A high-nuclearity metal-cyanide cluster [Mo6Cu14] with photomagnetic properties

Article abstract of DOI:10.1039/c6dt00743k

A high-nuclearity metal-cyanide cluster [Mo₆Cu₁₄] has been prepared and its photomagnetic properties investigated. The photoswitchable magnetic phenomenon observed is thermally reversible (T ≈ 230 K). In the field of photomagnetism, [Mo₆Cu₁₄] represents a unique example of a nanocage and the highest nuclearity observed so far.

Full text of DOI:10.1039/c6dt00743k

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Chamoreau, G. Gontard, H. von Bardeleben, J. Cantin and V. Marvaud, Dalton Trans., 2016, DOI:
10.1039/C6DT00743K.
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DOI: 10.1039/C6DT00743K
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ARTICLE
High-nuclearity Metal-Cyanide Cluster [Mo6Cu14] with
Photomagnetic Properties
Received 00th January 20xx,
Accepted 00th January 20xx
N. Bridonneau,a L.-M. Chamoreau,a G. Gontard,a J.-L. Cantin,b J. von Bardeleben,b and
V. Marvaud*a
DOI: 10.1039/x0xx00000x
A high-nuclearity metal-cyanide cluster [Mo6Cu14] has been prepared and its photomagnetic properties
investigated. The photoswitchable magnetic phenomenon observed is thermally reversible (T ≈ 230 K). In the
field of photomagnetism, [Mo6Cu14] represents a unique example of nanocage and the highest nuclearity
observed so far.
www.rsc.org/
heterometallic structures such as [M6Mn9]18 (M = Mo, W); [M6Co9]19
(M = Mo, W), [W7Cu13],20 [Fe8Co6],21 [Co6Fe4]21 or [Fe42] nanocage.22
Very few switchable architectures have been also reported in the
Introduction
There is an increased awareness of high-nuclearity clusters1 and
smart multi-metallic architectures, as they may substantially exhibit
magnetic2 or photo-magnetic properties.3 Thus, an extraordinary
variety of molecular clusters containing paramagnetic transition
metal ions have been obtained and have attracted a great deal of
interest for their specific properties, such as single-molecule
magnets,4 high spin molecules,5 or magnetic coolers.6 On the other
hand, photomagnetic materials draw a special attention due to
their potential application.
literature, especially by Holmes,23 Oshio24 and Sieklucka.25
In our group, we have demonstrated the feasibility of synthesizing
discrete polynuclear complexes based on polycyanometallate cores
(M = Co(CN)6, Cr(CN)6, Mo(CN)8, W(CN)8) surrounded by external
metallic building blocks (M = Cu, Ni, Mn, Co) bearing a capping
ligand.26 In particular, the use of octacyanometallate centers has
proven to be an effective way of getting multiple kinds of
architectures with promising photomagnetic properties27 due to its
versatile accessible coordination polyhedra (square base antiprism,
dodecahedron or mixed geometries).
Besides the synthetic challenge of getting such molecular
architectures, one could benefit from the important number of
metal centers to improve magnetic properties by optimizing spin
and anisotropy. Furthermore, designing multi-metallic compounds
might be
a fruitful strategy for reaching multifunctional
architectures. The first examples of polynuclear complexes with
attractive magnetic properties are [Mn12]5 and [Fe19]4 published by
Gatteschi’s and Powell’s groups respectively. Following this
approach, high spin molecules and single-molecule magnets have
been described in the late years by several teams.7-11 Recently,
Whitehead and Winpenny showed that heterometallic rings could
be assembled in different supramolecular architectures, like the
[(Ni12)(Cr7Ni)6]12 complex, where the central [Ni12] ring acts as a
Lewis acid bearing terminal THF ligands that can be removed by the
[Cr7Ni] Lewis base building blocks to form the “ring of ring”
structure. Many other examples of high-nuclearity clusters might be
found in the literature.13-17 Among them, several groups have taken
advantage of the cyanide ligand that is known to mediate strong
magnetic coupling between spin carriers, allowing to get various
Figure 1. Crystal structure of the [Mo6Cu14] cluster (1) (yellow: Mo;
dark blue: Cu; grey: C, N).
