Heterometallic hexanuclear isobutyrate clusters based on di- and tripodal alcohols

Article abstract of DOI:10.1016/j.poly.2010.03.013

Four hexanuclear coordination clusters containing {M₄^II M₂^III} cores of edge-sharing coordination octahedra exemplify how mixed-spin derivatives of a homonuclear parent structure, [Mn₄^II Mn₂^III L₈(N-O)₄], can be realized by a ligand 'shrink-wrapping' approach, resulting in [Mn₂^II Co₂^II Mn₂^III L₈(N-O)₄]- and [Co₄^II Fe₂^III L₈(N-O)₄]-type clusters (L = isobutyrate, N-O = methyldiethanolamine, n-butyldiethanolamine, or triethanolamine). The resulting core structures are either virtually isostructural to the parent structure or differ in the placement of the peripheral metal ions, depending on the mix of structure-directing carboxylate and alkoxyamine ligands with large, flexible alkyl chains. Whereas the {Mn₄^II Mn₂^III} and {Co₄^II Fe₂^III} complexes show dominant antiferromagnetic exchange, ferrimagnetic coupling features are exhibited by two {Mn₂^II Co₂^II Mn₂^III} clusters.

Full text of DOI:10.1016/j.poly.2010.03.013

Polyhedron 29 (2010) 1990–1997
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Heterometallic hexanuclear isobutyrate clusters based on di- and tripodal alcohols
Iurii L. Malaestean a, Manfred Speldrich a, Arkady Ellern b, Svetlana G. Baca c, Paul Kögerler a,
*
a Institut für Anorganische Chemie, RWTH Aachen University, D-52074 Aachen, Germany
b Dept. of Chemistry, Iowa State University, Ames, IA 50011, USA
c Institute of Chemistry, ASM, MD-2028 Chisinau, Republic of Moldova
a r t i c l e i n f o
a b s t r a c t
Four hexanuclear coordination clusters containing fMI4IM2IIIg cores of edge-sharing coordination octahedra
Article history:
exemplify how mixed-spin derivatives of a homonuclear parent structure, [MnI4IMn2IIIL8(N–O)4], can
Received 19 February 2010
Accepted 16 March 2010
Available online 23 March 2010
be realized by
a
ligand ‘shrink-wrapping’ approach, resulting in [MnI2ICoI2IMnI2IIL8(N–O)4]- and
[Co4IIFe2IIIL8(N-O)4]-type clusters (L = isobutyrate, N–O = methyldiethanolamine, n-butyldiethanolamine,
or triethanolamine). The resulting core structures are either virtually isostructural to the parent structure
or differ in the placement of the peripheral metal ions, depending on the mix of structure-directing car-
Keywords:
Transition metals
Carboxylates
Heteronuclear coordination clusters
Magnetism
N ligands
boxylate and alkoxyamine ligands with large, flexible alkyl chains. Whereas the fMnI4IMnI2IIg and {CoI4IFeI2II
}
complexes show dominant antiferromagnetic exchange, ferrimagnetic coupling features are exhibited by
two {Mn2IICo2IIMnI2II} clusters.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
methods. To this effect we are developing synthetic approaches
that allow us to change the spin composition of
a given
Work on high-nuclearity coordination clusters of transition me-
tal ions is in part motivated by the plethora of magnetic phenom-
ena realized in such quasi-zerodimensional systems, ranging from
slow magnetization relaxation in single-molecule magnets (SMMs)
to spin-glass transitions and magnetocaloric effects, and magnetic
coordination complexes have long been proposed as model sys-
tems for molecular spintronics and quantum computation [1].
The predominantly studied class of magnetic molecules so far in-
clude manganese-based SMMs comprising carboxylate ligands
[2], but numerous other SMMs systems have been identified, for
example iron clusters with {Fe4}, {Fe8O2}, {Fe9}, {Fe9O4}, {Fe10O6},
{Fe11O4}, or {Fe19O6} cores [3], or cobalt SMM with {Co4} [4a] and
{Co6} [4b] cores. Of particular interest to us in this respect is the
propensity of common core structures to incorporate different spin
centers and form heteronuclear coordination clusters. We aim to
probe the variation of magnetic properties caused by this (formal)
substitution of paramagnetic ions in such given spin arrays, possi-
bly leading to competing superexchange interactions. Importantly,
aggregating information about these magnetic effects should allow
us, based on magnetic susceptibility data, to differentiate between
scenarios in which structurally similar spin centers (e.g. Ni(II) and
Co(II)) are localized over a given spin array in different patterns, a
problem that cannot easily be resolved by standard structural
coordination cluster structure. Examples for larger binary 3d/3d
transition metal carboxylate clusters including benzoate-based
complexes containing {Mn2M4O2} (M = CoII, NiII) cores in hexanu-
clear [MnIIIMIIO2(O2CPh)10(DMF)4] [5] clusters; acetate- and
2
4
monochloroacetate-based complexes with a {Mn8Fe4} core in
dodecanuclear [Mn8Fe4O12(O2CMe)16(H2O)4] [6], and [Mn8Fe4-
O12(O2CCH2Cl)16(H2O)4] [7] aggregates. A series of mixed hetero-
nuclear MnIII/CrIII, MnIII/FeIII complexes which integrate
a
butterfly-like {M4O2} core [8] have been isolated, some of which
show slow relaxation of magnetization characteristic of SMMs.
Among recent examples, which incorporate both carboxylate and
amino alcohol ligands, are a pentanuclear mixed-valence complex
[CuIICoIICoIII(O2CMe)4(teaH2)(tea)2] [9] and a giant heterometallic
2
2
cluster [Cu17Mn28O40(tea)12(HCO2)6(H2O)4] [10].
We are interested in probing the extent to which our ‘shrink-
wrap’ approach, based on the use of semi-flexible, bulky ligands
such as amine polyalcohols and isobutyrate that tend to kinetically
stabilize particular coordination cluster geometries, can be used as
a general synthesis approach for polynuclear coordination clusters
with mixed spin centers, i.e. extending this approach beyond
homometal clusters [11]. Of particular importance in this respect
is whether the structure-directing effect of the ligand mix leading
to a particular homometallic coordination cluster core structure is
retained if various other 3d metal ions, with markedly different
coordination chemistry characteristics, are present in the reaction.
Herein we demonstrate the scope of this approach report the
synthesis and characterization of a family of four new homo- and
* Corresponding author. Tel.: +49 241 80 93642; fax: +49 241 80 92642.
