Tri-, tetra- and octa-metallic vanadium(III) clusters from new, simple starting materials: Interplay of exchange and anisotropy effects

Article abstract of DOI:10.1039/b911586b

The crystal structure of the monomeric vanadium(III) species mer-[V(bipy)Cl₃(MeCN)] (1; bipy = 2,2′-bipyridine) is reported. The solvothermal reaction of [V(bipy)Cl₃(MeCN)]with Na(O ₂CPh) yields the T-shaped cluster [V

Full text of DOI:10.1039/b911586b

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www.rsc.org/dalton | Dalton Transactions
Tri-, tetra- and octa-metallic vanadium(III) clusters from new, simple starting
materials: interplay of exchange and anisotropy effects†
Ian S. Tidmarsh,a Luke J. Batchelor,a Emma Scales,a Rebecca H. Laye,a Lorenzo Sorace,b Andrea Caneschi,b
Ju¨rgen Schnackc and Eric J. L. McInnes*a
Received 15th June 2009, Accepted 17th August 2009
First published as an Advance Article on the web 4th September 2009
DOI: 10.1039/b911586b
The crystal structure of the monomeric vanadium(III) species mer-[V(bipy)Cl3(MeCN)] (1; bipy =
2,2¢-bipyridine) is reported. The solvothermal reaction of [V(bipy)Cl3(MeCN)]with Na(O2CPh) yields
the T-shaped cluster [V3(O)Cl3(O2CPh)2(bipy)2(OEt)2], magnetic studies of which show strong
intramolecular antiferromagnetic coupling giving a well isolated S = 1 ground state. Solvothermal
treatment of 1 with triols yields a series of polymetallic clusters [V4Cl6(thme)2(bipy)3],
[V3Cl4(Hcht)2(bipy)2]Cl and [V8(OH)2Cl4(cht)4(O2CPh)6(bipy)2], structurally related to previously
reported {M4} centred triangles. Magnetic studies of this series reveal very weak intramolecular
antiferromagnetic exchange and very strong local zero-field splitting effects.
we report that on solvothermal reaction in alcohol solvents with
polyalcohol and/or carboxylate ligands we can isolate tri-, tetra-
Introduction
2+
and octa-metallic, homovalent clusters based on {VIII(bipy)Cl}
We have recently been exploring the cluster chemistry of the
vanadium(III) ion1–8 given the stark lack of literature compared
vertices. These materials exhibit VIII ◊ ◊ ◊ VIII exchange coupling
to other tri-valent first row transition ions9 and the interesting
magnetic properties of this ion.10 In most six-coordinate species
studied to date, distortions from true octahedral symmetry are
varying from |J| ca. 2 to 70 cm-1, and local magnetic aniostropies
(zero-field splittings of the spin triplet VIII ions) up to |D| ca.
10 cm-1. Hence, large magnetic anisotropies can be built into
clusters via these VIII fragments.
3
sufficient to quench the orbital degeneracy, giving a A ground
state: the zero-field splitting (zfs) of this spin triplet is typically
very large, with axial components |D| up to ª 20 cm-1.11 This is
attractive for materials such as single-molecule magnets in which
zfs provides the magnetic anisotropy (DS2) to block magnetisation
relaxation in single molecules.12
Results and discussion
Synthesis and structural studies
Solvothermal reaction of [VCl3(thf)3] and bipy (1:1) in MeCN
at 100 ◦C yields mer-[VCl3(bipy)(MeCN)] (1) in quantitative
yield. The analogous 1,10-phenanthroline (phen) derivative of 1,
mer-[VCl3(phen)(MeCN)] (2), can be prepared in equal yield by
the analogous reaction. Green crystals of 1, of sufficient quality
for X-ray diffraction, are obtained directly from slow cooling of
the reaction mixture (Fig. 1).
We have found solvothermal methods particularly successful
for preparing VIII clusters, with homovalent VIII and heterova-
IV
lent VIII/IV examples with nuclearities of up to 10 and 18 (VIII
V 2),
16
respectively.1,3 However, due to the air-sensitivity of vanadium(III)
there are relatively few readily available starting materials and to
date we have exploited commercially available or easily prepared
compounds including VCl3 and its adduct [VCl3(thf)3],4–6 VF3,2
[V3O(O2CR)6L3]X,1 [V(diketonate)3]3,6 and [tBu4N]3[V2Cl9].7 Here
we report the facile preparation and crystal structure of a sim-
ple, monomeric vanadium(III) complex, mer-[V(bipy)Cl3(MeCN)]
(bipy = 2,2¢-bipyridine). The complex was first reported by Fowles
and Greene in 1967,13 but its structure and reactivity were not
investigated. We report that this complex can be prepared in
quantitative yield and is air-stable over a period of months, making
it a very attractive starting material for further chemistry. Indeed,
aSchool of Chemistry, The University of Manchester, Manchester, UK M13
9PL. E-mail: eric.mcinnes@manchester.ac.uk; Fax: +44(0)161 275 4616;
Tel: +44 (0)161 275 4469
Fig. 1 Crystal structure of mer-[VCl3(bpy)(MeCN)] (1). Scheme as
˚
bDipartimento di Chimica and UdR INSTM, Universita` di Firenze, Via
della Lastruccia 3, Sesto Fiorentino, Italy. E-mail: andrea.caneschi@unifi.it;
Fax: +39 0554573372; Tel: +39 39-0554573327
labelled;
H omitted for clarity. Selected bond lengths (A): V-Cl
2.312(1)-2.339(1), V-N 2.111(2)-2.126(2). Inter-bond angles (◦): N1-V-N2
77.43(7), other cis-(L-V-L) angles 86.03(5)-92.93(6).
cFakulta¨t fur Physik, Universita¨t Bielefeld, Bielefeld, Germany. E-mail:
jschnack@uni-bielefeld.de; Fax: +49-521-106-6455; Tel: +49-521-106-6901
† Electronic supplementary information (ESI) available: Fig. S1. CCDC
reference numbers 736080–736088. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b911586b
The metal ion is six-coordinate with a chelating bipy, a coordi-
nated MeCN and three chlorides in a meridional arrangement.
