Synthesis and characterization of some new manganese(II) complexes, manganese(III) heterochelates, and μ-dioxo-dimanganese(IV) complexes involving tetradentate Schiff bases

Article abstract of DOI:10.1081/SIM-200026605

Condensation of 1,3-diaminopropane-2-ol with diacetylmonoxime and acetylacetone yielded the tetradentate Schiff bases N,N′-(2-hydroxy) propylene-bis{(2-imino-3-oximino)butane} (H₂L¹) and N,N′-(2-hydroxy) propylene-bis(acetylacetoneim

Full text of DOI:10.1081/SIM-200026605

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Synthesis and
Characterization of
Some New Manganese(II)
Complexes, Manganese(III)
Heterochelates, and
µ‐Dioxo‐dimanganese(IV)
Complexes Involving
Tetradentate Schiff Bases
Kamalendu Dey a , Susobhan Biswas a & Saikat
Sarkar a b
a Department of Chemistry , University of
Kalyani , Kalyani, 741235, West Bengal, India
b Department of Chemistry , Santipur College ,
Santipur, 741404, Nadia, West Bengal, India
Published online: 16 Nov 2010.
To cite this article: Kamalendu Dey , Susobhan Biswas & Saikat Sarkar (2004)
Synthesis and Characterization of Some New Manganese(II) Complexes,
Manganese(III) Heterochelates, and µ‐Dioxo‐dimanganese(IV) Complexes Involving
Tetradentate Schiff Bases, Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry, 34:9, 1615-1633, DOI: 10.1081/SIM-200026605
To link to this article: http://dx.doi.org/10.1081/SIM-200026605
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 9, pp. 1615–1633, 2004
Synthesis and Characterization of Some
New Manganese(II) Complexes,
Manganese(III) Heterochelates, and
m-Dioxo-dimanganese(IV) Complexes
Involving Tetradentate Schiff Bases
#
*
Kamalendu Dey, Susobhan Biswas, and Saikat Sarkar
Department of Chemistry, University of Kalyani,
Kalyani, West Bengal, India
ABSTRACT
Condensation of 1,3-diaminopropane-2-ol with diacetylmonoxime and
acetylacetone yielded the tetradentate Schiff bases N,N 0-(2-hydroxy)
propylene-bisf(2-imino-3-oximino)butaneg (H2L1) and N,N 0-(2-hydroxy)
propylene-bis(acetylacetoneimine) (H2L2), respectively. The ligands
form mononuclear manganese(II) complexes of the type [Mn(II)(L1)]
(1) and [Mn(II)(L2)] (3), which are used for the formation of the
manganese(III) heterochelates of the type [Mn(III)(L)(L-L)] (where
*
Correspondence: Kamalendu Dey, Department of Chemistry, University of Kalyani,
Kalyani 741235, West Bengal, India; E-mail: kdey@klyuniv.ernet.in.
#Current address: Department of Chemistry, Santipur College, Santipur 741404, Nadia,
West Bengal, India; E-mail: saikat_s@rediffmail.com.
1615
DOI: 10.1081/SIM-200026605
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

