Synthesis, spectral, crystallography and thermal investigations of novel Schiff base complexes of manganese (III) derived from heterocyclic β-diketone with aromatic and aliphatic diamine

Article abstract of DOI:10.1016/j.saa.2009.10.018

The Schiff base tetradentate ligands N,N-bis-(3,5-dimethyl-1-p-tolyl-1H-pyrazol-4-ylmethylene)-ethane-1,2-diamine (H₂L¹), N,N-bis-(3,5-dimethyl-1-p-sulfonyl-1H-pyrazol-4-ylmethylene)-ethane-1,2-diamine (H₂L²), N

Full text of DOI:10.1016/j.saa.2009.10.018

Spectrochimica Acta Part A 75 (2010) 235–242
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectral, crystallography and thermal investigations of novel Schiff
base complexes of manganese (III) derived from heterocyclic ␤-diketone with
aromatic and aliphatic diamine
Kiran R. Suratia,∗, B.T. Thakerb
a Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar, 388120 Anand, Gujarat, India
b Department of Chemistry, V.N.S.G. University, Surat 395 007, Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2009
Received in revised form 7 October 2009
Accepted 13 October 2009
The Schiff base tetradentate ligands N,N-bis-(3,5-dimethyl-1-p-tolyl-1H-pyrazol-4-ylmethylene)-
ethane-1,2-diamine (H2L1), N,N-bis-(3,5-dimethyl-1-p-sulfonyl-1H-pyrazol-4-ylmethylene)-ethane-
1,2-diamine (H2L2), N,N-bis-(3,5-dimethyl-1-p-tolyl-1H-pyrazol-4-ylmethylene)-benzene-1,2-diamine
(H2L3)
and
(H2L4) were prepared from the reaction between 5-oxo-3-methyl-1-p-tolyl-1H-pyrazole-
4-carbaldehyde or 4-(4-formyl-5-oxo-3-methyl-pyrazol-1-yl)-benzenesulfonic acid and
N,N-bis-(3,5-dimethyl-1-p-sulfonyl-1H-pyrazol-4-ylmethylene)-benzene-1,2-diamine
Keywords:
Manganese (III) complexes
Tetradentate Schiff base ligand
Spectroscopy
o-phenylenediamine or ethylenediamine. And these are characterized by elemental analysis, FT-
IR, 1H NMR and GC–MS. The corresponding Schiff base complexes of Mn(III) were prepared by
condensation of [Mn3(␮3-O)(OAc)6(H2O)3]·3H2O with ligands H2L1, H2L2, H2L3 and H2L4. All these
complexes have been characterized by elemental analysis, magnetic susceptibility, X-ray crystallog-
raphy, conductometry measurement, FT-IR, electronic spectra and mass (FAB) spectrometry. Thermal
behaviour of the complexes has been studied by TGA, DTA and DSC. Electronic spectra and magnetic
susceptibility measurements indicate octahedral stereochemistry of manganese (III) complexes, while
non-electrolytic behaviour complexes indicate the absence of counter ion.
Thermal behaviour
© 2009 Published by Elsevier B.V.
1. Introduction
using pyrazolone based ligand [16–19]. To gain more information
about the structure and stereochemistry of such type of complexes,
Manganese complexes have been of interest in connection with
the biological redox processes including catalytic disproportion-
ation of superoxide ion, O2 [1,2]. Metal catalysts with Schiff
a detailed investigation on a new mono- and binuclear manganese
(III) complexes with a ligand involving imine-nitrogen, phenolic
oxygen as donors has been initiated on our part [20]. Recently pyra-
zolone based compounds have been extensively reported by many
of the researchers [21,22]. Marchetti et al. have been extensively
contributed to the field of transition metal complexes with using
pyrazolone as ligands [23,24].
In view of the importance of manganese (III) compounds and
our interest in the chemistry of coordination compounds involv-
ing chelating Schiff bases [17,18], we report here the synthesis,
characterization, and reactivity of manganese (III) heterochelates
containing tetradentate Schiff base ligands with O, N, N, O, donor
set, etc.
