The use of di-2-pyridyl ketone in manganese(II) benzoate chemistry: Two novel Mn3II linkage isomers containing the ketone form of the ligand and a neutral Mn4II cubane containing the ligand in its gem-diolate(-1) form

Article abstract of DOI:10.1016/j.inoche.2007.11.025

The use of di-2-pyridyl ketone, (py)₂CO, in manganese(II) benzoate chemistry has yielded two Mn₃^II linkage isomers containing the ketone form of the ligand and a neutral Mn₄^II cubane cluster containing the gem-diolate(-1) form of the ligand. The 3:2 Mn(O₂CPh)₂ · 2H₂O/(py)₂CO reaction system in MeCN gives a mixture of the orange complex [Mn₃(O₂CPh)₆{(py)₂CO-κ ²N,N′}₂] (1) and the yellow compound [Mn₃(O₂CPh)₆{(py)₂CO-κ ²N,O}₂] · 2MeCN (2 · 2MeCN). The known compound [Mn₆O₂(O₂CPh)₁₀(MeCN) ₄] (3) appears as a by-product when the initial reaction solution, that leads to 1 and 2 · 2MeCN, is allowed to slowly evaporate in the air. The trinuclear molecules adopt a linear structure in both complexes, with one monoatomically bridging η¹:η¹:μ₂ and two syn,syn-η¹:η¹:μ₂ carboxylate groups spanning each pair of Mn^II ions. The terminal Mn^II ions are each capped by one chelating-N,N′ (py)₂CO ligand in 1 and by one chelating-N,O (py)₂CO molecule in 2. The 1:1 reaction of Mn(O₂CPh)₂ · 2H₂O and (py)₂CO in CH₂Cl₂ results in the isolation of[Mn₄(O₂CPh)₄{(py)₂C(OH)O} ₄] (4). The tetranuclear molecule has a cubane topology with the Mn^II ions and the deprotonated oxygen atoms from the (py)₂C(OH)O^- ligands occupying alternate vertices. The IR data are discussed in terms of the nature of the bonding. The magnetic properties of 4 in the 300-5 K range have been modeled with two J values and reveal weak intramolecular antiferromagnetic interactions. The low temperature X-band EPR spectra of 1, 2 and 4 are also discussed.

Full text of DOI:10.1016/j.inoche.2007.11.025

Available online at www.sciencedirect.com
Inorganic Chemistry Communications 11 (2008) 196–202
www.elsevier.com/locate/inoche
The use of di-2-pyridyl ketone in manganese(II) benzoate
chemistry: Two novel MnI3I linkage isomers containing the ketone
form of the ligand and a neutral MnI4I cubane containing the ligand in its
gem-diolate(-1) form
Constantinos C. Stoumpos a, Ian A. Gass b, Constantinos J. Milios a,b, Elena Kefalloniti a,
Catherine P. Raptopoulou c, Aris Terzis c, Nikolia Lalioti a, Euan K. Brechin b,*
Spyros P. Perlepes a,*
,
a Department of Chemistry, University of Patras, 265 04 Patras, Greece
b Department of Chemistry, The University of Edinburgh, West Mains Road, EH9 3JJ Edinburgh, UK
c Institute of Materials Science, NCSR ‘‘Demokritos”, 153 10 Aghia Paraskevi, Attikis, Greece
Received 25 September 2007; accepted 24 November 2007
Available online 8 December 2007
Dedicated to the memory of Xavier Solans, a great structural chemist and a great friend.
Abstract
The use of di-2-pyridyl ketone, (py)2CO, in manganese(II) benzoate chemistry has yielded two MnI3I linkage isomers containing the
ketone form of the ligand and a neutral MnI4I cubane cluster containing the gem-diolate(-1) form of the ligand. The 3:2
Mn(O2CPh)2 ꢀ 2H2O/(py)2CO reaction system in MeCN gives a mixture of the orange complex [Mn3(O2CPh)6{(py)2CO-j2N,N0}2] (1)
and the yellow compound [Mn3(O2CPh)6{(py)2CO-j2N,O}2] ꢀ 2MeCN (2 ꢀ 2MeCN). The known compound [Mn6O2(O2CPh)10(MeCN)4]
(3) appears as a by-product when the initial reaction solution, that leads to 1 and 2 ꢀ 2MeCN, is allowed to slowly evaporate in the air.