1616
Dey, Biswas, and Sarkar
H2L ¼ H2L1 or H2L2; L-L ¼ anion of acetylacetone or salicylaldehyde).
Cationic heterochelates of the type [Mn(L)(L-L)]ClO4 where
H2L ¼ H2L1 or H2L2 and L-L ¼ ethylenediamine and N,N0-propylene-
bis(benzaldimine) (L3) have been synthesized by the reactions of
bis(acetylacetonato)manganese(II) or bis(salicylaldehydato)mangane-
se(II) with the preformed Schiff bases or by the reactions of
[Mn(II)(L1)] or [Mn(II)(L2)] with L-L in absolute alcohol under reflux.
Some of the complexes, synthesized here, may be used as precursors in
the synthesis of higher nuclearity manganese complexes. Air oxidation of
[Mn(II)(L1)] (1) and [Mn(II)(L2)] (3) in DMF yielded the dark-brown
m-dioxo-bis-[N,N0-(2-hydroxy)propylene-bisf(2-imino-3-oximino)butaneg]-
dimangenese(IV) (2) and m-dioxo-bis[N,N0-(2-hydroxy)propylene-
bisf(acetylacetoneimine)g]dimangenese(IV) (4) complexes, respectively.
All of the complexes have been characterized with the help of elemental
analyses, molar conductance values, molecular weights, magnetic
moments, and spectroscopic (IR, UV-VIS, ESR) data.
Key Words: Manganese(II) complexes; Manganese(III) heterochelates;
m-Dioxo-dimanganese(IV) complexes; Tetradentate Schiff bases.
INTRODUCTION
The chemistry of the coordination compounds of manganese in its
various oxidation states is gaining increasing attention due to their biological
importance.[1–10] The three enzymes, viz., manganese superoxide dismutase,
azide insensitive catalase, and photosynthetic oxygen evolving complex poss-
ibly involve manganese(III) in the catalytic cycles in such enzymatic reac-
tions.[3] The enantioselective epoxidation of non-functionalized olefins
catalyzed by manganese(III) complexes has also been reported.[11] N,O
donor ligands are involved in such complexes, and such ligand systems
have been used to synthesize new mononuclear complexes of manga-
nese.[3,10,12–14] In addition, tetradentate Schiff base complexes of mangane-
se(III) have been used for the oxidation of organic substrates[15,16] using
oxygen-transfer agents such as PhIO, H2O2, or O2. Multinuclear mangane-
se(III) complexes having diverse structural features with Schiff bases are
known.[17,18] A recent report has also demonstrated the synthesis of mangane-
se(IV) complexes from manganese(III) precursors.[19] We report here the syn-
thesis, characterization, and reactivity of manganese(II) complexes and
manganese(III) heterochelates with tetradentate ligands and mixed tetraden-
tate/bidentate imine ligands, and tetradentate/bidentate O,O or N,N donor
ligands. The effects of aerial oxidation of manganese(II) complexes have

Manganese(II), Manganese(III), and Manganese(IV) Complexes
1617
also been studied leading to the isolation of m-dioxo-dimanganese(IV) com-
plexes and have been included in this paper.
RESULTS AND DISCUSSION
Syntheses
The reactions of 1,3-diaminopropane-2-ol with diacetylmonoxime and
acetylacetone yielded the tetradentate Schiff bases N,N0-(2-hydroxy)
propylene-bisf(2-imino-3-oximino)butaneg (H2L1) and N,N0-(2-hydroxy)
propylene-bis(acetylacetoneimine) (H2L2), respectively as shown below:
The neutral bidentate ligand N,N0-propylene-bis(benzaldimine) (L3) was also
used in this work.
1
2
.
The reaction of [Mn(CH3COO)2] 4H2O with H2L and H2L in oxygen-
free ethanol (under N2 atmosphere) gave the manganese(II) complexes
[Mn(II)(L1)] (1) and [Mn(II)(L2)] (3) in high yield. These manganese(II)
complexes are stable when dried, but in wet conditions the compounds
darkened, possibly due to aerial oxidation. In fact, oxidation of (1) and (3)
in DMF solution by dioxygen afforded dark-brown [fMn(IV)(L1)(O)g2]
(2) and [fMn(IV)(L2)(O)g2] (4). The reaction of [Mn(II)(L1)] (1) or