−
base ligands were mostly used in the field of catalytic hydrogena-
tion, addition polymerization, epoxidation reaction, bionic catalytic
oxidation, etc. [3–8]. Manganese in +3 state is also very impor-
tantly found in many enzyme protein systems like conalbumin
[9], transferrin [10], avimanganin [11], concanvalin A [12], pyru-
vate carboxylase [13] and superoxide dismutase from Escherichia
coli [14], evident now a days from their spectromagnetic measure-
ments. Manganese (III) complexes with tetradentate Schiff bases
have been used for the epoxidation of olefins in the presence
of aliphatic aldehydes. Such systems were very useful and many
approaches have been tried to develop efficient, enantioselective
epoxidation of non-functional olefins [15].
2. Experimental
Our interest in this area is focused for a considerable time on
the investigation of coordination chemistry of transition metal with
The solvents were used after purification by the standard
method described in the literature [25,26]. 1-Phenyl-3-methyl-
2-pyrazoline-5-one (E-Merck); ethylenediamine (BDH); and o-
phenylenediamine (Fluka A.G., Switzerland) were used as received.
Mn(OAc)3·2H2O was prepared by the oxidation of [Mn3(␮3-
O)(OAc)6(H2O)3]·3H2O using Christensen’s method [27].
∗
Corresponding author. Tel.: +91 09904368680.
E-mail address: kiransurati@yahoo.co.in (K.R. Surati).
1386-1425/$ – see front matter © 2009 Published by Elsevier B.V.
doi:10.1016/j.saa.2009.10.018

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Elemental analyses (C, H, N) were performed at CDRI, Lucknow.
(s, 6H, phenyl–CH3); 7.21–7.98 (m, 12H, phenyl multiplet); 8.99
(s, 2H, –HC N); 10.51 (s, 2H, –OHenol); MS (EI): (Calcd. for m/z
[M]+ = 504.23) [M+1]+ = 505; IR (cm−1), ꢀmax (KBr): 3100–3600 br.
(O–H), 3051m (C–Hphenyl), 2944–2873m (C–H), 1640 (C N), 1594vs
Manganese was determined by EDTA [28] after decomposing the
complex with a mixture of 10 mL HNO3, 5 mL conc. H2SO4 and
3 mL of HClO4. Solid-state infrared spectra were recorded with a
Perkin-Elmer IR spectrophotometer using KBr pellets at SICART,
Vallabha Vidhyanagar, Anand. 1H NMR spectra were recorded with
JEOL-GSX-400 using CDCl3 as a solvent and TMS as an internal
reference at SAIF, IIT Madras, Chennai. Mass spectra (EI) were
70 eV obtained on a JEOL D-300 mass spectrometer at SAIF, IIT
Madras, Chennai. The FAB mass spectra were recorded on a JEOL
SX 102 mass spectrometer using Argon/Xenon (6 kV, 10 mA) as
the FAB gas. The accelerating voltage was 10 kV and the spectra
were recorded at room temperature with using m-nitrobenzyl alco-
hol (NBA) as matrix. Electronic spectra in the 200–800 nm range
were obtained in DMF + methanol on “SHIMADZU” UV 160A using
quartz cell of 1 cm3. Magnetic measurements were carried out at
room temperature by the Gouy method using Hg[Co(SCN)4] as cal-
ibrant at Department of Chemistry, Vallabha Vidhyanagar, Anand.
Molar conductance of the Schiff base complexes was measured
on Systronics direct reading conductivity meter type CM - 82T.
TGA/DTA was carried out on universal V3.0G TA instrument in
the range 0–700 ◦C at a heating rate of 10 ◦C/min under nitro-
gen at Department of Chemistry, Vallabha Vidhyanagar, Anand.
DSC was carried out on universal V3.0G TA instrument in the
range 0–300 ◦C at Department of Chemistry, Vallabha Vidhyana-
gar, Anand. X-ray diffraction diagrams were obtained on a Philips
PW 1710diffractometer (Cu/Ka; scan rate 1◦ min−1) with a graphite
monochromator at SICART, Vallabha Vidhyanagar, Anand.
(C Ncyclic) cm−1
.