The metric parameters and regular octahedral geometry are
9402 | Dalton Trans., 2009, 9402–9409
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typical for VIII. Unusually for compounds of this metal ion, 1
is stable in air for a period of months when dry. Although drying
results in a colour change from green to black this material is
identical by IR, C:H:N:V analysis and unit cell, and the green
colour is restored on wetting with MeCN. In addition to the
quantitative yield and air-stability of 1, the labile chloride and
nitrile ligands make it a very attractive starting material for higher
nuclearity VIII clusters in the presence of suitable bridging ligands.
Hence, we have investigated its chemistry with triols and/or
carboxylates given our previous success in low-valent vanadium
cluster chemistry with these types of ligand.1–3,7 Although 1 is
only poorly soluble in common organic solvents, the solvothermal
conditions allow this difficulty to be overcome.14
salt [V(bipy)Cl4][V(bipy)2Cl2] which can be separated manually.
The ratio of product:salt is ca. 4:1.
4 crystallises in the triclinic space group P-1. The four metal ions
lie on a plane, with V1 being at the centre of a near-equilateral
triangle defined by V2-4, hence the molecule has pseudo-C3
symmetry (Fig. 3).
(i) Reaction of complex 1 with carboxylates. Solvothermal
reaction of 1 and Na(O2CPh) (3:2) in EtOH at 150 ◦C yields
[V3(O)Cl3(O2CPh)2(bipy)2(OEt)2] (3) in reasonable yield (36%,
Fig. 2). 3 has two-fold symmetry with a C2 axis along the O1-V2
vector. The three metal ions are VIII, from BVS considerations15
and as required to charge balance, and are bridged via a m3-oxide,
O1. O1 lies in the {V3} plane and has a T-shaped geometry with
V1-O1-V1A and V1-O1-V2 169.7(2) and 95.17(10)◦, respectively.
V2 and V1 [and symmetry equivalent (s.e.)] are also bridged by a
m-benzoate and a m-ethoxide. V1 and V1A each have a chelating
bipy, these are co-planar to each other but perpendicular to the
{V3O} plane. A terminal chloride on each metal ion completes the
hexa-coordination.
Fig. 3 Crystal structure of [V4Cl6(thme)2(bipy)3] (4) viewed perpen-
˚
dicular to {V4} plane. Bond length ranges (A): V-O 1.949(2)-2.022(2),
V-Cl 2.310(1)-2.361(1). Angles (◦): V-V1-V 118.76(2)-120.99(2), V-O-V
101.44(9)-103.37(9).
V1 is bound by the six alkoxide arms of the two fully
deprotonated thme3-, one above and one below the {V4} plane,
which bridge V1 to the three peripheral vanadium ions. The
coordination at each of V2-4 is completed by one bipy and two
(cis) chlorides. The three bipyridines point away from the {V4}
plane in the same sense, forming a cone-like shape.
The {M4} centred-triangle topology with alkoxides21a or tris-
alkoxides21b–d is well known for FeIII. This topology is also known
for MnII,22a CoII,22b NiII,22c and some heterometallic species,22d
for different bridging ligand systems. This class of clusters
has become known as metal “stars”, and 4 is the first VIII
example. The tris-alkoxide bridged {Fe4} examples include
[Fe4(thme)2(nPrOH)6Cl6]21c and [Fe4(thme)2(dpm)6]21b (Hdpm =
dipivolylmethane), clearly related to 4. Analogues to 4 with tmp3-
(5; 57%) and Hpeol3- (6; 28 %) in place of thme3- can be prepared
by the same route. It is also possible to vary the diimine: for
example, the 4,4¢-tBu2-bipy analogue of 4 is made by first reacting
[VCl3(thf)3] and 4,4¢-tBu2-bipy in MeCN at 100 ◦C, yielding a
green solution upon cooling. We assume that mer-[VCl3(4,4¢-
tBu2-bipy)(MeCN)] is formed although we have not been able to
crystallise it. Addition of two equivalents of H3thme followed by
solvothermal treatment at 150 ◦C yields large brown crystals of
[V4Cl6(thme)2(4,4¢-tBu2-bipy)3] (7; 11%).
Fig. 2 Crystal structure of [V3(O)Cl3(O2CPh)2(bipy)2(OEt)2] (3). V1-O1
1.8583(7) A, V2-O1 2.066(3) A, V1-O4-V2 94.48(11) .
◦
˚
˚
(ii) Reactions of complex 1 with triols. The tripodal alco-
hols RC(CH2OH)3 [R = Me (1,1,1-tris-hydroxymethylethane;
H3thme), Et (1,1,1-tris-hydroxymethylpropane, H3tmp), CH2OH
(pentaerythritol, H4peol)] have long been used as polynucleating
ligands in polyoxometallate chemistry,16,17 and more recently in
cluster chemistry more widely.18 For example, they have been used
to stabilize reduced, VIV polyoxovanadates.16,17 More recently we
have used them to prepare VIII and VIII/IV tetrametallic “butterfly”
clusters starting from diketonate precursors.7 Hence, we were
interested in the analogous chemistry with complex 1 as the VIII
source. In addition to RC(CH2OH)3 we have also used cis,cis-1,3,5
cyclohexanetriol (H3cht) which presents a similar disposition of
three alcohol groups.19
The reaction of 1 with the cyclohexane-based triol H3cht at
this ratio (1:2) gave no crystalline product, and we have been
unable to isolate any clean product. However, when carboxylate is
included in the reaction a crystalline product is obtained: reaction
of 1 with H3cht and Na(O2CPh) (4:2:3) in MeCN at 150 ◦C gives
[V3Cl4(Hcht)2(bipy)2]Cl·2MeCN (8, 32 %). Although there is no
Solvothermal reaction of 1 and H3thme (1:2) in MeCN at
150 ◦C yields crystals of [V4Cl6(thme)2(bipy)3]·2.5MeCN (4; 59%)
together with a separate crystalline side product of the known20
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benzoate in the product the reaction fails if Na(O2CPh) is not
included in the reaction; presumably it is acting as a base for
deprotonation of H3cht.
8 crystallises in the monoclinic space group P21/c (Fig. 4). The
structure can be considered as a {V4} “star” minus one vertex.
The two triols have only been doubly deprotonated and, as in 4,
they sandwich the central VIII ion (V2). V3 and V4 have identical
coordination to the equivalent ions in 4. The remaining alcohol
arms of the two Hcht2- (O2,5) form hydrogen bonds to the chloride
˚
counter-ion Cl5 [H ◊ ◊ ◊ Cl 2.138 and 2.139 A; V2-O2-Cl5 and V2-
O5-Cl5 113.50 and 108.76◦, respectively], which can be considered
to have replaced the “fourth” vanadium ion of the metal star. Thus,
˚
the {V3Cl} fragment is near-planar (0.013 A maximum deviation
from best least squares plane).
