Synthesis and characterization of four novel manganese(II) chains formed by 4,4′-azobis(pyridine) and benzoate or nitrobenzoates: Stabilization of unusual ladder structures

Article abstract of DOI:10.1016/j.poly.2012.10.036

Four new manganese(II) coordination polymers: [Mn(4,4′-azpy)(C ₆H₅COO)₂](4,4′-azpy)_0.5 (1), [Mn(4,4′-azpy)(p-(NO₂)C₆H₄COO) ₂] (2), [Mn(4,4′-azpy)(m-(NO₂)C₆H ₄COO)₂] (3) and [Mn(4,4′-azpy)(o-(NO ₂)C₆H₄COO)₂(H₂O) ₂] (4), where 4,4′-azpy = 4,4′-azobis(pyridine), have been synthesized by self-assembly of MnX₂ (X = benzoate, p-, m-, or o-nitrobenzoates) together with 4,4′-azpy. All four complexes were characterized by elemental analyses, IR spectroscopy, thermal analyses, single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. The structural analyses reveal that complexes 1, 2 and 3 feature a 1D molecular ladder formed by syn-syn (complex 1) or syn-anti (complexes 2 and 3) carboxylate-bridged dimeric Mn(II) units which are joined together by 4,4′-azpy ligands. In complex 1, these ladders assemble with the help of π-π and C-H?π interactions to form a nanoporous framework that incorporates non coordinated 4,4′-azpy molecules by exploiting host-guest C-H?π and hydrogen bonding interactions. Complex 2 presents a 3D supramolecular framework by π-π and CH?π interactions, whereas, complex 3 having a similar ladder structure to 1 and 2, forms a 2D grid through π-π interactions. On the other hand, complex 4 is a 4,4′-azpy bridged fish-bone chain of carboxylate-coordinated mononuclear manganese(II) units, which are linked together by strong hydrogen bonds to form a 2D structure. Variable-temperature (2-300 K) magnetic susceptibility measurements show the presence of weak antiferromagnetic interactions within the discrete Mn-(OCO)₂-Mn dimers for complexes 1, 2 and 3 that have been fitted with a S = 5/2 dimer model (J = -0.8, -0.5 and -0.4 cm^-1 respectively). The magnetic data of complex 4 can be reproduced with a S = 5/2 monomer model including a Zero Field Splitting (|D| = 1.7 cm^-1).

Full text of DOI:10.1016/j.poly.2012.10.036

Polyhedron 50 (2013) 229–239
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and characterization of four novel manganese(II) chains formed
by 4,40-azobis(pyridine) and benzoate or nitrobenzoates: Stabilization of unusual
ladder structures
a,
Paramita Kar a, Michael G.B. Drew b, Carlos J. Gómez-García c, , Ashutosh Ghosh
⇑
⇑
a Department of Chemistry, University College of Science, University of Calcutta, 92, A.P.C. Road, Kolkata 700 009, India
b School of Chemistry, The University of Reading, P.O. Box 224, Whiteknights, Reading RG6 6AD, UK
c Instituto de Ciencia Molecular (ICMol), C/Catedrático José Beltrán 2, Parque Científico, Universidad de Valencia, 46980 Paterna, Valencia, Spain
a r t i c l e i n f o
a b s t r a c t
Four new manganese(II) coordination polymers: [Mn(4,40-azpy)(C6H5COO)2](4,40-azpy)0.5 (1), [Mn(4,40-
azpy)(p-(NO2)C6H4COO)2] (2), [Mn(4,40-azpy)(m-(NO2)C6H4COO)2] (3) and [Mn(4,40-azpy)(o-(NO2)C6H4-
COO)2(H2O)2] (4), where 4,40-azpy = 4,40-azobis(pyridine), have been synthesized by self-assembly of
MnX2 (X = benzoate, p-, m-, or o-nitrobenzoates) together with 4,40-azpy. All four complexes were char-
acterized by elemental analyses, IR spectroscopy, thermal analyses, single-crystal X-ray diffraction anal-
yses and variable-temperature magnetic measurements. The structural analyses reveal that complexes 1,
2 and 3 feature a 1D molecular ladder formed by syn–syn (complex 1) or syn–anti (complexes 2 and 3)
carboxylate-bridged dimeric Mn(II) units which are joined together by 4,40-azpy ligands. In complex 1,
Article history:
Received 11 September 2012
Accepted 22 October 2012
Available online 16 November 2012
Keywords:
Manganese(II)
4,40-Azobis(pyridine)
Crystal structure
Thermal behavior
Magnetic property
these ladders assemble with the help of
p
–p
and C–Hꢀ ꢀ ꢀ
p interactions to form a nanoporous framework
that incorporates non coordinated 4,40-azpy molecules by exploiting host–guest C–Hꢀ ꢀ ꢀ
p
and hydrogen
and CHꢀ ꢀ ꢀ interac-
inter-
bonding interactions. Complex 2 presents a 3D supramolecular framework by
p–
p
p
tions, whereas, complex 3 having a similar ladder structure to 1 and 2, forms a 2D grid through p–p
actions. On the other hand, complex 4 is a 4,40-azpy bridged fish-bone chain of carboxylate-coordinated
mononuclear manganese(II) units, which are linked together by strong hydrogen bonds to form a 2D
structure. Variable-temperature (2–300 K) magnetic susceptibility measurements show the presence of
weak antiferromagnetic interactions within the discrete Mn–(OCO)2–Mn dimers for complexes 1, 2
and 3 that have been fitted with a S = 5/2 dimer model (J = ꢁ0.8, ꢁ0.5 and ꢁ0.4 cmꢁ1 respectively).
The magnetic data of complex 4 can be reproduced with a S = 5/2 monomer model including a Zero Field
Splitting (|D| = 1.7 cmꢁ1).
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
ular building blocks are usually controlled and modified by the
coordination geometry of the central metal, the structural chem-
The design and synthesis of coordination polymers and metal
organic frameworks (MOFs) have attracted tremendous interest
in the last decade [1–3]. These two kinds of complexes, which
are constructed from metal ions and organic linkers, are of special
relevance not only because of their potential applications in var-
ious fields such as gas storage [4–6], gas separation [7–9], catal-
ysis [10–13], etc. but also for their intriguing structural
architectures and topologies [14–16]. A judicious choice of the
suitable organic spacer and metal ion can provide the synthetic
chemist with some degree of control over the resultant architec-
ture and properties since the network topologies based on molec-
istry of the organic ligands and the metal to organic ligand ratio
[17–20]. As a result, many new systems can be designed in order
to explore the important relationship between the different syn-
thetic factors and the structural topologies of the coordination
polymers. Among the transition metal ions, manganese-based
coordination compounds have received considerable interest in
the fields of supramolecular chemistry and crystal engineering
not only for their remarkable magnetochemical properties [21–
24], but also for their rich biochemistry [25–27]. Furthermore,
due to their low cost and toxicity, manganese coordination com-
pounds are growing in importance as homogeneous catalysts
[28–31]. The carboxylate groups, which can display a wide variety
of coordination modes such as chelating (Scheme 1a), terminal
(Scheme 1b) and bridging syn–syn (Scheme 1c), anti–anti
(Scheme 1d) or syn–anti (Scheme 1e), are one of the most widely
⇑
Corresponding authors.
E-mail addresses: carlos.gomez@uv.es (C.J. Gómez-García), ghosh_59@yahoo.
com (A. Ghosh).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.10.036

230
P. Kar et al. / Polyhedron 50 (2013) 229–239
2.2. Synthesis of the ligand
The 4,40-azobis(pyridine) (4,40-azpy) was prepared as an orange
solid following the literature method [51] by using 4-aminopyri-
dine and sodium hypochlorite.