The trinuclear molecules adopt a linear structure in both complexes, with one monoatomically bridging g1:g1:l2 and two syn,syn-
g1:g1:l2 carboxylate groups spanning each pair of MnII ions. The terminal MnII ions are each capped by one chelating-N,N0 (py)2CO
ligand in 1 and by one chelating-N,O (py)2CO molecule in 2. The 1:1 reaction of Mn(O2CPh)2 ꢀ 2H2O and (py)2CO in CH2Cl2 results in
the isolation of [Mn4(O2CPh)4{(py)2C(OH)O}4] (4). The tetranuclear molecule has a cubane topology with the MnII ions and the depro-
tonated oxygen atoms from the (py)2C(OH)Oꢁ ligands occupying alternate vertices. The IR data are discussed in terms of the nature of
the bonding. The magnetic properties of 4 in the 300–5 K range have been modeled with two J values and reveal weak intramolecular
antiferromagnetic interactions. The low temperature X-band EPR spectra of 1, 2 and 4 are also discussed.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Di-2-pyridyl ketone complexes; EPR spectra; Magnetic properties; Manganese(II) benzoate clusters; Manganese(II) cubanes
Polynuclear manganese carboxylate chemistry is an area
of research that has attracted scientists from multi-disci-
plinary fields including biology [1], material science [2],
magnetochemistry [3], physics [4] and synthetic inorganic
chemistry [5]. For example, in material science a great num-
ber of polynuclear manganese carboxylate complexes have
been found to possess large spin ground states [6] and some
have also been shown to display the phenomenon of single-
molecule magnetism [7]. The latter property is the ability of
*
Corresponding authors. Tel.: +44 131 650 7545 (E.K. Brechin); tel.:
+30 2610 997146; fax: +30 2610 997118 (S.P. Perlepes).
E-mail addresses: ebrechin@staffmail.ed.ac.uk (E.K. Brechin), perle-
pes@patreas.upatras.gr (S.P. Perlepes).
1387-7003/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2007.11.025

C.C. Stoumpos et al. / Inorganic Chemistry Communications 11 (2008) 196–202
197
discrete molecules to exhibit the superparamagnetic-like
behaviour of slow magnetization relaxation and thus to
behave as magnets below their blocking temperature.
Discovering new preparative routes towards the syn-
thesis of manganese carboxylate clusters is thus of
intense interest not only for the discovery of completely
new compounds but also as a means of building up fam-
ilies of related species so that structure–property relations
can be developed. With this in mind, our group [8] and
others [9] have been exploring ‘ligand blend’ reactions
involving the monoanion, (py)2C(OH)Oꢁ, or the dianion,
ðpyÞ2CO22ꢁ, of the gem-diol form (derivative) of di-2-pyr-
idyl ketone, (py)2CO (the formulae of these ligands are
shown in Fig. 1) and carboxylates in Mn chemistry, with
the belief that they can foster the formation of discrete
clusters. The reactions of (py)2CO with 3d-metal ions
have been well studied over the years [10]. Water and
alcohols (ROH) have been shown to add to the carbonyl
group upon coordination of the carbonyl oxygen and/or
the pyridyl rings forming the ligands (py)2C(OH)2 [the
gem-diol form of (py)2CO] and (py)2C(OR)(OH) [the
hemiacetal form of (py)2CO], respectively (Fig. 1). The
immense structural diversity displayed by the 3d-metal
complexes reported stems in part from the ability of
(py)2C(OH)Oꢁ, (py)2C(OH)Oꢁ and ðpyÞ2CO22ꢁ to exhibit
not less than 10 distinct bridging (l2–l5) coordination
modes [10]. Employment of carboxylates as ancillary
ligands in the reaction mixtures gives an extraordinary
structural flexibility in the mixed-ligand systems, allowing
the synthesis of a variety of 3d-metal clusters with nucle-
arities ranging from 3 to 14 [8–12], and with interesting
physical properties including single-molecule magnetism
[13].