Fig.
5
Crystal structure of [V8(OH)2Cl4(cht)4(O2CPh)6(bipy)2] (9)
viewed perpendicular to the {V8} plane. Bond length ranges
(A): V-O(cht) 1.896(3)-2.054(3), V-Cl 2.313(1)-2.349(2). Angles (◦):
˚
V2-V3-V1/4 134.24(2) and 124.32(2), V1-V3-V4 101.40(2), V-O(cht)-V
100.4(1)-103.2(1), V2A-O7-V4 128.4(1).
Structural relationship between complexes 4–9
There is an obvious structural relationship between complexes 4-9
(Fig. 6). Substitution of the chloride in the {V3Cl} “star” of 8
+
with a {V(bipy)Cl2} fragment gives the complete {V4} structure
as found in 4-7. The core of 9 has two {V4} units. Looking more
closely at 9, the two metal ions not involved in linking the {V4}
fragments, V1 and s.e., have lost a single chloride in comparison
to the equivalent ions in 4-7. This is replaced by a carboxylate
which bridges to V4, also replacing a chloride at this ion. At both
V4 and V2 (and s.e.), the three remaining coordination sites are
taken by the two carboxylates and the hydroxide bridging to the
other {V4} fragment, formally replacing a bipy and a chloride
at each of these ions cf. 4-7. This results in considerably greater
distortion of the trigonal fragments in 9 cf. 4. In 9 the edges of
Fig. 4 Crystal structure of [V3Cl4(Hcht)2(bipy)2]Cl·2MeCN (8) viewed
˚
perpendicular to the {V3Cl} plane. Bond length ranges (A): V-O
1.945(2)-2.076(2), V-Cl 2.334(1)-2.371(1). Angles (◦): V1-V2-V3 131.59(2),
V-O-V 101.53(8)-103.94(8).
˚
the V1,2,4 triangle are 4.78, 5.42 and 5.66 A (the shortest being
the carboxylate bridged V1 ◊ ◊ ◊ V4 edge), while in 4 the outer V3
triangle is much nearer equilateral with 5.33, 5.36 and 5.39 A.
Repeating the reaction that gives 8 but with a 1:2:2 ratio
of 1:H3cht:Na(O2CPh) yields [V8(OH)2Cl4(cht)4(O2CPh)6(bipy)2]·
2MeCN (9, 42%; Fig. 5). Complex 9 is centrosymmetric and the
asymmetric unit contains two half molecules. 9 consists of two
linked {V4} “stars” (V1-4 and s.e.) and the resulting {V8} unit is
˚
˚
near-planar (0.080 A maximum deviation from the best plane).
Each {V4} star is bound by two fully deprotonated cht3-, centered
on V3 and s.e., analogous to the role of thme3- in 4. V1 and s.e. are
additionally bound by a bipy and one chloride, and a m-benzoate
bridges the V1 ◊ ◊ ◊ V4 edge of the star. V2 and s.e. have a single
terminal chloride Cl2. The two stars are linked via V2A ◊ ◊ ◊ V4
and s.e., each bridged by a m-hydroxide [O7] and two m-benzoates
Fig. 6 Representations of the oxometallic cores of 8 (left), 4 (centre) and
9 (right) illustrating the relationships between the triangular fragments.
˚
[O10-13]. The V-O7 bond lengths of 2.002(3) and 1.917(3) A are far
The difference in chemistry of the tripodal alcohols R(CH2OH)3
and H3cht with 1 may then be due to the greater rigidity of the
cyclohexane-based ligand. Although, there is at least one example
where thme3- and cht3- can form analogous clusters with no loss
of symmetry,19 this appears to be the exception23 and indeed the
reactions that give 4-7 give no crystalline product at all when
too long to be consistent with vanadyl, and BVS calculations and
magnetic data (see below) are only consistent with all vanadium
ions as VIII and O7 as hydroxide. The V-O(H) bond lengths and
V-O(H)-V angles are comparable to those in the cyclic complex
[VIII8(EtO)8(OH)4(O2CPh)12].1
9404 | Dalton Trans., 2009, 9402–9409
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repeated with H3cht. On addition of an additional source of base,
Na(O2CPh), 8 is isolated where a single metal vertex is missing (cf.
4-7) as a result of the triol being only doubly deprotonated. On
increasing the amount of carboxylate in the reaction, the ligand is
now fully deprotonated and coordinates in an analogous fashion
to R(CH2O)33-, but carboxylate is also now incorporated into the
structure to give 9.
is irrelevant since, in the approximation of isotropic g and with
the data insensitive to D1,1A, it is the only anisotropic term in (1).
These parameters also fit the low temperature M(B) data (Fig. 7).
A more sensitive method of determining the zfs is EPR: Q-band
data at 5 K are only consistent with a substantially rhombic triplet
and simulation gives |D| = 2.2 with E = 0.71 cm-1 (see ESI†).
Hence, in 3 the exchange interactions are much larger than
the local (single-ion) zfs. The moderately AF J2 is similar
to that observed in [V3O(O2CMe)6(pyridine)3]ClO4 with mixed
carboxylate/oxide-bridging.24 However, it is perhaps surprising
that the “linear” interaction is strongly AF given that known linear
V-O-V dimers are ferromagnetically coupled:10a,25 presumably
the third vanadium significantly perturbs the orbital overlap.
Anyhow, this situation is straightforward: the magnetic data can
be modelled with a simple isotropic Hamiltonian (other than at
the lowest temperatures), the strong exchange limit holds and the
ground state is a well defined total spin multiplet (S = 1).
Magnetic studies
For the T-shaped trimetallic VIII cluster 3, cM T is 2.08 emu K mol-1
(cM = molar magnetic susceptibility) at room temperature and is
already decreasing rapidly with decreasing temperature (Fig. 7).
This is indicative of strong antiferromagnetic (AF) coupling
between the VIII ions. cM T plateaus below ca. 70 K at 1.08 emu K
mol-1 which implies an S = 1 ground state. This is confirmed by
low temperature magnetisation (M) vs. applied magnetic field (B)
data which are tending to saturation at ca. 2.0 mB (Fig. 7, inset).
