Systematic investigation into the influence of base and substituents on the coordination chemistry of MnIII and MnIII/II salicylate complexes

Article abstract of DOI:10.1080/10610278.2012.703323

A systematic investigation into the coordination chemistry of Mn ^III salicylates is presented revealing the influence on the shape and dimensionality of the final products of base, the presence or absence of co-ligands and the substituents on the salicylates. We report the synthesis, structures, characterisation and magnetic properties of seven compounds, (NHEt₃)[Mn^III(3-MeOsal)₂(MeOH)(H₂O)] (1), [NaMn^III(3-MeO-sal)₂(MeOH)₂] (2), [NaMn^III(sal)₂(H₂O)(MeOH)] · (MeOH) (3), [KMn^III(sal)₂(H₂O)(MeOH)] · (MeOH) (4), [Mn^IIMn₂ ^III(3-MeOsal)₄(py) ₆(H₂O)₂] · 4H₂O, (5), [Mn^IIMn₂ ^III(3-MeO-sal)₄(py) ₄(H₂O)₄] · 4MeOH, (6) and [Mn ^IIMn₂ ^III(3-MeO-sal)₄(2,2-bipy) (H₂O)₃(MeOH)₂] · 3MeOH (7). Magnetic studies show the presence of antiferromagnetic interactions between the paramagnetic centres in all cases.

Full text of DOI:10.1080/10610278.2012.703323

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Systematic investigation into the influence of base and
substituents on the coordination chemistry of MnIII and
MnIII/II salicylate complexes
Sudarshana Mukherjee a , Yanhua Lan a , George E. Kostakis b , Rodolphe Clérac c d
Christopher E. Anson a & Annie K. Powell a b
,
a Institute of Inorganic Chemistry, Karlsruhe Institute of Technology, Engesserstrasse 15,
D-76131, Karlsruhe, Germany
b Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz
Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
c CNRS, CRPP, UPR 8641, F-33600, Pessac, France
d Université de Bordeaux, CRPP, UPR 8641, F-33600, Pessac, France
Version of record first published: 08 Aug 2012.
To cite this article: Sudarshana Mukherjee, Yanhua Lan, George E. Kostakis, Rodolphe Clérac, Christopher E. Anson & Annie K.
Powell (2012): Systematic investigation into the influence of base and substituents on the coordination chemistry of MnIII and
MnIII/II salicylate complexes, Supramolecular Chemistry, 24:8, 533-546
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Supramolecular Chemistry
Vol. 24, No. 8, August 2012, 533–546
Systematic investigation into the influence of base and substituents on the coordination chemistry
of MnIII and MnIII/II salicylate complexes
a
a
b
Sudarshana Mukherjee , Yanhua Lan , George E. Kostakis , Rodolphe Cleracc,d, Christopher E. Ansona and
´
Annie K. Powella,b
*
b
aInstitute of Inorganic Chemistry, Karlsruhe Institute of Technology, Engesserstrasse 15, D-76131 Karlsruhe, Germany; Institute of
Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, Germany;
c
d
CNRS, CRPP, UPR 8641, F-33600 Pessac, France; Universite de Bordeaux, CRPP, UPR 8641, F-33600 Pessac, France
´
(Received 19 March 2012; final version received 12 June 2012)
Asystematic investigation into thecoordination chemistry ofMnIII salicylates ispresentedrevealing theinfluence onthe shape
and dimensionality of the final products of base, the presence or absence of co-ligands and the substituents on the salicylates.
We report the synthesis, structures, characterisation and magnetic properties of seven compounds, (NHEt3)
[MnIII(3-MeOsal)2(MeOH)(H2O)] (1), [NaMnIII(3-MeO-sal)2(MeOH)2] (2), [NaMnIII(sal)2(H2O)(MeOH)]· (MeOH) (3),
[KMnIII(sal)2(H2O)(MeOH)]· (MeOH) (4), [MnIIMn2III(3-MeOsal)4(py)6(H2O)2]· 4H2O, (5), [MnIIMn2III(3-MeO-sal)4(py)4
(H2O)4]· 4MeOH, (6) and [MnIIMn2III(3-MeO-sal)4(2,20-bipy)(H2O)3(MeOH)2]· 3MeOH (7). Magnetic studies show the
presence of antiferromagnetic interactions between the paramagnetic centres in all cases.
Keywords: manganese(III); salicylic acid; coordination polymers; magnetic properties
1
Introduction
salicylic acids have received less attention than systems
based on other aromatic carboxylic acids (11). Inspired by
the MBB concept, we previously reported that substituted
salicylates along with trivalent metal centres can lead to the
formation of a monoanionic MBB-linker which, in
conjunction with the details of the coordination sphere of
the metal centre node, allows the dimensionality of the final
product to be tuned (12). This monoanionic MBB consists
of a trivalent metal centre (M ¼ MnIII and FeIII) which is
octahedrally coordinated by two substituted salicylates or
salicylate itself with one bidentate or two monodentate co-
ligands to complete the coordination sphere. Two different
MBBs, A and B, can form (Scheme 1) depending on
whether the co-ligands X and Y occupy cis or trans
positions. We note, of course, that both A and B themselves
can occur in different isomeric forms. Of particular
relevance to the work we report here, A can have two
forms depending on whether the phenoxo (or carboxylato)
oxygens from the two ligands in the equatorial square plane
are mutually trans or cis to each other.
Recent years have witnessed a burgeoning interest in
exploring the use of combinations of metal ions and organic
ligands for the synthesis of coordination polymers of
various dimensionalities such as 1D chains, 2D sheets and
3D frameworks, which are also known as metal-organic
frameworks (MOFs) (1). This research is often driven by
the possibility of creating new materials with various
functions or even multiple functions and potential
applications include gas storage (2), catalysis (3) and
magnetism (4). In addition, coordination chemists have
realised that specific coordination geometries of metal ions
can be used to provide nodes which can then be linked by
organic ligands acting as spacers (5) to give networks of
specified topologies often corresponding to those found in
mineral structures (6). More recently, polynuclear clusters
have begun to be used as nodes in place of single metal ions
(7), and more complicated organic ligands to act as linkers
have been synthesised (8). Furthermore, the molecular
building block (MBB) approach, in which a building block
is created for the positional assembly of components, has
emerged as a powerful strategy for the design and
construction of solid-state materials (9).
Thus we found, for example that in the series of 3D
diamondoid networks formed using this MBB approach
(12a), the MnIII-MBB of type A (Scheme 1) has the trans
axial positions occupied by nitrogen atoms of two pyridine
ligands (X ¼ Y ¼ pyridine, Z ¼ Me). When this is
combined with MnII-‘nodes’, we found that if MnII is 4
or 5 coordinated, a 3D diamondoid net is constructed. On
the other hand, when the MnII node adopts coordination
It is well established that salicylic acid is a versatile
ligand in polynuclear cluster chemistry (10), although in the
field of coordination polymers the complexes of 3d
transition metal elements and salicylic acid and substituted
*Corresponding author. Email: annie.powell@kit.edu
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2012 Taylor & Francis
http://dx.doi.org/10.1080/10610278.2012.703323
http://www.tandfonline.com