2.3. Synthesis of [Mn(4,40-azpy)(C6H5COO)2](4,40-azpy)0.5 (1),
[Mn(4,40-azpy)(p-(NO2)C6H4COO)2] (2), [Mn(4,40-azpy)(m-(NO2)C6H4
COO)2] (3) and [Mn(4,40-azpy)(o-(NO2)C6H4COO)2(H2O)2] (4)
A solution of 0.920 g (5 mmol) of 4,40-azpy in 10 mL of metha-
nol was added drop-wise to a stirred solution of 1.845 g (5 mmol)
of Mn(C6H5COO)2ꢀ4H2O in 20 mL of methanol. The resulting solu-
tion was stirred for ca. half-an-hour and then filtered to remove
a small amount of orange precipitate. The dark orange filtrate
was left at room temperature. Deep-orange single crystals suitable
for X-ray diffraction were obtained after a few days.
Complexes 2, 3 and 4 were obtained by following a similar pro-
cedure to that of 1, by using Mn(p-(NO2)C6H4COO)2ꢀ4H2O (2.295 g,
5 mmol), Mn(m-(NO2)C6H4COO)2ꢀ2H2O (2.115 g, 5 mmol), and
Mn(o-(NO2)C6H4COO)2ꢀH2O (2.025 g, 5 mmol), respectively, in-
stead of Mn(C6H5COO)2ꢀ4H2O.
Scheme 1. Different coordination modes of the carboxylate group.
used bridging ligands for designing polynuclear complexes with
interesting structures and topologies [3].
The magnetic properties of such species are fascinating to the
chemists as the number and symmetry of the magnetic orbitals
of the metal ion along with their possible overlap through this
bridging ligand account for the ferro- or antiferromagnetic nature
of the magnetic coupling [32–35].
The neutral and rigid N-donor ligand, 4,40-azobis(pyridine)
(4,40-azpy) has been widely used to construct supramolecular
architectures along with various anionic species that compensate
the charge of the resulting metal–organic frameworks [36,37].
The ligand is well-suited for the construction of supramolecular
assemblies based on aromatic interactions due to its molecular pla-
2.3.1. Complex 1
Yield: 2.09 g; 73%. Anal. Calc. for C58H44Mn2N12O8 (1146.92): C,
60.74; H, 3.87; N, 14.65. Found: C, 60.63; H, 3.75; N, 14.51%. IR (KBr
pellet, cmꢁ1): 1642, 1594
mas(COO), 1392 and 1353 ms(COO), 1590
m(N@N).
narity provided by the p-conjugated system and p-orbitals. How-
2.3.2. Complex 2
ever, this spacer has seldom been used to construct
manganese(II)-based coordination polymers [38,39] and, in fact, a
CCDC search (updated Feb. 2012) shows only nine Mn(II) com-
plexes with the 4,40-azpy ligand [36,39,40–46] of which only one,
recently reported, also contained a carboxylate ligand [46]. This
low number contrasts with the more than two hundred examples
found with 4,40-bipyridine (4,40-bpy) instead of 4,40-azpy [47–49].
Given the interesting increase in the dimensionality (from a 1D
ladder to a 2D sheet and a 3D network) that we have recently
found in a group of carboxylate-bridged Mn(II) complexes with
4,40-bpy [49], we have decided to explore the supramolecular
structural changes induced by these four benzoate ligands when
used with 4,40-azpy instead of 4,40-bpy. Thus here we report the
synthesis, single crystal X-ray structures and magnetic properties
of four new manganese(II) polymers based on the ligand 4,40-azpy
with benzoate and different benzoate derivatives: [Mn(4,40-
azpy)(C6H5COO)2](4,40-azpy)0.5 (1), [Mn(4,40-azpy)(p-(NO2)C6H4-
COO)2] (2), [Mn(4,40-azpy)(m-(NO2)C6H4COO)2] (3) and [Mn(4,40-
azpy)(o-(NO2)C6H4COO)2(H2O)2] (4). Complexes 1–3 present simi-
lar ladder structures where carboxylate bridged Mn(II) dimers are
further connected by 4,40-azpy ligands, albeit, their supramolecular
interactions are very different. In complex 4 the carboxylate group
is monodentate, leading to the formation of a 4,40-azpy bridged 1D
polymer. The preference for the ladder structure in the present
Yield: 2.17 g; 76%. Anal. Calc. for C48H32Mn2N12O16 (1142.72): C,
50.45; H, 2.82; N, 14.71. Found: C, 50.29; H, 2.71; N, 14.60%. IR (KBr
pellet, cmꢁ1): 1653, 1526
mas(COO), 1405, 1365 ms(COO), 1593
m
(N@N).
2.3.3. Complex 3
Yield: 2.02 g; 71%. Anal. Calc. for C48H32Mn2N12O16 (1142.72): C,
50.45; H, 2.82; N, 14.71. Found: C, 50.34; H, 2.69; N, 14.66%. IR (KBr
pellet, cmꢁ1): 1667, 1519
mas(COO), 1388, 1361 ms(COO), 1592
m
(N@N).
2.3.4. Complex 4
Yield: 2.09 g; 69%. Anal. Calc. for C24H20MnN6O10 (607.39): C,
47.46; H, 3.32; N, 13.84. Found: C, 47.29; H, 3.23; N, 13.72%. IR
(KBr pellet, cmꢁ1): 1526
mas(COO), 1375 ms(COO), 3405 mbroad(OH),
1594
m(N@N).
2.4. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were per-
formed using a 2400 series II CHN analyzer. IR spectra in KBr
(4500–500 cmꢁ1) were recorded using a Perkin-Elmer RXI FT-IR
spectrophotometer. Thermal analyses (TG-DTA) were carried out
on a Mettler Toledo TGA/SDTA 851 thermal analyzer in a dynamic
atmosphere of N2 (flow rate 30 cm3 minꢁ1). The samples were
heated in an alumina crucible at a rate of 10 °C minꢁ1. The DC mag-
netic susceptibility measurements were carried out in the temper-
ature range 2–300 K with an applied magnetic field of 0.1 T on
polycrystalline samples of compounds 1–4 (with masses of 41.81,
25.19, 23.75 and 27.03 mg, respectively) with a Quantum Design
MPMS-XL-5 SQUID susceptometer. The isothermal magnetizations
were performed on the same samples at 2 K with magnetic fields
up to 5 T. The susceptibility data were corrected for the sample
holders previously measured using the same conditions and for
cases seems to be originated from the
p–p interactions between
the pyridine rings of the two uprights in the ladder.
2. Experimental
2.1. Starting materials
All four metal carboxylate salts i.e. Mn(C6H5COO)2ꢀ4H2O,
Mn(o-(NO2)C6H4COO)2ꢀH2O, Mn(m-(NO2)C6H4COO)2ꢀ2H2O and
Mn(p-(NO2)C6H4COO)2ꢀ4H2O were synthesized by the procedures
described previously [50]. All other chemicals purchased were of
reagent grade and used without further purification.
the diamagnetic contributions of the salts as deduced by using Pas-
´
,
cals constant tables
(
v
dia = ꢁ319.89 ꢂ 10ꢁ6
,
ꢁ299.83 ꢂ 10ꢁ6

P. Kar et al. / Polyhedron 50 (2013) 229–239
231
Table 1
Crystal data and structure refinement of complexes 1, 2, 3 and 4.