a. IPCM – CNRS UMR-8232, UPMC- Univ. Paris 6, 4 place Jussieu, 75252 Paris cedex
05, FRANCE, Fax : 33 (0)1 44 27 38 41, E-Mail : valerie.Marvaud@upmc.fr
b. INSP - CNRS UMR-7588, UPMC- Univ. Paris 6, 4 place Jussieu, 75252 Paris cedex
05, FRANCE.
The design of these assemblies enabled a precise control of
nuclearity and magnetic properties. In particular, the role of the
blocking ligand has proven to be of crucial influence on the metal-
ion environment and consequently on the overall topology of the
final product. By using blocking ligands that leave only one
Electronic
Supplementary
Information
(ESI)
are
available:
See
DOI: 10.1039/x0xx00000x
CCDC numbers are 1052206 and 1426776 for 1 and 2 respectively
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The characterization of the polynuclear complexes 1 and 2
DOI: 10.1039/C6DT00743K
performed by infrared spectroscopy indicates similarities between
accessible position on the metal ions, we succeeded in obtaining
high nuclearity complexes such as [CrMn6]26 or [MoCu6].27 This
latter example exhibits impressive photomagnetic response up to
room temperature. However, steric hindrance coupled to charge
repulsion between the peripheral metal atoms prevent from
increasing the nuclearity of the [MoCu6] complex, despite the eight
cyanide ligands available for complexation. In order to get higher
nuclearity complexes, we selected blocking ligands with potentially
two free reactive positions instead of one: tacn (1,4,7-
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the samples. In the 2000-2200 cm-1 range, characteristic of the
anti-symmetric stretching vibration of the cyanido groups, two
bands are observed for 1: at 2152 cm-1 relative to the bridging
cyanide and another at 2124 cm-1 assigned to the free cyanides
(2153 and 2123 cm-1 for 2 respectively, with a slightly different
ratio).
[Mo6Cu14–tacn] (1) is composed of six octacyanomolybdate centers
Mo1, Mo2 and Mo3 forming an octahedron, each molybdenum
apex being linked together through a copper atom via cyanide
bonds. Finally, two supplementary centrosymmetric copper atoms
(Cu7) occupy the center of the structure (Figure 1), giving an overall
positively charged architecture with the following chemical formula:
[(Mo(CN)7)6{(μ-CN)(CuC6H15N3)12(CuOH)2}](ClO4)2⋅xH2O and (x~23).
Molybdenum atoms thus connect four different copper ions plus
the central ones and have three free cyanides directed outwards
the structure. The outer copper atoms (Cu1 to Cu6) have a
coordination number of five and adopt a square based pyramidal
environment. The central copper atom Cu7 is disordered (2
crystallographic positions in an approx. 70/30 proportion,
Cu7/Cu7b), with a Cu7…Cu7 distance of 3.074(2) Å. Cu7 adopts a
particular 4-coordinated environment, connecting three
molybdenum centers and an oxygen atom located close the Cu7b
triazacyclononane)
and
Me3tacn
(1,4,7-trimethyl-1,4,7-
triazacyclononane). Following such approach, we succeeded in
carrying out two new high nuclearity complexes based on
octacyanometallate core and peripheral copper atoms: [Mo6Cu14-
tacn] (1) and [Mo3Cu4-Me3tacn] (2). In addition, both complexes
exhibit photomagnetic behavior, the [Mo6Cu14-tacn] (1) being the
most effective one with a relaxation temperature above 200 K.