534
S. Mukherjee et al.
Z
(a)
(b)
X
M
Y
X
M
O
O
O
Y
O
O
O
O
O
O
O
=
O
O
O
Scheme 1. A schematic representation of the MBBs A and B
built up from co-ligands X and Y and salicylate (with substituents
Z) and a trivalent metal centre.
number 6, the arrangement of the ligands around MnII
determine the structural motif such that a cis arrangement
of two water molecule ligands results in a 3D diamondoid
net, whereas a trans arrangement results in the construc-
tion of a 1D coordination polymer.
In this paper, we have focused our attention on the study
of the influence of the base, the presence or absence of co-
ligands and the influence of bulky substituents on the
aromatic ring of the salicylate on the shape and
dimensionality of the final products with reference to
the seven compounds (NHEt3)[MnIII(3-MeOsal)2
(MeOH)(H2O)] (1), [NaMnIII(3-MeO-sal)2(MeOH)2] (2),
[NaMnIII(sal)2(H2O)(MeOH)]· (MeOH) (3), [KMnIII(sal)2
(H2O)(MeOH)] · (MeOH) (4), [MnIIMn2III(3-MeOsal)4
(py)6(H2O)2] · 4H2O, (5), [MnIIMn2III(3-MeO-sal)4(py)4
(H2O)4]· 4MeOH, (6) and [MnIIMn2III(3-MeO-sal)4(2,20-
bipy)(H2O)3(MeOH)2]· 3MeOH (7) which illustrate this.
2
Results and discussion
2.1 Synthesis
All compounds can be prepared by the reaction of the
corresponding salicylate with a MnII salt on addition of
either base (NaOH, KOH, Et3N) or NBu4MnO4 in a
methanolic solution at room temperature. Under such
conditions, MnII is easily oxidised to MnIII. All compounds
are stable and retain their crystallinity on exposure to air.
2.2 Description of structures of compounds 1–7
2.2.1 (NHEt3)[MnIII(3-MeOsal)2(MeOH)(H2O)], 1
Compound 1 consists of an anionic mononuclear MnIII
complex with a triethylammonium counter cation
(Figure 1). The equatorial plane of the metal centre is
occupied by four phenoxo or carboxylate oxygen atoms
(O1, O2, O5 and O6) belonging to two bidentate 3-MeO-
sal22 ligands (mode I, Scheme 2). The two phenoxo
oxygens are cis to each other, as are the two carboxylate
oxygens, so that the two salicylate ligands are related by
idealised mirror symmetry. The axial positions X and Yare
occupied by a methanol and a water molecule so that the
MnIII complex forms a MBB of type A (Scheme 1). The
Figure 1. Structure of (NHEt3)[MnIII(3-MeOsal)2(MeOH)
(H2O)], 1 (top) and packing diagrams viewed along the b-axis
(centre) and a-axis (below). Hydrogen bonds are shown dotted.
four equatorial MnZO bond lengths (1.885(2), 1.910(2),
˚
1.883(2) and 1.921(2) A) and the two axial bond lengths
III
(2.245(2) and 2.265(2) A) are typical for Mn with an
˚
elongated Jahn–Teller axis. There is a hydrogen bond
between the NZH of the triethylammonium cation and the
carboxylate oxygen O7. Further intermolecular hydrogen
bonding, involving the aqua and methanol ligands together

Supramolecular Chemistry
535
H3CO
H3CO
H3CO
M
O
O
O
O
O
O
M
O
M
M
O
M
O
M
Mode I
Mode II
Mode III
M
O
O
O
M
O
M
O
M
M
O
M
M
Mode V
Mode IV
Scheme 2. Coordination modes of the salicylates found in compounds 1–7 (mode I, 1, 5, 6, 7; mode II, 2; mode III, 5, 6, 7 and mode IV
and mode V 3, 4).
with p–p stacking interactions (shortest C· · ·C distance
˚
3.413 A), builds the complexes into 2D supramolecular
sheets parallel to the [1 0 0] plane.
3-MeO-sal22 ligands (through phenoxo and carboxylate
oxygen atoms) and two methanol molecules in axial sites
(X ¼ Y ¼ MeOH, Scheme 1). Mn1 shows the expected
Jahn–Teller distortion, with equatorial bond lengths
Mn1ZO1 and Mn1ZO2 being 1.8650(14) and
2.2.2 [MnNa(3-MeO-sal)2(MeOH)2], 2
˚
1.9279(13) A, respectively, and that of Mn1ZO5 being
˚
2.2269(16) A. Na1 lies on a crystallographic twofold axis
The structure of compound 2 (Figure 2) consists of a 1D
coordination polymer of MnIII and Naþ ions arranged
alternately and bridged by the 3-MeO-sal22 ligands. Mn1 is
situated on a crystallographic inversion centre, thus
forming the trans A type MBB, ligated by two bidentate
and has a distorted octahedral environment being
coordinated by phenoxo, carboxylato methoxy oxygen
atoms from each of two adjacent MBBs. Mn1 and Na1 are
thus bridged by m-phenoxo (O1) and m-carboxylato (O2)
Figure 2. Structure of the 1D polymer, [MnIIINa(3-MeO-sal)2(MeOH)2], 2. Organic H-atoms are omitted for clarity. Colour code
(online): MnIII, purple; Na, orange; C, black and O, red.