½MnI4IðO2CMeÞ3fðpyÞ2CðOHÞOg4ðH2OÞꢂðClO4Þ [9] with a
cubane topology and a mixed-valent acetate cluster
½MnI1I0MnI4IIO4ðO2CMeÞ fðpyÞ CðOHÞOg4ꢂ
comprising
subcores each of which is
20
2
10þ
two ½MnI4IMnI2IIðl4 ꢁ OÞ ꢂ
2
attached to a seventh MnII ion [8]. In the present work,
we describe the first use of (py)2CO in Mn benzoate chem-
istry that resulted in the isolation of two novel MnI3I linkage
isomers containing the ketone form of the ligand [(py)2CO,
see Fig. 1] and a MnI4I cubane containing the ligand in its
gem-diolate(-1) form [(py)2C(OH)Oꢁ, see Fig. 1].
The 3:2 reaction between Mn(O2CPh)2 ꢀ 2H2O and
(py)2CO in freshly distilled MeCN at room temperature gave
a pale yellow solution which upon storage in a closed flask
for one week turned to pale orange and yielded crystals that
were obviously a mixture of two products. Microscopic
examination showed both orange and yellow prisms to be
present in a visual ratio of 4:1. The total yield (based on
the total available Mn) is ꢃ55%. The difference in colour
was fortuitous and allowed easy manual separation of the
two materials. The orange crystals are stable in the normal
laboratory atmosphere for at least 3 days, whereas the yel-
low ones collapse rapidly giving a yellow powder. The IR
spectra of the orange and yellow samples show a strong band
at 1710 and 1640 cmꢁ1, respectively, suggesting that the
ligand is present in its ketone form [14]. Somewhat to our
surprise both dried samples gave identical analytical results,
consistent with the empirical formula Mn(O2CPh)2-
{(py)2CO}0.7 [15]. Full single crystal X-ray data sets were
collected for both compounds and the structures solved
[16,17]. The orange crystals proved to be [Mn3(O2CPh)6-
{(py)2CO}2] (1), while the yellow ones were shown to be
[Mn3(O2CPh)6{(py)2CO}2] ꢀ 2MeCN (2 ꢀ 2MeCN). If the
initial reaction solution – that leads to 1 and 2 ꢀ 2MeCN –
is left to slowly evaporate in the air, its colour turns to red
brown and few reddish brown crystals of the known
(py)2CO-free cluster ½MnI4IMn2IIIO2ðO2CPhÞ ðMeCNÞ ꢂ (3)
Although the use of (py)2CO-based ligands has been
investigated widely in Fe, Co, Ni, Cu and Zn carboxylate
chemistry [8–13], its use in Mn carboxylate chemistry is
confined to two examples: the cationic acetate complex
10
4
[18] appear as a by-product [19].
OH
C
OR
C
C
N
N
N
N
N
N
O
OH
OH
(py)2CO
(py)2C(OR)(OH)
(R=Me, Et, ...)
(py)2C(OH)2
OR
C
OH
C
N
N
N
N
N
N
C
O-
O-
-O
O-
2-
(py)2C(OR)O-
(R=Me, Et, ...)
(py)2C(OH)O-
(py)2CO2
Fig. 1. The structural formulae of the ligands discussed in the text; note that (py)2C(OH)2, (py)2C(OR)(OH) and all four anions do not exist as free species
but exist only in their respective metal complexes.

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C.C. Stoumpos et al. / Inorganic Chemistry Communications 11 (2008) 196–202
The crystal structure of 1 [17] reveals the formation of
The centrosymmetric {Mn(O2CPh)3Mn(O2CPh)3Mn}
unit present in complex 2 ꢀ 2MeCN (Fig. 3) is almost iden-
tical to that present in 1; however, the termini of the former
are each capped by one bidentate chelating-N,O(g2 or
jN,O) (py)2CO ligand. The Mn(1)NO5 octahedron of
2 ꢀ 2MeCN is more distorted than the corresponding
Mn(1)N2O4 octahedron of 1; for example, the three trans
angles around Mn(1) are 145.8(1), 160.2(1) and 156.4(1)°
in 2 ꢀ 2MeCN (average 154.1(1)°) compared to 147.0(1),
162.6(1) and 174.4(1)° in 1 (average 161.3(1)°). The more
severe distortions in the former arise from the five-mem-
bered chelating ring with a narrow N(1)–Mn(1)–O(1) bond
angle (70.4(1)°) and an acute O(6)–Mn(1)–O(7) angle
(57.5(1)°). The Mn(1)–O(7) bond is relatively strong with
trinuclear molecules (Fig. 2). The central metal ions,
Mn(2), which is located on a crystallographic inversion
center, is coordinated by six oxygen atoms belonging to
six different benzoates. Thus, the trinuclear molecule
adopts a linear structure, with one monoatomically bridg-
ing g1:g1:l2 and two syn,syn-g1:g1:l2 carboxylate groups
spanning each pair of MnII. The termini of the
{Mn(O2CPh)3Mn(O2CPh)3Mn} unit are each capped by
one bidentate chelating-N,N0 (g2 or jN,N0) (py)2CO ligand,
resulting in six coordination at these sites (Mn(1),Mn(10)).