E-mail address: paul.koegerler@ac.rwth-aachen.de (P. Kögerler).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.03.013

I.L. Malaestean et al. / Polyhedron 29 (2010) 1990–1997
1991
heterometallic hexanuclear carboxylates employing isobutyrate as
well as alkoxyamines ligands. The resulting clusters all feature
identical core structures comprising six edge-sharing ML6 coordina-
tion octahedra with general formula [MIIIMII(O2CHMe2)8(N–O)4]
2.2.1. Structure of [Mn6(O2CCHMe2)8(bdaH)2(bda)2] (1)
Complex 1 contains of six manganese centers bridged by eight
isobutyrate ligands and four butyldiethanolamine (bdaH2) mole-
cules to yield [Mn6(O2CCHMe2)8(bdaH)2(bda)2] (Fig. 1, Table 1).
The molecular structure of complex 1 with the atomic numbering
scheme is shown in Fig. 1. Four Mn sites (Mn2 and Mn3 and their
symmetry partners) form a central planar Mn4 rhombus bridged by
2
4
where MIII = Mn or Fe; MII = Mn or Co; N–O = methyldiethanol-
amine (mdaH2), n-butyldiethanolamine (bdaH2), or triethanola-
mine (teaH3).
l
3-O11 and
bda2ꢀ groups and by two alkoxide
from other arms of bda2ꢀ groups. One edge [Mn2 and Mn3] of
the Mn4 rhombus is additionally bridged by one 3-isobutyrate
group, while the other edge of Mn2 and Mn3A is bridged by a
2-isobutyrate group. The edge bridged by the 3-O11 atom is
characterized by
slightly longer Mn2ꢁ ꢁ ꢁMn3A distance of
3.687(2) Å than that bridged by both 2-O10 and 3-O11
l
3-O11A from one arm of two doubly deprotonated
l
2-O atoms [O10 and O10A]
2. Results and discussion
l
2.1. Synthetic methodology and characterization
l
l
a
Interaction of [Mn(O2CCHMe2)2] with N-butyldiethanolamine
in CH3CN at room temperature results in the formation of hexanu-
clear mixed-valence fMn4IIMn2IIIg cluster 1. The addition of Co2+ ions
to the reaction solution (molar ratio Mn:Co = 1:0.42) directly re-
sults in heterometallic hexanuclear {MnI2IIMn2IICo2II} clusters (com-
plexes 2 and 4) when the reaction mixture is refluxed. An
analogous {FeI2IICo4II} cluster derivative (complex 3) can be prepared
by reaction of [Fe3O(O2CCHMe2)6(H2O)3]NO3, [Co(O2CCHMe2)2]
and N-methyldiethanolamine in the same solvent at room temper-
ature. In all instances, single crystals formed in the reaction solu-
tion in the course of a few days.
l
l
[Mn2ꢁ ꢁ ꢁMn3: 3.175(2) Å]. The central Mn3ꢁ ꢁ ꢁMn3A separation is
Table 1
Selected bond distances (Å) in complex 1.
Mn1–O1
Mn1–O4
Mn1–O7
Mn1–O5
Mn1–O3
Mn1–N1
Mn2–O10
Mn2–O5
Mn2–O6
Mn2–O11
Mn2–O9
Mn2–O7
2.109(4)
2.125(4)
2.198(3)
2.203(3)
2.226(4)
2.415(5)
1.874(3)
1.893(3)
1.972(3)
2.006(3)
2.128(4)
2.328(3)
Mn3–O12
Mn3–O8
Mn3–O10
Mn3–O11A
Mn3–O11
Mn3–N2
2.109(3)
2.157(3)
2.187(3)
2.257(3)
2.261(3)
2.334(4)
The IR spectra of complexes 1–4 have strong broad bands in the
regions 1562 and 1419 cmꢀ1 for 1, 1573 and 1421 cmꢀ1 for 2, 1592
and 1418 cmꢀ1 for 3, and 1564 and 1421 cmꢀ1 for 4, respectively,
corresponding to the asymmetric and symmetric vibrations of
the coordinated carboxylic groups [12,13]. The bonds with med-
ium intensity in all complexes in the regions 2968–2863 cmꢀ1
Mn1ꢁ ꢁ ꢁMn2
Mn2ꢁ ꢁ ꢁMn3
Mn2ꢁ ꢁ ꢁMn3A
Mn3ꢁ ꢁ ꢁMn3A
3.257(2)
3.175(2)
3.687(2)
3.172(2)
and the bands at 1472–1369 cmꢀ1 are assigned to
m(C–H) stretch-
Symmetry code A: ꢀx + 1, ꢀy + 1, ꢀz + 1.
ing and bending modes. Broad medium bands at 3442 for 1, 3434
for 2, 3435 for 3 and 3413 cmꢀ1 for 4 are
m(OH) vibrations of hydro-
xyl groups of alkoxyamines.
Thermogravimetic and thermodifferential analyses (Figs. S3–
S6) of all complexes were performed in the temperature range
25–600 °C under N2 flow. Onset of mass loss steps (all endother-
mic): Compound 1: 160 °C, slow decomposition of two isobutyrate
ligands (calcd. 10.6%, found 11.7%). 350 °C, loss of the remaining
carboxylate ligands and decomposition of one butyldiethanole
molecule (calcd. 41.1%, found 35.7%). 400 °C, loss of remaining alk-
oxyamines (calcd. 29.0%, found 26.3%). Compound 2: 180 °C, re-
lease of two isobutyrate ligands, (calcd. 11.6%, found 11.1%).
330 °C, decomposition of four isobutyrate molecules (calcd.
23.2%, found 21.7%). 390 °C, release of remaining two carboxylic li-
gands as well as four alkoxyamines molecules (calcd. 43.2%, found
41.9%). Compound 3: 200 °C, loss of a first isobutyrate (calcd. 5.8%,
found 5.2%). 250 °C, loss of three carboxylate groups (calcd. 17.3%,
found 18.5%). 350 °C, loss of the remaining isobutyrate ligands and
three alkoxyamine molecules (calcd. 52.4%, found 50.3%). 400 °C,
decomposition of the last methyldiethanolamine molecule. Com-
pound 4: 170 °C, slow decomposition of the two isobutyrate li-
gands (calcd. 10.84%, found 9.61%). 350 °C, decomposition of six
carboxylate and one alkoxyamine ligand (calcd. 41.4%, found
41.2%). 400 °C, decomposition of triethanolamine groups (calcd.
27.5%, found 23.1%). In all cases, a residue mixture of oxides re-
mained at 600 °C.