2.1.1.4. H2L4. Yellow crystals, yield 86%; m.p. 252 ◦C; Calcd.: C,
52.82; H, 3.80; N, 13.20. Found: C, 52.51; H, 3.18; N, 13.52. 1H NMR
(CDCl3, TMS, ıppm): 2.36 (s, 6H, pyrazolone–CH3); 7.23–8.02 (m,
12H, phenyl multiplet); 8.99 (s, 2H, –HC N); 10.51 (s, 2H, –OHenol);
MS (EI): (Calcd. for m/z [M]+ = 636.66) [M+2]+ = 639; IR (cm−1),
ꢀ
max (KBr): 3100–3600 br. (O–H), 3051m (C–Hphenyl), 2944–2873m
(C–H), 1640 (C N), 1594vs (C Ncyclic) cm−1
.
2.2. Synthesis of Schiff base complexes of manganese (III)
All the manganese (III) complexes of the Schiff base were
prepared by the following general method. Mn(OAc)3·2H2O
(2.68 g, 0.01 mol) solution in methanol (15 mL) was added to
a warm (∼65 ◦C), stirred solution of the corresponding Schiff
H2L1 (4.56 g, 0.01 mol) or H2L2 (5.88 g, 0.01 mol) or H2L3 (5.04 g,
0.01 mol) or H2L4 (6.36 g, 0.01 mol) in 25 mL 1:1 mixed solvent
(DMF + methanol). After the complete addition, 2 g of sodium per-
clorate was added and the reaction mixture refluxed for 6–7 h and
then concentrated to half of its volume. The resulting precipitate
was filtered by suction and dried in vacuum over anhydrous CaCl2
(Fig. 1).
3. Results and discussion
2.1. Synthesis of
5-oxo-3-methyl-1-p-tolyl-1H-pyrazole-4-carbaldehyde or
4-(4-formyl-5-oxo-3-methyl-pyrazol-1-yl)-benzenesulfonic acid
[18]
The newly synthesized tetradentate ONNO donor Schiff base lig-
ands H2L1, H2L2, H2L3 and H2L4 and complexes with manganese
(III) complexes are stable at atmospheric temperature and pres-
sure. They are insoluble in organic solvents like methanol, ethanol,
and acetone while soluble in coordinating solvents such as DMF
and DMSO and mixed solvents DMF + methanol and DMF + ethanol.
The analytical data are good agreements with the proposed struc-
ture of Schiff base ligands as well as complexes. The analytical data
are of Mn(III) complexes summarized in Table 1.
2.1.1. Synthesis of Schiff base ligands (H2L1), (H2L2), (H2L3) and
(H2L4)
The Schiff bases were synthesized by refluxing methanolic solu-
tions of ethylenediamine (0.60 g, 0.01 mol) or o-phenylenediamine
(1.08 g, 0.01 mol) with 5-oxo-3-methyl-1-p-tolyl-1H-pyrazole-4-
carbaldehyde (4.32 g, 0.02 mol) or 4-(4-formyl-5-oxo-3-methyl-
pyrazol-1-yl)-benzenesulfonic acid (5.64 g, 0.02 mol) in 20 mL
methanolic solution. A solid mass separated was collected and
washed by ether. Crystallization was done with ethanol and then
dried over CaCl2.
3.1. 1H NMR spectra
The 1H NMR spectra of Schiff base ligand (H2L1), (H2L2), (H2L3)
and (H2L4) were carried out in DMSO-d6 at room temperature and
the important assignment is summarized as above. Ligands (H2L1)
and (H2L3) show two singlet with the integration of six protons near
the ı ∼2.35 and ∼2.79 ppm for methyl group attached to pyrazolone
ring and phenyl ring, respectively [29]. Ligands (H2L1) and (H2L2)
show triplet at ∼1.5 ppm for methylene proton of ethylenediamine.
The enolic nature of all Schiff base ligand shows broad singlet at ı
∼10.52 ppm, due to rapid exchange interaction of keto–enol tau-
tomerism [30]. The sharp singlet at ı ∼8.91 ppm, observed due
to aldehydic proton in all Schiff base ligand. The phenyl multiplet
observed in the range of ı ∼7.31–7.98 ppm. From the NMR data it
is observed that the present ligand shows keto–enol tautomerism
as shown below.