1618
Dey, Biswas, and Sarkar
[Mn(II)(L2)] (3) with ethylenediamine (en) or the neutral bidentate Schiff base
L3 in air produced the cationic heterochelates, [Mn(L)(L-L)]ClO4 where,
H2L ¼ H2L1, L-L ¼ en (9); H2L ¼ H2L2, L-L ¼ en (10); H2L ¼ H2L1,
3
2
3
.
L-L ¼ L (11) and H2L ¼ H2L , L-L ¼ L (12). When [Mn(II)(acac)2] 2H2O
.
(where Hacac ¼ acetylacetone) or [Mn(II)(sal)2] 2H2O (where Hsal ¼
salicylaldehyde) was allowed to react with the preformed Schiff bases H2L1
or H2L2 in absolute ethanol and in the presence of dioxygen, heterochelates
(5)–(8) of the type [Mn(III)(L)(L-L)] (where L ¼ dianions of the tetradentate
Schiff bases H2L1 and H2L2; L-L ¼ anion of acetylacetone or salicylaldehyde)
were isolated. The formation of the complexes may be expressed by the
following chemical equations:
H2L1 or H2L2 þ Mn(CH3COO)2 ꢀ 4H2O
N2;Ethanol
ꢁꢁꢁꢁꢁꢁ! [Mn(II)(L1Þꢂ ð1Þ or [Mn(II)(L2Þꢂ ð3Þ
reflux;2 hr
H2L1 or H2L2 þ Mn(acac)2 ꢀ 2H2O
O2; Ethanol
ꢁꢁꢁꢁꢁꢁ! [Mn(III)(L1Þ(acac)ꢂ ð5Þ or [Mn(III)(L2Þ(acac)ꢂ ð6Þ
reflux;2 hr
H2L1 or H2L2 þ Mn(sal)2 ꢀ 2H2O
O2; Ethanol
ꢁꢁꢁꢁꢁꢁ! [Mn(III)(L1Þ(sal)ꢂ ð7Þ or [Mn(III)(L2Þ(sal)ꢂ ð8Þ
reflux;2 hr
[Mn(II)(L1Þꢂ ð1Þ or [Mn(II)(L2Þꢂ ð3Þ
en; O2; Ethanol
ꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁ! [Mn(III)(L1Þ(en)ꢂClO4 ð9Þ
reflux;2 hr; NaClO4
or [Mn(III)(L2Þ(en)ꢂClO4 ð10Þ
[Mn(II)(L1Þꢂ ð1Þ or [Mn(II) (L2Þꢂ ð3Þ
L3;Ethanol
ꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁ! [Mn(III)(L1Þ(L3ÞꢂClO4 ð11Þ or
reflux;2 hr;NaClO4
[Mn(III)(L2Þ(L3ÞꢂClO4 ð12Þ
The characterization data of the manganese(II), manganese(III), and
manganese(IV) complexes are summarized in Table 1, which support their
formulations. The molecular weights (Table 1) of some of the compounds
(measured by the Rast method) are also in good agreement with these
formulations.

Manganese(II), Manganese(III), and Manganese(IV) Complexes
1619
m

1620
Dey, Biswas, and Sarkar
m

Manganese(II), Manganese(III), and Manganese(IV) Complexes
Molar Conductance Data
1621
The molar conductance values (Table 1) of the manganese(II) and mangane-
se(III) complexes [except the complexes (9)–(12)] in DMSO and DMF solutions
(found within the range 6–15 V21 cm2 mol21 for 1023 M solutions), suggest
their non-electrolytic nature.[20] The manganese(III) complexes (9)–(12), on
the other hand, behaved as 1 : 1 electrolytes in DMSO solution (Table 1).
Magnetic Moments and ESR Spectra
The complexes (1) and (3) are soluble in CHCl3, THF, pyridine, and other
organic solvents, but rapidly darken on exposure to oxygen. The magnetic
moment of ca. 5.92 B.M. is as expected for a high-spin manganese(II)
complex, since an 6S ground state persists in all symmetries of manganese(II)
complexes. The manganese(II) complexes (1) and (3) exhibit magnetic
moment 5.90 [for (1)] and 5.89 [for (3)], respectively, and are indicative of
high-spin manganese(II). Complexes (1) and (3) exhibit strong, broad ESR
signals centered at g ¼ 2, consistent with manganese(II).[21] The passage
of dioxygen (10 hr) through the yellow compounds (1) and (3) as slurries in
DMF at room temperature causes a colour change to dark-brown. This
brown solution yielded the dark-brown complexes [fMn(IV)(L1)(O)g2] (2)
and [fMn(IV)(L2)(O)g2] (4), respectively. The room temperature magnetic
moment values of 2.0 and 1.9 B.M. (per Mn atom), respectively, for (2) and
(4) suggest the presence of manganese(IV) ion (a d3 system). As these two
dimeric complexes are ESR-active, the presence of antiferromagnetically
coupled high-spin manganese(III) (a d4 system) is less likely.[22] The solid-
state ESR spectra at room temperature of the manganese(IV) complexes (2)
and (4) are characterized by a strong broad signal at g ¼ 2, which fits the
proposed m-dioxo structure[7] shown in Fig. 1.
The manganese(III) heterochelates (5)–(8) are soluble in DMSO, DMF,
and pyridine, while the heterochelates (9)–(12) are soluble in water,
ethanol, DMSO, DMF, and pyridine. All these heterochelates are para-
magnetic and show magnetic moment values in the range 4.75–4.85 B.M.
at room temperature (Table 1) indicating the presence of trivalent manganese.
These values show the absence of exchange or superexchange interactions.
UV-VIS Spectra
The electronic absorption spectra of the manganese(II) complexes (1)
and (3) were obtained in DMF in an inert atmosphere, and are characterized