2.2. Description of structures
Fig. 1. Top: Structure of complex 1 emphasizing the edge-sharing of the MnL6
coordination polyhedra (Mn(II): purple, Mn(III): dark green) in the fMnI4IMn2IIIg core.
bda groups are shown with grey bonds, isobutyrate groups with green bonds (O:
red, N: blue, uncoordinated O: orange; H omitted for clarity). Below: coordination
environments with numbering scheme. The enlongated Mn(III)–O bonds are
highlighted in black. (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
Single-crystal X-ray analysis of compounds 1–4 (Table 4) reveal
that all compounds solely contain polynuclear coordination clus-
ters and no additional constituents such as solvent molecules.
See Supplementary data for selected bond angles, packing dia-
grams, and bond valence sums.

1992
I.L. Malaestean et al. / Polyhedron 29 (2010) 1990–1997
3.172(2) Å. The terminal manganese centers Mn1 and Mn1A are
connected to the Mn2 and Mn2A centers of the Mn4 rhombus via
one bridging carboxylate group, a l2-O carboxylate atom [O7 and
O7A] and an alkoxide O atom [O5 and O5A] of a singly deproto-
nated bdaHꢀ group (Mn1ꢁ ꢁ ꢁMn2: 3.257(2) Å).
Six isobutyrate ligands form bridges between manganese cen-
ters: four of them are coordinating to Mn in the usual l2-1,3 coor-
dination fashion, whereas the other two isobutyrate ligands
function as tridentate ligands where one carboxylate oxygen atom
O7 (O7A) bridges two metal centers [Mn1, Mn2 and symmetry
partners], and the other oxygen site O8 (O8A) is coordinated only
to Mn3 (Mn3A). The remaining two isobutyrate ligands are coordi-
nated to terminal Mn1 and Mn1A atoms in a monodentate fashion
[C28–O1: 1.264(6) Å], and the second oxygen atom O2 [C28–O2:
1.252(6) Å] remains unbound and participates in the formation of
intramolecular hydrogen bonds O3–Hꢁ ꢁ ꢁO2 of 2.559(5) Å with a
bda group. bda ligands in 1 are both singly and doubly deproto-
nated, using all ethoxy arms to coordinate to metal atoms. Next
to coordination via N, two doubly deprotonated bda2ꢀ groups bind
one each to the Mn ions in a hexadentate mode: one alcohol arm
(O11A) bridges three Mn sites (Mn3, Mn3A and Mn2A) in a l3
coordination mode while a second
l2-bridged alcohol arm (O10)
links Mn2 and Mn3 centers. Two singly deprotonated bdaHꢀ
groups coordinate to metal ions in a tetradentate fashion via the
nitrogen atom and both ethanol arms (including the protonated
alcohol arm), one of them bridges Mn1 and Mn2 atoms through O5.
In complex 1 each manganese ion is six-coordinated, adopting a
distorted octahedral geometry. Mn1 and Mn3 and their symmetry
partners are both NO5-coordinated. Mn1 binds to one nitrogen
atom [Mn1–N: 2.415(5) Å] and to two alkoxide oxygen atoms of
a singly deprotonated bdaHꢀ ligand, and to three oxygen atoms
of different isobutyrate ligands [Mn–O: 2.109(4)–2.226(4) Å],
while the coordination sphere at Mn3 is completed by one nitrogen
[Mn3–N: 2.335(4) Å] and two alkoxide oxygen atoms of doubly
deprotonated bda2ꢀ ligand, one alkoxide oxygen atom from neigh-
boring bda2ꢀ group, and two carboxylate oxygen atoms from the
different isobutyric ligands [Mn–O: 2.109(3)–2.261(3) Å]. Mn2
atom is in an O6 environment, bound to three oxygen carboxylate
atoms of three bridging isobutyrate ligands and three alkoxide
sites from three neighboring, both doubly deprotonated bda2ꢀ
and singly deprotonated bdaHꢀ ligands [equatorial Mn–O dis-
tances: 1.874(3)–2.006(3) Å, elongated axial Mn–O distances:
2.128(4) and 2.328(3) Å].
Bond lengths and charge considerations suggest a mixed-va-
lence (Robin-Day class I) MnI4IMn2III nature for this complex. The
short Mn–O distances and irregular coordination geometries with
one elongated axis and bond-valence sum calculations (Supple-
mentary data) are indicative of Mn2 and Mn2A ions being Mn(III)
and exhibiting characteristic Jahn–Teller distortion. On the basis
of the longer Mn–ligand distances and bond-valence sum calcula-
tions Mn1 and Mn3 can be assigned as Mn(II) centers. We note that
a related fMnI4IMnI2IIg complex with a related core structure with
edge- and corner-sharing MnL6 octahedra based on diphenylace-
tate ligands but that differs starkly in the connectivity of the Mn
coordination polyhedra (see Fig. S7) and that consequently dis-
plays very different magnetic properties (see below) was reported
by Christou and co-workers [14].
Fig. 2. Top: Structure of complex 3 emphasizing the {CoI4IFe2III} core (Co(II): violet,
Fe(III): yellow). mda groups are shown with grey bonds, isobutyrate groups with
green bonds (see Fig. 1 for color codes). Below: coordination environments with
numbering scheme. The four slightly longer Fe(III)–O bonds are highlighted in
black. (For interpretation of the references to colour in this figure legend, the reader
is referred to the web version of this article.)
Table 2
Selected bond distances (Å) in complexes 2 and 3.
Complex 2
Complex 3
Mn1–O1
Mn1–O3
Mn1–O4
Mn1–O5
Mn1–O7
Mn1–N1
Mn2–O11
Mn2–O3
Mn2–O5
Mn2–O8
Mn2–O10
Mn2–O12
Co3–O6
2.049(4)
2.115(4)
2.164(4)
2.108(4)
2.108(4)
2.223(5)
1.874(4)
1.891(4)
2.289(4)
1.963(4)
2.121(4)
1.991(4)
2.132(4)
2.050(5)
2.123(4)
2.188(4)
2.211(4)
2.200(5)
3.190(2)
3.106(2)
3.586(2)
3.121(2)
Co1–O1
Co1–O3
Co1–O4
Co1–O5
2.027(4)
2.129(4)
2.046(3)
2.147(4)
2.072(4)
2.182(5)
1.925(4)
1.937(4)
2.135(3)
2.023(4)
1.980(4)
2.036(3)
2.084(4)
2.049(4)
2.032(4)
2.146(4)
2.108(3)
2.133(5)
3.153(2)
3.069(2)
3.577(1)
3.007(2)
Co1–O7
Co1–N1
Fe1–O11
Fe1–O4
Fe1–O5
Fe1–O8
Fe1–O10
Fe1–O12
Co2–O6
Co3–O9
Co2–O9
Co3–O11
Co3–O12
Co3–O12A
Co3–N2
Mn1ꢁꢁꢁMn2
Mn2ꢁꢁꢁCo3
Mn2ꢁꢁꢁCo3A
Co3ꢁꢁꢁCo3A
Co2–O11
Co2–O12
Co2–O12A
Co2–N2
Co1ꢁ ꢁ ꢁFe1
Fe1ꢁ ꢁ ꢁCo2
Fe1ꢁ ꢁ ꢁCo2A
Co2ꢁ ꢁ ꢁCo2A
Co1 is a symmetry equivalent of Mn1. Mn3 is a symmetry equivalent of Co3.