Complex
1
2
3
4
Formula
C
58H44Mn2N12O8
C48H32Mn2N12O16
1142.74
P1
C48H32Mn2N12O16
1142.74
P1
C24H20MnN6O10
607.40
Pbcn
orthorhombic
17.8427(12)
13.6790(8)
10.6426(6)
90
90
90
2597.5(3)
4
1.553
Formula weight
Space group
Crystal system
a (Å)
b (Å)
c (Å)
1146.94
P1
triclinic
ꢀ
ꢀ
ꢀ
triclinic
triclinic
10.434(6)
10.453(6)
11.808(7)
107.42(1)
94.26(1)
99.14(1)
1203.0(12)
1
8.3494(14)
12.8390(16)
13.4258(14)
70.827(10)
72.940(12)
84.669(12)
1299.6(3)
1
10.1724(5)
10.7477(5)
11.8371(6)
89.543(4)
70.806(5)
80.296(4)
1203.16(11)
1
a
(°)
b (°)
(°)
c
V (Å)
Z
Calculated density Dcalc (g cmꢁ3
)
1.466
(Cu K
590
1.577
1.577
Absorption coefficient (
F(000)
l
) (mmꢁ1
)
a) 4.536
(Mo K
a
) 0.612
(Mo K
a
) 0.627
(Mo Ka) 0.578
582
582
1244
Crystal size(mm)
h (°)
0.15 ꢂ 0.18 ꢂ 0.20
0.04 ꢂ 0.04 ꢂ 0.22
2.6–30.0
0.05 ꢂ 0.05 ꢂ 0.30
1.8–25.0
0.05 ꢂ 0.05 ꢂ 0.30
2.7–30.0
3.6–61.9
Rint
0.083
0.029
0.026
0.042
No of data measured
No. of unique data
11908
3638
8667
6820
5553
3797
10077
3661
Data with I > 2
r(I)
2803
3946
2853
2179
R1, wR2
Maximum, minimum residual
Electron density (e/Å3)
0.0743,0.1756
0.864 and ꢁ1.039
0.0678, 0.2018
2.830 and ꢁ0.306
0.1202, 0.3440
3.030 and ꢁ1.023
0.0917, 0.2835
1.582 and ꢁ1.146
ꢁ299.83 ꢂ 10ꢁ6 and ꢁ325.83 ꢂ 10ꢁ6 cm3 molꢁ1 for 1–4, respec-
Mn(C6H5COO)2ꢀ4H2O, Mn(p-(NO2)C6H4COO)2ꢀ4H2O, Mn(m-(NO2)
C6H4COO)2ꢀ2H2O or Mn(o-(NO2)C6H4COO)2ꢀH2O were allowed to
react with 4,40-azpy in methanol solution at ambient temperature
in a 1:1 M ratio to obtain compounds 1–4 as red crystals. All four
compounds were formed by self-assembly of the primary ligands,
(benzoate or the corresponding nitrobenzoates) together with
4,40-azpy as the secondary spacer (Scheme 2). Compounds 1, 2
and 3 which are synthesized by using benzoate, p-nitrobenzoate
and m-nitrobenzoate, respectively present a 1D ladder structure.
However, in compound 1 one 4,40-azpy ligand is present as an aro-
matic guest in the pores formed by supramolecular interactions. In
compound 4 the ligand o-nitrobenzoate acts as a monodentate li-
gand and two water molecules complete the hexa-coordination
around Mn(II) to generate a 4,40-azpy bridged linear chain struc-
ture. A strong hydrogen-bond between the uncoordinated oxygen
atom of the carboxylate and the metal coordinated water molecule
may play an important role in stabilizing the structure.
tively) [52].
2.5. Crystallographic data collection and refinement
3608, 3597, 3661 independent reflection data for 1, 2 and 4,
respectively, were collected at 150(2) K on an Oxford Diffraction
X-Calibur CCD System using Cu K
a for 1 and Mo Ka for 2 and 4.
The crystals were positioned at 50 mm from the CCD. 1464 frames
were measured with a counting time of 1 s for 1 while 321 frames
were measured with a counting time of 10 s for 2 and 4. Data anal-
yses were carried out with the CrysAlis program [53]. 3797 inde-
pendent reflection data for 3 were collected at 293(2) K using a
Bruker SMART diffractometer equipped with a graphite monochro-
mator and Mo Ka radiation. The crystal was positioned at 60 mm
from the CCD. 360 frames were measured with a counting time
of 10 s. All four structures were solved using direct methods with
the SHELXS97 program [54]. The non-hydrogen atoms were refined
with anisotropic thermal parameters. The hydrogen atoms bonded
to carbon atoms were included in geometric positions and given
thermal parameters equivalent to 1.2 times those of the atom to
which they were attached. The hydrogen atoms bonded to oxygen
atoms in 4 were located in a difference Fourier map and refined
with distance constraints. One of the 4,40-azpy ligands in 4 was dis-
ordered over the 2-fold axis and the two possible orientations were
refined isotropically with 50% occupancy using distance con-
straints. In 2 and 3 there was significant positive residual electron
density close to the metal atoms. Absorption corrections for 1, 2
and 4 were carried out using the ABSPACK program [55] and for 3
SADABS program [56].The structures were refined on F2 to R1
0.0743, 0.0685, 0.1202, 0.0917; wR2 0.1756, 0.1729, 0.3196,
3.2. IR spectra of the complexes
The IR spectroscopic data and their assignments are given in the
Section 2. The attributions of IR spectra of all the complexes are dif-
ficult due to the appearance of several absorption bands from the
secondary spacer 4,40-azpy and the benzoate/nitro-benzoate li-
gands. Assignments are based on the structures of 1–4 and related
complexes previously reported [37]. In the region expected for the
m
as(COOꢁ) absorption, compounds 1–3 exhibit two sharp and strong
bandsat 1642 and1594 cmꢁ1 (for 1), 1653 and1526 cmꢁ1 (for 2) and
1667 and 1519 cmꢁ1 (for 3), respectively, attributable to the pres-
ence of two different coordination modes of the carboxylate groups
in the structures. In contrast, complex 4 shows one single and sharp
band at 1526 cmꢁ1 indicating the presence of one type of carboxyl-
ate group. In addition, the sharp peaks at 1392 cmꢁ1 with a shoulder
at1353 cmꢁ1 (for1), 1405 cmꢁ1 witha shoulderat 1365 cmꢁ1 (for2),
1388 cmꢁ1 with a shoulder at 1361 cmꢁ1 (for 3) and 1375 cmꢁ1 (for
4) appear due to the characteristic symmetric stretching modes of
the carboxylates. In complex 4, a broad band at 3405 cmꢁ1 can be as-
signed to the characteristic stretching mode of water. In the region,
expected for the N@N stretch vibration, all four compounds exhibit
one single, sharp and strong band at 1593 cmꢁ1, attributable to the
presence of the 4,40-azpy moiety in all the structures.
0.2632 for 2803, 2452, 2853, 2179 data with I > 2r(I). Data collec-
tion and structure refinement parameters and crystallographic
data for the four complexes are given in Table 1.
3. Results and discussion
3.1. Synthesis
The four coordination polymers have been synthesized under
the same conditions: the Mn(II) salts of respective acids,

232
P. Kar et al. / Polyhedron 50 (2013) 229–239
Scheme 2. Formation of the complexes.
3.3. Thermal analyses
The structure contains a basic centrosymmetric dimeric unit
[Mn2L4] (where L = C6H5COOꢁ) in which the equatorial plane of
both six-co-ordinate Mn(II) ions is formed by the two oxygen
atoms (O11 and O13) from one chelating benzoate and two oxygen
atoms (O21 and O230 (0 = ꢁx, 2ꢁy, ꢁz)) from two different bridging
benzoate ligands. The distorted octahedral coordination sphere is
completed by two trans axial nitrogen atoms (N31 and N4200
(00 = x + 1, y ꢁ1 + z)) from two 4,40-azpy ligands. In addition, there
The thermogravimetric analyses were carried out in air on pow-
der samples of 1–4. In 1, the first endothermic weight loss of 8.01%,
corresponding to the departure of a half guest azpy molecule per
asymmetric unit (calcd 8.02%), was observed between 190 and
250 °C (Fig. S1 of the Supporting information). The coordinated azpy
ligand is held more strongly and, consequently, the second endo-
thermic weight loss of 15.97% observed at higher temperature (be-
tween 250 and 315 °C) is attributable to the loss of the coordinated
azpy ligand (calcd 16.04%). After removal of the guest azpy molecule
at 250 °C, the isolated solid is dissolved in methanol and the crystal-
line product obtained on slow evaporation of solvent is found to be
identical to that of compound 1 as evidenced from elemental anal-
yses. For compounds 2 and 3, the first endothermic weight loss of
15.98% (calcd 16.10%) (for 2) between 260 and 300 °C and 15.96%
(calcd 16.10%) between 286 and 350 °C corresponds to the depar-
ture of coordinated azpy (Figs. S2 and S3 of the Supporting informa-
tion). In spite of having the same molecular structure, compounds 2
is
a
non coordinated 4,40-azpy guest molecule per dimeric
[Mn2L4] unit. The Mn–O bond distances to the bridging carboxyl-
ates (2.088(4) and 2.141(3) Å) are shorter than those to the chelat-
ing one (2.223(3) and 2.294(3) Å) whereas the Mn–N bond
distances (2.251(3) and 2.294(3) Å) are longer than the Mn–O ones.