2.1.1.1. H2L1. Yellow crystals, yield 88%; m.p. 209 ◦C; Calcd.: C,
68.40; H, 6.18; N, 18.41. Found: C, 68.9; H, 6.18; N, 18.2. 1H
NMR (CDCl3, TMS, ıppm): 1.4 (t, 4H, –CH2–CH2); 2.35 (s, 6H,
pyrazolone–CH3); 2.79 (s, 6H, phenyl–CH3); 7.32–7.98 (m, 12H,
phenyl multiplet); 8.90 (s, 2H, –HC N); 10.52 (s, 2H, –OHenol);
MS (EI): (Calcd. for m/z [M]+ = 456.23) [M+1]+ = 458; IR (cm−1),
ꢀ
max (KBr): 3100–3600 br. (O–H), 3051m (C–Hphenyl), 2944–2873m
(C–H), 1640 (C N), 1598vs (C Ncyclic) cm−1
.
2.1.1.2. H2L2. Yellow crystals, yield 82%; m.p. 214 ◦C; Calcd.: C,
48.97; H, 4.11; N, 14.28; S, 10.90. Found: C, 48.9; H, 4.18; N, 14.2; S,
10.76. 1H NMR (CDCl3, TMS, ıppm): 1.02 (t, 4H, –CH2–CH2); 2.32 (s,
6H, pyrazolone–CH3); 7.32–7.98 (m, 12H, phenyl multiplet); 8.90
(s, 2H, –HC N); 10.52 (s, 2H, –OHenol); MS (EI): (Calcd. for m/z
[M]+ = 588.62) [M+2]+ = 590; IR (cm−1), ꢀmax (KBr): 3100–3600 br.
(O–H), 3051m (C–Hphenyl), 2944–2873m (C–H), 1646 (C N), 1592vs
3.2. Infrared spectra
The infrared spectra of the ligand show a broad band in a region
3100–3600 cm−1, which may be due to ꢀ(OH). Free ꢀ(OH) is gen-
erally observed between 3500 and 3600 cm−1. The low value of this
band is due to intermolecular H-bonding [29,30], which suggests
the presence of keto–enol tautomeric form (Fig. 2), at least in the
solid state. The same is also confirmed from its NMR signal at about
ı ∼10.52 ppm due to an enolic proton. The phenyl group shows
(C Ncyclic) cm−1
.
2.1.1.3. H2L3. Yellow crystals, yield 81%; m.p. 232 ◦C; Calcd.: C,
71.41; H, 5.59; N, 16.66. Found: C, 71.51; H, 5.18; N, 16.52. 1H
NMR (CDCl3, TMS, ıppm): 2.35 (s, 6H, pyrazolone–CH3); 2.76

K.R. Surati, B.T. Thaker / Spectrochimica Acta Part A 75 (2010) 235–242
237
Fig. 1. Synthesis pathway of tetradentate Schiff base ligands.
ꢀ(CH) at 3060 cm−1 and ꢀ(C C) at 1540 cm−1. The bands at ∼1620,
∼1594, and ∼1300 cm−1 may be assigned to ꢀ(C N) (azomethine),
ꢀ(C N) (pyrazoline ring) [18], and ꢀ(C–O) [20], respectively [31].
The ligand as well as its corresponding complexes shows
absorptions in the regions 3000–2800 cm−1 which may be due to
ꢀ(C–H). The Schiff base ligand of the present study shows a strong
band due to ı(O–H) in the region 1210–1270 cm−1. Although all
of the metal complexes show this band, its intensity is found to
be lower than that of the ligand [32,33]. This may be due to the
deprotonation of the 5-OH group of the ligand [33]. All of the metal

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K.R. Surati, B.T. Thaker / Spectrochimica Acta Part A 75 (2010) 235–242
A characteristic band of intermediate intensity is found at
∼1300 cm−1, which may be due to ꢀ(C–O) [17,18]. On coordina-
tion, this band is shifted towards higher frequency indicating that
the oxygen of the 5-OH group of the pyrazoline ring of the lig-
and has taken part in the coordination [33,16,18]. The observed
low-energy shift of ꢀ(C N) (azomethine) in the metal chelates sug-
gests nitrogen coordination. While ꢀ(C N) (cyclic) observed at the
same energy in the chelates indicates the non-participation of the
cyclic nitrogen in the coordination [17,30,31]. In all the complexes
of manganese (III), a weak band is obtained at 1566–1551 cm−1
region. This may be due to asymmetric COO stretching of the
acetate group. The symmetric COO stretching band appeared at
1433–1423 cm−1 region [33,34].
