Pyridine-2,6-dicarboxylate and perchlorate bridged hydrogen bonded 1D chains involving manganese(III)-cyclam moiety: Synthesis, X-ray crystal structures and magnetic study

Article abstract of DOI:10.1016/S0020-1693(03)00380-3

Two compounds H[Mn(cyclam)(pyridine-2,6-dicarboxylate)₂] ·H₂O (1) and [Mn^III(cyclam)Cl₂]ClO ₄ (2) (where cyclam=1,4,8,11-tetraazacyclotetradecane) have been synthesized and structurally characterized. The complex 1 crystallizes in the monoclinic space group P2(1)/c with a=11.4328(11), b=14.4275(14), c=8.5782(9) A?, V=1343.1(2)A?³, Z=2, R=0.0453. Complex 1 is octahedral in which [Mn(cyclam)]³⁺ unit occupies the basal plane having two pyridine-2,6-dicarboxylate anions in the axial positions. Molecular packing of the crystal is dominated by string of molecules along the b-axis. The strings are held together by extensive intermolecular hydrogen bonds involving N-HO, N-HN and O-HO which impart it an infinite 1D chain. Complex 2 on the other hand crystallizes in the space group P2₁2₁2₁ (No. 19) of the orthorhombic system. Mn(III) ions occupy the center of a distorted octahedron and two chloride ions occupy the axial positions. The packing diagram of 2 reveals that the complex is percholrate-bridged hydrogen bonded 1D chain along a-axis. Cyclic voltammogram of complex 1 shows a reduction wave at -0.25 V coupled to an oxidation wave at -0.05 V versus SCE in aqueous solution. The complex 2 is characterized by an irreversible reduction wave at -0.11 V versus SCE and is identical to that observed for [Mn^III(cyclam) Cl₂]Cl·5H₂O. The magnetic measurements in the temperature range 1.9-300 K have been carried out for complex 1 which exhibits a very weak ferromagnetic interaction at low temperature. Complex 2 shows room temperature magnetic moment value of 4.92 BM consistent with the high spin d⁴ electronic configuration.

Full text of DOI:10.1016/S0020-1693(03)00380-3

Inorganica Chimica Acta 357 (2004) 25–32
www.elsevier.com/locate/ica
Pyridine-2,6-dicarboxylate and perchlorate bridged hydrogen
bonded 1D chains involving manganese(III)-cyclam
moiety: synthesis, X-ray crystal structures and magnetic study q
a
a
a,
b
Nizamuddin Shaikh , Anangamohan Panja , Pradyot Banerjee *, Maria Kubiak ,
b
b
b,
c
*
ꢀꢁ
Zbigniew Ciunik , Malgorzata Puchalska , Janina Legendziewicz , Pavel Vojtısek
a
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A&2B Raja S.C. Mullick Road, Kolkata 700 032, India
b
Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie Str., 14, 50383 Poland
Department of Inorganic Chemistry, Universita Karlova, Albertov 2030, 128 40 Prague 2, Czech Republic
c
Received 4 February 2003; accepted 7 June 2003
Abstract
Two compounds H[Mn(cyclam)(pyridine-2,6-dicarboxylate)2] ꢀ H2O (1) and [MnIII(cyclam)Cl2]ClO4 (2) (where cyclam ¼ 1,4,8,11-
tetraazacyclotetradecane) have been synthesized and structurally characterized. The complex 1 crystallizes in the monoclinic space
ꢂ
ꢂ3
group P2ð1Þ=c with a ¼ 11:4328ð11Þ, b ¼ 14:4275ð14Þ, c ¼ 8:5782ð9Þ A, V ¼ 1343:1ð2Þ A , Z ¼ 2, R ¼ 0:0453. Complex 1 is octa-
hedral in which [Mn(cyclam)]3þ unit occupies the basal plane having two pyridine-2,6-dicarboxylate anions in the axial positions.