Symmetry code A for complex 2: ꢀx, ꢀy + 1, ꢀz + 1.
Symmetry code A for complex 3: ꢀx, ꢀy, ꢀz + 2.
2.2.2. Structures of [Mn4Co2(O2CCHMe2)8(mdaH)2(mda)2] (2) and
[Fe2Co4(O2CCHMe2)8(mdaH)2(mda)2] (3)
the formation of hexanuclear metallic core which is similar to that
of complex 1 with a difference in the nature of the ditopic alcohol
ligand, here: methyldiethanolamine (mdaH2) instead of butyl-
dietanolamine. The complexes [MnIIIMnIICoII(O2CCHMe2)8(mdaH)2
The heterometallic complexes 2 and 3 crystallize in the same
monoclinic space group P2(1)/c and are virtually isostructural
(Fig. 2, Table 2). Therefore, only a detailed structural description
of 3 and relevant structural differences of complex 2 will be dis-
cussed. The molecular structure of complex 3 with the atomic
numbering scheme is shown in Fig. 2. Both complexes exhibit
2
2
2
(mda)2] 2 and [FeIIICoII(O2CCHMe2)8(mdaH)2(mda)2] 3 each com-
2
4
prise two M(III) and four M(II) ions linked by eight isobutyrate
ligands and four methyldiethanolamine groups. Because the posi-
tion of Mn and Co or Fe and Co atoms cannot be distinguished

I.L. Malaestean et al. / Polyhedron 29 (2010) 1990–1997
1993
based on the available X-ray data, our metal site assignments in
the structures of 2 and 3 are based on the relative metal–ligand
bonds distances (Table 2), the presence or absence of Jahn–Teller
distortions of MnIII and FeIII, respectively, bond-valence sum calcu-
lations. Elemental analysis data for 2 and 3 yield the actual Mn:Co
ratio as 4:2 in 2, and the Fe:Co ratio as 2:4 in 3. Accordingly, in M6
core in 2 consists of a central tetranuclear unit containing two
M(II) centers and two Mn(III) centers, which is further connected
to two peripheral M(II) centers (each M(II) ion represents 1/2 MnII
and 1/2 CoII). In the M4 rhombus of 2 both the MnIIIꢁ ꢁ ꢁMII separa-
tions [Mn2ꢁ ꢁ ꢁM3: 3.106(2), Mn2ꢁ ꢁ ꢁM3A: 3.586(2) Å] and MIIꢁ ꢁ ꢁMII
separation [M3ꢁ ꢁ ꢁM3A: 3.121(2) Å] are slightly shorter than those
in the homonuclear complex 1. In complex 3 the M6 core consists
of two FeIII ions and four CoII ions (Fig. 3) comprising a central
FeI2IICoI2I rhombus with two peripheral CoII sites. Here, the Fe1ꢁ ꢁ ꢁCo2
distance of 3.069(1) Å is significantly shorter than the Fe1ꢁ ꢁ ꢁCo2A
distance of 3.577(1) Å. The Co2ꢁ ꢁ ꢁCo2A distance is equal to
3.007(1) Å. A decrease to 3.153(2) Å is also observed between Fe1
and the peripheral Co1. Fe1 is octahedrally coordinated by three
oxygen carboxylate atoms [O5, O8 and O10] of three bridging
isobutyrate ligands and three alkoxide sites [O4, O11 and O12]
from two neighboring mda2ꢀ and one mdaHꢀ ligands. The Fe–O
distances ranging from 1.925(4) to 2.135(3) Å show the absence
of Jahn–Teller distortions for high-spin FeIII(d5) in 3 in contrast to
high-spin MnIII (d4) in near-octahedral symmetry in 2 [four short
equatorial Mn–O bonds: 1.874(4)–1.991(4) Å, two long axial
bonds: 2.121(4) and 2.289(4) Å]. Each Co site adopts a distorted
octahedral NO5 arrangement: Co2 is coordinated by one nitrogen
[Co2–N2: 2.133(5) Å] and two alkoxide oxygen atoms [O11 and
O12A] of doubly deprotonated mda2ꢀ ligand, one alkoxide oxygen
atom [O12] from a neighboring mda2ꢀ group and two carboxylate
oxygen atoms [O6 and O9] from the different isobutyric ligands
[Co2–O: 2.032(4)–2.146(4) Å], whereas Co1 is bound to one nitro-
gen atom [Co1–N1: 2.182(5) Å] and two alkoxide O3 and O4 sites
of a singly deprotonated mdaHꢀ ligand, and O1, O5, and O7 of dif-
ferent isobutyrate ligands [Co1–O: 2.027(4)–2.147(4) Å].
Four methyldiethanolamines act as chelating and bridging li-
gands in 3, two of them interlink all metal atoms of the central
M4 rhombus via their nitrogen [N2, N2A] and two oxygen atoms
[O11, O12A and their symmetry equivalents], whereas two
remaining alkoxyamines ligands coordinate to the peripheral Co1
and Co1A atoms by nitrogen [N1, N1A] and two oxygen atoms
[O3 and O4, and their symmetry equivalents] and their alkoxide
O4 and O4A atoms additionally connect the terminal cobalt sites
to neighboring iron sites.