The FT-IR characteristic frequencies of metal complexes are
summarized in Table 2.
3.3. Electronic spectra
UV–visible spectra of manganese (III) complexes were carried
out in DMF + methanol. The data are summarized in Table 2.
The Schiff base ligands H2L1–H2L4 show another broad band at
254 nm, which may be due to conjugated system. In H2L3 ligands
show another intense peak at 395 nm after coordination these band
disappeared. From these spectra it is confirmed that broad band
observed only for ligand conjugation when metal coordinated with
ligands intense band observed is only due to charge transfer. The
absorption spectraofSchiff basecomplexes ofmanganese (III)show
an intensecharge transferat ∼235and ∼348 nm. Theband observed
at ∼550 for [Mn(L1)(OAc)(H2O)] and [Mn(L3)(OAc)(H2O)], ∼556
for [Mn(L3)(OAc)(H2O)] and [Mn(L4)(OAc)(H2O)]. Second band
observed at 613 nm for [Mn(L2)(OAc)(H2O)] and ∼648 nm for other
manganese(III) complexes. Third band observed at ∼681–695 nm,
5
5
5
5
these three bands can be assigned to B1g → Eg, B1g → B2g and
5B1g → A2g transition, respectively, suggesting a distorted octahe-
5
dral arrangement around the manganese (III) [35–37] (Fig. 3).
3.4. Mass spectra
Mass spectra of tetradentate Schiff base ligands H2L1, H2L2, H2L3
and H2L4 are in good agreement with proposed structure, the rep-
resentative mass spectra shown in Fig. 4. Melting point of all the
ligands is higher (above 200 ◦C), as a result of this, the mass spec-
tra were carried out by EI. Cleavage takes place in the Schiff base
ligands and fragments observed were in good agreement with the
structural ligand [38,39].
Fig. 2. Keto–enol tautomerism.
chelates show bands in the region 3100–3600 cm−1, which may be
due to the presence of water molecules [33]. As shown by TGA of
all the metal chelates, this band may be assigned to the one coor-
dinated water molecules, which can be also inferred from bands at
∼710 cm−1, and may be due to the bending modes of vibrations of
the water [33].
Fig. 3. Stereochemistry of manganese (III) complexes.

K.R. Surati, B.T. Thaker / Spectrochimica Acta Part A 75 (2010) 235–242
239
Table 2
FT-IR and electronic spectral data of complexes and their assignments.
Complexes
ꢄH2O
ı(H2O)
ꢄC N coord.
ꢄC N (cyclic)
ꢄC–O Str.
d–d nm (ε) (Lit. cm−1 mol−1
)
Charge transfer band (nm)
568 (6000)
647 (5825)
696 (5800)
566 (6070)
648 (5860)
690 (5820)
568 (6054)
647 (5840)
695 (5799)
567 (6020)
645 (5862)
695 (5810)
[Mn(L1)(OAc)(H2O)]
232, 347
235, 348
234, 347
232, 348
3479
714
1600
1592
1349
[Mn(L2) (OAc)(H2O)]
[Mn(L3)(OAc)(H2O)]
[Mn(L4)(OAc)(H2O)]
–
3479
3479
3479
1612
1630
1625
1594
1592
1594
1346
1354
1346
710
711
Fig. 4. Mass spectra of H2L1.
Fig. 5. Mass spectra of [Mn(L1)(OAc)(H2O)].

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K.R. Surati, B.T. Thaker / Spectrochimica Acta Part A 75 (2010) 235–242
Molecular mass of all the metal complexes performed with FAB
mass spectrometer. A FAB mass spectrum (Fig. 5) of representa-
tive complex [Mn(L1)(OAc)(H2O)] was recorded and the largest
m/z isotropic peak appeared at 570 which corresponding to the
composition [Mn(L1)(OAc)] (586.52 molecular mass—H2O), respec-
tively. Fragmentation of a weakly coordinated molecule/ion in FAB
mass spectrum is not unlikely. To confirm the presence of weakly
coordinating H2O molecules in the complexes, we carried out ther-
mogravimetric analyses of complexes. However the coordinated
ion OAc was strongly coordinated to metal.