Molecular packing of the crystal is dominated by string of molecules along the b-axis. The strings are held together by extensive
intermolecular hydrogen bonds involving N–H ꢀ ꢀ ꢀ O, N–H ꢀ ꢀ ꢀ N and O–H ꢀ ꢀ ꢀ O which impart it an infinite 1D chain. Complex 2 on the
other hand crystallizes in the space group P212121 (No. 19) of the orthorhombic system. Mn(III) ions occupy the center of a distorted
octahedron and two chloride ions occupy the axial positions. The packing diagram of 2 reveals that the complex is percholrate-bridged
hydrogen bonded 1D chain along a-axis. Cyclic voltammogram of complex 1 shows a reduction wave at )0.25 V coupled to an ox-
idation wave at )0.05 V versus SCE in aqueous solution. The complex 2 is characterized by an irreversible reduction wave at )0.11 V
versus SCE and is identical to that observed for [MnIII(cyclam)Cl2]Cl ꢀ 5H2O. The magnetic measurements in the temperature range
1.9–300 K have been carried out for complex 1 which exhibits a very weak ferromagnetic interaction at low temperature. Complex 2
shows room temperature magnetic moment value of 4.92 BM consistent with the high spin d4 electronic configuration.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Manganese(III) complexes; Hydrogen bonding; 1D chains; Magnetic study
1. Introduction
ers. In the construction of such networks various type of
interactions are being exploited; (a) coordinate covalent
bonds connecting metal centers with appropriate ligands
[11–13], (b) noncovalent hydrogen bonded interaction
[14–16], (c) p–p stacking interaction [17,18], and (d)
electrostatic interaction [19,20]. The use of transition
metal ions to control assembly of molecular architec-
tures has become a popular and rapidly growing disci-
pline [21,22]. Infinite complexes involving macrocyclic
frameworks are often assembled through metal coordi-
nation of suitable bridging ligands [23].
Owing to their potential applications in various fields,
e.g., molecular recognition [1–3], nonlinear optics [4,5],
magnetism [6,7] and structural and functional analogues
of inorganic zeolites [8–10], supramolecular architec-
tures are gaining considerable attention from research-
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/S0020-1693(03)00380-3.
* Corresponding authors. Tel.: +91-33-2473-4971; fax: +91-33-2473-
2805.
The macrocyclic ligand, 1,4,8,11-tetraazacyclote-
tradecane (cyclam) is reported to yield trans-complexes
with manganese(III), [MnIII(cyclam)Cl2]Cl ꢀ 5H2O [24].
E-mail addresses: icpb@mahendra.iacs.res.in (P. Banerjee),
jl@wchuwr.chem.uni.wroc.pl (J. Legendziewicz).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0020-1693(03)00380-3

26
N. Shaikh et al. / Inorganica Chimica Acta 357 (2004) 25–32
The binuclear di-l-oxo-bis(cyclam)dimanganese(III,IV)
ion has also been characterized through X-ray crystal-
lography [25]. However, literature lacks any report for
compounds utilizing manganese(III)-cyclam as a precur-
sor molecule, partly due to its instability in aqueous so-
lution as well as in different organic solvents. To meet the
major current challenges to design coordination com-
pounds with special structures, properties and/or func-
tionalities, the two manganese(III)-cyclam complexes
H[Mn(cyclam)(pyridine-2,6-dicarboxylate)2] ꢀ H2O (1)
and [Mn(cyclam)Cl2]ClO4 (2) have been prepared and
characterized. The use of dicarboxylate spacers, e.g.,
terephthalate, oxalate, malonate and fumarate is a
continuing field of study for the chemists [26–29]. We note
that a pyridine-2,4-dicarboxylate coordination polymer
with a bimetallic ZnII–CuII assembly having a micropo-
rous network has appeared recently [30]. The crystal
structures of both 1 and 2 and magnetic properties of 1 are
reported herein.
Na(2,6-dipicH) dissolved in 20 cm3 of double distilled
water. The color changed from deep green to light green.
It was filtered to remove any suspended material and
kept at room temperature for 3 days to produce green
crystals of complex 1. It was filtered and washed first by
cold water followed by acetone and then dried in air.
Yield ca. 80%. Anal. Calcd. for C24H35N6O10Mn: C,
46.3; H, 5.6; N, 13.5. Found: C, 46.2; H, 5.7; N, 13.4%.