2.2.3. Structure of [Mn4Co2(O2CCHMe2)6(HO2CCHMe2)2(teaH)4] (4)
Complex 4 (Fig. 3, Table 3) consists of a hexanuclear heterome-
tallic core which is similar to that of complexes 1–3 comprising a
central tetranuclear unit [MnI2IIM2II] and two terminal MII centers
bridged by eight isobutyrate ligands and four molecules of trieth-
anolamine that [Mn4Co2(O2CCHMe2)6(HO2CCHMe2)2(teaH)4] is
formed. Four MII centers are in a six-coordinate NO5 environment
(each MII ion contains 1/2 MnII and 1/2 CoII). Two terminal MII
are coordinated by one amine [N1] and two alkoxide groups [O8
and O11] of one teaH2ꢀ ligand [M1–N1: 2.200(7), M1–O:
2.095(6) and 2.171(6) Å], and three carboxylate oxygen sites
[O4A, O8 and O12] of different isobutyric acids with the M1–O dis-
tances range from 2.067(6) to 2.146(6) Å. Two central MII [M3 and
M3A] sites are bound to one amine [N2], two alkoxide groups [O6
and O7A] of teaH2ꢀ, one alkoxide [O7] from a neighboring teaH2ꢀ
ligand, and two isobutyric ligands [O2 and O3] [M–N: 2.241(7) Å,
M–O: 2.089(7)–2.230(5) Å]. The coordination spheres of the
remaining two manganese centers are completed by oxygen do-
nors, three carboxylate groups [O1, O9 and O4A] of different isobu-
tyrate ligands and three alkoxide groups [O6, O7 and O8] of three
triethanolamines [four short equatorial Mn–O bonds: 1.890(5)–
2.004(5) Å and two long axial bonds: 2.117(6) and 2.268(6) Å].
On the basis of the Mn–ligand distances and bond-valence sum cal-
culations, M1 and M3 are assigned as M(II), while Mn2 and Mn2A
are assigned as Mn(III) centers. The intracluster separations be-
tween Mn(III) and M(II) centers in the central tetranuclear unit
are 3.108(2) and 3.600(2) Å, that between Mn(III) and peripheral
M(II) is 3.197(3) Å. The M3IIꢁ ꢁ ꢁM3AII distance equals 3.185(3) Å.
All triethanolamine ligands in 4 are doubly deprotonated. Next
to coordination via N, four teaH2ꢀ groups bind via two ethanol
arms with the pendant third one participating in intermolecular
hydrogen bonds, causing extensive hydrogen bonding and the for-
mation of hydrogen-bonded two-dimensional layers in 4. Intermo-
lecular hydrogen bonds are formed between teaH2ꢀ and teaH2ꢀ
pairs [O14ꢁ ꢁ ꢁO5 [x ꢀ 1, y, z ꢀ 1]: 2.758(9) Å] and teaH2ꢀ–isobuty-
rate pairs [O5ꢁ ꢁ ꢁO13[x, y, z + 1]: 2.760 and O13ꢁ ꢁ ꢁO11: 2.590(1) Å]
Table 3
Selected bond distances (Å) in complex 4.
Mn1–O12
Mn1–O10
Mn1–O8
Mn1–O4A
Mn1–O11
Mn1–N1
Mn2–O6
Mn2–O8
Mn2–O9
Mn2–O7
Mn2–O1
Mn2–O4A
2.067(6)
2.085(6)
2.095(6)
2.146(6)
2.171(6)
2.200(7)
1.890(5)
1.894(5)
1.971(6)
2.004(5)
2.117(6)
2.268(6)
Co3–N2
Co3–O3
Co3–O2
Co3–O6
Co3–O7A
Co3–O7
Mn1ꢁ ꢁ ꢁMn2
Mn2ꢁ ꢁ ꢁCo3
Mn2ꢁ ꢁ ꢁCo3A
Co3ꢁ ꢁ ꢁCo3A
2.241(7)
2.089(7)
2.103(6)
2.112(5)
2.189(6)
2.230(5)
3.197(3)
3.108(2)
3.600(2)
3.185(3)
Fig. 3. Top: Structure of complex 4 emphasizing the {MnI2ICo2IIMn4III} core (Mn/Co(II):
light blue, Mn(III): dark green). tea groups are shown with grey bonds, isobutyrate
groups with green bonds (see Fig.
1 for color codes). Below: coordination
environments with numbering scheme. (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)

1994
I.L. Malaestean et al. / Polyhedron 29 (2010) 1990–1997
Table 4
Summary of crystal data collection and refinement details.
Complex
1
2
3
4
Formula
C64H126Mn6N4O24
1665.3
C52H102Co2Mn4N4O24
1505.0
C52H102Co4Fe2N4O24
1514.80
C56H110Co2Mn4N4O28
1625.10
Formula weight (g molꢀ1
)
T (K)
173(2)
173(2)
173(2)
173(2)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
P1
monoclinic
P2(1)/c
12.140(5)
27.505(12)
11.009(5)
90
108.209(7)
90
3492(3)
monoclinic
P2(1)/c
11.951(8)
27.5697(12)
11.032(8)
90°
109.307(6)°
90°
3430(3)
triclinic
P1
11.129(7)
13.293(9)
ꢀ
ꢀ
12.948(10)
13.379(10)
14.674(11)
109.433(13)
98.917(14)
113.875(13)
2065(3)
13.447(9)
a
(°)
95.664(7)°
108.998(8)°
95.479(7)°
1854(2)
b (°)
k (°)
V (Å3)
Z
1
2
2
1
q
l
(g cmꢀ3
)
1.339
0.959
1.431
1.238
1.467
1.431
1.455
1.176
(mmꢀ1
)
Crystal size (mm)
h range for data collection (°)
Index ranges
0.29 ꢂ 0.24 ꢂ 0.22
1.83–23.26
ꢀ14 6 h 6 14, ꢀ14 6 k 6 14,
ꢀ16 6 l 6 16
13 394
0.46 ꢂ 0.25 ꢂ 0.21
2.08–23.26
ꢀ13 6 h 6 13, ꢀ30 6 k 6 30,
ꢀ12 6 l 6 12
22 656
0.41 ꢂ 0.23 ꢂ 0.19
1.95–25.00
ꢀ14 6 h 6 14, ꢀ32 6 k 6 32,
ꢀ13 6 l 6 13
25 598
0.28 ꢂ 0.18 ꢂ 0.11
1.95–23.26
ꢀ12 6 h 6 12, ꢀ14 6 k 6 14,
ꢀ14 6 l 6 14
12 246
Reflections collected
Independent reflections (Rint
Completeness to theta (%)
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R1, wR2
)
5903 (0.0453)
99.6
5903/40/463
1.074
0.0474, 0.1049
0.0812, 0.1239
0.946 and ꢀ0.421
5001 (0.0731)
99.9
5001/0/389
1.082
0.0510, 0.1173
0.0853, 0.1423
0.769 and ꢀ0.469
6037 (0.0709)
99.9
6037/6/409
1.123
0.0569, 0.1232
0.0860, 0.1406
0.673 and ꢀ0.539
5284 (0.0680)
99.3
5284/16/438
1.033
0.0724, 0.1774
0.1115, 0.2109
1.734 and ꢀ0.629
R indices (all data)
Largest difference in peak and
hole (e Åꢀ3
)
4T1(F), 4T2, and 4A2 terms, while the 4P term transforms into a
4T1(P) term [15]. The 4T1(F) ground state for a high-spin CoII center
implies a significant orbital momentum contribution [16].