536
S. Mukherjee et al.
oxygen atoms (mode II, Scheme 2), with MnZOZNa bond
angles 104.58(6)8 and 99.11(6)8, respectively, forming a 1D
coordination polymer. The chain structure is reinforced by
hydrogen bonds between the OZH groups of the methanol
ligands and non-coordinated carboxylate oxygens from
adjacent MBB. The distance between the Na and Mn ions is
2.2.4 [MnIIMn2III(3-MeOsal)4(py)6(H2O)2]· 4H2O, 5
The mixed-valence trinuclear structure of 5 is shown in
Figure 4. The central MnII, Mn(2), occupies an inversion
centre. The two equivalent MnIII centres, Mn(1) and
Mn(10), are each chelated (mode I, Scheme 2) in their
equatorial planes by two 3-MeOsal22 ligands, with two
trans-related pyridine ligands in the Jahn–Teller axial
sites, forming a type A MBB in which the salicylate
ligands are cis-related. The non-chelating carboxylate
oxygen O(3) from each of the MnIII MBBs coordinates to
Mn(2), forming syn-anti carboxylate bridges, with
3.3091(5) A, whereas the distance between two MnIII ions
˚
˚
in the chain is 6.0658(6) A. The inversion symmetry about
Mn1 forces the Na· · ·Mn· · ·Na angles in the chain to be
strictly 1808. However, the crystallographic twofold
symmetry about Na1 allows the Mn· · ·Na· · ·Mn angle to
be 132.85(4)8, resulting in the observed zigzag chain.
Hydrogen-bonded chains of alternating 3d and sodium ions
have been previously reported, for example with the 2,20-
biphenol ligand (13).
˚
Mn(1)· · ·Mn(2) being 5.134(5) A; Mn(1), Mn(2) and
Mn(10) are collinear as imposed by the crystallographic
symmetry. The octahedral coordination environment of
Mn(2) is completed by two pyridine and two aqua ligands.
The Mn-ligand bond lengths are typical for the respective
oxidation states. The four equatorial Mn(1)ZO distances
˚
are in the range 1.874(2)–1.925(2) A, whereas the two
˚
axial Mn(1)ZN lengths are 2.348(3) and 2.358(3) A;
distances Mn(2)ZO(3), Mn(2)ZO(9) and Mn(2)ZN(3)
2.2.3 [NaMnIII(sal)2(H2O)(MeOH)]· MeOH, 3 and
[KMnIII(sal)2(H2O)(MeOH)]· MeOH, 4
Compounds 3 and 4 crystallise isomorphously in the
triclinic space group P-1 with Z ¼ 2; therefore, only the
structure of 4 will be described here. The asymmetric unit
contains two independent half-MnIII cations (each on a
crystallographic inversion centre) and one Kþ cation (on a
general site), two salicylates, one aqua ligand and one
methanol ligand, and one lattice methanol. The two MnIII
centres Mn1 and Mn2 are each hexacoordinated in an
octahedral environment. Each is chelated, through
phenoxo and carboxylato oxygens, by two inversion-
related (sal)22 ligands, forming centrosymmetric type A
MBBs (Scheme 1), although the axial positions are
occupied differently in the two cases. For Mn1, the axial
positions are occupied by oxygen atoms O8 and O80 of two
methanol ligands, whereas for Mn2 they are occupied by
carboxylate oxygen O3 and its symmetry-equivalent,
belonging to two Mn1-based MBBs. Mn1 is thus linked by
syn-anti carboxylate bridges to Mn2 and Mn20, such as to
form a 1D chain with alternating Mn1 and Mn2 centres, in
which all Mn· · ·Mn linkages are equivalent (Mn1· · ·Mn2
˚
are 2.180(2), 2.200(2) and 2.262(3) A, respectively. The
trinuclear molecular structure is reinforced by hydrogen
bonds involving the aqua ligands on Mn(2) and the four
lattice waters per Mn3 unit.
2.2.5 [MnI2IIMnII(3-MeO-sal)4(py)4(H2O)4]· 2MeOH, 6
The centrosymmetric structure ofcompound6(Figure4(b))
is very similar to that of 5, but with the difference that one of
the two axial pyridine ligands on Mn(1) in 5 has been
replaced by an aqua ligand in 6. As in 5, the syn-anti
carboxylate bridges between the metal centres are
reinforced by hydrogen bonding involving the aqua ligands
on Mn(2) and the lattice methanol molecules. However, in
contrast to 5, the aqua ligand O(9) on Mn(1) now forms
intermolecular hydrogen bonds. Each hydrogen on O(9)
forms a bifurcated hydrogen bond to a phenoxo and a
methoxy oxygen (either O(1) and O(4), or O(5) and O(8)) of
a (3-MeO-sal)22 ligand on an adjacent molecule (Figure
4(c)), such that each trinuclear unit is linked by hydrogen
bonding to two other units, forming a staircase-like
supramolecular 1D chain.
˚
5.4954(12) A) and the Mn centres are strictly co-linear; the
chain is parallel to a þ b. The Kþ cation K1 is ligated by
two oxygens from the Mn1 MBB (O10 and O2) and two
from the Mn2 MBB (O4 and O500) (coordination modes V
and IV, respectively, see Scheme 2) so reinforcing the
structure of the chain. It is also ligated by O6 from an
adjacent chain, and in this way the chains are linked
into 2D sheets parallel to (0 0 1) through the Kþ cations
(Figure 3). The interchain Mn· · ·Mn distances are all
2.2.6 [MnI2IIMnII(3-MeO-sal)4(2,20-
bipy)(H2O)3(MeOH)2]· 2MeOH, 7
Compound 7 is also a trinuclear, mixed-valence manga-
nese complex, but here the metal centres form a triangular
array (Figure 5) in contrast to the linear arrangements in 5
and 6. The two MnIII ions Mn(1) and Mn(2) both form type
A MBBs and in both the respective salicylate ligands are
oriented cis to each other within the equatorial plane. The
two axial sites on Mn(1) are occupied by a methanol ligand
and a water ligand. One of the axial sites on Mn(2) is
˚
greater than 7.6 A.
The structure of 3 is very similar to that of 4, apart
from the expected shorter Na–O bond lengths than the
corresponding KZO distances in 4; the replacement of Kþ
by Naþ does not seem to have had a significant effect on
the overall structure.