2.4. Preparation of [MnIII (cyclam)Cl2]ClO4 (2)
To an aqueous solution (30 cm3) of [Mn(cy-
clam)Cl2]Cl ꢀ 5H2O was added an aqueous solution (5
cm3) of NaClO4 in 1:1 ratio. (Caution! Although no
problems have been encountered in this work, perchl-
orates are potentially explosive and should be handled
with care and in only small quantities). The mixture was
stirred for 20 min and filtered. The solution was kept for
several days whereby deep green crystals of 2 were iso-
lated in 75% yield. Anal. Calcd. for C10H24N4Cl3O4Mn:
C, 28.2; H, 5.6; N, 13.1. Found: C, 28.1; H, 5.5; N, 13.4%.
2. Experimental
2.5. Physical measurements
2.1. Materials and reagents
Microanalysis (CHN) was performed in a Perkin–
Elmer 240C elemental analyzer. Magnetic susceptibility
measurement was carried out with SQUID magnetom-
eter down to 1.9 K. IR spectra were obtained on a
Nicolet, MAGNA-IR 750 spectrometer with samples
prepared as KBr pellets. Cyclic voltammetry was per-
formed at a planar EG&G PARC G0229 glassy carbon
milli-electrode using an EG&G PARC electrochemical
analysis system (model 250/5/0) in water under dry ni-
trogen atmosphere in conventional three electrode con-
figurations with a scan rate of 0.05 V sꢁ1. Spectral
measurements were performed in an UV–Vis Spectro-
photometer (UV-2100, Shimadzu, Japan).
All the chemicals including manganous chloride,
manganous acetate, methanol, sodium hydroxide, Na-
ClO4 and HClO4 were of reagent grade. Pyridine-2,6-
dicarboxylic acid was purchased from Aldrich and used
without further purification. Double distilled water was
used throughout. The ligand cyclam (1,4,8,11-tetraaza-
cyclotetradecane) was synthesized according to the lit-
erature procedure [31] and was checked by the elemental
analysis and 1H NMR spectroscopy. [Mn(cyclam)Cl2]Cl
was synthesized according to the reported method [24]
and was checked as reported earlier [32].
2.2. Preparation of monosodium salt of pyridine-2,6-
dicarboxylic acid, Na(2,6-dipicH)
2.6. X-ray crystallography
About 0.84 g (5 mmol) of pyridine-2,6-dicarboxylic
acid (2,6-dipicH2) was suspended in a minimum volume
of water. To this mixture was added 0.1 g (2.5 mmol) of
NaOH dissolved in 5 cm3 water. The mixture was stirred
magnetically for 30 min at 50 °C. The solution was then
filtered to remove any suspended material. To the fil-
trate was added dehydrated ethanol slowly thereby
yielding the white micro-crystalline monosodium salt of
dipicolinic acid, Na (2,6-dipicH).
The X-ray diffraction measurements were carried out
on a KUMA KM4CCD diffractometer for 1 [33] and an
Enraf-Nonious CAD4 diffractometer for 2, all using a
graphite monochromated Mo Ka radiation. Intensity
data were collected by x scan technique. All data were
corrected for Lorentz polarization effects [34]. Absorp-
tion corrections based on least-squares fitting against
jFcj ꢁ jF0j differences were also employed [35]. The
structure was solved by direct methods (SHELXS 97)
[36] and refined by full-matrix least-squares based on F 2
using SHELXL 97 [36]. Non-hydrogen atoms were re-
fined with anisotropic thermal parameters, whereas the
hydrogen atoms were included at calculated positions
and refined isotropically. Informations concerning
crystallographic data collection and refinement of the
structures for 1 and 2 are compiled in Table 1.