The Mn(1)N2O4 octahedron is significantly distorted; the
main distortion arises from the acute O(6)–Mn(1)–O(7)
angle (56.8(1)°). The Mn(2)O6 octahedron is almost per-
fect. The Mn(2)–O bond lengths are in the narrow
˚
a distance of 2.209(3) A and thus 2 ꢀ 2MeCN belongs to
˚
2.133(2)–2.214(2) A range, with the Mn(2)–O(6) distance
class III in Lippard’s classification scheme [22]. The intral-
igand pyridyl ring dihedral angle is 49.6°.
(that involving the bridging oxygen) longer as expected.
˚
The C(6)–O(1) distance (1.210(6) A) is comparable to the
Complexes 1 and 2 ꢀ 2MeCN are linkage isomers. This is
the first case of true linkage isomerism in the coordination
chemistry of (py)2CO. Toyama et al. have recently
prepared the complexes trans(Cl), cis(S)-[RuCl2{(py)2CO-
j2N,O}(dmso-S)2] and cis(Cl),cis(S)-[RuCl2{(py)2CO-
j2N,N0}(dmso-S)2] [20] which can be considered as linkage
isomers; however, these complexes also exhibit geometrical
isomerism.
The most interesting feature of structure 2 ꢀ 2MeCN is
the j2N,O coordination mode of (py)2CO (II in Fig. 4).
In the majority [10,20] of the metal complexes containing
bidentate chelating (py)2CO molecules, the ligands are in
the j2 N,N0 mode (I in Fig. 4). Complex 2 ꢀ 2MeCN is
reported double bond values [20]. The six-membered che-
lating ring Mn(1)N(1)C(5)C(6)C(7)N(2) adopts a slight
boat conformation with the Mn(1) and C(6) atoms 0.032
˚
and 0.099 A, respectively, below the plane defined by the
remaining four atoms. The Mn–N and Mn–O bond lengths
agree well with the values expected for octahedral high-spin
Mn(II) complexes [21]. Complex 1 is characterized by mod-
˚
erate Mn(1)–O(7) (2.346(3) A) and Mn(1)ꢀ ꢀ ꢀMn(2)
˚
(3.552(2) A) distances and can be placed in class II in the
‘‘carboxylate shift” classification scheme established by
Lippard [22]. The dihedral angle between the two 2-pyridyl
rings of the (py)2CO ligand is 10.0°.
Fig. 2. Partially labeled plot of the linear trinuclear molecule present in complex 1. Primes are used for symmetry related (ꢁx,ꢁy,ꢁz + 1) atoms. Selected
˚
interatomic distances (A) and angles (°): Mn(1)ꢀ ꢀ ꢀMn(2) 3.552(2), Mn(1)–N(2) 2.240(3), Mn(1)–O(6) 2.238(2), Mn(2)–O(6) 2.214(2), C(6)–O(1) 1.210(6),
N(1)–Mn(1)–N(2) 83.7(1), Mn(1)–O(6)–Mn(2) 105.9(1).

C.C. Stoumpos et al. / Inorganic Chemistry Communications 11 (2008) 196–202
199
Fig. 3. Partially labeled plot of the linear trinuclear molecule present in complex 2 ꢀ 2MeCN. Primes are used for symmetry related (ꢁx,ꢁy,ꢁz) atoms.