Supramolecular Chemistry
537
Figure 3. Structure of [MnIIIK(sal)2(OH2)(MeOH)], 4: the 1D chain of MnIII MBBs showing linkage to Kþ cations (above) and the 2D
sheet parallel to (0 0 1) (below). Organic H-atoms are omitted for clarity. Colour code (online): MnIII, purple; K, plum; C, black and O,
red.
occupied by an outer carboxylate oxygen O(3) from the
MBB based on Mn(1) and the other by an aqua ligand. The
outer carboxylates, O(7) and O(11), from each MnIII MBB,
coordinate to the MnII ion Mn(3) cis to each other. The
distorted octahedral coordination sphere of Mn(3) is
completed by coordination from the two nitrogens of the
2,20-bipyridyl and the oxygens of two water molecules.
The three metal centres are thus linked by three syn, anti-
carboxylate bridges, forming an approximately isosceles
triangle, in which the two MnII· · ·MnIII distances,
products are 3.01 and 2.98 cm3 K/mol, respectively,
consistent with the expected value of 3.0 cm3 K/mol for
an isolated MnIII ion (S ¼ 2, g ¼ 2). Upon lowering the
temperature, the xT products gradually decrease to minima
of 1.52 cm3 K/mol at 4.5 K and 1.56 cm3 K/mol at 3.5 K for
3 and 4, respectively, and then increase up to 2.0 cm3 K/mol
at 1.8 K for both compounds, indicating that antiferromag-
netic interactions dominate between the MnIII centres. The
subsequent increase in xT below 5 K cannot be explained in
terms offerrimagnetic arrangements of spins since there are
equal number of the two types of MnIII centres within the
structure. However, it could be associated with spin canting
behaviour, although there is no evidence for the latter
phenomenon from M versus H measurements, (Figure S1 of
the Supplementary Information, available online). We thus
assume that the upturn in the xT product at low temperature
is due to slight canting of the spins within the layers in the
crystal packing, but with the critical temperature being too
low (below 1.8 K) for the canting to be observable in other
measurements (Figures S2 and S3 of the Supplementary
˚
4.6523(11) and 4.6874(11) A, are significantly shorter
than the MnIII· · ·MnIII separation of 5.2418(11) A.
˚
2.3 Magnetic properties
DC magnetic studies were carried out on polycrystalline
samples of 3–7. The temperature dependence of the xT
products in the 1.8–300 K temperature range at 1000 Oe is
shown in Figure 6. Isomorphous compounds 3 and 4 show
similar magnetic behaviour and the room temperature xT

538
S. Mukherjee et al.
Figure 4. Molecular structures of [MnIIMn2III(3-MeO-sal)4(py)6(H2O)2] · 4H2O
5
(upper) and [MnI2IIMnII(3-MeO-
sal)4(py)4(H2O)4]· 2MeOH 6 (middle) with the intermolecular hydrogen bonding in 6 (lower). Colour code (online): MnIII purple,
MnII pink, C black, O red, N blue, H grey, hydrogen bonds are shown as dotted green lines, organic H-atoms are omitted for clarity.
Information, available online). This idea is supported by the
structural data which show that the Jahn–Teller axes of
Mn(1) and Mn(2) are not co-parallel, which is consistent
with the presence of canting between their spins.
Furthermore, the data indicate that no long-range ordering
is promoted within the 2D layers, in contrast to related 3D
networks published previously (12a). The M versus H
measurements as a function of the field reveal a continuous
increase in the magnetisation, which reaches a value of 2.7
and 3.1 mB at 7 T for compounds 3 and 4, respectively. The
lack of saturation in the M versus H plot suggests the
presence of low-lying excited states that might be populated
when a field is applied. At higher field when the magnetic
interactions are overcome, a saturation of the magnetisation
at around 3 mB should be observed, since all spins will be
parallel as is indeed the case. The agreement between the
experimental magnitude of the magnetisation and the
expected value suggests that the magnetic interactions
between the spins are weak.