The linking of the adjacent dinuclear cores by the trans coordinated
4,40-azpy ligand forms a 1D molecular ladder that extends along
the b-direction with the dimer serving as the rungs and the 4,40-
azpy ligands as the uprights. Selected bond lengths and angles
are summarized in Table 2. The four oxygens in the equatorial
plane are approximately coplanar with a r.m.s. deviation of
0.073 Å. The Mn(1) ion deviates from this mean plane by
0.047(1) Å. The chelating bidentate benzoate forms a four-mem-
bered chelate ring. The bridging mode of the carboxylate group
linking the Mn(1) atom to its centrosymmetrically related Mn(1)
atom (x, 2ꢁy, ꢁz) to make the dinuclear [Mn2(C6H5CO2)4] core is
syn-syn with torsion angles of ꢁ72.9(8)° (O23–C22–O21–Mn1)
and 2.2(6)° (O21–C22–O23–Mn1). The Mnꢀ ꢀ ꢀMn distance within
this dimeric unit is 4.177(2) Å. The two pyridine nitrogens in axial
positions subtend an angle of 174.02(15)° and the Mn–N bonds are
approximately perpendicular to the equatorial plane. The main dis-
tortions from the octahedral geometry are due to the small bite an-
gle 58.15(14)° of the bidentate carboxylate and to the
corresponding small trans angles of these oxygen atoms:
150.85(14)° and 148.39(13)°. The C–N@N–C link between the pyr-
idine rings shows torsion angles of ꢁ7.9(7)°, ꢁ177.8(4)° and
ꢁ16.6(7)o.
and 3 have different supramolecular
pꢀ ꢀ ꢀ
p
and C–Hꢀ ꢀ ꢀ
p interactions
which seem to be reflected in different degree of thermal stability of
these two species. In compound 4, the first endothermic weight loss
of 5.87%, (calcd 5.92%) was observed (Fig. S4 of the Supporting infor-
mation) between 80 and 105 °C and corresponds to the departure of
two molecules of water per asymmetric unit. The crystalline sample
turns into amorphous powders upon removal of water molecules. In
the second step, between 256 and 310 °C an endothermic weight
loss of 30.31% is observed which corresponds to the loss of one
4,40-azpy per formula unit (calcd 30.48%).
3.4. Description of structures of the complexes
Complex 1 features a one-dimensional coordination polymer
with a ladder-like structure as shown in Fig. 1 together with the
atomic numbering scheme.

P. Kar et al. / Polyhedron 50 (2013) 229–239
233
Fig. 1. Ladder structure of 1 with ellipsoids at 30% probability.
Table 2
of a CHꢀ ꢀ ꢀ
p interaction (Fig. 3(a)) between the H17 atom of the
Bond distances (Å) and angles (°) in the metal coordination spheres of complexes 1–3.
phenyl ring of the chelating benzoate group of the ladder and a
pyridine ring of the guest azpy molecule (the distance H17ꢀ ꢀ ꢀCg
is 2.73 Å and the C17–H17ꢀ ꢀ ꢀCg angle is 136° [Cg = centroid of
the phenyl ring].) and a weak hydrogen bond (Fig. 3(b)) between
a non coordinated nitrogen atom (N91) of the pyridine ring of
the guest 4,40-azpy molecule and a hydrogen atom (H35) of a pyr-
idine ring of the coordinated 4,40-azpy ligand (Hꢀ ꢀ ꢀN = 2.62 Å, C–
Hꢀ ꢀ ꢀN = 141° and Cꢀ ꢀ ꢀN = 3.393(8) Å).
Complex
1
2
3
Mn(1)–O(23)0
Mn(1)–O(21)
Mn(1)–O(11)
Mn(1)–O(13)
Mn(1)–N(31)
Mn(1)–N(42)00
O(23)0–Mn(1)–O(21)
O(23)0–Mn(1)–O(11)
O(21)–Mn(1)–O(11)
O(23)0–Mn(1)–O(13)
O(21)–Mn(1)–O(13)
O(11)–Mn(1)–O(13)
O(23)0–Mn(1)–N(31)
O(21)–Mn(1)–N(31)
O(11)–Mn(1)–N(31)
O(13)–Mn(1)–N(31)
O(23)0–Mn(1)–N(42)00
O(21)–Mn(1)–N(42)00
O(11)–Mn(1)–N(42)00
O(13)–Mn(1)–N(42)00
N(31)–Mn(1)–N(42)00
2.141(3)
2.088(4)
2.223(3)
2.294(3)
2.290(3)
2.251(3)
2.174(3)
2.162(3)
2.254(3)
2.307(3)
2.257(3)
2.266(3)
2.144(7)
2.182(6)
2.291(6)
2.252(6)
2.268(7)
2.283(7)
126.4(3)
88.1(3)
145.4(3)
145.6(2)
87.9(2)
57.5(2)
88.5(3)
92.3(3)
89.8(3)
92.7(2)
86.2(3)
89.8(3)
91.3(3)
92.4(3)
174.5(3)
117.90(14)
92.85(13)
148.39(13)
150.85(14)
91.24(13)
58.15(12)
87.29(13)
84.13(13)
90.63(12)
95.31(12)
92.20(13)
91.02(13)
95.16(13)
87.95(13)
174.20(14)
127.58(10)
86.84(10)
145.58(11)
144.55(10)
87.85(10)
57.75(10)
88.75(10)
89.12(10)
91.72(10)
93.50(10)
90.75(10)
87.25(10)
93.21(10)
89.78(10)
175.01(10)
The structures of complexes 2 and 3 are shown in Fig. 4 and
Fig. S5, respectively, with the atomic numbering scheme. The coor-
dination environment around the Mn(II) centers and the polymeric
structures are equivalent to that found in 1. Thus, compounds 2 and
3 also contain centrosymmetric [Mn2L4] dimers (L = para-nitro-
benzoate in 2 and meta-nitrobenzoate in 3) linked by bidentate
4,40-azpy ligand with Mnꢀ ꢀ ꢀMn distances of 3.891(9) Å (in 2) and
3.897(3) Å (in 3). The torsion angles, (O23–C22–O21–Mn1 =
ꢁ165.17(5)° and O21–C22–O23–Mn1 = 7.73(4)° for 2 and O21–
C22–O23–Mn1 = 130.08(7)° and O23–C22–O21–Mn1 = ꢁ1.80(5)°
for 3 show that the carboxylate bridges are syn-anti in both
compounds in contrast with the syn-syn mode found in 1.
As in compound 1, the Mn(II) ions in 2 and 3 present an octahe-
dral environment with an equatorial plane formed by four oxygen
atoms: O11, O13, O21 and O230 (0 = 1ꢁx, 1ꢁy, 1ꢁz) from two bridg-
ing and one chelating carboxylate group. The axial positions are
occupied by two nitrogens atoms: N31 and N4200 (00 = x + 1, yꢁ1,
z) from two 4,40-azpy ligands in axial positions that bridge the di-
meric units to form a ladder similar to that found in 1. The main
difference with 1 is the absence of any guest 4,40-azpy molecule
in 2 and 3. Bond lengths around the metal ions in 2 and 3 are also
similar to those in 1 (see Table 2). As in 1, the four oxygens in the
equatorial plane are approximately coplanar with a maximum
deviation of 0.019 and 0.010 Å, whereas the Mn(II) ion deviates
from the equatorial mean plane by 0.006(1) and 0.027(4) Å in 2
and 3, respectively.
0
Symmetry operations: = ꢁx, 2ꢁy, ꢁz (for 1), 1ꢁx, 1ꢁy, ꢁz (for 2), –x, 1ꢁy, ꢁz (for
00
3); = 1 + x, y, ꢁ1 + z (for 1), 1 + x, ꢁ1 + y, z (for 2), ꢁ1 + x, ꢁ1 + y, z (for 3).