2.3. Synthesis of H[Mn(cyclam)(pyridine-2,6-dicarb-
oxylate)2] ꢀ H2O (1)
About 0.36 g (1 mmol) of [Mn(cyclam)Cl2]Cl was
dissolved in 20 cm3 double distilled water to give a green
solution. To this solution was added 0.21 g (1 mmol) of

N. Shaikh et al. / Inorganica Chimica Acta 357 (2004) 25–32
27
Table 1
Crystal data and structure refinements for H[Mn(cyclam)(pyridine-2,6-dicarboxylate)2] ꢀ H2O (1) and [Mn(cyclam)Cl2]ClO4 (2)
Complex
1
2
Empirical formula
Formula weight
Temperature (K)
C
622.52
24H35N6O10Mn
C10H24Cl2MnN4ClO4
425.62
293
100(2)
0.71073
ꢂ
Wavelength (A)
0.71070
orthorhombic
P212121 (number 19)
6.5380(1)
13.2990(3)
19.8350(3)
880
Crystal system
Space group
monoclinic
P2ð1Þ=c
11.4328(11)
14.4275(14)
8.5782(9)
108.331(9)
1343.1(2)
2
ꢂ
a (A)
ꢂ
b (A)
ꢂ
c (A)
b (°)
ꢂ3
V (A )
1724.63(5)
4
1.3
Z
l (Mo Ka) (mmꢁ1
F ð000Þ
)
0.560
652
880
h range for data collection (°)
Reflections collected
3.39–28.52
16573
2.0–27.5
3940
3940
Independent reflections (Rint
Final R1; wR2 indices (I > 2rI)
Þ
3243 (0.0399)
0.0453, 0.0955
0.0307, 0.0804
3. Results and discussion
which is very much comparable to that in trans-
[Mn(cyclam)Cl2]þ reported earlier [24]. Two oxygen
atoms of pyridine-2,6-dicarboxylate (dipic) ligand with
3.1. Structure of the complex, H[Mn(cyclam)(pyridine-
2,6-dicarboxylate)2] ꢀ H2O (1)
ꢂ
the Mn–O distance 2.102 A occupy the two axial posi-
tions. The metal ion is located in the plane of four ni-
trogen atoms. The hydrogen atoms bonded to N(2) and
N(3) are above the four-nitrogen plane whereas those to
N(1) and N(4) are below. The expected trans-III con-
formation as classified by Bosnich et al. [37] is thereby
The anion of the complex 1 features a hydrogen
bonded Mn(III) 1D chain as shown in Figs. 1 and 2.
Important bond distances and bond angles appear in
Table 2. The manganese ion lies on one inversion center.
The geometry of manganese is trans-pseudo-octahedral
with the four nitrogen atoms of the cyclam in equatorial
ꢂ
position having an average Mn–N distance 2.033 A
Fig. 1. Molecular structure of H[Mn(cyclam)(pyridine-2,6-dicarboxy-
late)2] ꢀ H2O (1) showing the atom labeling scheme.
Fig. 2. Packing diagram showing both intra- and intermolecular
hydrogen bonding interaction of 1.

28
N. Shaikh et al. / Inorganica Chimica Acta 357 (2004) 25–32
Table 2
ꢂ
Selected bond distances (A) and angles (°) for H[Mn(cyclam) (pyridine-2,6-dicarboxylate)2] ꢀ H2O
Mn–N(2)#1
Mn–N(3)
Mn–O(2)
2.0332(16)
2.0341(16)
2.1020(13)
Mn–N(2)
Mn–N(3)#1
Mn–O(2)#1
2.0332(16)
2.0341(16)
2.1020(13)
N(2)#1–Mn–N(2)
N(2)–Mn–N(3)
180.0
N(2)#1–Mn–N(3)
N(2)#1–Mn–N(3)#1
N(3)–Mn–N(3)#1
N(2)–Mn–O(2)
85.85(6)
94.15(6)
180.0
94.15(6)
85.85(6)
91.36(6)
90.76(6)
88.64(6)
89.24(6)
180.0
N(2)–Mn–N(3)#1
N(2)#1–Mn–O(2)
N(3)–Mn–O(2)
88.64(6)
89.24(6)
91.36(6)
90.76(6)
N(3)#1–Mn–O(2)
N(2)–Mn–O(2)#1
N(3)#1–Mn–O(2)#1
N(2)#1–Mn–O(2)#1
N(3)–Mn–O(2)#1
O(2)–Mn–O(2)#1
achieved. The in-plane distortions are introduced by the
ligand bite angles N(2)–Mn–N(3) of 85.85° and 94.15°.
The complex is stabilized by intermolecular hydrogen
bonds involving N–H ꢀ ꢀ ꢀ O, N–H ꢀ ꢀ ꢀ N and O–H ꢀ ꢀ ꢀ O
which control the overall chelate ring conformations.