1622
Dey, Biswas, and Sarkar
Figure 1. Proposed structure for [fMn(IV)(L1)(O)g2] (2) and [fMn(IV)(L2)(O)g2] (4).

Manganese(II), Manganese(III), and Manganese(IV) Complexes
1623
by well-defined bands around 24,500 cm21 (broad) and a well-defined
shoulder at about 24,700 cm21. They probably originate from charge transfer
phenomena and the findings are in accord with octahedral geometry (possibly
solvent coordinated) of manganese(II) complexes.[15,16] However, the bands
around 24,500 cm21 diminished on passing dioxygen through the DMF
solution, and shoulders appeared at the higher energy regions. In addition,
a very weak band appeared around 20,000 cm21 assignable to a d–d transition
of manganese(IV).[23] Therefore, the dimanganese(IV) structure (Fig. 1) may
be proposed for the complexes (2) and (4). The electronic spectra of the
isolated dimeric manganese(IV) complexes [fMn(IV)(L1)(O)g2] (2) and
[fMn(IV)(L2)(O)g2] (4) were also measured in chloroform and pyridine
solutions. The absorption spectra of the dimers are difficult to analyse
because of the lack of well-resolved bands; i.e., only broad, poorly resolved
shoulders are seen. Nonetheless, the ligand p ! pꢃ (ꢀ31,000 cm21) and
dp ! pꢃ (ꢀ24,000 and 28,000 cm21) bands can be identified if not accurately
placed.
The fact that both infrared (see later discussion) and UV spectra of the
other manganese(III) complexes, (5)–(12), of this study are qualitatively
similar to those of the dimeric manganese(IV) complexes (2) and (4) supports
the notion that the Schiff base ligands are not altered (i.e., oxidized) in the
formation of the dimers.
The major difference between the spectra of the manganese(III) com-
plexes and those of the dimeric complexes is the presence of a moderate-
intensity band (1 ꢀ 3800) at ꢀ21,500 cm21. The intensity is such that the
band cannot be assigned to a ligand field transition but is consistent with
a charge-transfer transition. This band can most likely be associated with
a charge-transfer from the bridging O22 ligand to the metal dp orbital. Similar
assignments have been made for dimeric Mn(IV)[24] and dimeric Fe(III).[24]
The question may arise at this point as to whether the electronic spectra of
the dimer can be used to distinguish between the two possible oxidation
states, Mn(III) or Mn(IV), and this aspect has been thoroughly discussed.[24]
The presence of a strong oxygen-to-metal charge-transfer transition in
the visible region presents the possibility of photoactivated liberation of
oxygen from this type of complex, as suggested by Calvin.[25] The chemical
properties of the dimers are thus particularly relevant to the suggested role
of manganese in green plant photosynthesis and, in particular, to the nature
of the manganese photocatalyst that mediates the formation of oxygen from
water in the chloroplast. It is interesting to note that the dimeric complexes
are stable in solution, e.g., in pyridine and methanol. Comparable electronic
spectra in the solid state and also in solution were observed in which the
charge-transfer band was at around 21,500 cm21. The stability of the dimeric
compounds may be related to the presence of strong O22(pp) ! Mn(dp)