These 1D ladders are held together by two types of p–p stacking
interactions: (i) One involving the pyridine rings of the coordinated
4,40-azpy ligands that form the uprights of the ladder with a cen-
troid–centroid distance of 3.821(3) Å, a dihedral angle of 10.46°
and a slip angle of 13.92° (Fig. 2). (ii) A second
involving the phenyl rings of the chelating carboxylate group of
one ladder and the phenyl ring of the bridging carboxylate group
of adjacent ladders with
3.902(3) Å, a dihedral angle between the rings of 4.93° and a slip
angle of 24.93°. These interactions propagate along a- and c-direc-
tions to create an overall 3D supramolecular framework (Fig. 2).
p–p interaction
a centroid–centroid distance of
The axially coordinated pyridine nitrogen atoms form an angle
of 175.0(1)° and 174.5(3)° for 2 and 3 respectively and the Mn–N
bonds are approximately perpendicular to the equatorial planes
in both complexes. As in 1, the main distortions from the octahe-
dral geometry are due to the small bite angles of the bidentate che-
lating carboxylate ligand (57.8(1)° and 57.5(2)° for 2 and 3,
respectively), and to the small trans angles of 145.6(1)° and
144.6(1)° (for 2) and 145.4(3) and 145.6(2)o (for 3). The C–N@N–
This 3D framework is further stabilized by a C–H–p interaction be-
tween a hydrogen atom, H(25), of the phenyl ring of the bridging
carboxylate of one ladder and a pyridine ring of a 4,40-azpy moiety
of a neighboring ladder. The distance between H(25) and the cen-
troid of the ring is 2.77 Å and the C25–H(25)ꢀ ꢀ ꢀCg angle is 146°.
[Cg = centroid of the phenyl ring].
This nanoporous framework generated by supramolecular
interactions incorporate guest 4,40-azpy molecules with the help

234
P. Kar et al. / Polyhedron 50 (2013) 229–239
Fig. 2. Supramolecular network in 1 formed by interchain
pꢀ ꢀ ꢀp and interchain CHꢀ ꢀ ꢀp interactions.
Fig. 3. Host–guest (a) CHꢀ ꢀ ꢀ
p and (b) hydrogen bonds (phenyl rings of carboxylate group have been removed for clarity) in 1.
C link between the pyridine rings shows torsion angles of 37.3(5)°,
angle of 3.16°. All these interactions generate a 3D supramolecular
framework as shown in Fig. 5a. In compound 3 the phenyl rings of
the chelating carboxylate groups interact with the symmetry re-
178.3(3)° and ꢁ30.3(5)° in
2 and 22.5(18)°, 179.6(8)° and
ꢁ19.0(20)° in 3.
Although the coordination environment and polymeric struc-
tures are similar in compounds 2 and 3, they present different
supramolecular frameworks due to the presence of different types
of intermolecular interactions. In complex 2, the 1D ladders are
lated rings of neighboring ladders by means of
p–p interactions
with a centroid–centroid distance of 3.713(7) Å, a dihedral angle
of 1.61° and a slip angle of 1.50°. A second p–p association is ob-
served between the pyridine rings of the 4,40-azpy linkers of the
same ladder with a centroid–centroid distance of 3.863(3) Å, a
dihedral angle of 0.03° and a slip angle of 29.84° leading to a 2D
sheet as illustrated in Fig. 5b. Interestingly, in compound 3, no
held together by face to face
tween the phenyl rings of the chelating carboxylate groups of two
neighboring ladders. This stacking leads to a centroid–cen-
troid distance of 3.755(3) Å, a dihedral angle between the rings
of 0.00° and a slip angle of 58.48°. In addition to this, slipped
stacking interactions are also present between the rings of the
bridging carboxylates of adjacent ladders. This second interac-
pꢀꢀꢀ
p stacking interactions formed be-
p–p
p–p interactions are observed between the phenyl rings of the
bridging and chelating carboxylates, unlike in 1 and 2.
p–
p
Although there are more than forty thousand first row transi-
tion metal complexes with carboxylate ligands (CCDC search up-
dated to Nov. 2011), the number of polymeric complexes
showing a ladder structure is relatively low. If we restrict to Mn(II)
then we can find more than two thousand carboxylate complexes
and ca. five hundred complexes containing Mn(II) ions connected
with double carboxylate bridges, as in compounds 1–3. Albeit,
p–p
tion leads to a distance between the centroids of 3.758(2) Å, a dihe-
dral angle of 5.31° and a slip angle of 28.11°. The pyridine rings of
the coordinated 4,40-azpy moieties of the same ladder are also in-
volved in
p–p interactions with a distance between centroids of
the pyridine rings of 3.700(2) Å, a dihedral angle of 5.31° and a slip

P. Kar et al. / Polyhedron 50 (2013) 229–239
235
Fig. 4. Ladder structure of 2 with ellipsoids at 30% probability.
Fig. 5. Supramolecular networks in 2 (left) and 3 (right) formed by interchain p–p interactions.
the number of Mn(II) complexes with a ladder structure is quite
limited. As far as we know, only three very similar structures,
formed by acetate [57] or o-nitro benzoate [49] and 4,40-bipy,
ligands sitting on the twofold axis. The Mn–O bond lengths in
the equatorial plane (2.160(3) and 2.164(3) Å) are shorter than
the axial Mn–N ones (2.322(3) and 2.330(5) Å) (Table 3). The C–
N@N–C link between the pyridine rings in the 4,40-azpy ligand
shows torsion angles of ꢁ12.9(8)°, ꢁ178.9(4)° and 3.4(9)°.
and benzoate and
l2-1,2-bis(4-pyridyl) ethylene [58] have been
reported. Among them only the compound which is formed by o-
nitro benzoate and 4,40-bipy has been characterized both structur-
ally and magnetically.
Compound 4 presents a fish-bone chain running along the crys-
tallographic b-axis formed by Mn(II) ions connected through 4,40-
azpy bridges as shown in Fig. 6. The Mn(II) ion is located on a two-
fold axis and exhibits an octahedral environment formed by two
monodentate o-nitrobenzoate ligands and two water molecules
in the equatorial plane together with two axial bridging 4,40-azpy
The hydrogen atom H2 of the coordinated water molecule par-
ticipates in a moderate intramolecular hydrogen bond to the unco-
ordinated oxygen atom O(13) of the monodentate o-nitrobenzoate
anion (Oꢀ ꢀ ꢀO = 2.703(4) Å, O–Hꢀ ꢀ ꢀO = 130° and Hꢀ ꢀ ꢀO = 2.08 Å). The
4,40-azpy bridged chains further assemble along the c direction
with the help of strong hydrogen bonds between the coordinated
carboxylate oxygen atom O(11) of one chain and the hydrogen
atom H(1) of a coordinated water molecule (Oꢀ ꢀ ꢀO = 2.722(4) Å,

236
P. Kar et al. / Polyhedron 50 (2013) 229–239
Fig. 6. Chain structure of compound 4 with the metal on a 2-fold axis. Only one of the two possible orientations for the ligand 4,40-azpy based on N(31) is shown. Hydrogen
bonds shown as dotted lines.
the crystal lattices, dinuclear motifs of Mn(II) with doubly carbox-
Table 3
ylate bridges are connected with 4,40-azpy, we can neglect the
Bond distances (Å) and angles (°) in the metal coordination
spheres of complex 4.
magnetic coupling through the 4,40-azpy bridges since the shortest
Mn–Mn distance through this 4,40-azpy bridges is ca. 13.5 Å. There-
Complex
4
fore, we can assume that the magnetic properties in these com-
pounds correspond to those of the isolated Mn–(OCO)2–Mn
dimers. Accordingly, we have used a S = 5/2 dimer model to fit
the magnetic data of compounds 1–3. This model reproduces very
satisfactorily the magnetic properties of compounds 1–3 in the
whole temperature range with the following parameters:
g = 2.018 and J = ꢁ0.8 cmꢁ1 (for 1); g = 2.016 and J = ꢁ0.5 cmꢁ1
(for 2) and g = 2.011 and J = ꢁ0.4 cmꢁ1 (for 3) (solid lines in Fig. 8).