3.5. Thermal study
Thermal analyses of all the complexes were carried out by the
TG, DTA and DSC techniques. The experimental results revealed
that the degradation occurred in multiple stages, following a com-
plex mechanism. For each stage the kinetic parameters and the
thermogravimetric characteristics have been estimated.
Fig. 6. DSC curves of manganese (III).
Thermal behaviour of all complexes explains as follows.
the mass loss (80.66% est.; 82.65% calcd.) is accompanied in the TG
curve by exothermic processes at 389 ◦C in DTA. This degradation
is due to pyrolysis of the organic ligand molecule. The final product
of the thermal decomposition MnO was determined by elemental
analysis.
3.5.1. [Mn(L1)(OAc)(H2O)]
The TG and DTA curves of the [Mn(L1)(OAc)(H2O)] are given
following degradation scheme. The compound slowly started to
decompose at 176 ◦C. The first mass loss (9.06% est.; 10.53% calcd.)
up to 248 ◦C is attributed to the removal of one coordinated water
molecule and CO2. This process is accompanied by exothermic pro-
cess at 189 ◦C in DTA curve. In the temperature range 264–711 ◦C
the mass loss (73.96% est.; 77.66% calcd.) is accompanied in the TG
curve by exothermic processes at 423 ◦C in DTA. This degradation
is due to pyrolysis of the organic ligand molecule. The final product
of the thermal decomposition MnO was determined by elemental
analysis.
3.5.5. General scheme of degradation of manganese (III)
complexes from TG
−H O + CO
2
2
[Mn(Ln) · (OAc)(H2O)] −→ [Mn(Ln) ·
(CH3)]organic ligand
−→
MnO (residue), where n = 1, 2, 3, 4
From the above results it is confirmed that manganese (III)
complexes contain one coordinated water molecule. Also one
coordinated ion acetate is present in manganese (III) complexes,
respectively.
Schiff base complexes of manganese (III) contain coordinated
water and acetate ion. The TG curves show two step degradation:
first removal of one coordinated water and one acetate ion. Ther-
mal stability measured qualitatively by TG order of stability is as
follows.
3.5.2. [Mn(L2)(OAc)(H2O)]
The TG and DTA curves of the [Mn(L2)(OAc)(H2O)] are given fol-
lowing the degradation scheme. The compound slowly started to
decompose at 170 ◦C. The first mass loss (9.06% est.; 10.57% calcd.)
up to 239 ◦C is attributed to the removal of one coordinated water
molecule and CO2. This process is accompanied by exothermic pro-
cess at 192 ◦C in DTA curve. In the temperature range 289–709 ◦C
the mass loss (79.96% est.; 81.49% calcd.) is accompanied in the TG
curve by exothermic processes at 432 ◦C in DTA. This degradation
is due to pyrolysis of the organic ligand molecule. The final product
of the thermal decomposition MnO was determined by elemental
analysis.
[Mn(L3)(OAc)(H2O)] > [Mn(L1)(OAc)(H2O)]
> [Mn(L2)(OAc)(H2O)] > [Mn(L4)(OAc)(H2O)]
3.6. Differential scanning calorimetry (DSC)
3.5.3. [Mn(L3)(OAc)(H2O)]
The TG and DTA curves of the [Mn(L3)(OAc)(H2O)] are given fol-
lowing the degradation scheme. The compound slowly started to
decompose at 186 ◦C. The first mass loss (9.06% est.; 9.77% calcd.)
up to 236 ◦C is attributed to the removal of one coordinated water
molecule and CO2. This process is accompanied by exothermic pro-
cess at 184 ◦C in DTA curve. In the temperature range 315–720 ◦C
the mass loss (77.96% est.; 79.04% calcd.) is accompanied in the TG
curve by exothermic processes at 409 ◦C in DTA. This degradation
is due to pyrolysis of the organic ligand molecule. The final product
of the thermal decomposition MnO was determined by elemental
analysis.