The O atoms of dipic and H2O (water of crystallization)
provide the potential hydrogen bond acceptor sites in
addition to the amine N atoms of cyclam. Possible hy-
drogen bonds are listed in Table 3 with the widely ac-
cepted criteria that the hydrogen bonds should be less
than the sum of the van der Waals radii of hydrogen and
the acceptor atom. The molecular packing of the crystal
is dominated by string of molecules along the b direction
due to intermolecular hydrogen bonding. As can be seen
from the packing diagram the 1D chain is formed by the
hydrogen bonding between the –COOH of one
[Mn(cyclam)(dipic)2]ꢁ moiety to –COOꢁ of another
unit. The water of crystallization also participates in the
hydrogen-bonding interaction to stabilize the crystal
lattice. In the packing diagram two types of Mn–Mn
bond distances were located. The bond distance along z-
(No. 19) of the orthorhombic system with four formula
units in the unit cell. Informations regarding crystallo-
graphic data collection and refinement of the structures
are complied in Table 1. An ORTEP view of the isolated
complex is shown in Fig. 3 and packing diagram
showing intra- and intermolecular hydrogen bonding
interaction appears in Fig. 4. The manganese atom lies
on one inversion center. The principal bond lengths and
angles are listed in Table 4. As in the trans-[Mn(cy-
clam)Cl2]Cl ꢀ 5H2O reported earlier [24], as well as
complex 1, complex 2 is roughly octahedral. The inde-
pendent Mn–N bond lengths are 2.039(2), 2.045(2),
ꢂ
2.036(2) and 2.044(2) A. These values are shorter than
those found for the corresponding bonds in the salts of
[Mn(cyclam)O]22þ which is probably indicative of the
trans-influence of oxygen in the later ion [25]. The av-
ꢂ
erage Mn–N distance here (2.041 A) is, however, slightly
ꢂ
higher than that (2.033 A) observed in trans-[Mn(cy-
clam)Cl2]Cl ꢀ 5H2O [24]. The axial Mn–Cl bond lengths
ꢂ
of 2.532(1) and 2.521(1) A are as expected, very long and
comparable to reported values. This bond distance is
much longer than that found in the similar cation
ꢂ
axis was found to be (Mn–MnA and Mn–MnB) 8.578 A
and that along the x- and y-axis (Mn–MnC, Mn–MnD,
ꢂ
Mn–MnE and Mn–MnF) was found to be 8.363 A.
[Co(cyclam)Cl2]þ where the Co–Cl distance is 2.252 A
ꢂ
[38]. The cis N–Mn–N bond angles are 95.18(9)° and
93.70(8)° with the smaller value being associated with
the five-membered ring [Mn, N(11), C(10), C(9), N(8)]
as expected. Similarly the bond distances and angles in
the cyclam ligand are thoroughly consistent with those
in the literature [39,40]. The metal ion is located in the
plane of four nitrogen atoms. Hydrogen atoms bonded
3.2. Structure of [MnIII (cyclam)Cl2]ClO4 (2)
The structure of complex 2 consists of the complex
cation [Mn(cyclam)Cl2]þ and one perchlorate anion.
The complex crystallizes in the space group P212121
Table 3
ꢂ
Hydrogen bonds for H[Mn(cyclam)(pyridine-2,6-dicarboxylate)2]ꢀH2O (A and °)
D–H ꢀ ꢀ ꢀ A
d(D–H)
d(H ꢀ ꢀ ꢀ A)
2.27(2)
d(D ꢀ ꢀ ꢀ A)
<(DHA)
N(3)–H(12) ꢀ ꢀ ꢀ N(1)#1
N(3)–H(12) ꢀ ꢀ ꢀ O(3)#1
N(2)–H(14) ꢀ ꢀ ꢀ O(1W)#2
O(1W)–H(01) ꢀ ꢀ ꢀ O(4)#3
O(1W)–H(02) ꢀ ꢀ ꢀ O(1)
O(3)–H(03) ꢀ ꢀ ꢀ O(3)#4
O(3)–H(03) ꢀ ꢀ ꢀ O(4)#4
0.81(2)
0.81(2)
3.071(2)
3.003(2)
2.810(2)
2.801(2)
2.781(2)
2.470(3)
3.288(2)
167(2)
123(2)
151(2)
174(3)
166(3)
180.0
2.49(2)
2.02(2)
0.87(2)
0.88(4)
1.92(4)
2.04(3)
0.76(3)
1.2349(13)
1.2349(13)
1.2349(13)
2.5204(14)
118.12(7)
Symmetry transformations used to generate equivalent atoms: #1, ꢁx; ꢁy; ꢁz; #2, x; y; z ꢁ 1; #3, x ꢁ 1; y; z; #4, ꢁx þ 1; ꢁy; ꢁz.