˚
Selected interatomic distances (A) and angles (°): Mn(1)ꢀ ꢀ ꢀMn(2) 3.573(2), Mn(1)–N(1) 2.260(3), Mn(1)–O(1) 2.311(3), Mn(1)–O(6) 2.322(3) Mn(2)–O(6)
2.272(3), C(6)–O(1) 1.220(4), O(1)–Mn(1)–N(1) 70.4(1), Mn(1)–O(6)–Mn(2) 102.2(1).
O
OH
N
C
C
O
C
O
N
N
N
N
N
Mn
Mn
Mn
Mn
Mn
I
II
III
Fig. 4. The crystallographically established coordination modes of (py)2CO and (py)2C(OH)Oꢁ in complexes 1, 2 ꢀ 2MeCN and 4.
the third structurally characterized example of a compound
that contains (py)2CO in its j2N,O ligation mode; the
previous two examples are the above mentioned Ru(II)
complex [20] and the organometallic compound [(g5-
C5H5)Rh{(py)2CO}] [23]. Based on their excellent synthetic
and NMR studies in RuII/Clꢁ/dmso/(py)2CO chemistry
[20], Toyama et al. have reached the conclusion that the
j2N,O coordination mode of (py)2CO is kinetically favour-
able due to the small O donor atom of the carbonyl group,
but the j2N,N0 mode is more thermodynamically stable. In
accordance with this, the Mn(O2CPh)2/(py)2CO reaction
solution was yellow (i.e. the colour of 2 ꢀ 2MeCN) in the
initial stage, which suggested that the species with j2N,O-
(py)2CO formed. The solution turned orange (i.e. the
colour of 1) upon storage and the amount of crystalline 1
precipitated and was significantly larger than that of
2 ꢀ 2MeCN. It should be mentioned at this point that when
reflux was applied to the reaction only orange crystals of 1
were isolated [24]. Furthermore, once formed and isolated,
the orange isomer 1 does not transform into 2 in MeCN
even though the reaction mixture is refluxed overnight.
With hindsight: (i) the instability of the yellow crystals is
attributed to the lattice MeCN molecules, and (ii) the low
wavenumber (1640 cmꢁ1) for the m(CO) vibration in the
IR spectrum of 2 ꢀ 2MeCN is due to the carbonyl coordina-
tion in the yellow isomer; this vibration appears at
1684 cmꢁ1 in the spectrum of free (py)2CO [14].
Complexes 1 and 2 ꢀ 2MeCN join a small family of tri-
nulear Mn(II) carboxylate complexes containing the
{Mn3(g1:g1:l2-O2CR)6} unit [21,22,25].
The X-band powder EPR spectra of 1 and 2 at 4 K are
similar and quite complicated with resonances at g = ꢃ6.3,
ꢃ3.4 and ꢃ2.0 denoting [26] that the populated spin state
exhibits zero-field splitting (ZFS). If the ZFS effects are
negligible only a narrow signal may arise around g = 2.
However, if the ZFS is considerable, this signal should be
split into several features and thus signals at low field
may be observed [26], as found here.
Complexes 1 and 2 are not the only products from the
general Mn(O2CPh)2 ꢀ 2H2O/(py)2CO reaction system.
The 1:1 reaction of Mn(O2CPh)2 ꢀ 2H2O and (py)2CO in
CH2Cl2 (used as received) gives a colourless solution which

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C.C. Stoumpos et al. / Inorganic Chemistry Communications 11 (2008) 196–202
upon layering with n-hexane yields polyhedral, colourless
crystals of [Mn4(O2CPh)4{(py)2C(OH)O}4] (4) according
to Eq. (1); the yield is ꢃ55%.The metal ion-mediated nucle-
ophilic attack of H2O (from the solvent and/or the starting
material) on the carbonyl group is responsible for the for-
mation of the gem-diolate(-1) ligand (py)2C(OH)Oꢁ
(Fig. 1) [10]. The eletrophilic character of the carbonyl car-
bon atom of (py)2CO is increased by coordination of the
carbonyl oxygen to MnII (direct polarization) and/or coor-
dination of the more remote 2-pyridyl sites (induced polar-
ization) [10]
MnII atoms and one of the four l3-oxygen atoms originat-
ing from the (py)2C(OH)Oꢁ ligands. In addition to three
l3-oxygen atoms, each MnII is coordinated to two N atoms
belonging to two different (py)2C(OH)Oꢁ ligands and to
one oxygen atom belonging to a monodentate benzoate
group to complete a distorted octahedral N2O4 coordina-
tion environment. One oxygen atom (O(2)) of each
(py)2C(OH)Oꢁ ligand remains protonated and unbound
to the metal ions. The resultant monoanion functions as
an g1:g1:g1:l3 ligand (III in Fig. 4) forming two five-mem-
bered MnNCCO chelating rings with two different metal
ions (these rings share a common C–O edge) and an alkox-
ide-type bond to a third MnII atom.