The carboxylate bridged dimeric core present in compounds 1–
3 is quite common. Among the l1,3 carboxylate bridging modes,
the syn–anti configuration is less common than the syn–syn one
[59,60]. On the basis of the respective geometries, it is expected
that a poorly efficient overlap between the 3d magnetic orbital of
the Mn2+ center and the 2p orbital of the carboxylate oxygen atom
Mn(1)–O(1)
Mn(1)–O(11)
Mn(1)–N(31)
Mn(1)–N(42)0
2.160(3)
2.164(3)
2.322(3)
2.330(4)
173.76(17)
90.31(12)
89.39(12)
174.53(15)
88.5(2)
85.2(2)
90.4(2)
84.2(2)
93.5(9)
O(1)–Mn(1)–O(1)0
O(1)–Mn(1)–O(11)
O(1)–Mn(1)–O(11)0
O(11)–Mn(1)–O(11)0
O(1)–Mn(1)–N(31)
O(1)0–Mn(1)–N(31)
O(11)0–Mn(1)–N(31)
O(11)–Mn(1)–N(31)
O(1)–Mn(1)–N(42)00
O(1)0–Mn(1)–N(42)00
O(11)–Mn(1)–N(42)00
O(11)0–Mn(1)–N(42)00
N(31)–Mn(1)–N(42)00
92.7(9)
88.5(7)
97.0(7)
172.4(8)
would lead to weak antiferromagnetic interaction through the l1,3
-
0
00
carboxylate bridging ligand, and its magnitude depends on the
coordination mode of the carboxylate ligand. A syn–syn configura-
tion usually provides small metal–metal distances and a better
overlap of the magnetic orbitals leading to stronger antiferromag-
netic coupling. Syn–anti carboxylato bridges induce smaller J val-
ues because of the expanded metallic core and a mismatch in the
orientation of the magnetic orbitals [59–61]. This usual trend is fol-
lowed in the case of the present three complexes as the syn–syn
carboxylato bridged compound 1 induces higher J value in compar-
ison to 2 and 3, where the carboxylato bridge is syn–anti. Note,
however, that the J values are small in all cases, precluding a more
detailed magneto-structural correlation since small structural
changes in the carboxylato bridge may play an important role
and change the magnitude of the coupling constant. Thus, the rel-
ative orientations of the two magnetic orbitals taking part in the
super-exchange could be affected by several factors as the Mn–O
Symmetry elements: = 1ꢁx, y, 1.5ꢁz, = 1ꢁx, ꢁ1 + y, 1.5ꢁz.
⁄Note that there are alternative positions for all atoms in the 4,4-
azpy ligand including N(31) and N(42) around the 2-fold axis.
Distances involving bonds from metals to these alternative
nitrogen atoms, which are similar to those reported here, are not
included here for simplicity but are available in the deposited cif
file.
O–Hꢀ ꢀ ꢀO = 167° and Hꢀ ꢀ ꢀO = 1.88 Å). This last interaction leads to
the formation of layers parallel to the bc plane (Fig. 7).
3.5. Magnetic properties
The thermal variation of the molar magnetic susceptibility per
Mn(II) dimer times the temperature (
at room temperature a value of ca. 8.5–8.7 cm3 K molꢁ1 (Fig. 8).
These values are close to the expected ones (8.75 cm3 K molꢁ1
for two isolated high spin Mn(II) (S = 5/2) ions with g = 2. When
the temperature is lowered, the three compounds show very sim-
vmT) of complexes 1–3 shows
distance, the O–Mn–O angle (a), and the Mn–O–C angles (b/c).
Small changes in these parameters could also change the overlap
through the carboxylate group.
)
Table 4 shows some structural parameters for compounds 1–3
along with those of other analogous double carboxylato-bridged
Mn(II) compounds described in the literature. The data of this table
suggest that the Mn–Osyn distance (in case of syn–syn mode, the
shorter Mn–Osyn) and the corresponding Mn–Osyn–C angle (b) are
the two most important factors controlling the magnitude of the
antiferromagnetic coupling. In general, shorter Mn–Osyn distance
and smaller b favor stronger antiferromagnetic coupling. Thus,
the Mn–Osyn distance and the b angle in 2 (2.174(3) Å and
ilar thermal behaviors:
vmT remains almost constant down to ca.
50 K and below this temperature it shows a progressive decrease
to reach values of ca. 1.5, 2.5 and 3.4 cm3 K molꢁ1 for 1–3, respec-
tively. This behavior suggests the presence of antiferromagnetic
exchange interactions inside the Mn(II) dimer forming the rungs
of the ladders.
To evaluate the exchange coupling, we have to identify the
dominant interaction pathways in the metal–organic framework.
Although the structures of compounds 1, 2 and 3 show that in

P. Kar et al. / Polyhedron 50 (2013) 229–239
237
Fig. 7. Formation of a 2D sheet by hydrogen-bonding interactions in compound 4. Only one of the two possible orientations for the ligand 4,40-azpy based on N(31) is shown.
All hydrogen atoms of the phenyl and pyridine rings have been removed for clarity.
10
8
10
9
(a)
(b)
8
1
2
7
6
6
4
5
4
2
3
0
2
0
50 100 150 200 250 300
T (K)
0
50 100 150 200 250 300
T (K)
10
9
4.6
4.4
4.2
4.0
3.8
3.6
3.4
(c)
(d)
8
3
4
7
6
5
4
3
0
50 100 150 200 250 300
T (K)
0
50 100 150 200 250 300
T (K)
Fig. 8. Thermal variation of the
vmT product per Mn(II) dimer for compounds 1–3 (a–c) and per Mn(II) ion in 4 (d). Solid lines are the best fits to the models (see text).
Table 4
Comparison of the structural parameters (distances [Å] and angles [°]) and magnetic interaction (J [cmꢁ1]) for some doubly carboxylate-bridged Mn(II) polynuclear complexes.
Compound
Mn–Osyn
Mn–Osyn/anti
J (cmꢁ1
)
Mnꢀ ꢀ ꢀMn
Osyn–Mn–Osyn/anti
Mn–Osyn–C
Mn–Osyn
/
anti–C
Refs.
[Mn(bpy)(3-ClC6H4COO)2]n
[Mn(ClCH2COO)2(phen)]n
[Mn(FcC6H4COO)2(phen)]n
2.104
2.134
2.101
2.150
2.118
2.060
2.129
2.196anti
2.183anti
2.224syn
2.129anti
2.139anti
2.160anti
2.179syn
ꢁ0.88
ꢁ0.45
ꢁ1.6
4.515
4.530
4.817
4.613
4.509
4.145
4.876
4.503
4.087
4.295av
5.044
4.723
4.152
3.891
3.897
100.50
97.95
98.75av
99.92
103.55
107.6
93.90
124.24
107.80
116.03av
90.20
101.68
120.85
127.56
126.42
134.4
123.9
134.87
138.2
151.9
131.92
130.91
163.41
135.31
126.38
128.0
133.48
155.43
120.79
138.11av
132.60
[63]
[64]
[65]
[64]
[63]
[66]
[49]
[Mn2(
[Mn2(
[Mn2(
l
l
l
-ClCH2COO)2(phen)4]2+
-PhCOO)2(bpy)4]2+
-AcO)2(tpa)2]2+
ca. 0
ꢁ0.86
ꢁ0.97
133.5
[Mn(bpy)(C6H5COO)2]n
ꢁ0.779(2)
ꢁ0.354(2)
147.24
119.50
169.06
144.28av
139.89
153.81
164.13
106.75
108.37
[Mn(bpy)(o-C6H4(NO2)COO)2]n
2.121av
2.121av
[49]
[Mn(bpy)(m-C6H4(NO2)COO)2]n
[Mn(bpy)(p-C6H4(NO2)COO)2]n
[Mn(azpy)(C6H5COO)20.5(azpy)]n (1)
[Mn(azpy)(p-C6H4(NO2)COO)2]n (2)
[Mn(azpy)(m-C6H4(NO2)COO)2]n (3)
2.145
2.131
2.095
2.175
2.182
2.168anti
2.199syn
2.119syn
2.163anti
2.144anti
ꢁ0.855(2)
ꢁ0.536(2)
ꢁ0.8
[49]
[49]
this work
this work
this work
134.24syn
123.29syn
177.20
ꢁ0.5
ꢁ0.4
175.70
106.7(2)°) are slightly shorter than in 3 (2.182(6) Å and 108.4(5)°)
and, accordingly, the J value of complex 2 is slightly greater than
that of complex 3, although the differences are too small to extract
any conclusion.