1624
Dey, Biswas, and Sarkar
mixing in the
unit. However, it is more probable that the electronic
charge is being distributed in a localized molecular orbital, which encom-
passes the whole unit. The main feature of the m-dioxo-dimangan-
ese(IV) structure of complexes (2) and (4) is possibly a planar, four-membered
Mn2O2-ring, as reported recently by x-ray crystal structure analysis of an
analogous complex,[26] [Mn(C-X-salpn)(m–O)]2 Me2CO, where Hsalpn ¼
.
N,N0-bis(salicylidene)-1,3-diaminopropane and X ¼ –CH2C(55O)CH3.
The electronic absorption bands, with their log
1 values, of
manganese(III) heterochelates are given in Table 2. Usually, high-spin
manganese(III) complexes with octahedral geometry are expected to give
one charge-transfer band around 25,000 cm21 (log 1 ¼ 3.5) and a spin-
5
allowed d–d transition band, 5Eg ! T2g, around 20,000 cm21 (log
1 ¼ 2.5). The electronic absorption spectra of these manganese(III) heteroche-
lates (5) to (12) measured in the region 41,000–26,000 cm21, consist of
several intense bands and shoulders. The positions of the bands can be
roughly divided into two areas, between 14,000–15,000 and 16,000–
26,000 cm21. The bands at high wave numbers are seen as shoulders on
intense charge-transfer absorptions. The absorptions in the visible region at
5
5
16,000–26,000 cm21 can be assigned to the Eg ! T2g transition, though
there is the possibility that the bands at around 25,000 cm21 may be of
charge-transfer in origin. The splitting of the bands is most likely due
to the Jahn–Teller distortion as observed in many complexes of
Table 2. Electronic spectral data of some Mn(III) heterochelates and dimanganese(IV)
complexes.
Compound
Solvent
nmax in cm21 (log 1)a
20,600; 24,000; 30,000
21,000; 23,600
(2) [fMn(IV)(L1)(O)g2]
CHCl3
Py
(4) [fMn(IV)(L2)(O)g2]
(5) [Mn (III)(L1)(acac)]
CHCl3
Py
MeOH
20,980; 24,200; 31,000
21,000; 25,000; 30,000
40,000 (4.4); 35,700 (4.2); 24,800 (sh);
20,600 (sh); 16,500 (2.4)
(8) [Mn(III)(L2)(sal)]
(9) [Mn(III)(L1)(en)]ClO4
DMSO
DMSO
25,500 (3.8); 15,600 (sh); 14,500 (sh)
41,666 (4.5); 40,450 (4.5); 36,000 (4.2);
32,500 (sh); 29,400 (sh); 27,000 (sh);
17,000 (sh); 14,500 (sh)
(10) [Mn(III)(L2)(en)]ClO4
EtOH
41,500 (4.1); 40,000 (4.4); 35,800 (4.0);
32,000 (sh); 27,800 (sh); 16,800 (sh);
15,000 (sh)
alog 1 values are not quoted for shoulders and ill-defined bands.

Manganese(II), Manganese(III), and Manganese(IV) Complexes
1625
manganese(III).[27–32] Despite much work on manganese(III) chelates,[27–30]
difficulties have arisen in the assignments of the bands in the near-infrared
region. High-spin manganese(III) complexes always show at least one absorp-
tion in the region 8,000–13,000 cm21. The relationship of this band to the
structure of the complexes has not been clarified. We also observed a band
in the region 14,000–15,000 cm21. Such a band has been assigned as a
low-energy charge-transfer transition in such chelates.[31,32]
Infrared Spectra
The infrared spectra of the ligands show medium to strong bands in the
range 3200–3300 cm21 assignable to n(OH) f55C(CH3)OHg in the case of
H2L2 and a band at 3000–3400 cm21 assignable to n(OH) (oxime) in the
case of the ligand H2L1. The presence of the secondary alcoholic OH in
these two ligands has been demonstrated by the appearance of a band
around 3400 cm21. The broad nature of the bands suggests hydrogen
bonding.[33–35] The n(C55N) (azomethine) band in the ligands H2L1, H2L2,
and L3 appeared in the range 1610–1620 cm21 as a very strong band. The
n(C55N) (oxime linkage) mode in the free ligand H2L1 is possibly submerged
by an other strong band at around 1615 cm21. The n(N–O) mode for the
ligand H2L1 is observed as a strong band[36] at 940 cm21. The n(C–O) band
(secondary alcohol) appeared around 1350 cm21 in the free ligands H2L1
and H2L2 and remains unchanged in the metal complexes demonstrating
non-involvement of this group in these complexes.[36] The disappearance of
bands around 3000–3300 cm21 suggest deprotonation of oxime OH (of
H2L1) and alcoholic OH f55C(CH3)OH of H2L2g allowing these ligands to
function in a dibasic tetradentate fashion. The presence of a broad band
around 3400 cm21 (secondary alcoholic group), however, complicates this
interpretation. The bands due to C55N (both azomethine and oxime) shifted
to lower frequencies by about 10–25 cm21 compared with the free ligand
values, indicating bonding through 4N atoms (involving ligand H2L1), 2N
and 2O atoms (involving ligand H2L2) and 2N atoms (involving ligand L3).
For the complexes [Mn(III)(L1)(acac)] (5) and [Mn(III)(L2)(acac)] (6), the
chelate oxygen-bonded acetylacetonate anion is shown in the vibrational
spectral data[28–30] where we found n(C–O) at 1555 and 1540 cm21, respect-
...
ively, for complexes (5) and (6), while n(C22C) is observed at about
1500 cm21 for both chelates. Infrared spectral data of the heterochelates of tri-
valent metal ions involving ligands of the present types have been discussed
thoroughly elsewhere.[37] The infrared spectral data of complexes (9) to
(12) show a strong and broad band in the range of 1070–1140 cm21 assignable
to the n3 mode of the ClO4 ion vibration (in Td system).[28–30] This band

