, D.N. Hendrickson, G. Christou, J. Am. Chem. Soc. 115
(1993) 12353.
[14] C. Kaes, A. Katz, M.W. Hosseini, Chem. Rev. 100 (2000) 3553.
[15] G. Psomas, C. Dendrinou-Samara, P. Philippakopoulos, V. Tangoulis, C.P.
Raptopoulou, E. Samaras, D.P. Kessissoglou, Inorg. Chim. Acta 272 (1998) 24.
[16] P. Losier, M.J. Zaworotko, Angew. Chem., Int. Ed. Engl. 35 (1996) 2779.
[17] R. Kruszynski, B. Kuznik, T.J. Bartczak, D. Czakis-Sulikowska, J. Coord. Chem. 58
(2005) 165.
[18] J. Li, Y. Zhang, J . Chen, L. Rui, Q. Wang, X. Wu, Polyhedron 19 (2000) 1117.
[19] J.H. Liao, S.H. Cheng, C.T. Su, Inorg. Chem. Commun. 5 (2002) 761.
[20] A.K. Saxena, J.K. Koacher, J.P. Tandon, Inorg. Nucl. Chem. Lett. 17 (1981) 229.
[37] A. Gordon, R. Ford, S. Khimika, A Handbook of Practical Data, Techniques and
References, John Wiley and Sons, Moscow, 1976.
[38] B. Chiswell, J.P. Crawford, E.J. O’reilly, Inorg. Chim. Acta 49 (1980) 223.
[39] N. Nawar, N.M. Hosny, Trans. Met. Chem. 25 (2000) 1.
[40] N. Raman, S. Ravichandran, C. Thangaraja, J. Chem. Sci. 116 (2004) 215.
[41] M.M. Abd-Elzahar, J. Chin. Chem. Soc. 48 (2001) 153.
[42] S.N. Rao, K.N. Munshi, N.N. Rao, M.M. Bhadbhade, E. Suresh, Polyhedron 18
(1999) 2491.
[43] A.B.P. Lever, Inorganic Electronic Spectroscopy, second ed., Elsevier,
Amsterdam, 1984.
[44] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[45] R. Kannappan, S. Tanase, I. Mutikainen, U. Turpeinen, J. Reedijk, Polyhedron 25
(2006) 1646.
[46] A.D. Kulkarni, S.A. Patil, P.S. Badami, Int. J. Electrochem. Sci. 4 (2009) 717.
[47] H.H. Monfared, S. Sadighian, M.A. Kamyabi, P. Meyer, J. Mol. Catal. A: Chem.
304 (2009) 139.
[48] B. Delley, J. Chem. Phys. 92 (1990) 508.