In a ligand field of octahedral symmetry the 5D0 ground term of
an Mn(III) ion splits into E and T terms. The 5E ground term implies
a significant dependence of the thermodynamic magnetic proper-
ties on the spin-orbit coupling and the ligand field if the ligand
field strength is lower than Dq = 1600 cmꢀ1 [17]. In this situation
a temperature independent
vm T value is observed for mononu-
clear Mn(III) complexes where the Curie constant is a function of
the ligand field strength and spin-orbit coupling. On the other hand
Fe(III) and Mn(II) (3d5) in a octahedral ligand field (6A1(6S)) are
considered pure spin-only centers [16].
The exchange coupling scheme in Fig. 5 represents the four (J1–
J4) nearest-neighbor exchange pathway connectivities for com-
plexes 1–4. Table S5 represents the different connections between
the magnetic centers of the compounds with the following ligands:
L0 = bda for 1, mda for 2 and 3, teaH for 4; L00 =
l2–O2CCHMe2;
Fig. 4. Intermolecular hydrogen bonding in 4, indicated by dotted lines.
(Fig. 4). Similar to 1–3 four isobutyrate ligands are coordinating to
metal centers in the common l2-1,3 coordination fashion whereas
the other two isobutyrate ligands function as tridentate ligands
bridging three metal centers [M1, Mn2 and M3A, and symmetry
partners]. The remaining two isobutyrate ligands are coordinated
to terminal M1 and M1A sites as monodentate groups.
2.3. Magnetic properties
The magnetochemical interpretation of complexes 2, 3, and 4
containing Co(II) (3d7) centers is complicated by a multitude of fac-
tors, notably the fact that the free-ion 4F ground term of CoII is sep-
arated by the first excited 4P state by more than 104 cmꢀ1. In a
weak ligand field with octahedral symmetry, the 4F term splits into
Fig. 5. Coupling scheme representing the exchange pathways between the local
spin sites (M1(2+) = Mn or Co, M2(3+) = Mn or Fe and M3(2+) = Mn or Co) in
complexes 1–4.

I.L. Malaestean et al. / Polyhedron 29 (2010) 1990–1997
1995
L000
= g1:l2–O2CCHMe2. The exchange interactions are described by
the Heisenberg-type spin Hamiltonian [18]
"
#
^
^
^
^
^
^
J1ðS3 ꢁ S4Þ þ J2ðS2 ꢁ S3 þ S4 ꢁ S5Þþ
Hex ¼ ꢀ2
^
^
^
^
^
^
^
^
J3ðS2 ꢁ S4 þ S3 ꢁ S5Þ þ J4ðS1 ꢁ S2 þ S5 ꢁ S6Þ
Due to the fact that an accurate magnetic simulation of the
Co(II)-based complexes 2–4 requires to take into account the li-
gand-field effects, interelectronic repulsion, spin-orbit coupling,
and exchange coupling (Hex), we limit our simulations to com-
pound 1 with a limited set of fitting parameters with no orbital
momentum contribution. The temperature dependencies of the
low-field molar susceptibility vm (inset) and
vmT of 1 are shown
in Fig. 6. At room temperature
v
mT = 21.2 cm3 K molꢀ1 is slightly
lower than the expected spin-only value for six isolated magnetic
centers of 23.5 cm3 K molꢀ1 (four S = 5/2 Mn(II) and two S = 2
Mn(III) centers; g = 2.00).
vmT continually decreases with decreas-
ing temperature, and m reaches a maximum at Tmax = 3.5 K, indic-
v
ative for dominant antiferromagnetic exchange in 1. The expected
singlet ground state of 1 is confirmed by field-dependent magneti-
zation measurements at T = 2 K. Using our computational frame-
work CONDON [19], a least-squares fit to the experimental molar
susceptibility data at 0.1 Tesla for T = 2–290 K yields all-antiferro-
Fig. 7.
v
mT vs. T plots of [Mn4Co2(O2CCHMe2)8(Hmda)2 (mda)2] (2, circles) and
[Mn4Co2(O2CCHMe2)6 (HO2CCHMe2)2(teaH)4] (4, triangles) at 0.1 Tesla. Inset: field
dependence of the magnetization at 2.0 K for both compounds.
pronounced Co(II) single-ion effects. Note that at ca. 5 K
vmT
magnetic exchange energies J1 = ꢀ2.20 cmꢀ1 J2 = ꢀ3.01 cmꢀ1
,
reaches a maximum (2) or a corresponding shoulder (4), indicating
competing weak interactions leading to ferrimagnetic order. Fur-
thermore, note that compounds 2 and 4 inherently represents sev-
eral isomers which differ in the permutations of the four Co(II) and
Mn(II) sites (see structural discussion for the MII disorder in these
clusters). Consequently, the exchange coupling in each of these
compounds cannot be characterized by a single Heisenberg model.
In addition, due to the considerable ligand-field and spin-orbit cou-
pling effects of the Co(II) centers in these compounds, no reason-
J3 = ꢀ0.47 cmꢀ1, and J4 = ꢀ3.01 cmꢀ1 (SQ = 0.5%; g = 2.0), shown
as red graphs in Fig. 6. A singlet ground state follows from both
the calculations of the spin states and from field-dependent mag-
netization measurements (0–5 T, 2.0 K). Note that the magnetism
of 1 is strikingly different from the high-spin ground state and
SMM characteristics reported by Christou et al. for a similar
fMnI4IMnI2IIg complex which differs not only in the nature of the
bridging ligands but also in the connectivity between the outer
MnIIO5N coordination octahedra and the neighboring MnIIIO6 octa-
hedra, see Fig. S7 [12].
able ground state quantum number
S can be assigned.
Correspondingly, the low-temperature field-dependence of the
magnetization for these compounds does not follow a Brillouin
function.