Results and discussion
Synthesis and X-ray Structures: [Mo6Cu14–tacn] (1) complex
(Figure 1) was synthesized by the reaction of four equivalents of
[CuII(tacn)](ClO4)2 prepared in situ from Cu(ClO4)2.2H2O and tacn,
with one equivalent of K4[MoIV(CN)8].4H2O in a water/acetonitrile
mixture (v:v = 1:2). Slow evaporation of the solution gave purple
diamond shaped crystals. X-ray diffraction analysis shows that 1
crystallizes in the triclinic space group P -1. Cell parameters are a =
19.1825(10) Å, b = 19.3041(10) Å, c = 19.3498(10) Å, α = 76.569(3)°,
β = 75.823(3)° and γ = 75.935(3)°, with a cell volume of V =
6624.1(6) Å3.
crystallographic position, with
a distorted geometry already
observed in literature.28 Hence a different way of describing the
[Mo6Cu14] structure is to consider four [Mo3Cu4] moieties
connected together by two copper atoms in the center of the
octahedron (see SI, Figure S4). This particular arrangement can be
explained by the great similarity of the two capping ligands Me3tacn
and tacn, which impose the same geometry to the copper ions.
Molybdenum atoms in the [Mo6Cu14] complex (1) adopt a mixed
geometry between square based antiprism and dodecahedron (as
shown by Shape30 analysis, see SI, tableS1). The Mo…Cu distances
Under similar conditions, an apparent capping ligand (Me3tacn),
leads to a different compound, [Mo3Cu4–Me3tacn] noted 2 in the
present paper (Figure 2). Taking into account that the quality of the
X-ray structure can lead to a discussion (vide supra), we shall focus
mainly on compound 1. Nevertheless, it is important to note that are comprised between 5.108(2) (Mo3-Cu2) and 5.269(1) Å (Mo3-
Cu1). Mo-C(≡N) bond lengths are similar to the previous Mo3Cu4
structure and range from 2.116(9) Å to 2.189(12) Å and the C-N
ones from 1.112(13) Å to 1.171(15) Å. Cyano bridges are linear on
the molybdenum side with Mo-C≡N angles ranging from 172.5(8)°
to 178.1(10)°. C≡N-Cu angles are bended and range from 157.5(9)°
to 177.1(10)°. [Mo6Cu14] complexes are well separated from each
other by perchlorate anions and solvent molecules; the shortest
distance separating two metal atoms from different molecules is
7.448(1) Å, reported between molybdenum and copper ions.
compound 2 has been identified without ambiguity and the
proposed structure is wholly consistent with the analytical,
spectroscopic and magnetic data.
[Mo3Cu4–Me3tacn] (2). Complex 2 crystallizes in the orthorhombic
space group Pnnm. Cell parameters are a = 33.5532(15) Å, b =
16.9349(7) Å and c = 27.2581(11) Å with a cell volume of V =
15488(1) Å3. 2 is composed of three molybdenum and three copper
atoms alternatively linked by cyanide bonds and forming a ring that
exhibits a chair conformation, in the center of which a fourth
copper atom connects the three octacyanomolybdate centers
(Figure 2). This last copper atom Cu2 is offset to the side of the
hexagonal ring, giving a bowl shape to the whole molecule. All
molybdenum centers in 2 adopt a similar environment with a mixed
geometry between a square based antiprism and dodecahedron (as
shown by Shape analysis, see SI, Table S3). Each molybdenum atom
connects two different copper ions and the central one Cu2. The
Mo…Cu distances are comprised between 5.208(2) Å and 5.408(1)
Å. Due to the Me3tacn ligand, copper atoms forming the ring, Cu1
Figure 2. Crystal structure of 2 (yellow: Mo; dark blue: Cu; grey: C, N).