N. Shaikh et al. / Inorganica Chimica Acta 357 (2004) 25–32
29
molecular hydrogen bonding involves the coordinated
Clꢁ ions and the N–H hydrogen of cyclam. The inter-
molecular hydrogen bond involving the non-coordi-
nated perchlorate anion and N–H hydrogen of the
cyclam ligand leads to an endless 1D chain along a-axis
(Fig. 4). Important hydrogen bonds are listed in Table 4.
It is noticeable that in the trans-[Mn(cyclam)Cl2]
Cl ꢀ 5H2O molecule, this type of chain does not exist.
The solubility of 2 salt decreases significantly in NaClO4
medium owing to larger ClO4ꢁ counter anion. Evolution
of the one dimensional chain is facilitated through tet-
rahedral perchlorate anion which forms two O–H–N
hydrogen bonds with adjacent [Mn(cyclam)Cl2]þ units.
3.3. UV–Vis spectroscopy
The complex 1 is insoluble almost in all organic sol-
vents. It is, however, sparingly soluble in water and,
therefore, quantitative determination of extinction co-
efficient was not possible. The spectrum exhibits two
sharp peaks at 203 and 271 nm with a weak maximum at
about 354 nm. These bands are due to the ligand to
metal charge transfer. The d–d transition band is very
weak and appears as relatively broad in the 550–800 nm
region. The spectrum is virtually identical with
[Mn(cyclam)Cl2]Cl [32] in aqueous medium which ex-
hibits peaks at 630 ðe ¼ 25Þ, 373 ðe ¼ 1155Þ, 267
ðe ¼ 10; 941Þ nm. Complex 2 also exhibits similar spec-
tral features having a broad weak band at 620 nm
ðe ¼ 20Þ due to the d–d transition and characteristics of
the manganese(III) complexes [41]. The intense bands at
370 ðe ¼ 1150Þ and 267 nm (10,800) are similar to that
observed for [Mn(cyclam)Cl2]Cl [24].
Fig. 3. An ORTEP plot of complex 2 showing atom labeling scheme.
The thermal ellipsoids are represented at the 50% probability level.
to N(4) and N(8) are above the four nitrogen planes,
whereas the hydrogen atoms bonded to N(11) and N(1)
are below giving rise to the trans-III conformation.
Extensive intra- and intermolecular hydrogen bonding
occurs among the [Mn(cyclam)Cl2]ClO4 units. Intra-
Fig. 4. Molecular packing diagram of [Mn(cyclam)Cl2]ClO4 (2) showing intra- and intermolecular hydrogen bonding interaction giving rise to infinite
1D chain.