Supramolecular Chemistry
539
Based on the structures, both compounds can be
viewed as S ¼ 2 MnIII chains with the magnetic
interaction, J, between the MnIII sites mediated by syn-
anti carboxylate bridges. Such a regular antiferromagnetic
quantum S ¼ 2 spin chain model can be modelled with the
Hamiltonian (14):
X
H ¼ 22J SiSiþ1
:
i
The temperature dependence of the magnetic suscep-
tibility above 7 K could be reproduced by the analytical
expression deduced from the above equation. The fit of the
data gives g ¼ 1.99(1) and J/kB ¼ 21.15(2) K for 3 and
g ¼ 2.00(1) and J/kB ¼ 20.81(1) K for 4 (Table 1). The
interaction parameter, J, is in good agreement with the
weak antiferromagnetic interaction expected for such syn-
anti carboxylate bridges (12a).
Figure 5. Structure of the trinuclear cluster [MnI2IIMnII(3-MeO-
sal)4(2,20-bipy)(H2O)3(MeOH)2] in 7. Colour code (online):
MnIII purple; MnII pink; C black; O red; N blue and H grey.
The data for compounds 5 and 6 show that they have
similar magnetic behaviour as can be expected from the fact
that both have the same trinuclear MnIII–MnII–MnIII
metallic core. At 300 K, the xT products are 9.6 and
9.87 cm3 K/mol for 5 and 6, respectively, slightly lower than
the expected value of 10.38 cm3 K/mol for one MnII
(S ¼ 5/2, g ¼ 2) and two MnIII (S ¼ 2, g ¼ 2) ions
(Figure 6). On decreasing the temperature, the xT products
decrease continuously reaching 1.75 and 1.70 cm3 K/mol,
respectively, at 1.8 K, indicating that antiferromagnetic
interactions dominate within the trinuclear complexes and
compatible with S ¼ 3/2 ground states. The magnetic
behaviour of each compound follows the Curie–Weiss law
over the full temperature range of 1.8–300 K (Figure S4 of
the Supplementary Information, available online) with
Curie constants, C, of 9.8 and 10.9 cm3 K/mol, comparable
with the value of 10.375 cm3 K/mol expected for one MnII
(S ¼ 5/2, g ¼ 2) and two MnIII ions (S ¼ 2, g ¼ 2). The
negative Weiss constants, u, of 25.6 and 25.9 K,
respectively, also indicate the presence of antiferromag-
netic interactions between the spin carriers.
The M versus H measurements (Figures S5 and S6 of
the Supplementary Information, available online) at 1.8 K
both show a slow increase in the magnetisation with field,
reaching values of 9.1 for 5 and 10.5 mB at 7 T for 6. Full
saturation of the magnetisation was not observed, probably
as a result of the anisotropy of the high spin MnIII ion and
or the presence of low-lying excited states that might be
populated when a field is applied. For fields high enough to
overcome the antiferromagnetic interactions and align all
the spins parallel, the saturation magnetisation should be
13 mB for g ¼ 2. It is noteworthy that the M versus H curve
of 6 is S-shaped, which is a further indication of the
presence of antiferromagnetic interactions.
Figure 6. Temperature dependence of the xT products for 3 and
4 (left) 5–7 (right) at 1000 Oe (with x defined as the DC
magnetic susceptibility equal to M/H and normalised per
complex unit). The red solid lines correspond to the best fits,
see the text for fitting parameters. Inset: the semi-log plots to
magnify the low temperature regions.
The temperature dependence of the magnetic suscep-
tibility was modelled using a simple symmetrical trimer
approach assuming that the MnII–MnIII interactions (J1)

540
S. Mukherjee et al.
Table 1. Fitting parameters for compounds 3–7 obtained using the models discussed in the text.
Compounds
[NaMnIII(sal)2(H2O)(MeOH)]· MeOH (3)
[KMnIII(sal)2(H2O)(MeOH)]· MeOH (4)
g
J1/kB in K for MnII–MnIII J2/kB in K for MnIII–MnIII
1.99(1)
2.00(1)
1.93(1)
2.00(1)
–
–
21.15(2)
20.81(1)
[MnIIMnI2II(3-MeOsal)4(py)6(H2O)2]· 4H2O (5)
[MnI2IIMnII(3-MeOsal)4(py)4(H2O)4]· 4MeOH (6)
20.64(1)
20.57(1)
20.63(1)
–
–
[Mn2IIIMnII(3-MeOsal)4(2,20-bipy)(H2O)3(MeOH)2]· 3MeOH (7) 1.98(1)
20.50(3)
are identical by symmetry and with the Heisenberg spin
Hamiltonian:
Information, available online), suggesting the presence
of low-lying excited states that might be populated when a
field is applied. This observation again indicates that the
antiferromagnetic interactions are weak in this complex.
The temperature dependence of the magnetic suscep-
tibility was treated with the symmetrical trimer model and
the MnII–MnIII interactions (J1) were considered equiv-
alent although this is not imposed by crystal symmetry.
Nevertheless, this is a good approximation given that the
syn-anti carboxylate bridges are very similar and the
Heisenberg spin Hamiltonian can then be written as
H ¼ 22J1ðS1AS2 þ S1BS2Þ;
where J1 is the exchange interactions in the trimer between
adjacent MnII and MnIII ions, S1A ¼ S1B ¼ 2 is for MnIII,
and S2 ¼ 5/2 is for MnII. The application of the van Vleck
equation (15) to the Kambe vector coupling scheme (16)
allows a determination of the low-field analytical
expression of the magnetic susceptibility (17). The
experimental data from 300 to 1.8 K can be reproduced
very well using this model (Figure 6) with the best sets of
parameters being J1/kB ¼ 20.64(1) K and g ¼ 1.93(1) for
5 and J1/kB ¼ 20.57(1) K and g ¼ 2.00(1) for 6,
respectively. This model gives an estimate for these values
but does not take into account any contribution arising
from zero-field splitting. The magnitude of these
interactions through the syn-anti carboxylate bridge
between MnIII and MnII is comparable with those found
for 3 and 4 and those in the literature (12a). It is
noteworthy that for 6 below 5 K, the theoretical curve after
fitting the data is a bit higher than the experimental values.
We can ascribe this to the presence of additional inter-
complex antiferromagnetic interactions facilitated by the
hydrogen bonds found in the structures. Although
changing the reaction solvent from pyridine for 5 to
methanol for 6 does lead to some changes in structural
details, the basic magnetic signature of the trinuclear core
dominates the susceptibility data until relatively low
temperatures allow for the influence of the changes in
hydrogen bonding affecting the long-range interactions in
the structure to be observed.
H ¼ 22J1ðS1AS2 þ S1BS2Þ 2 2J2ðS1AS1BÞ;
where J1 and J2 are the exchange interactions in the trimer
between MnII and MnIII ions and between two MnIII ions,
respectively. S1A ¼ S1B ¼ 2 is for MnIII and S2 ¼ 5/2 is for
MnII centres. The application of thevan Vleck equation (15)
to Kambe’s vector coupling scheme (16) allows a
determination of the low field analytical expression of the
magnetic susceptibility given (17). This model reproduces
the experimental data very well from 300 to 1.8 K (Figure 5)
with the best set of parameters J1/kB ¼ 20.63(1) K,
J2/kB ¼ 20.50(3) K and g ¼ 1.98(1). The magnitude of
these interactions through the syn-anti carboxylate bridges
between MnII and MnIII or between two MnIII ions is
comparable with those obtained for compounds 5 and 6 and
published data (12a).
2.4 Discussion
Now, we can consider what we have found to be the guiding
principle behind this coordination chemistry, or, to put it in
another way, how we can understand how to use the happy
chance of serendipity, or serendipitous self-assembly, to
persuade chemical systems towards our targets. In fact, we
can compare this interplay and interaction of organic and
inorganic moieties with what occurs in biological systems
in terms of ordering and fitting structures for specific
purposes. We can also relate this to recent endeavours in the
field of natural product synthesis by which it has been
shown that metal centres can lead to regio-, stereo-,
enantio-selectivity as well as increasing the ‘atom
efficiency’ of chemical reactions (18). In particular, we
have here a type of ‘policeman’ molecular entity (MBB)
The room temperature magnetic susceptibility product
of 7 at 1000 Oe is 10.0 cm3 K/mol (Figure 6) in agreement
with the expected value (10.38 cm3 K/mol) for the
presence of one MnII metal ion (S ¼ 5/2, g ¼ 2) and two
MnIII ions (S ¼ 2, g ¼ 2). On decreasing the temperature,
the xT product continuously decreases to reach
1.7 cm3 K/mol at 1.8 K, indicating dominant antiferro-
magnetic interactions in the triangular complex, compa-
tible with an S ¼ 3/2 ground state. The M versus H
measurements at 1.8 K reveal similar magnetic behaviour
to compounds 5 and 6. The magnetisation curve again
shows a steadily continuous increase to reach a value of
9.6 mB at 7 T (Figure S7 of the Supplementary