The vmT versus T plots of [Mn4Co2(O2CCHMe2)8(Hmda)2(mda)2]
(2) and [Mn4Co2(O2CCHMe2)6(HO2CCHMe2)2(teaH)4] (4) reach
maximum values of 17.5 cm3 K molꢀ1 (2) and 17.6 cm3 K molꢀ1
(4) at room temperature, slightly below the spin-only value for
the uncorrelated six magnetic centers (2 ꢂ CoII with S = 3/2,
2 ꢂ MnIII with S = 2, 2 ꢂ MnII with S = 5/2) of 18.51 cm3 K molꢀ1
The temperature dependence of
vmT of [Fe2Co4(O2CCH-
Me2)8(Hmda)2(mda)2] (3) shows a monotonous decrease from
17.29 cm3 K molꢀ1 at 290 K to 2.5 cm3 K molꢀ1 at 2 K, and no max-
imum is observed for vm versus T (Fig. 8). Again, we attribute a
combination of both Co(II) single-ion effects and antiferromagnetic
exchange interactions as the primary factors determining the ob-
served magnetic properties. Similar to the situation in 2 and 4,
(Fig. 7). In both cases the decrease of vmT towards lower tempera-
tures is associated both with antiferromagnetic exchange and
Fig. 6.
vmT vs. T and vm vs. T (inset) plots at 0.1 Tesla for [Mn6(O2CCHMe2)8(b-
daH)2(bda)2] (1). Experimental data: circles, best fit to model Hamiltonian (see
text): solid lines. The horizontal line represents the expected spin-only value for six
isolated magnetic centers (4 ꢂ MnII with SMn = 5/2 and 2 ꢂ MnIII with SMn = 2).
Fig. 8.
vmT vs. T plot of [Fe2Co4(O2CCHMe2)8(Hmda)2(mda)2] (3) at 0.1 Tesla. Inset:
field dependence of the magnetization at 2.0 K.

1996
I.L. Malaestean et al. / Polyhedron 29 (2010) 1990–1997
Due to significant orbital momentum in the octahedrally coordi-
nated Co(II) sites in 3, no reasonable ground state quantum num-
ber S can be assigned and the low-temperature field-dependence
of the magnetization strongly deviates from that of a Brillouin
function.
100%; 758.1 {Fe3O(O2CCHMe2)6(OH)3}ꢀ, 39%; 823.0 {Fe3O(O2CC-
HMe2)6(H2O)3NO3}ꢀ, 37%.
4.2.2. [Mn6(O2CCHMe2)8(Hbda)2(bda)2] (1)
A solution of [Mn(O2CCHMe2)2] (0.23 g, 1.00 mmol) and bdaH2
(0.17 ml, 1.05 mmol) in 5 ml CH3CN was combined with a solution
of NEt3 (0.15 ml, 1.08 mmol) in 5 ml CH3CN. The resulting solution
was stirred for 30 min, filtered off and left in a covered vial. Result-
ing black crystals were filtered off after several days, washed with
CH3CN and dried in air (yield 0.15 g, 55% based on Mn). Elemental
Anal. Calc. for C64H126N4O24Mn6: C, 46.15; H, 7.62; N, 3.36. Found:
C, 46.06; H, 7.40; N, 3.38%. IR data (KBr, cmꢀ1): 3442br, m, 2964s,
2963m, 2929sh, 2898sh, 2863w, 1593w, 1562s, 1471m, 1419s,
1371w, 1284m, 1080m, 1080m, 1040sh, 991w, 916w, 894m,
829w, 773w, 641m, 584m, 500w, 418w.
3. Conclusions
The four presented complexes represent the structure-direct-
ing effect achieved by the combination of bulkier carboxylates
(isobutyrate) and flexible alkoxyamines (methyldiethanolamine,
butyldiethanolamine, or triethanolamine) ligands. This particular
‘shrink-wrapping’ effect apparently stabilizes the observed hexa-
nuclear core structure of edge-linked coordination polyhedra even
if mixtures of transition metal ions with significantly different
coordination properties are present and thereby allows us to real-
ize nearly isostructural heterometallic (Mn/Co, Fe/Co) derivatives
(2–4) of an archetypal homometallic fMnI4IMn2IIIg coordination
cluster (1). We note that a variation of the employed alkoxyamine
ligand groups can alter the way in which the peripheral ML6 octa-
hedra are joined to the {M4} cluster core. Antiferromagnetic intra-
molecular exchange coupling is evident for all compounds, and for
the mixed-spin systems 2 and 4 weak ferrimagnetic features are
observed. We will continue to probe the degree to which the com-
bination of ‘shrink-wrapping’ ligands can be employed to either
derive novel coordination cluster cores or to integrate a mix of
spin centers into existing homonuclear cluster architectures.
4.2.3. [Mn4Co2(O2CCHMe2)8(Hmda)2(mda)2] (2)
0.12 ml mdaH2 (1.00 mmol) were added to a solution of
[Mn(O2CCHMe2)2] (0.23 g, 1.00 mmol) and [Co(O2CCHMe2)2]
(0.1 g, 0.42 mmol) in 10 ml CH3CN. The resulting solution was re-
fluxed for 10 min, filtered off and left in a covered vial. The
brown-violet crystals were filtered off in two days washed with
CH3CN and dried in air (yield 0.19 g, 76% based on Mn). Elemental
Anal. Calc. for C52H102Co2Mn4N4O24: C, 41.48; H, 6.83; N, 3.72; Mn,
14.60; Co, 7.83. Found: C, 41.42; H, 6.59; N, 3.71; Mn, 13.1, 14.0;
Co, 8.95, 8.44%. IR data (KBr, cmꢀ1): 3434m, 2967m, 2925w,
2902w, 2864m, 1573s, 1472m, 1421s, 1369m, 1287m, 1079m,
1033m, 997w, 889m, 850m,756w, 642m, 577w, 460w.
4. Experimental
4.2.4. [Fe2Co4(O2CCHMe2)8(Hmda)2(mda)2] (3)
0.17 ml mdaH2 (1.42 mmol) were added to a solution of
[Fe3O(O2CCHMe2)6(H2O)3]NO3 (0.2 g, 0.24 mmol) and [Co(O2
CCHMe2)2] (0.06 g, 0.25 mmol) in 8 ml CH3CN. The resulting solu-
tion was stirred for 20 min, filtered off and left in a covered vial.
The red-brown crystals were filtered off in several days, washed
with CH3CN and dried in air (yield 0.045 g, 75% based on Co). Ele-
mental Anal. Calc. for C52H102Co4Fe2N4O24: C, 41.23; H, 6.79; N,
3.69; Fe, 7.37; Co, 15.56. Found; C, 41.3; H, 6.30; N, 3.85; Fe,
7.41, 7.01; Co, 15.04, 14.8%. IR data (KBr, cmꢀ1): 3435m, 2967m,
2927w, 2859w, 1592s, 1534sh, 1471m, 1418s, 1370m, 1285m,
1092m, 1061w, 1042m, 1000sh, 906w, 886m, 849w, 657w,
632w, 607w, 572m, 451w.
4.1. Materials and methods
All reagents were purchased from commercial sources and used
without further purification. The infrared spectra were recorded on
a Perkin–Elmer Spectrum One spectrometer using KBr pellets in
the region 4000–400 cmꢀ1
.