The fact that cT plateaus below ca. 70 K indicates that the ground
state is well isolated, also consistent with strong AF exchange.
The situation is very different in the {V4} “star” complex 4. 4
has a room temperature cM T value of 3.38 emu K mol-1, consistent
with four VIII ions with g = 1.9, decreasing slowly with temperature
to ca. 100 K implying weak exchange. Below this cMT falls more
rapidly, reaching 0.78 emu K mol-1 at 2 K (Fig. 8). M(B) at 2 K
reaches 2.49 mB at 6 T and is still increasing, indicative of a high
density of low-lying states (Fig. 9).
Fig. 7 cM T(T) for 3 (black squares) and best fit (line) using the coupling
scheme in the insert and spin-Hamiltonian (1) with the parameters in the
text. Inset: M(B) for 3 at 2 (filled squares) and 4.5 K (open squares) and
best fit (solid lines).
Fig. 8 cM T(T) for 4 (squares) and best fit (solid line) using the coupling
scheme in the insert and the spin-Hamiltonian (2) with the first set of
parameters Table 1.
The cMT(T) data above ca. 10 K can be fit to Hamiltonian (1),
using only the isotropic exchange and Zeeman terms, with J1 =
-67.6 and J2 = -13.2 cm-1 with g = 2.07 (Fig. 7). [Although, g
is higher than expected for VIII this is presumably masking slight
errors in e.g. sample mass.]
Table 1 Best fit parameters to M(B) and cM T(T) for 4 using spin-
Hamiltonian (2)
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
H = −2J1 S1⋅S1A−2J 2 S ⋅S + S1A⋅S2
+
gi mB Si .B +
lsqa
J1/cm-1
J2/cm-1
D1/cm-1
D
2-4/cm-1
q/◦
g1-4
(
)
1
2
∑
i
(1)
2
0.0269
0.0355
-2.42
+0.96
-0.17
-3.51
-5.82
-19.02
+11.70
+10.60
90
60
1.90
1.90
ˆ
Di Si ,z
∑
i
ꢀ
a
{[M(exp) - M(calc)]2 + [cM T(exp) - cM T(calc)]2} over T = 2 and 4 K
M(B) and cM T(T) data.
Hence, J1
- corresponding to the approximately linear
V1 ◊ ◊ ◊ V1A interaction - is totally dominant, giving a ground state
spin triplet that corresponds to the isolated V2. The first excited
state is S = 0 at 82.4 cm-1. We then attempted to model the collapse
of cT below 10 K by inclusion of the zfs terms in Hamiltonian
(1). Because of the dominant (AF) J1, the curve is only sensitive to
D2 and can be fit with D2 +0.8 to +1.2 cm-1, assuming axial local
zfs for simplicity (Fig. 7). Note the orientation of this parameter
Attempts to fit the data to an isotropic model considering
either only the exchange between the central and outer VIII ions
(J1) or also including exchange between the outer VIII ions (J2)
[Hamiltonian (2) neglecting the final term] were unsuccessful.
Hence, we have used the full Hamiltonian (2) incorporating local
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◦
down the trigonal axis in Fig. 3 (38 dihedral angles). Large
zfs have also been observed in homoleptic complexes such as
[V(H2O)6]3+ (D = +4.8 cm-1) and [V(acac)3] (D = +7.4 cm-1);
zfs parameters of the VIII ion are very sensitive to even small
distortions.26,27 [The much smaller zfs of V2 in complex 3 (|D| ª
1 cm-1) is consistent with its more regular geometry.]
Hence, in 4 the local zfs dominate and the low-lying multiplets
cannot be described as total S states. In both of the fits in Table 1,
the zfs of the central ion (V1) is easy-axis type (D negative), and
those of the outer ions (V2-4) are easy-plane type (D positive).
Importantly, the hard axis (z) of each the outer ions is in the {V4}
plane (q = 90◦ in the best fit). These factors lead to many low-
lying states with very small magnetic moment, hence M only grows
slowly with B. This is probably also the reason that 4 is essentially
EPR silent (at Q-band and low temperature).
It is interesting to compare these results to the {Fe4} “stars”
of Sessoli and co-workers.21a In {Fe4} there is strong AF coupling
(2J ª -20 cm-1) between the inner and outer FeIII ions, cf. the
local zfs of |Di| ª 0.7 cm-1. This leads to a well-isolated S = 5
ground state (the outer ions “spin up” with the central ion “spin
down”) and the projections of the Di lead to a cluster ground
state D ª -0.4 cm-1. These parameters lead to the {Fe4} family
being among the best characterised single-molecule magnets. If
{V4} were strongly AF coupled an S = 2 ground state would
result with a very large negative axial zfs, since the easy-axis of V1
and easy planes of V2-4 all project negative components along the
molecular C3 axis. The weak exchange destroys this simple picture.
The situation of |J| << |Di| can also lead to unusual magnetic
effects. Sessoli, Powell and co-workers have recently reported a
weakly coupled {DyIII3} triangle28 where there is huge easy-axis
anisotropy at each metal site and where the local z axes are oriented
in the {Dy3} plane. Hence, the Ising-like local magnetic moments
are confined to the plane at low temperature, leading to degenerate
ground states of differing spin chirality.29 In contrast, although the
local z-axes of the outer ions in 4 are in the {V4} plane, they are of
easy-plane type, approximating to XY spins at low temperature.
These VIII spins preferentially lie on discs perpendicular to the C3
axis (Fig. 10).
Fig. 9 M(B) for 4 measured at 2 (filled squares) and 4 K (open squares)
and best fits (solid lines) using spin-Hamiltonian (2) with the first set of
parameters Table 1.
zfs effects. We have only considered the axial component of local
zfs (where z refers to the local principal axis at the metal ion sites)
and have made the further approximation that the molecule has
C3 symmetry. Hence, Dz for the central ion (V1) is restricted to
being parallel to the molecular C3 axis. The local Dz axes for the
outer ions (V2-4) are only restricted in that they are related to each
other by a 3-fold rotation about the molecular C3 axis. We define
their orientations by the inclination angle q from the C3 towards
the {V4} plane. The azimuthal angles f are chosen as 0, 120 and
240◦, respectively.