Supramolecular Chemistry
541
standing at a junction and directing how the chemical traffic
should proceed. The nature of the policeman’s signals
places the reactants in ideal positions in order to create
specified structures. The development of this principle will
allow us to set goals in targeted syntheses so that the
serendipitous self-assembly approach becomes more like
the programmed approach of organic synthesis. Further-
more, this is an important point of relevance to Systems
Chemistry, for if we are evergoing to recreate the extremely
complicated chemistry behind complex molecular machin-
ery such as is found, for example in Photosystem II, then we
need to develop coordination chemistry principles to a
higher level and, indeed, the level in which the exquisite
control over the oxidation, spin and lability states of metal
ions which is exercised in the biological chemistry of
organisms on our planet can be achieved.
compounds 2–4 shows that the bulky methoxy substituent
on the phenyl ring of 2 ‘blocks’ the dimensionality of the
final product to give a molecular compound, whereas 3 and
4 are heterometallic 2D coordination polymers. A similar
effect is observed in compounds 5 and 6, which are
trinuclear, in contrast towhat we found previously, in which
the substituent was methyl rather than methoxy and a 3D
diamondoid framework resulted. Thus, the bulky MeO
substituent does not allow for the MBB to be extended into
a 3D structure in this way (12a). The change in co-ligand
also affects the structural motif of the final product. We
have seen previously (12b) that using 2,20-bipy as co-ligand
leads to a type B MBB (Scheme 1, right), although in the
case of compound 7 further coordination on the ‘node’
sterically favours the formation of a triangular structure
formed.
Scheme 3 shows a representation of the ‘policeman’
important in the context of the results we present here. The
relevant structure-directing features are the trans arrange-
ment of the outer carbonyl oxygens, which define the
geometry of the node, and the nature of the substituents Z
on the phenyl ring. In the cases we have discussed here, Z
is always at the third position, but we have discussed
elsewhere about the influence on the resulting superstructure
if we move Z to other positions on the phenyl ring (12a).
Here, we find that whenever a sodium source is used
(NaN3, NaOAc, Na2CO3, 3-MeO-salHNa or salHNa), we
always obtain compound 2 as the most favoured product
and this is also true for the reactions with the ligand 3-MeO-
salHNa and 3 for reactions with ligand salH2. Also,
comparing compounds 5 and 6, excess pyridine in the
reaction solution results in all the axial positions of the
metal centres in the MBB as well the ‘nodes’ being
occupied. Furthermore, delaying the addition of the base to
the reaction solution of 6 (see Section 5 for details) results
in the isolation of the different MBB 5. From a structural
point of view, compound 1, which is a mononuclear
compound, can be isolated with excess of Et3N, although
changing the base to NaOH in 2 results in a heterometallic
1D coordination polymer. A comparison of the structures of
3
Conclusion
A systematic investigation into the coordination chemistry
of MnIII salicylates has been made. It has been possible to
judge the influence of base, the presence or absence of co-
ligands and the nature of the substituents on the phenyl ring
of the salicylate on the shape and dimensionality of the final
products by considering the seven new compounds
summarised in Table 2 as well as previous results on
related systems revealing the usefulness of this MBB
approach in directing product formation. In particular,
comparing the results to those obtained by us previously
(12a) in which similar trinuclear units can form the
repeating units of the polymeric chain and networks, this
study demonstrates that the bulkier methoxy group of 3-
MeO-salH2 prevents the bridging of the MnIII centres to the
MnII centres of another trinuclear unit. Instead, the
coordination sphere of each MnII is completed by two
pyridine molecules, leading to discrete structures rather
than diamondoid networks. Although the modification of
solvents and substituents on salicylate influences the final
resulting structures, this does not affect the magnetic
properties in any significant way. All complexes show
antiferromagnetic interactions between the metal centres
similar tothoseobservedin the extended systems. However,
as a result of the 3D nature of the networks we described
previously, these showed remanent magnetisation consist-
ent with ferrimagnetic long-range ordering (12a).
Node
Z
O
X
M
Y
O
O
O
O
4
Experimental
4.1 Physical measurements
O
All chemicals and solvents were obtained from commer-
cial sources and were used as received. The reactions were
carried out under aerobic conditions. The elemental
analyses (C, H and N) were carried out using an Elementar
Vario EL analyser, FT-IR spectra were measured on a
Z
Node
Scheme 3. A schematic representation of MBB.