30
N. Shaikh et al. / Inorganica Chimica Acta 357 (2004) 25–32
Table 4
Selected bond distances (A), angles (°) and hydrogen bond distances (A) for complex [MnIII(cyclam)Cl2]ClO4 (2)
ꢂ
ꢂ
Mn(1)–Cl(1)
Mn(1)–N(1)
Mn(1)–N(8)
2.5322(7)
2.039(2)
2.036(2)
Mn(1)–C(l2)
Mn(1)–N(4)
Mn(1)–N(11)
2.5205(7)
2.045(2)
2.044(2)
Cl(1)–Mn(1)–Cl(2)
Cl(1)–Mn1–N(4)
178.99(2)
Cl(1)–Mn(1)–N(1)
Cl(1)–Mn(1)–N(8)
Cl(2)–Mn(1)–N(1)
Cl(2)–Mn(1)–N(8)
N(1)–Mn(1)–N(4)
N(1)–Mn(1)–N(11)
N(4)–Mn(1)–N(11)
87.52(6)
92.11(6)
91.54(6)
88.84(6)
85.89(9)
95.18(9)
178.88(8)
92.17(6)
87.54(7)
88.12(6)
92.19(7)
179.43(10)
93.70(8)
85.23(9)
Cl(1)–Mn(1)–N(11)
Cl(2)–Mn(1)–N(4)
Cl(2)–Mn(1)–N(11)
N(1)–Mn(1)–N(8)
N(4)–Mn(1)–N(8)
N(8)–Mn(1)–N(11)
N(1)–H(1) ꢀ ꢀ ꢀ Cl(2)
N(8)–H(8) ꢀ ꢀ ꢀ Cl(1)
3.265(2)
3.239(2)
N(4)–H(4) ꢀ ꢀ ꢀ O(1)
3.136(4)
3.055(4)
N(11)–H(11) ꢀ ꢀ ꢀ O(4)
3.4. IR spectroscopy
The complex 1 shows two distinct bands corre-
sponding to the carboxylate stretching at 1643 and 1732
cmꢁ1. A broad band is also observed at 3476 cmꢁ1 due
to the presence of H2O molecule. Two separate bands at
1643 and 1732 cmꢁ1 indicate two types of carboxylate
groups and are consistent with the free and coordinated
carboxylates. In addition to these, the aromatic C–H
stretching frequency is observed at 1605 cmꢁ1. For
complex 2, two intense unsplit bands at 1081 and 630
cmꢁ1 are observed corresponding to the perchlorate
counter ion. In addition to this, bands due to N–H
stretching are observed at 3300–3350 cmꢁ1. Consistent
with the structural features the bands at 3400–3500
cmꢁ1 region due to H2O are not observed for 2.
Fig. 5. Cyclic voltammogram of 1 at a scan rate of 50 mV/sꢁ1 in water
at a platinum electrode. TEAP was used as supporting electrolytes.
3.5. Electrochemistry
V versus SCE at pH 7.0 [32]. No oxidation wave was
observed for this complex in the range +1.0 to +1.5 V in
aqueous solution.
Complex 1 is insoluble in most of the organic sol-
vents. It is, however, sparingly soluble in water and,
therefore, electrochemistry was performed in aqueous
medium as illustrated in Fig. 5. In aqueous solution
[Mn(cyclam)Cl2]Cl undergoes one electron irreversible
reduction at )0.12 V versus SCE at pH 6.5 corre-
sponding to Mn(III)/Mn(II) couple [32]. The corre-
sponding peak in complex 1 was observed at )0.25 V
versus SCE coupled to an oxidation wave at )0.05 V
versus SCE ðE1=2 ¼ 100 mV, DEp ¼ 200 mV). The larger
negative shift of the redox potential in comparison to
the parent complex might be due to the fact that coor-
dination of dipic moiety renders the metal center less
susceptible towards reduction. This is exemplified by the
coordination of phosphate anion to the metal in
[MnIII(cyclam)Cl2]þ [32]. Carboxylato bridged dinuclear
complex, [Mn(salen)2(pth)] ꢀ 2H2O (pth ¼ terephthalic
acid) also exhibits similar cyclic voltammetric pattern in
aqueous solution [42]. Complex 2 exhibits cyclic vol-
tammetric pattern, which is identical to that observed
for [Mn(cyclam)Cl2]Cl with one reduction wave at )0.11
3.6. Magnetic studies
The variable temperature magnetic susceptibility
measurements for complex 1 were performed in the
temperature range of 1.9–300 K. The room temperature
effective magnetic moment value ð4:86lBÞ agrees well to
that observed for a high spin d4 system (S ¼ 2) [43–45].
The temperature dependence of the vMT (3.41 cm3 molꢁ1
K) shows a weak maximum at approximately 7 K and
then decreases at lower temperature (see supplementary
materials, Fig. S2a). The magnetic moment value in-
creases with temperature and reaches a maximum
ð5:24lBÞ at approximately 7 K and then decreases (see
supplementary materials, Fig. S2b). This feature indi-
cates ferromagnetic ordering at lower temperature. The
magnetic susceptibility obeys Curie–Weiss law and a plot
of 1=vM versus T yields a straight line (Fig. 6) with
C ¼ 2.89 cm3 molꢁ1 K and h ¼ þ0:93. The positive Weiss
constant h also suggests a very weak ferromagnetic in-

N. Shaikh et al. / Inorganica Chimica Acta 357 (2004) 25–32
31
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