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ ˆ
3 4
H = −2J1 S ⋅S +S ⋅S +S ⋅S −2J S ⋅S +S ⋅S +S ⋅S
(
)
(
)
1
2
1
3
1
4
2
2
3
2
4
2
ˆ
ˆ
Di Si ,z
+
gi mB Si .B +
∑
∑
i
i
(2)
Fitting was simultaneously to the M(B) (at 2 and 4 K) and
cM T(T) data using an automated procedure. There were two
parameter sets that gave least square deviations of <0.04 (summed
over the three data fits; Table 1), giving excellent reproduction of
both cM T(T) and M(B) which are indistinguishable by eye (Fig. 8
and 9). The next best fits were an order of magnitude poorer.
Although both fits are excellent we favour the better of the two
(and use these values in the discussion below) because it is unlikely
that |J2| >> |J1| and that |D1| >> |D2-4|. Nevertheless,
both fits give the local zfs much greater than the exchange
interactions. The latter, which are only via the alkoxide arms of the
deprotonated triol ligands, are very weak (|J| ª 2 cm-1). In fact,
these interactions are much weaker than have been observed for
simple bis-alkoxide bridged VIII dimers,25a and related species,4,7
where J is between ca. -10 and -40 cm-1. The reason for this
is unclear, and there is no simple correlation with, for example,
V-O(R)-V angles. The very large zfs for the outer VIII ions (|D| ª
12 cm-1) are entirely feasible given the low symmetry {VO2N2Cl2}
coordination sphere and are in keeping with halide-containing
monometallic complexes such as [VX3(thf)3] (X = Cl, D ª -10 cm-1;
X = Br, D = -16 cm-1).11 At first sight the substantial zfs for the
{VO6} environment at the central VIII ion (|D| ª 6 cm-1) is more
surprising; however, the geometry is significantly distorted from
octahedral towards trigonal prismatic, as apparent from the view
Fig. 10 Cartoon of the preferential spin orientations in complex 4. The
spin at the central VIII ion is easy-axis, parallel to the molecular C3
axis; the spins at the peripheral VIII ions are easy-plane type with their
hard axes perpendicular to C3 (here pointing out from the {V4} triangle,
corresponding to f = 0, 120 and 240◦. The specific values of f are not
crucial to the powder magnetic data as long as they are related by a 3-fold
rotation).
The trimetallic cluster 8, a {V3Cl} “star”, shows qualitatively
similar behaviour to 4. cM T is 2.84 emu K mol-1 at room
temperature, consistent with three uncoupled VIII ions, decreasing
to 0.54 emu K mol-1 at 2 K (Fig. 11); M(B) increases only slowly
9406 | Dalton Trans., 2009, 9402–9409
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Found: C 40.64, H 2.90, N 11.74, Cl 29.60, V 14.28; Calc for
C12H11N3Cl3V: C 40.65, H 3.13, N 11.85, Cl 30.00, V 14.37%.
Selected IR data (KBr), u/cm-1: 3079, 2283, 1599, 1469, 1438,
1310, 1028, 771, 730, 415.
Synthesis of mer-[VCl3(phen)(MeCN)] (2). [VCl3(THF)3]
(0.54 mmol), phen (0.54 mmol) and MeCN (9 ml) were treated as
above to yield bright green needle-like crystals of 2 (quantitative
yield). Found: C 44.97, H 3.24, N 10.89; Calc for C14H11N3Cl3V:
C 44.42, H 2.93, N 11.10%. Selected IR data (KBr), u/cm-1: 3091,
2275, 1628, 1519, 1425, 1107, 851, 722, 651, 432.
Synthesis
of
[V3(O)Cl3(O2CPh)2(bipy)2(OEt)2]
(3). 1
(0.71 mmol), PhCO2Na (0.47 mmol) and EtOH (9 ml) were
placed in a sealed Teflon container and heated for 12 h at
150 ◦C. Slow cooling gave two separate crystalline products, 3
and the salt [V(bipy)Cl4][V(bipy)2Cl2] in 4:1 ratio. Brown needles
of 3 were separated manually (36%). Found: C 49.47, H 3.88, N
6.24, Cl 11.76; Calc for C38H36O7N4Cl3V: C 49.62, H 3.94, N 6.09,
Cl 11.56%.
Fig. 11 cT(T) in 1 T applied magnetic field for 8 (filled squares) and 9
(open squares). Inset: M(B) at 2 K for 8 and 9.
and does not saturate up to fields of 7 T, reaching a value of 1.73
mB at this field (Fig. 11, inset). Given the similar building blocks
and exchange pathways we expect a similar situation to 4, with
large local zfs and weak exchange rather than the S = 1 ground
state that would result from dominant AF exchange.
For the octa-metallic species 9, cM T is 6.64 emu K mol-1 at room
temperature, decreasing to 0.76 emu K mol-1 at 2 K (Fig. 11). M(B)
fails to saturate up to 7 T, reaching 2.30 mB at 2 K. The greater slope
of cM T(T) cf. 4 or 8 suggests some stronger AF interactions. We
speculate that these correspond to the links between the {V4} units
(V2 ◊ ◊ ◊ V4A and s.e.) which are bridged by a hydroxide and two
carboxylates: the interactions via the alkoxide arms within each
{V4} unit are likely to be weak by analogy with compound 4. Given
the number of independent variables that would be necessary to
make the model physically meaningful, we have not attempted to
fit the magnetic data for 9.
General procedure for the synthesis of [V4Cl6(RC{CH2O}3)2-
(bipy)3]·2.5MeCN (4-6). 1 (0.71 mmol), RC{CH2OH}3 (R =
Me [4]; Et [5]; CH2OH [6], 1.41 mmol) and MeCN (9 ml)
were treated as above. Again, the brown needles of the product
crystallize directly on cooling of the reaction solution, together
with [V(bipy)Cl4][V(bipy)2Cl2] which was separated manually (56,
57 and 18% for 4–6, respectively). Compound 4: Found: C 44.24,
H 4.25, N 8.84, Cl 17.32, V 16.30; Calc. for C45H49.5O6N8.5Cl6V4:
C 44.23, H 4.08, N 9.74, Cl 17.41, V 16.68%. Selected IR data
(KBr), u/cm-1: 3082, 2929, 1601, 1444, 1314, 1126, 1049, 782,
734, 600. Compound 5: 57% yield. Found: C 44.64, H 4.30,
N 9.38, Cl 18.03, V 16.10; Calc. for C47H53.5O6N8.5Cl6V4: C 45.16,
H 4.31, N 9.52, Cl 17.02, V 16.30%. Selected IR data (KBr),
u/cm-1: 3400, 2965, 1601, 1473, 1443, 1314, 1060, 1028, 781, 597.