542
S. Mukherjee et al.

Supramolecular Chemistry
Perkin-Elmer Spectrum One spectrometer with samples 4.2.2 Compound 2
543
prepared as KBr discs, and X-ray powder diffraction
patterns for all compounds were measured at room
temperature using a Stoe STADI-P diffractometer with Cu-
Ka radiation. Phase purity was confirmed by comparison
of the powder diffraction pattern of bulk product with that
simulated from the crystal structure. Magnetic suscepti-
bility measurements were obtained using a Quantum
Design SQUID MPMS-XL susceptometer. The magnet-
ometer operates between 1.8 and 400 K for DC applied
fields of 27 to þ7 T. Measurements were carried out on
polycrystalline samples of 18.6 mg (3), 17.8 mg (4),
26.96 mg (5), 9.6 mg (6) and 16.2 mg (7). AC susceptibility
measurements were measured with an oscillating AC field
of 3 Oe and AC frequencies ranging from 1 to 1500 Hz.
The magnetic data were corrected for the sample holder
and the diamagnetic contribution. The samples were first
checked for the presence of ferromagnetic impurities by
measuring the magnetisation as a function of the field at
100 K. For pure paramagnetic or diamagnetic systems, a
perfect straight line is expected and is indeed observed for
these compounds indicating the absence of any ferromag-
netic impurities. Single-crystal X-ray crystallographic data
were collected at 150 K on a Stoe IPDS II area detector
diffractometer (1, 4 and 6), or at 100 K on a Bruker
SMART Apex CCD diffractometer (2, 3, 5 and 7) using
graphite-monochromated Mo-Ka radiation (Table 3).
Semi-empirical absorption corrections were applied
using SADABS (19a) or XPREP in SHELXTL (19b). The
structures were solved using direct methods, followed by
full-matrix least-squares refinement against F 2 (all data)
using SHELXTL (19b). Anisotropic refinement was used
for all ordered non-H atoms; organic H atoms were placed
in calculated positions, whereas coordinates of hydroxo or
water H atoms were refined in most cases. CCDC
776386–776392 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Mn(ClO4)2 · 6H2O (0.036 g, 0.2 mmol) was added to a
methanolic solution (15 ml) of 3-MeO-salH2 (0.017 g,
0.1 mmol) and Et3N (0.013 ml, 0.2 mmol) to give a light
yellow solution. After a few minutes, NaN3 (0.013 g,
0.2 mmol) dissolved in 5 ml H2O was added slowly
followed by stirring for 2 h. The resulting black solution
was filtered and left to evaporate. After 2 days, small black
crystals were obtained. The crystals were isolated by
filtration, washed with methanol and dried in air. Yield:
32%. Anal. calcd for C18H20MnNaO10 (found): C, 45.57
(45.48); H 4.22 (4.25)%. Selected IR data (KBr disc,
cm21): 3498 (s), 2984 (m), 2932(m), 1596 (s), 1579 (s),
1545 (s), 1476 (s), 1325 (s), 1252 (m), 1208 (m), 1154 (m),
1069 (s), 856 (s), 809 (m), 755 (s), 698 (s), 465 (m), 420 (m).
4.2.3 Compound 3
Mn(OAc)2 · 4H2O (0.250 g, 1.0 mmol) was added to a
methanolic solution (20 ml) of Na(SalH) (0.240 g,
1.5 mmol) to give a black solution. The solution was
stirred for 2 h. The solution was filtered and the filtrate was
left to evaporate slowly. Black crystals were obtained the
next day. Yield: 78%. Anal. calcd for C16H18MnNaO9
(found): C, 44.46 (44.12); H, 4.20 (4.31)%. IR (KBr disc,
cm21): 3378 (b), 3062 (w), 2928 (w), 1604 (s), 1577 (s),
1534 (s),1460 (s), 1367 (s), 1345 (s), 1231 (s), 1145 (s),
1104 (w), 1040 (m), 897 (m), 842 (s), 754 (s), 694 (m), 656
(m) 592 (m).
4.2.4 Compound 4
Mn(OAc)2 · 4H2O (0.250 g, 1.0 mmol) was added to a
methanolic solution (20 ml) of SalH2 (0.210 g, 1.5 mmol)
and KOH (0.168 g, 3.0 mmol) was added giving a black
solution which was stirred for 2 h and then filtered and left
to evaporate slowly. Black crystals were obtained the next
day. Yield: 78%. Anal. calcd for C16H18KMnO9 (found): C,
42.86 (42.77); H, 4.05 (3.98)%. IR (KBr disc, cm21): 3379
(b), 3062 (w), 2928 (w), 1603 (s), 1579 (s), 1535 (s),1461
(s), 1365 (s), 1344 (s), 1230 (s), 1142 (s), 1104 (w), 1040
(m), 897 (m), 843 (s), 755 (s), 694 (m), 656 (m) 592 (m).
4.2 Synthesis
4.2.1 Compound 1
Mn(ClO4)2 · 6H2O (0.180 g, 0.5 mmol) was added to a
methanolic solution (20 ml) of 3-MeO-salH2 (0.168 g,
1 mmol) and Et3N (0.130 ml, 2 mmol) to give a yellow
solution. After 1 h, a small amount of precipitate was
observed and colour of the solution turned greyish black.
The solution was stirred for 2 h. The solution was filtered
and the filtrate was left to evaporate. Black diamond-shaped
crystals were obtained the next day. Yield: 78%. Anal.
calcd for C23H34MnNO10 (found): C, 51.21 (51.19); H, 6.31
(6.34); N, 2.59 (2.56)%. IR (KBr disc, cm21): 3435 (b),
2935 (m), 1594 (s), 1546 (s), 1492 (s), 1320 (m), 1248 (s),
1150 (s), 1056 (m), 758 (m), 678 (m), 435 (w).
4.2.5 Compound 5
3-MeO-salH2 (1.01 g, 6.00 mmol) and Mn(OAc)2 · 4H2O
(0.5 g, 2.0 mmol) were dissolved in pyridine (10 ml) to
give a clear yellow solution. The solution was stirred while
solid (NBu4)(MnO4) (0.15 g, 0.4 mmol) was added in
small portions over approximately 10 min leading to a
black liquor which was layered with an equal volume of
petroleum ether. After 2 days, dark green crystals suitable
for X-ray diffraction studies were deposited. The crystals
were isolated by filtration, washed with ether and dried in