238
P. Kar et al. / Polyhedron 50 (2013) 229–239
10
8
plings mediated through the double syn–syn (in 1) and syn–anti
(in 2 and 3) carboxylate bridges whereas the linear chain com-
pound 4 behaves as isolated monomers with a ZFS since the cou-
pling through the 4,40-azpy ligand is negligible.
1
6
3
2
4
4
Acknowledgments
2
P.K. is thankful to CSIR, India, for research fellowship [Sanction
no. 09/028(0733)/2008-EMR-I]. We thank EPSRC and the Univer-
sity of Reading for funds for the X-Calibur CCD Diffractometer
and the DST-FIST, India-funded Single Crystal Diffractometer Facil-
ity at the Department of Chemistry, University of Calcutta for the
Bruker-Smart Diffractometer. We also thank the Spanish Ministe-
rio de Economía y Competividad (Project CTQ2011-26507) and
the Generalitat Valenciana (Projects PROMETEO 2009/095 and
ISIC).
0
0
1
2
3
4
5
H (T)
Fig. 9. Isothermal magnetization at 2 K for compounds 1–4 per Mn(II) dimer (1–3)
or monomer (4).
The thermal variation of the
vmT product per Mn(II) ion for
compound 4 shows a room temperature value of ca. 4.4 cm3 -
K molꢁ1, close to the expected one for an isolated S = 5/2 Mn(II)
Appendix A. Supplementary data
ion. When the temperature is lowered vmT remains constant down
to ca. 10 K and below this temperature it shows a sharp decrease to
reach a value of ca. 3.5 cm3 K molꢁ1 at 2 K (Fig. 8d). Although com-
pound 4 shows chains of Mn(II) ions, the 4,40-azpy bridge connect-
ing the monomers is very long and, therefore, as observed in
compounds 1–3, we can consider that the coupling through this
bridge is negligible. Accordingly, we have fit the magnetic data of
compound 4 to a simple S = 5/2 monomer model with a zero field
splitting (ZFS) to account for the sharp decrease observed at low
temperatures. This model reproduces very satisfactorily the mag-
netic properties of this compound in the whole temperature range
with g = 1.999 and |D| = 1.7 cmꢁ1. Note that although this D value is
within the normal range observed for isolated Mn(II) ions [62], it
could include a very weak AF interaction.
Finally, the isothermal magnetizations at 2 K (Fig. 9) show lin-
ear behaviors in a large field range, confirming the presence of
weak antiferromagnetic couplings. Although saturation is not
reached at 5 T in all cases, the extrapolated saturation values are
close to the expected ones for a Mn(II) dimer (ca. 10 lB in 1–3)
and a Mn(II) monomer (ca. 5 lB in 4) with g ꢃ 2.
CCDC 891663, 448 891664, 891665 and 891666; contains the
supplementary crystallographic data for 1–4. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.poly.2012.10.036.
References
[1] S. Kitagawa, R. Matsuda, Coord. Chem. Rev. 251 (2007) 2490–2509.
[2] Y. Yan, J. Huang, Coord. Chem. Rev. 254 (2010) 1072–1080.
[3] C. Biswas, P. Mukherjee, M.G.B. Drew, C.J. Gomez-Garcia, J.M. Clemente-Juan,
A. Ghosh, Inorg. Chem. 46 (2007) 10771–10780.
[4] D. Sun, S. Ma, Y. Ke, D.J. Collins, H.-C. Zhou, J. Am. Chem. Soc. 128 (2006) 3896–
3897.
[5] E. Atci, I. Erucar, S. Keskin, J. Phys. Chem. C 115 (2011) 6833–6840.
[6] E. Klontzas, A. Mavrandonakis, E. Tylianakis, G.E. Froudakis, Nano Lett. 8 (2008)
1572–1576.
[7] L. Duan, Z.-H. Wu, J.-P. Ma, X.-W. Wu, Y.-B. Dong, Inorg. Chem. 49 (2010)
11164–11173.
[8] J. Hu, H. Cai, H. Ren, Y. Wei, Z. Xu, H. Liu, Y. Hu, Ind. Eng. Chem. Res. 49 (2010)
12605–12612.
[9] J.-R. Li, Y. Ma, M.C. McCarthy, J. Sculley, J. Yu, H.-K. Jeong, P.B. Balbuena, H.-C.
Zhou, Coord. Chem. Rev. 255 (2011) 1791–1823.
[10] A.M. Shultz, O.K. Farha, J.T. Hupp, S.T. Nguyen, J. Am. Chem. Soc. 131 (2009)
4204–4205.
[11] F. Gándara, B. Gomez-Lor, E. Gutiérrez-Puebla, M. Iglesias, M.A. Monge, D.M.
Proserpio, N. Snejko, Chem. Mater. 20 (2008) 72–76.
[12] F. Gándara, A.d. Andrés, B. Gómez-Lor, E. Gutiérrez-Puebla, M. Iglesias, M.A.
Monge, D.M. Proserpio, N. Snejko, Cryst. Growth Des. 8 (2008) 378.
[13] C. Martínez, A. Corma, Coord. Chem. Rev. 255 (2011) 1558–1580.
[14] Z. Lin, M.-L. Tong, Coord. Chem. Rev. 255 (2011) 421–450.
[15] A.M. Kirillov, Coord. Chem. Rev. 255 (2011) 1603–1622.
[16] C.L. Cahill, D.T. De Lill, M. Frisch, CrystEngComm 9 (2007) 15–26.
[17] O. Sengupta, P.S. Mukherjee, Inorg. Chem. 49 (2010) 8583–8590.
[18] K.C. Mondal, M.G.B. Drew, P.S. Mukherjee, Inorg. Chem. 46 (2007) 5625–5629.
[19] K.C. Mondal, P.S. Mukherjee, Inorg. Chem. 47 (2008) 4215–4225.
[20] P.H. Dinolfo, K.D. Benkstein, C.L. Stern, J.T. Hupp, Inorg. Chem. 44 (2005) 8707–
8710.
4. Conclusions
The reaction of the 4,40-azpy ligand with Mn(II) together with
different benzoato derivatives as co-ligands (benzoate, o-, m- and
p-nitrobenzoate) has afforded four different Mn(II) polymers:
[Mn(4,40-azpy)(C6H5COO)2](4,40-azpy)0.5 (1), [Mn(4,40-azpy)(p-
(NO2)C6H4COO)2] (2), [Mn(4,40-azpy)(m-(NO2)C6H4COO)2] (3) and
[Mn(4,40-azpy)(o-(NO2)C6H4COO)2(H2O)2] (4). Compounds 1–3
present a quite original structure where the common carboxylate
bridges (syn–syn in 1 and syn–anti in 2 and 3) Mn(II) dimers are fur-
ther connected through 4,40-azpy ligands to form a ladder-type
structure in which the Mn(II) dimers are the rungs and the 4,40-azpy
ligands are the uprights. The formation of this unusual structure is
attributed to the presence of two pyridine rings in the 4,40-azpy li-
[21] E. Cremades, J. Cano, E. Ruiz, G. Rajaraman, C.J. Milios, E.K. Brechin, Inorg.
Chem. 48 (2009) 8012–8019.
gand that favors intra-ladder p–p interactions. Despite the similar-
ities of the building blocks used in all the cases, compound 4
presents a different structure where the o-nitrobenzoato ligand acts
as monodentate and the 4,40-azpy ligand connects Mn(II) ions to
form a linear chain. The steric hindrance due to the proximity of
the –NO2 and –COOꢁ groups in the o-nitrobenzoato ligand may
be the reason for this different behavior of the o-compared to the
m- and p-nitrobenzoato ligands. In fact, in compounds 1–3 the
bridging benzoato derivatives are located very close to to the
chelating ones and most probably there is not enough space to
accommodate the ortho-NO2 group.