Compound 6: 18% yield. Found: C 42.84, H 4.62, N 8.75; Calc. for
C45H49.5O8N8.5Cl6V4: C 43.10, H 3.98, N 9.49%. Selected IR data
(KBr), u/cm-1: 3310, 2858, 1602, 1444, 1314, 1115, 1017, 775, 602.
Conclusions
Synthesis of [V4Cl6(MeC{CH2O}3)2(4,4¢-tBu2-bipy)3]·2MeCN·
H2O (7). [VCl3(thf)3] (0.55 mmol), 4,4¢-tBu2-bipy (0.55 mmol)
and MeCN (8 ml) were placed in a sealed Teflon container and
heated for 12 h at 100 ◦C. Slow cooling to room temperature
gave a bright green solution. H3thme (1.10 mmol) was added to
the solution which was then heated solvothermally at 150 ◦C for a
further 12 h. Large brown blocks of the product crystallize directly
on cooling of the reaction solution. They were washed with MeCN
and dried in the glove box (11%). Found: C 51.17, H 6.22, N 7.96,
Cl 13.02, V 12.25. Calc. for C68H100O8N8Cl6V4 C 51.96, H 6.41,
N 7.13, Cl 13.36, V 12.97%.
In conclusion, we have shown that mer-[VCl3(bipy)(MeCN)] is
an excellent starting material for the synthesis of VIII clusters; in
this work we have isolated examples with nuclearity 3-8 in good
yield from simple reactions. Moreover, we have shown that mixed-
ligand VIII building blocks such as that provided by 1 can lead
to very large local magnetic anisotropies in large clusters. This is
promising for the synthesis of future molecular magnetic materials.
Experimental
Synthesis
Synthesis
of
[V3Cl4(Hcht)2(bipy)2]Cl·2MeCN
(8). 1
[VCl3(thf)3] was prepared via a reported procedure.30 All solvents
were distilled before use. All manipulations were conducted under
anaerobic conditions (dinitrogen purged glove box and argon
served Schlenk line).
(0.71 mmol), H3cht (0.35 mmol), PhCO2Na (0.53 mmol)
and MeCN (9 ml) were treated as above to give yellow/brown
plate-like crystals of 7 (32%). Found: C 44.49, H 4.19, N 8.21, Cl
17.49. Calc. for C36H42O6N6Cl5V3: C 43.90, H 4.30, N 8.53, Cl
18.00%. Selected IR data (KBr), u/cm-1: 3392, 2922, 1604, 1442,
1310, 1098, 930, 773, 672, 538.
Synthesis of mer-[VCl3(bipy)(MeCN)] (1). [VCl3(thf)3]
(3.00 mmol), bipy (3.00 mmol) and MeCN (50 ml) were placed
in a sealed Teflon container and heated for 12 h at 100 C. Slow
cooling to room temperature gave bright green needle-like crystals
◦
Synthesis of [V8(OH)2Cl4(cht)4(O2CPh)6(bipy)2]·2MeCN (9).
1 (0.35 mmol), H3cht (0.71 mmol), PhCO2Na (0.71 mmol) and
MeCN (9 ml) were treated as above to give brown needle-like
of 1 in quantitative yield which were separated by filtration.
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crystals of 9 which were separated manually from the reaction
mixture (42%). Found: C 48.21, H 5.55, N 4.20, V 18.00; Calc. for
C90H90O26N6Cl4V8: C 48.67, H 4.08, N 3.78, V 18.35%. Selected
IR data (KBr), u/cm-1: 3402, 2915, 1602, 1547, 1410, 1110, 941,
721, 673, 543.
4. C45H49.5O6N8.5Cl6V4, M = 1221.89, triclinic, a = 11.4530(6),
˚
b = 12.7770(8), c = 19.8817(7) A, a = 83.718(4), b = 78.696(4),
◦
3
˚
g = 66.155(5) , U = 2608.0(2) A , T = 100 K, space group P-1,
Z = 2, m = 1.057 mm-1, 20125 reflections measured, 10626 unique
(Rint = 0.0263). Final wR2 [I>2s(I)] = 0.0882.
5. C47H53.5O6N8.5Cl6V4, M = 1249.94, triclinic, a = 11.8469(4),
Physical measurements
˚
b = 12.7487(5), c = 19.7931(8) A, a = 83.295(3), b = 78.009(3),
◦
3
˚
Variable-temperature magnetic data were measured with a Cryo-
genic S600 SQUID magnetometer on polycrystalline samples at
1 (32–300 K) and 0.1 T (2–32 K) applied magnetic fields. The
data were corrected for the contribution of the sample holder
and for the diamagnetism of the sample estimated from Pascal’s
constants. Magnetic data for 3 were modelled using MAGPACK.31
Magnetic data for 4 were fit using home written software described
elsewhere:32 the fitting starts with random values of the parameters
J1, J2, D1, D2-4, g1-4, q (and fixed f) and follows the gradient of
the least-squares deviation from experiment until step sizes of
0.01 cm-1 (J, D) or 1◦ (q) leads to worse fits. Several starting
points are evaluated.
Single crystal X-ray diffraction data were measured on an
Oxford Diffraction XCalibur2 diffractometer. Structural solution
and refinement were preformed with SHELXTL,33 and the struc-
tures solved by direct methods. Refinement of F2 was against all
reflections. All non-hydrogen atoms were refined anisotropically
except for the disordered MeCN in the lattices of 6, 7 and 9, due
to disorder. H-atoms were added geometrically to carbon atoms.
This was not possible with the OH groups in 9 and these H-atoms
were omitted. The protons of the OH groups in 8 [H2F,5F] were
located from the data. In 3 the ethyl group C18,19 is disordered
over two sites. Structures 4-7 contain disordered MeCN solvent
molecules, the nature of which is similar in all four cases. For
example, in 4 the molecule N9 C45 C46 is disordered over two sites
while the molecule N8 C43 C44 has a mirror plane perpendicular
to the C43 C44 bond resulting in these atoms sharing the same
atomic coordinates. The free alcohol groups of Hpeol3- in 6 are
disordered over three sites [O7,8]. For 9 the phenyl group C31¢-36¢
is disordered over two sites while the solvent molecule N5 C48 C49
is disordered over three. Geometrical and displacement restraints
have been used in the refinements of 3-9, where appropriate, to
model this disorder.
g = 65.219(4) , U = 2653.43(17) A , T = 100 K, space group P-1,
Z = 2, m = 1.040 mm-1, 27231 reflections measured, 15797 unique
(Rint = 0.0314). Final wR2 [I>2s(I)] = 0.0901.