4MnðO2CPhÞ2 ꢀ2H2Oþ4ðpyÞ2CO
CH2Cl2
The Mn4 tetrahedron is distorted by compression along
a S4 axis and this gives four shorter Mnꢀ ꢀ ꢀMn distances
! ½Mn4ðO2CPhÞ4fðpyÞ2CðOHÞOg4ꢂþ4PhCO2Hþ4H2O
4
˚
˚
ð1Þ
(3.353 A) and two longer (3.445 A). There are two types
of Mn–O (alkoxide-type) bonds for each metal ion: one
The tetranuclear molecule of 4 (Fig. 5) lies on an inverse
four-fold axis (S4 symmetry) and the asymmetric unit con-
tains a quarter of the cluster molecule. The molecule has a
cubane [Mn4(l3-OR)4]4+ core with MnII and oxygen atoms
occupying alternate vertices of the cube. Thus, the molecule
consists of two interpenetrating tetrahedra: one of the four
˚
bond is long (2.327(5) A), whereas the other two distances
˚
are shorter (average 2.174(4) A). The cube deviates from
the ideal geometry. The internal cube angles at the metal
vertices (RO–Mn–OR) average 80.2°, whereas the corre-
sponding angles at the alkoxide corners (Mn–OR–Mn)
are larger averaging 99.0°. Each (py)2C(OH)Oꢁ hydroxyl
group is strongly intramolecularly hydrogen bonded to
the uncoordinated oxygen atom of a benzoate ligand; the
dimensions of the intracubane hydrogen bonds are
˚
˚
O(2)ꢀ ꢀ ꢀO(4) 2.693 A, HO(2)ꢀ ꢀ ꢀO(4) 1.884 A and O(2)–
HO(2)ꢀ ꢀ ꢀO(4) 168.4°. A few more cubane clusters contain-
ing the [Mn4(l3-OR)4]4+ cores have been reported previ-
ously [9,11f,27].
The IR spectrum of 4 does not exhibit a band in the
region for the carbonyl stretching vibration as expected,
with the nearest band at 1596 cmꢁ1 which can be assigned
as a 2-pyridyl stretching mode (this band also has a
mas(CO2) character) raised from 1582 cmꢁ1 on coordina-
tion, as observed earlier [11f] upon complex formation
involving hydration of (py)2O. The strong band at
1390 cmꢁ1 is assigned to the ms(CO2) mode. The difference
D(D = mas(CO2) ꢁ ms(CO2) = 1596 ꢁ 1390 = 206 cmꢁ1
)
is
larger than that for NaO2CPh (184 cmꢁ1), as expected
[28] for the monodentate mode of carboxylate ligation.
Variable-temperature dc magnetic susceptibility data
(Fig. 6) were collected at 1000G for powdered 4 over the
temperature range 5 6 T 6 300 K. The room temperature
vMT value is 16.5 cm3 molꢁ1 K, slightly lower than the
expected value of 17.5 cm3 molꢁ1 K for four S = 5/2
uncoupled spins with g = 2. The vMT product remains
practically constant down to 150 K and then decreases
sharply, reaching a value of 5.57 cm3 molꢁ1 K at 5 K.
The data suggest that the cluster appears to possess weak
intramoleular antiferromagnetic interactions [9,11f,27].
Since the spin carriers are all d5 MnII ions, and therefore
orbital singlet (S) ions, only the isotropic part of the
exchange interaction was considered.