2 | J. Name., 2012, 00, 1-3
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and Cu3, adopt a square base pyramid environment. The last causes no decrease of the recorded magnetization, proving that a
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DOI: 10.1039/C6DT00743K
copper atom Cu2 situated in the center of the ring is linked to the long-lived metastable state is obtained. After switching off the laser
three molybdenum atoms as well as the ligand, thus adopting a the temperature was cooled down to 2 K, then the magnetization
slightly distorted octahedron geometry (N-Cu2-N angles are 81.368° data were recorded on the heating mode (2 - 300 K). Magnetic
on the ligand side and 92.011° on the ring side). The susceptibility data recorded after irradiation showed a clear
hexacoordinated geometry imposes sensibly longer Cu2-N(≡C) bond increase, as depicted in Figure 3 for complex 1 (see SI, Figure S12
lengths (2.0037(9) to 2.118(6) Å) than the ones observed for Cu1- for 2). Maximum of the observed χmT product for 1 evolved from
N(≡C) and Cu3-N(≡C). Cyano bridge angles are linear on the 5.22 to 8.97 cm3.mol-1.K at 5 K. This positive deviation to the Curie’s
molybdenum side with Mo-C≡N angles ranging from 176.3(6)° to law indicates ferromagnetic interactions between the spin carriers.
177.8(7)°; but slightly distorted on the copper side with C≡N-Cu When increasing temperature χmT product gradually decreases and
angles comprised between 167.7(8)° and 177.6(8)°. The Mo-C(≡N) both curves merge to the same value at a temperature approaching
bond lengths range from 2.138(8) Å to 2.177(9) Å and the C≡N ones 230 K for 1 (~90 K for 2), showing unambiguously that the system is
from 1.130(12) Å to 1.157(13) Å. See SI, Table S2 for additional thermally reversible. Small evolution of the magnetization curves
interatomic distances and angles.
recorded after irradiation was also reported (SI Figure S9 and S12),
the increase being completely reversible after heating the
compound to 300 K and cooling it, demonstrating again the thermal
reversibility of the process.
Within the crystal, the complexes are ordered in a head to tail
manner, forming large channels along the b axis, with a diameter of
approximately 19 Å, that contain highly disordered molecules (see
SI, Figure S6). The presence of this disorder thus reduces resolution
Similar results have been obtained for compound (2) and on
of the overall MOF-like structure as already observed in literature.29 desolvated samples. See details in supplementary information.
The unit cell containing four negatively charged [Mo3Cu4]
complexes alongside two perchlorate anions, we can therefore
expect the presence of potassium and residual copper ions in the
cavity. Unfortunately, despite all our efforts, it was not possible to
accurately locate them and we preferred to leave the channels
empty. However, with an approximate volume of 3800 Å3 per unit
cell, the channel seems large enough to accommodate potassium
and copper complexes without any organisation. The resulting
chemical formula for the crystal would be [(Mo(CN)7)3{(µ-
CN)CuC9H21N3}4][CuC9H21N3]2(ClO4)2K2⋅ 20 H2O, in accordance with
the elementary analysis as well as the magnetic and EPR
experiments.
Photomagnetic properties were investigated for the two complexes
1 and 2 and showed that both compounds exhibit photomagnetic
behavior. Properties recorded for 1 are depicted hereafter (see SI
Figure S10-S12 for 2). The temperature dependence of magnetic
susceptibility was measured on crystalline samples under a 1000 Oe
field in the 300 - 2 K range. At room temperature χmT values
5.22 cm3.mol-1.K for 1 are in good agreement with the expected
theoretical values of 5.52 cm3.mol-1.K corresponding to fourteen
independent copper ions (CuII, d9, S = 1/2, g = 2.05), MoIV centers
being diamagnetic. At low temperature, a decrease is observed that
might be explained by the two central copper ions (Cu7), bridged by
the hydroxo groups and antiferromagnetically coupled. On the
whole, before irradiation, χmT plots show the expected
paramagnetic behavior for isolated CuII centers. M versus H plot
recorded for 1 (SI, Figure S7) showed a saturation value of 13.5 µB
at 50 kOe and is well simulated with a Brillouin’s law for fourteen
independent CuII atoms (gCu = 2.06).
Figure 3. χmT versus T plots of complex 1 before (black) and after (red)
irradiation with a 405 nm laser for 3.5 h (lines are guides for the eye).