1626
Dey, Biswas, and Sarkar
demonstrates the presence of ionic perchlorate in these chelates. The com-
plexes (5) to (12) may attain pseudooctahedral structures where tetradentate
Schiff bases have been rearranged from a planar to a twisted conformation
by the displacement of only one oxygen atom from the equatorial plane of
the planar isomer and the bidentate ligands are in cis-position (Fig. 2). The
presence of Mn–O and Mn–N bonds in the complexes are demonstrated by
the appearance of infrared absorption bands in the regions 400–430 cm21
and 350–390 cm21, respectively.
Figure 2. Proposed structure for heterochelates (5) to (12).

Manganese(II), Manganese(III), and Manganese(IV) Complexes
1627
The infrared spectra of the complexes (2) and (4) exhibit ligand bands
essentially unchanged from those of their manganese(II) precursors (1)
and (3), and in addition, there are some new, medium-intensity bands
at about 635 and 600 cm21, which are predicted to be characteristic of a
di-m-oxobridged manganese system[22] (Fig. 1).
EXPERIMENTAL
Materials and Instruments
All the chemicals used were of AR grade. Solvents were purified and
dried before use by the usual procedures. Infrared spectra were recorded in
KBr, Nujol, or hexachlorobutadiene (more than one media were used for
some compounds) on a Perkin–Elmer 1330 spectrophotometer. The electronic
spectra were recorded on a Hitachi 200-20 spectrophotometer. Conductance
measurements were made with a conductivity bridge (Elico Pvt. Ltd., model
CM 80). Molecular weights were determined by the Rast method. The mag-
netic susceptibility was determined by the Guoy method at room temperature.
The elemental analyses of the complexes were carried out at the Regional
Sophisticated Instrumentation Centre, the Central Drug Research Institute,
Lucknow, India. Some spectroscopic data were also collected from this centre.
Preparation of the Ligands and Starting Materials
.
bis(Acetylacetonato)manganese(II) dihydrate, [Mn(II)(acac)2] 2H2O,
was prepared by a previously published method[38] as a pale yellow solid.
.
The yellow bis(salicylaldehydato)manganese(II) dihydrate, [Mn(II)(sal)2]
2H2O, was also prepared following a previously published method.[38]
The Schiff bases H2L1, H2L2, and L3 were prepared by our previously
published methods[39–42] involving the condensation of 1,3-diaminopropane-
2-ol with diacetylmonoxime, acetylacetone and 1,3 diaminopropane with
benzaldehyde, respectively.
Preparation of Manganese(II) Complexes
Due to the instability of solutions of these manganese(II) complexes in
air the complexes were prepared under nitrogen. The general methods of
preparation was as follows.

1628
Dey, Biswas, and Sarkar
[Mn(II)(L1)] (1)
To the stirred solution of H2L1 (2.56 g, 10 mmol) in dioxygen-free ethanol
(60 mL) was added a solution of manganese(II) acetate tetrahydrate, Mn(CH3-
.
COO)2 4H2O (2.45 g, 10 mmol) drop-wise in dioxygen-free ethanol (50 mL).
The mixture was refluxed on a water bath for 2 hr and filtered while hot.
The filtrate on concentration to 60 mL and cooling to about ꢀ10 8C gave a
yellow-brown solid, which was filtered, washed with dioxygen-free ethanol
and dried in vacuo. The complex was stored and handled under nitrogen.
Yield, 2.47 g (80%).
[fMn(IV)(L1)(O)g2] (2)
A slurry of the yellow-brown complex [Mn(II)(L1)] (1) (0.77 g, 2.5 mmol)
was made in DMF (50 mL) at room temperature, through which dioxygen was
passed for 10 hr with occasional stirring. A dark-brown solution was obtained,
which was filtered, concentrated to 30 mL, and on standing at room tempera-
ture the dark-brown complex (2) was obtained. It was filtered off, washed with
dioxygen-free ethanol and dried in vacuo. Yield, 0.98 g (60%).
[Mn(II)(L2)] (3)
This light-brown compound was prepared following the method used for
complex (1) using H2L2 in place of H2L1. Yield, 2.45 g (80%).
[fMn(IV)(L2)(O)g2] (4)
This dark-brown compound was prepared following the method used for
complex (2) by oxidation of complex (3). Yield, 1.05 g (65 %).
Preparation of Manganese(III) Heterochelates
[Mn(III)(L1)(acac)] (5)
.
bis(Acetylacetonato)manganese(II) dihydrate, [Mn(II)(acac)2] 2H2O
(1.45 g, 5 mmol) was dissolved in dry ethanol (60 mL) and was added to the
solution of the Schiff base H2L1 (1.28 g, 5 mmol) in dry ethanol (40 mL).
Air was then drawn through the mixture for about 5 hr, followed by heating
on a water bath under gentle reflux for 2 hr and then the mixture was filtered.
The brown filtrate on concentration to 1/3 of the original volume and cooling
to ꢀ10 8C afforded a brown gummy mass. It was washed several times with