[22] S. Naiya, S. Biswas, M.G.B. Drew, C.J. Gómez-García, A. Ghosh, Inorg. Chem. 51
(2012) 5332–5341.
[23] C.C. Stoumpos, R. Inglis, O. Roubeau, H. Sartzi, A.A. Kitos, C.J. Milios, G. Aromi,
A.J. Tasiopoulos, V. Nastopoulos, E.K. Brechin, S.P. Perlepes, Inorg. Chem. 49
(2010) 4388–4390.
[24] C.C. Stoumpos, R. Inglis, G. Karotsis, L.F. Jones, A. Collins, S. Parsons, C.J. Milios,
G.S. Papaefstathiou, E.K. Brechin, Cryst. Growth Des. 9 (2009) 24–27.
[25] S. Mukhopadhyay, S.K. Mandal, S. Bhaduri, W.H. Armstrong, Chem. Rev. 104
(2004) 3981–4026.
[26] F. Rappaport, B.A. Diner, Coord. Chem. Rev. 252 (2008) 259–272.
[27] M. Carboni, J.-M. Latour, Coord. Chem. Rev. 255 (2011) 186–202.
[28] D. Lieb, A. Zahl, T.E. Shubina, I. Ivanovic-Burmazovic, J. Am. Chem. Soc. 132
(2010) 7282–7284.
From the magnetic point of view, the ladder compounds 1–3 be-
have as S = 5/2 Mn(II) dimers with weak antiferromagnetic cou-
[29] G. Maayan, G. Christou, Inorg. Chem. 50 (2011) 7015–7021.
[30] P. Mukherjee, P. Kar, S. Ianelli, A. Ghosh, Inorg. Chim. Acta 365 (2011) 318–324.

P. Kar et al. / Polyhedron 50 (2013) 229–239
239
[31] P. Kar, R. Haldar, C.J. Go´mez-García, A. Ghosh, Inorg. Chem. 51 (2012) 4265.
[32] P. Gómez-Saiz, R. Gil-García, M.A. Maestro, F.J. Arnaiz, L. Lezama, T. Rojo, J.L.
Pizarro, M.I. Arriortúa, M. González-Alvarez, J. Borrás, V. Diez-Gómez, J. García-
Tojal, Eur. J. Inorg. Chem. (2009) 373–388.
[48] X.-Y. Wang, Z.-M. Wang, S. Gao, Chem. Commun. (2007) 1127–1129.
[49] P. Kar, R. Biswas, Y. Ida, T. Ishida, A. Ghosh, Cryst. Growth Des. 11 (2011) 5305–
5315.
[50] W. Ferenc, Gazz. Chim. Ital. 125 (1995) 6–23.
[33] W.-L. Meng, G.-X. Liu, T.-A. Okamura, H. Kawaguchi, Z.-H. Zhang, W.-Y. Sun, N.
Ueyama, Cryst. Growth Des. 6 (2006) 2092.
[34] P. Kar, P.M. Guha, M.G.B. Drew, T. Ishida, A. Ghosh, Eur. J. Inorg. Chem. (2011)
2075–2085.
[35] M.S. Ray, A. Ghosh, A. Das, M.G.B. Drew, J. Ribas-Ariño, J. Novoa, J. Ribas, Chem.
Commun. (2004) 1102–1103.
[36] S. Noro, S. Kitagawa, T. Nakamura, T. Wada, Inorg. Chem. 44 (2005) 3960–
3971.
[37] Y. Niu, Y. Song, T. Chen, Z. Xue, X. Xin, CrystEngComm 3 (2001) 152–154.
[38] P. Kar, R. Biswas, M.G.B. Drew, A. Frontera, A. Ghosh, Inorg. Chem. 51 (2012)
1837–1851.
[39] B. Li, G. Yin, H. Cao, Y. Liu, Z. Xu, Inorg. Chem. Commun. 4 (2001) 451–453.
[40] J.-K. Tang, L.-N. Zhu, X.-Z. Li, W. Dong, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, P. Cheng,
Z. Anorg. Allg. Chem. 629 (2003) 2000–2003.
[51] E.V. Brown, G.R. Granneman, J. Am. Chem. Soc. 97 (1975) 621–627.
[52] G.A. Bain, J.F. Berry, J. Chem. Educ. 85 (2008) 532–536.
[53] CrysAlis, Oxford Diffraction Ltd., Abingdon, UK, 2006.
[54] G. M. Sheldrick, Shelxs97 and Shelxl97, Programs for Crystallographic solution
and refinement, Acta Crystallogr., Sect. A 64 (2008) 112.
[55] ABSPACK Oxford Diffraction Ltd, Oxford, UK, 2005.
[56] SAINT, version 6.02, SADABS, version 2.03, Bruker AXS, Inc., Madison, WI, 2002.
[57] G.-H. Wang, Z.-G. Li, J.-W. Xu, N.H. Hu, Acta Crystallogr., Sect. E 63 (2007)
m289–m299.
[58] R.A. Polunin, S.V. Kolotilov, M.A. Kiskin, K.S. Gavrilenko, L. Uahab, I.L.
Eremenko, V.M. Novotortsev, V.V. Pavlishchuk, Izv. Akad. Nauk SSSR, Ser.
Khim. (Russ.) (Russ. Chem. Bull.) (2010) 1217.
[59] D.K. Towle, K. Hoffmann, W.E. Hatfield, P. Singh, P. Chaudhuri, Inorg. Chem. 27
(1988) 394–399.
[41] M. Ito, S. Onaka, Inorg. Chim. Acta 357 (2004) 1039–1046.
[42] Y.-P. Zhang, X.-Y. He, X.-H. Lu, Z.-F. Yu, Y. Zhang, B.-L. Li, Huaxue Yanjiu Yu
Yingyong (Chem. Res. Appl.) 16 (2004) 677.
[43] L.-N. Zhu, O.-Y. Yan, Z.-Q. Liu, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, P. Cheng, Z.
Anorg. Allg. Chem. 631 (2005) 1693–1697.
[60] E. Colacio, J.-M. Dominguez-Vera, J.-P. Costes, R. Kivekäs, J.-P. Laurent, J. Ruiz,
M. Sundberg, Inorg. Chem. 31 (1992) 774.
[61] R.L. Carlin, K. Kopinga, O. Kahn, M. Verdaguer, Inorg. Chem. 25 (1986). 1786-
1786.
[62] R. Boca, Coord. Chem. Rev. 248 (2004) 757–815.
[63] B. Albela, M. Corbella, J. Ribas, I. Castro, J. Sletten, H. Stoeckli-Evans, Inorg.
Chem. 37 (1998) 788–798.
[44] M. Kondo, M. Shimamura, S. Noro, S. Minakoshi, A. Asami, K. Seki, S. Kitagawa,
Chem. Mater. 12 (2000) 1288–1299.
[45] B. Li, B. Li, J. Lang, Y. Zhang, Chem. Lett. 32 (2003) 478–479.
[46] L.-M. Zhao, H.-H. Li, Y. Wu, S.-Y. Zhang, Z.-J. Zhang, W. Shi, P. Cheng, D.-Z. Liao,
S.-P. Yan, Eur. J. Inorg. Chem. (2010) 1983.
[64] G. Fernandez, M. Corbella, J. Mahıa, M.A. Maestro, Eur. J. Inorg. Chem. (2002)
2502–2510.
[65] H. Hou, L. Li, Y. Zhu, Y. Fan, Y. Qiao, Inorg. Chem. 43 (2004) 4767–4774.
[66] H. Oshio, E. Ino, I. Mogi, T. Ito, Inorg. Chem. 32 (1993) 5697–5703.
[47] C. Ma, C. Chen, Q. Liu, D. Liao, L. Li, L. Sun, New J. Chem. 27 (2003) 890–894.