Fig. 5. Partially labeled plot of the linear tetranuclear molecule present in
complex 4. Identical numbers are used for symmetry related atoms. Most
carbon atoms of the 2-pyridyl rings have been omitted for clarity. Only the
ipso atoms of the PhCOꢁ2 ligands have been drawn. O(1) and O(2) are the
oxygen atoms of the (py)2C(OH)Oꢁ ligands, while O(3) and O(4) belong
˚
to the benzoate group. Selected interatomic distances (A) and angles (°):
Mnꢀ ꢀ ꢀMn 3.353(2) and 3.445(2), Mn–N(1) 2.250(6), Mn–N(2) 2.273(5),
Mn–O(1) 2.170(4), 2.178(4) and 2.327(5), Mn–O(3) 2.086(5), O(1)–Mn–
O(3) 165.4(2), N(1)–Mn–O(1) (ꢁx + 2,ꢁy,z) 146.0(2), Mn–O(1)–Mn
96.4(1), 99.7(1) and 100.9(1).
When a symmetrical spin Hamiltonian, H = Ri,j(i=j) 2J
(SiSj), with all coupling constants assumed to be equal
was applied, the high-temperature vMT could not be

C.C. Stoumpos et al. / Inorganic Chemistry Communications 11 (2008) 196–202
201
energy. The J values of 4 are within (J1) or close (J2) to
18
16
14
12
10
8
the narrow antiferromagnetic range (ꢁ0.22 to ꢁ4.11 cmꢁ1
)
reported [9,11f,27] for other cubane complexes containing
the [Mn4(l3-OR)4]4+ core.
The X-band powder EPR spectrum of 4 at 18 K exhibits
an almost featureless broad resonance with a g = ꢃ2.0
value. The broadness of this isotropic EPR absorption is
consistent with the presence of magnetically interacting
MnII ions in the solid-state [30].
An important chemical message from this preliminary
work is that the PhCO2ꢁ=ðpyÞ2CO ‘blend’ looks like a
promising candidate ligand system for the generation of
interesting Mn complexes. Complexes 1, 2 and 4 augur well
that they are merely the first members of a new family of
Mn carboxylate clusters with (py)2CO-based ligands.
Attempts to prepare high-nuclearity Mn(III) and/or
mixed-valence Mn benzoate clusters involving various
forms of (py)2CO (including the dianionic ligand
ðpyÞ2CO22ꢁ) are in progress.
6
4
2
0
0
50
100
150
200
250
300
Temperature (K)
Fig. 6. Plot of vMT as a function of T for a powdered sample of 4. The
solid line represents the simulated data function plot.
Supplementary material
CCDC 660964, 660965 and 660966 contain the supple-
mentary crystallographic data for 1, 2 ꢀ 2MeCN and 4.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
Acknowledgements
SPP thanks the European Social Fund (ESF), the Oper-
ational Program for Educational and Vocational Training
II (EPEAEK II) and particularly the Program PYTHA-
GORAS (Grant b.365.037) for funding this work. EKB
thanks the EPSRC and Leverhulme Trust (UK).
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˚
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˚
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,
˚
˚
ꢀ
M = 1342.0, triclinic, P1, a = 14.33(1) A, b = 10.957(4) A,
˚
c = 11.197(9) A,
a = 99.58(3)°,
b = 109.05(2)°,
c = 99.47(3)°,
3
V = 1593(2) A , Z = 1, Dc = 1.399 g cmꢁ3, l(MoKa) = 0.656 mmꢁ1
,
˚
T = 298 K, 5309 reflections collected, 5008 unique (Rint = 0.0355), R1
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3
˚
˚
˚
˚
a = 14.56(1) A, b = 14.56(1) A, c = 38.27(3) A, V = 8117(11) A ,
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,
l(MoKa) = 0.671 mmꢁ1
,
T = 298 K,
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on F2) = 0.0560 (0.1646) for 2819 observed (I > 2r(I)) reflections.
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˚
˚
˚
a = 12.086(4) A, b = 11.481(4) A, c = 11.771(4) A, a = 80.92(1)°, b =
3
ꢁ3
,
˚
68.34(1)°, c = 69.73(1)°, V = 1423.2(8) A , Z = 1, Dc = 1.470 g cm
l(MoKa) = 0.728 mmꢁ1, T = 298 K, 5267 reflections collected, 4992