TGA/DTA measurements were carried out with a Mettler Toledo
TGA/SDTA851 in dry N2 (60 ml minꢀ1
) at a heating rate of
10 K minꢀ1. FAB mass spectra were obtained on a Finnegan MAT
95 spectrometer. Metal analyses (ICP-OES) were performed by
Zentralabteilung für Chemische Analysen (Forschungszentrum
Jülich GmbH).
4.2.5. [Mn4Co2(O2CCHMe2)6(HO2CCHMe2)2(teaH)4] (4)
4.2. Syntheses of complexes
0.15 ml teaH3 (1.13 mmol) were added to
a solution of
[Mn(O2CCHMe2)2] (0.23 g. 1.00 mmol) and [Co(O2CCHMe2)2]
(0.1 g, 0.42 mmol) in 10 ml CH3CN. The resulting solution was re-
fluxed for 20 min, filtered off and left in a covered vial. The
brown-violet crystals were filtered off in two days washed with
CH3CN and dried in air (yield: 0.24 g, 88 % based on Mn). Elemental
Anal. Calc. for C56H110Co2Mn4N4O28: C, 41.39; H, 6.82; N, 3.45; Mn,
13.52; Co, 7.25. Found: C, 41.5; H, 6.56; N, 3.68; Mn, 13.6, 12.3, Co,
7.02. 8.38%. IR data (KBr, cmꢀ1): 3413m, 2968m, 2927w, 2867w,
1564s, 1471m, 1421s, 1371m, 1286m, 1083m, 932w, 640m,
555w, 450w.
4.2.1. Syntheses of the precursors
[Mn(O2CCHMe2)2] was prepared according to the previously re-
ported procedure [11a]. [Co(O2CCHMe2)2] was obtained by heating
Co(O2CMe)2ꢁ4H2O (2 g, 8.02 mmol) in 20 ml of isobutyric acid. The
obtained microcrystalline product was filtered off in several days,
washed with pentane and dried in air (Yield: 1.21 g, 64.7%). Ele-
mental Anal. Calc. for C8H14O4Co: C, 41.19; H, 6.05. Found: C,
40.92; H, 6.12%. IR data (KBr, cmꢀ1): 3436 m, 2957 m, 2871w,
1557s, 1413s, 1326w, 1107w, 725w. Synthesis of the precursor
[Fe3O(O2CCHMe2)6(H2O)3]NO3: An aqueous solution of Fe
(NO3)3 ꢁ 9H2O (5 g, 12.37 mmol) in 25 ml of water was added to a
solution of isobutyric acid (3.45 ml) and NaOH (1.5 g, 37.5 mmol)
in 25 ml of water. The formed orange microcrystalline solid was fil-
tered off, washed with water and dried in air. (Yield: 3 g, 88.49%).
Elemental Anal. Calc. for C24H48NO19Fe3: C, 35.03; H, 5.88; N, 1.70.
Found: C, 34.71; H, 5.96; N, 1.37%. IR data (KBr, cmꢀ1): 3432br, m,
2968m, 2928w, 2873w, 1578s, 1474m, 1429s, 1382m, 1305m,
1170w, 1099w, 508m. FAB MS+: 445.1 {Fe3O(O2CCHMe2)3}+,
100%; 706.17 {Fe3O(O2CCHMe2)6}+, 78%; 531.95 {Fe3O(O2C-
CHMe2)4}+, 41%; FAB MSꢀ: 599.2 {Fe3O(O2CCHMe2)4 (OH)4}ꢀ,
4.3. Magnetic measurements
Magnetic susceptibility data were recorded using a Quantum
Design MPMS-5XL SQUID magnetometer as a function of field
(0.1–5.0 Tesla) and temperature (2.0–290 K). Experimental data
were corrected for the sample holder (PTFE tubes) and diamagnetic
contributions calculated from tabulated values:
v
dia(1) =
ꢀ0.724 ꢂ 103 m3 molꢀ1
;
v
v
dia(2) = ꢀ0.832 ꢂ 103 m3 molꢀ1
; vdia(3) =
ꢀ0.86 ꢂ 103 m3 molꢀ1
,
dia(4) = ꢀ0.756 ꢂ 103 m3 molꢀ1
.

I.L. Malaestean et al. / Polyhedron 29 (2010) 1990–1997
1997
126 (2004) 2156;
4.4. X-ray crystallography
(i) M. Murugesu, M. Habrych, W. Wernsdorfer, K.A. Abboud, G. Christou, J. Am.
Chem. Soc. 126 (2004) 4766;
(j) L.F. Jones, R. Inglis, M.E. Cochrane, K. Mason, A. Collins, S. Parsons, S.P.
Perlepes, E.K. Brechin, Dalton Trans. 44 (2008) 6205;
(k) S.K. Langley, K.J. Berry, B. Moubaraki, K.S. Murray, Dalton Trans. 6 (2009)
973.
A red block crystal for 1 with approximate dimensions 0.24 ꢂ
0.22 ꢂ 0.24 mm3, a red prism for 2 (0.46 ꢂ 0.25 ꢂ 0.21 mm3), a
red prism for 3 (0.41 ꢂ 0.23 ꢂ 0.19 mm3) and a black block crystal
data for 4 (0.28 ꢂ 0.18 ꢂ 0.11 mm3) were mounted separately on a
[3] (a) Fe SMMS. K. Wieghardt, K. Pohl, I. Jibril, G. Huttner, Angew. Chem., Int. Ed.
23 (1984) 77;
Bruker CCD-1000 diffractometer (Mo Ka radiation, graphite mono-
(b) C. Beneli, S. Parsons, G.A. Solan, R.E.P. Winpenny, Angew. Chem., Int. Ed. 35
(1996) 1825;
(c) C. Sangregorio, T. Ohm, C. Paulsen, R. Sessoli, D. Gatteschi, Phys. Rev. Lett.
78 (1997) 4645;
(d) A.-L. Barra, A. Caneschi, A. Cornia, F. Biani, D. Gatteschi, C. Sangregorio, R.
Sessoli, L. Sorace, J. Am. Chem. Soc. 121 (1999) 5302;
(e) H. Oshio, N. Hoshino, T. Ito, J. Am. Chem. Soc. 122 (2000) 12602;
(f) M. Moragues-Canovas, E. Riviere, L. Ricard, C. Paulsen, W. Wernsdorfer, G.
Rajaraman, E.K. Brechin, T. Mallah, Adv. Mater. 16 (2004) 1101;
(g) A.K. Boudalis, B. Donnadieu, V. Nastopoulos, J.M. Clemente-Juan, A. Mari, Y.
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x. Obtained
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Funded by the Excellence Initiative of the German federal and
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