Differential scanning calorimetry (DSC) curves are shown in
Fig. 6. The complexes of iron (III) exhibited exothermic process
at temperature ∼279 ◦C, which corresponds to the melting point
of the complexes [40]. Manganese (III) complexes show two pro-
cess one at 112–211 ◦C, endothermic process for the dehydration
of coordinated water and second endothermic process corresponds
to the melting point of the complexes [40]. The area of the
endothermic peak corresponding to the heat of fusion and the peak
temperature corresponds to the melting point. The melting (Tp),
transition temperature (T1, T2), heat of reaction (ꢅH), and entropy
(ꢅS) of the complexes were calculated from DSC results and are
given in Table 3. The heat capacities Cp of the complexes were
calculated from DSC results and are summarized in Table 3.
3.5.4. [Mn(L4)(OAc)(H2O)]
The TG and DTA curves of the [Mn(L4)(OAc)(H2O)] are given fol-
lowing the degradation scheme. The compound slowly started to
decompose at 163 ◦C. The first mass loss (7.61% est.; 8.08% calcd.)
up to 242 ◦C is attributed to the removal of one coordinated water
molecule and CO2. This process is accompanied by exothermic pro-
cess at 191 ◦C in DTA curve. In the temperature range 321–706 ◦C
3.7. X-ray diffraction study
From X-ray diffraction analysis we have successfully calculated
the unit cell parameters and crystal systems of Schiff base com-
plexes of manganese (III) by using Ito’s method [41].

K.R. Surati, B.T. Thaker / Spectrochimica Acta Part A 75 (2010) 235–242
241
Table 3
The thermodynamic and decomposition parameters for complexes.
Complex
Step
Cp (kJ g−1 C−1
)
Ts
T1
T2
Tp
ꢅH* (kJ mol−1
)
ꢅS* (J K−1 mol−1
)
ꢅE* (kJ mol−1
)
I
1.85
4.25
–
2.27
3.90
–
1.45
2.69
–
2.12
4.34
–
112
258
–
172
326
–
81
305
–
79
300
–
173
282
–
223
352
–
156
342
–
135
324
–
151
274
–
209
336
–
123
323
–
109
306
–
112.96
102.23
–
116.26
101.56
–
109.25
99.58
–
119.03
104.20
–
0.74
0.37
–
0.55
0.30
–
0.88
0.30
–
20.23
72.35
–
20.82
77.02
–
21.35
77.69
–
16.62
69.56
–
[Mn(L1)(OAc)(H2O)]
II
III
I
II
III
I
II
III
I
II
III
176
[Mn(L2)(OAc)(H2O)]
[Mn(L3)(OAc)(H2O)]
[Mn(L4)(OAc)(H2O)]
170
186
163
10.9
0.34
–
Manganese (III) complexes show simple triclinic crystal sys-
tem with six coordinates of the cell parameters: a = 14.026 Å,
b = 13.823 Å, c = 14.149 Å, ˛ = 97.7 8◦, ˇ = 102.4 8◦, = 88.3 8◦. Rel-
ative intensity, d-spacing, angle (2Â) and miller indices were
calculated.
In view of the orientation effects and samples preparation error,
we check all the complexes with different orientations. Also the
background was minimized by taking blank.
3.9. Magnetic measurements
Manganese (III) complexes have magnetic moment values
which range from 4.9 to 4.84 B.M., indicating the presence of four
unpaired electrons per Mn(III) ion. These magnetic moments are
in good agreement with Mn(III) in an octahedral configuration
[18,35,37]. All these data are summarized in Table 1.
4. Conclusion
3.8. Molar conductance
On the basis of above studies the general structure of the Mn(III)
complexes is proposed as shown in Fig. 7. The Schiff base ligands
are behaving as O, N, N, O donor tetradentate ligands. Also the
anion OAc is coordinated with metal ion. All these studies give good
evidence of proposed structure.
The observed molar conductances of the manganese (III) com-
plexes in 10−3 molar DMF solution are in the range 29–46 ꢂ−1
cm2 mol−1, which are consistent with the non-electrolytic nature
of all the complexes [42].
Acknowledgements
The authors express their sincere thanks to the Head, Depart-
ment of Chemistry, Sardar Patel University, CDRI, Lucknow, SICART,
Vallabha Vidhyanagar, Anand, SAIF, IIT Madras, and Chennai
for providing instrumental facility. One of the author KRS is
thankful to Mrs. Bharati Ratilal Surati for providing library assis-
tance at Central Library Veer Narmad South Gujarat University,
Surat.
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