6. C45H49.5O8N8.5Cl6V4, M = 1253.89, triclinic, a = 11.8723(6),
˚
˚
b = 12.7119(6), c = 19.8113(8) A, a = 83.160(4), b = 77.797(4),
◦
3
g = 65.316(5) , U = 2653.7(2) A , T = 100 K, space group P-1,
Z = 2, m = 1.043 mm-1, 15443 reflections measured, 7561 unique
(Rint = 0.0273). Final wR2 [I>2s(I)] = 0.1118.
7. C72H104Cl6N10O7V4, M = 1638.11, triclinic, a = 14.0160(5),
˚
b = 19.1213(8), c = 19.4392(8) A, a = 119.051(4), b = 92.253(3),
◦
3
˚
g = 104.919(3) , U = 4316.7(3) A , T = 100 K, space group P-1,
Z = 2, m = 0.657 mm-1, 25458 reflections measured, 14766 unique
(Rint = 0.0534). Final wR2 [I>2s(I)] = 0.1150.
8. C36H42O6N6Cl5V3,
M
=
984.83, monoclinic,
˚
a
=
◦
22.4708(19), b = 14.8055(13), c = 12.4733(11) A, b = 100.043(7) ,
3
˚
U = 4086.2(6) A , T = 100 K, space group P2(1)/c, Z = 4,
m = 1.052 mm-1, 23227 reflections measured, 6965 unique (Rint
0.0367). Final wR2 [I>2s(I)] = 0.0730.
=
9. C90H90O26N6Cl4V8, M = 2221.0, triclinic, a = 15.3600(5),
˚
b = 15.7265(6), c = 22.6366(8) A, a = 109.056(4), b = 97.906(3),
◦
3
˚
g = 105.983(3) , U = 4810.5(3) A , T = 100 K, space group P-1,
Z = 2, m = 0.930 mm-1, 31809 reflections measured, 16265 unique
(Rint = 0.0328). Final wR2 [I>2s(I)] = 0.1502.
Acknowledgements
We are grateful to the EPSRC, the EC (“MagMaNet” NoE),
the German Science Foundation (FOR 945), and the Leverhulme
Trust for funding. We are also grateful to Dr C. Muryn (Manch-
ester) for help with preparation of some of the figures.
Crystal data for 1-9
Notes and references
1. C12H11N3Cl3V, M = 354.53, monoclinic, a = 8.1267(4), b =
1 R. H. Laye, M. Murrie, S. Ochsenbein, A. R. Bell, S. J. Teat, J. Raftery,
H. U. Gu¨del and E. J. L. McInnes, Chem.–Eur. J., 2003, 9, 6215.
2 R. H. Laye, F. K. Larsen, J. Overgaard, C. A. Muryn, E. J. L. McInnes,
E. Rentschler, V. Sanchez, S. J. Teat, H. U. Gu¨del, O. Waldmann, G. A.
Timco and R. E. P. Winpenny, Chem. Commun., 2005, 1125–1127.
3 I. S. Tidmarsh, R. H. Laye, P. R. Brearley, M. Shanmugan, E. C.
San˜udo, L. Sorace, A. Caneschi and E. J. L. McInnes, Chem. Commun.,
2006, 2560; I. S. Tidmarsh, R. H. Laye, P. R. Brearley, M. Shanmugam,
◦
3
˚
˚
6.6923(3), c = 25.9029(10) A, b = 92.583(4) , U = 1407.33(11) A ,
T = 100 K, space group P2(1)/c, Z = 4, m = 1.261 mm-1, 13877
reflections measured, 4295 unique (Rint = 0.0341). Final wR2
[I>2s(I)] = 0.0729.
2. C14H11N3Cl3V, M = 378.55, monoclinic, a = 7.1643(3),
◦
˚
E. C. Sa
n˜udo, L. Sorace, A. Caneschi and E. J. L. McInnes,
b = 13.6669(6), c = 15.3407(7) A, b = 101.388(4) , U =
Chem.–Eur. J., 2007, 13, 6329.
3
˚
1472.49(11) A , T = 100 K, space group P2(1)/c, Z = 4, m =
4 R. H. Laye, Q. Wei, P. V. Mason, M. Shanmugan, S. J. Teat, E. K.
Brechin, D. Collison and E. J. L. McInnes, J. Am. Chem. Soc., 2006,
128, 9020.
1.212 mm-1, 10981 reflections measured, 2970 unique (Rint
0.0171). Final wR2 [I>2s(I)] = 0.0511.
=
5 R. Shaw, R. H. Laye, L. F. Jones, D. M. Low, C. Talbot-Eeckelaers,
Q. Wei, C. J. Milios, S. Teat, M. Helliwell, J. Raftery, M. Evangelisti,
M. Affronte, D. Collison, E. K. Brechin and E. J. L. McInnes, Inorg.
Chem., 2007, 46, 4968.
6 S. Khanra, M. Kloth, H. Mansaray, C. A. Muryn, F. Tuna, E. C.
San˜udo, M. Helliwell, E. J. L. McInnes and R. E. P. Winpenny, Angew.
Chem., Int. Ed., 2007, 46, 5568.
3. C38H36O7N4Cl3V, M = 919.88, monoclinic, a = 10.5712(6),
◦
˚
b = 21.0167(15), c = 17.3205(10) A, b = 91.323(5) , U =
3
˚
3847.1(4) A , T = 100 K, space group C2/c, Z = 4, m =
0.977 mm-1, 17704 reflections measured, 5794 unique (Rint
0.0278). Final wR2 [I>2s(I)] = 0.1442.
=
9408 | Dalton Trans., 2009, 9402–9409
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7 I. S. Tidmarsh, E. Scales, P. R. Brearley, J. Wolowska, L. Sorace, A.
Caneschi, R. H. Laye and E. J. L. McInnes, Inorg. Chem., 2007, 46,
9743.