Manganese(II), Manganese(III), and Manganese(IV) Complexes
1629
diethyl ether and then triturated with petroleum ether (40–60 8C) to yield a
brown solid compound. Yield, 1.25 g (60%).
[Mn(III)(L2)(acac)] (6)
Following the method of (5) this brown compound was prepared by the
reaction of H2L2 (1.25 g, 5 mmol) and [Mn(II)(acac)2] 2H2O (1.45 g,
.
5 mmol). Yield, 1.3 g (65%).
[Mn(III)(L1)(sal)] (7)
.
To the solution of [Mn(II)(sal)2] 2H2O (1.66 g, 5 mmol) in ethanol
(50 mL) a solution of H2L1 (1.28 g, 5 mmol) in ethanol (50 mL) was added.
Air was then bubbled through this mixture for about 6 hr followed by reflux
on a water bath for an hour. The reddish-brown solid compound thus obtained
was filtered, washed with a diethyl ether-alcohol mixture (50 : 50 v/v) and
finally with diethyl ether. The compound was dried in a desiccator over
fused CaCl2. Yield, 1.4 g (65%).
[Mn(III)(L2)(sal)] (8)
Following the method of (7), this reddish-brown compound was prepared
2
by the reaction of [Mn(II)(sal)2] 2H2O (1.66 g, 5 mmol) and H2L (1.27 g,
.
5 mmol). Yield, 1.29 g (60%).
[Mn(III)(L1)(en)]ClO4 (9)
A mixture of [Mn(II)(L1)] (1) (1.54 g, 5 mmol) and ethylenediamine
(0.3 g, 5 mmol) in ethanol (80 mL) was oxidized by drawing air through the
solution (6 hr) followed by refluxing for 2 hr and then the mixture was filtered
while hot. The brown filtrate was treated with the stoichiometric amount of a
methanolic solution of NaClO4 (0.7 g, 5 mmol) and then the volume was
reduced to half. This, on standing at room temperature, yielded a brown
solid compound, which was filtered, washed with a cold water–ethanol
mixture (1 : 4, v/v) and then with methanol–diethyl ether mixture (1 : 1, v/v),
and dried in a desiccator over fused CaCl2. Yield, 1.52 g (65%).
[Mn(III)(L2)(en)]ClO4 (10)
This brown compound was prepared following the same procedure used
for (9) by the reaction of [Mn(II)(L2)] (3) (1.53 g, 5 mmol) with ethylenedia-
mine (0.3 g, 5 mmol). Yield, 1.4 g (60%).

1630
Dey, Biswas, and Sarkar
[Mn(III)(L1)(L3)]ClO4 (11)
Following the method of (9) this brown compound was prepared by the
reaction of [Mn(II)(L1)] (1) (1.54 g, 5 mmol) and L3 (1.25 g, 5 mmol). Yield,
1.98 g (60%).
[Mn(III)(L2)(L3)]ClO4 (12)
Following the method of (9) this brown compound was prepared by the
reaction of [Mn(II)(L2)] (3) (1.53 g, 5 mmol) and L3 (1.25 g, 5 mmol). Yield,
1.97 g (60%).
ACKNOWLEDGMENTS
The work was financially supported by the University of Kalyani. The
authors are thankful to the Regional Sophisticated Instrumentation Centre,
Central Drug Research Institute, Lucknow, India for elemental analyses and
spectral data.
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Received January 21, 2004
Accepted May 14, 2004