544
S. Mukherjee et al.
s
s
a
b
g
r
m

Supramolecular Chemistry
545
Soc. Rev. 2008, 37, 191–214; (d) Robson, R. Dalton Trans.
2008, 37, 5113–5131; (e) Long, J.R.; Yaghi, O.M. Chem.
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air. Yield: 72%. Anal. calcd for C62H62Mn3N6O22 (found):
C, 52.82 (52.84); H, 5.91 (5.97); N, 4.44 (4.40)%. Selected
IR data (KBr disc, cm21): 3505 (s), 3461 (b), 2986 (m),
2934 (m), 1594 (s), 1578 (s), 1549 (s), 1474 (s), 1443 (s),
1372 (m), 1348 (m), 1327 (s), 1249 (m), 1206 (m), 1152
(m), 1066 (s), 853 (s), 809 (m), 760 (s), 699 (s), 674 (m),
470 (m), 417 (m).
˘
(2) (a) Dinca, M.; Long, J.R. Angew. Chem. Int. Ed. 2008, 47,
6766–6779; (b) Chae, H.K.; Siberio-Perez, D.Y.; Kim, J.;
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(3) (a) Proch, S.; Herrmannsdorfer, J.; Kempe, R.; Kern, C.;
Jess, A.; Seyfarth, L.; Senker, J.; Chem. Eur. J. 2008, 14,
8204–8212; (b) Sun, C.-Y.; Liu, S.-X.; Liang, D.-D.; Shao,
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1060–1071.
4.2.6 Compound 6
MnCl2 · 4H2O (0.079 g, 0.4 mmol) was added to a
methanolic solution (20 ml) of 3-MeO-salH2 (0.101 g,
0.6 mmol) and pyridine (0.202 ml, 1.6 mmol) to give a
light yellow solution. The solution was left stirring
overnight and then Et3N (0.100 ml, 0.7 mmol) was added
slowly. Within a few minutes, the solution turned blacks.
The following day black needle-shaped crystals were
obtained. The crystals were collected by filtration, washed
with cold methanol and air dried. Yield: 64%. Anal. calcd
for C54H60Mn3N4O22 (found): C, 49.71 (50.54); H, 4.62
(4.68); N, 4.31 (4.36)%. Selected IR data (KBr disc,
cm21): 3448 (s), 3465 (b), 2985 (m), 2932 (m), 1592 (s),
1575 (s), 1542 (s), 1469 (s), 1444 (s), 1366 (m), 1342 (m),
1324 (s), 1237 (m), 1145 (m), 1062 (s), 849 (s), 798 (m),
754 (s), 694 (s), 670 (m), 465 (m), 419 (m).
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a cds network:
4.2.7 Compound 7
(b) Kostakis, G.E.; Casella, L.; Hadjiliadis, N.; Monzani,
E.; Kourkoumelis, N.; Plakatouras, J.C. Chem. Commun.
2005, 3859–3861; for mog networks: (c) Kostakis, G.E.;
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Mn(OAc)2 · 4H2O (0.368 g, 1.5 mmol) was added to a
methanolic solution (20 ml) of 3-MeO-salH2 (0.168 g,
1 mmol). After 5 min, 2,20-bipy (0.039 g, 5 mmol) was
added giving a yellow solution and then Et3N (0.100 ml,
0.7 mmol) was added. The resulting black solution was left
to stand and after a few days black crystals suitable for X-
ray analysis were obtained. The crystals were collected by
filtration, washed with cold methanol and air dried. The
crystals lost crystallinity when left in air without the
mother liquor for more than 1 week. Yield: 48%. Anal.
calcd for C46H54Mn3N2O23 (found): C, 47.23 (47.26); H,
4.61 (4.62); N, 2.39 (2.40)%. Selected IR data (KBr disc,
cm21): 3400 (b), 2925 (m), 1587 (s), 1551 (s), 1480 (s),
1442 (s), 1363 (m), 1335 (m), 1244 (m), 1065 (m), 857
(m), 750 (m), 430 (w).
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Acknowledgements
Support from the EU network of Excellence MAGMANet
(NMP3-CT-2005-515767), the EC-TMR Network QuEMolNa
(MRTN-CT-2003-504880), the University of Bordeaux, the
´
CNRS, the Region Aquitaine, the DFG (CFN and SPP-1137) is
acknowledged.
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