8 R. Shaw, F. Tuna, W. Wernsdorfer, A.-L. Barra, D. Collison and E. J. L.
McInnes, Chem. Commun., 2007, 5161.
9 R. E. P. Winpenny, Adv. Inorg. Chem., 2001, 52, 1.
10 For example, see:(a) P. Knopp, K. Weighardt, B. Nuber, J. Weiss and
W. S. Sheldrick, Inorg. Chem., 1990, 29, 363; (b) S. L. Castro, Z. Sun,
C. M. Grant, J. C. Bollinger, D. N. Hendrickson and G. Christou, J. Am.
Chem. Soc., 1998, 120, 2365.
11 J. Krzystek, A. T. Fiedler, J. J. Sokol, A. Ozarowski, S. A. Zvyagin, T. C.
Brunold, J. R. Long and J. Telser, Inorg. Chem., 2004, 43, 5645.
12 R. Sessoli, D. Gatteschi, A. Caneschi and M. Novak, Nature, 1993,
365, 141.
R. Sessoli, L. Sorace, W. Wernsdorfer and L. Zobbi, J. Am. Chem. Soc.,
2006, 128, 4742.
22 (a) E.-Q. Gao, S.-Q. Bai, Z. He and C.-H. Yan, Inorg. Chem., 2005,
44, 677; (b) M. Du, Y.-M. Gao, X.-H. Bu and J. Ribas, Eur. J. Inorg.
Chem., 2004, 3228; (c) V. Pavlishchuk, F. Birkelbach, T. Weyermu¨ller,
K. Wieghardt and P. Chaudhuri, Inorg. Chem., 2002, 41, 4405; (d) R. W.
Saalfrank, I. Bernt, M. M. Chowdhry, F. Hampel and G. B. M.
Vaughan, Chem.–Eur. J., 2001, 7, 2765.
23 A Prescimone, J. Wolowska, G. Rajaraman, S. Parsons, W. Wernsdorfer,
M. Murugesu, G. Christou, S. Piligkos, E. J. L. McInnes and E. K.
Brechin, Dalton Trans., 2007, 5282.
24 S. L. Castro, W. E. Streib, J.-S. Sun and G. Christou, Inorg. Chem.,
1996, 35, 4462.
25 (a) K. Kanamori, Coord. Chem. Rev., 2003, 237, 147; (b) H. Weihe and
H. Gu¨del, J. Am. Chem. Soc., 1998, 120, 2870 and references therein.
26 P. L. W. Treggena-Piggott, H. Weihe, J. Bendix, A.-L. Barra and H.-U.
Gu¨del, Inorg. Chem., 1999, 38, 5928.
13 G. W. A. Fowles and P. T. Greene, J. Chem. Soc. A, 1967, 1869.
14 R. H. Laye and E. J. L. McInnes, Eur. J. Inorg. Chem., 2004, 2811 and
references therein.
15 W. Liu and H. H. Thorp, Inorg. Chem., 1993, 32, 4102.
16 M. I. Khan and J. Zubieta, Prog. Inorg. Chem., 1995, 43, 1.
17 A. Mu¨ller, J. Meyer, H. Bo¨gge, A. Stammler and A. Botar,
Chem.–Eur. J., 1998, 4, 1388.
27 D. Gatteschi, L. Sorace, R. Sessoli and A.-L. Barra, Appl. Magn.
Reson., 2001, 21, 299.
28 J. Tang, I. Hewitt, N. T. Madhu, G. Chastenet, W. Wernsdorfer, C. E.
Anson, C. Benelli, R. Sessoli and A. K Powell, Angew. Chem., Int. Ed.,
2006, 45, 1729.
18 E. K. Brechin, Chem. Commun., 2005, 5141.
19 R. Shaw, I. S. Tidmarsh, R. H. Laye, B. Breeze, M. Helliwell, E. K.
Brechin, S. L. Heath, M. Murrie, S. Ochsenbein, H. U. Gu¨del and
E. J. L. McInnes, Chem. Commun., 2004, 1418.
29 (a) J. Luzon, K. Bernot, I. J. Hewitt, C. E. Anson, A. K. Powell and
R. Sessoli, Phys. Rev. Lett., 2008, 100, 247205; (b) L. F. Chibotaru, L.
Ungur and A. Soncini, Angew. Chem., Int. Ed., 2008, 47, 4126.
30 L. E. Manzer, Inorg. Synth., 1982, 21, 135.
31 J. J. Borras-Almenar, J. M. Clemente-Juan, E. Coronado and B. S.
Tsukerblat, J. Comput. Chem., 2001, 22, 985.
32 (a) T. Glaser, M. Heidemeier, E. Krickemeyer, H. Bo¨gge, A. Stammler,
R. Fro¨lich, E. Bill and J. Schnack, Inorg. Chem., 2009, 48, 607; (b) J.
Schnack, M. Bru¨ger, M. Luban, P. Ko¨gerler, E. Morosan, R. Fuchs, R.
Modler, H. Nojiri, R. C. Rai, J. Cao, J. L. Musfeldt and X. Wei, Phys.
Rev. B: Condens. Matter Mater. Phys., 2006, 73, 094401.
33 SHELX-PC Package, Bruker Analytical X-ray Systems, Madison, WI,
1998.
20 J. C. Dobson and H. Taube, Inorg. Chem., 1989, 28, 1310.
21 (a) A.-L. Barra, A. Caneschi, A. Cornia, F. Fabrizi de Biani, D.
Gatteschi, C. Sangregorio, R. Sessoli and L. Sorace, J. Am. Chem. Soc.,
1999, 121, 5302; (b) A. Cornia, A. C. Fabretti, P. Garrisi, C. Mortalo`,
D. Bonacchi, D. Gatteschi, R. Sessoli, L. Sorace, W. Wernsdorfer
and A.-L. Barra, Angew. Chem., Int. Ed., 2004, 43, 1136; (c) H.
Moragues-Ca´novas, E. Rivie`re, L. Ricard, C. Paulsen, W. Wernsdorfer,
G. Rajaraman, E. K. Brechin and T. Mallah, Adv. Mater., 2004, 16,
1101; (d) S. Accorsi, A. L. Barra, A. Caneschi, G. Chastanet, A. Cornia,
A. C. Fabretti, D. Gatteschi, C. Mortalo`, E. Olivieri, F. Parenti, P. Rosa,
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 9402–9409 | 9409
©