EPR spectroscopy measurements were performed on crystalline
samples of 1 and 2 (X-band studies, frequency of 9.35 GHz). Crystals
were placed in a tube and directly irradiated at 4 K with the same
405 nm laser light. Before irradiation, spectra showed the expected
CuII signal centered in Bres = 3149 Oe for 2 (giso = 2.13) and
Bres = 3148 Oe for 1 (giso = 2.13), as shown in Figure 4 for complex 1
(see SI, Figure S13 for 2). Upon irradiation the signal immediately
decreased, reflecting the coupling of the CuII ions. Complex 1
exhibited an almost complete quenching of the CuII signal (Figure 4,
red curve) that persists when irradiation is switched off. The
samples were heated to room temperature, before being cooled
again to show complete relaxation of the signal (Figure 4, green
curve), hence supporting the total thermal reversibility of the
phenomenon.
Samples were then irradiated for 4 hours at 18 K using a 405 nm
laser beam (20 mW) equipped with a fiber. A clear increase of
magnetization was immediately observed upon light irradiation and
saturation occurred typically after 3 to 4 hours (SI, Figure S8 for 1
and Figure S11 for 2). For both complexes, stopping the irradiation
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well as a low relaxation temperature, as it has been seen on
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DOI: 10.1039/C6DT00743K
other tungsten compounds. Due to the complexity of the
1500
[Mo6Cu14] structure, all the performed analyses were not
sufficient enough to demonstrate unambiguously the
occurring photomagnetic mechanism. However, no photo-
magnetic response was observed when conducting
experiments on the analogous zinc compound Mo6Zn14, which
tends to favor the photo-induced electron transfer process, as
we suggested above.
Before irradiation
Under irradiation
After relaxation
1000
500
0
From a synthetic point of view, these new compounds open
the route to high nuclearity functional complexes.
Furthermore, bearing either a positive or negative charge, the
complexes 1 and 2, might be viewed as very promising clusters
for the design of even more complex architectures.
-500
-1000
-1500
2800
3000
3200
3400
3600
Experiment section
Magnetic field / G
Synthetic procedures. Tacn (1,4,7-triazacyclononane) ligand was
synthesized as described in the literature,33,34 following slightly
modified procedures, as presented in the SI-FigureS1. Me3tacn
(1,4,7-trimethyl-1,4,7-triazacyclononane) ligand was commercially
available and used without purification. Caution! Cyanides are very
toxic and must be handled with care.
Figure 4. EPR spectra of complex 1 before irradiation (black), under
irradiation (red) and after relaxation (green) at 4 K.
Complexes 1 and 2 presented herein exhibit unambiguously
photomagnetic response. Magnetic and EPR experiments support
the existence of a long-lived photo-induced metastable state for
both compounds. The photomagnetic properties of these
compounds can be rationalized considering the two usually
assumed hypotheses for “Molybdenum-Copper” complexes, as
suggested by us and others3,31: spin transition on the molybdenum
center (MoIV-LS (d2, S = 0) → MoIV-HS (d2, S = 1)) and a photo-induced
IR spectra were obtained between 4000 and 250 cm-1 on a Bio-Rad
FTS 165 FT-IR spectrometer on KBr pellets.
Crystallography. Suitable crystals for X-ray crystallography were
directly obtained from the reaction medium. A single crystal of the
compounds was selected rapidly, mounted onto a cryoloop, and
transferred in a cold nitrogen gas stream. Intensity data were
electron transfer between molybdenum and copper atoms (MoIV-LS
-
CuII → MoV-CuI). In the present study, and especially for the
[Mo6Cu14] (1) complex, the remarkably high relaxation temperature
observed from the magnetic data (Trelax ~ 230 K) is consistent with
the electron transfer hypothesis31 and is also supported by previous
calculations realized on [MoCux] complexes32 and preliminary
results on [Mo6Zn14] analogue with no photomagnetic effect.
Considering the hypothesis of an electron transfer involving the CuII
centers located at the center of the structure (i.e. a diamagnetic
copper dimer leading to a paramagnetic center), the expected χmT
value would then be of 10.25 cm3.mol-1.K at low temperature
collected with
a
BRUKER Kappa-APEXII with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å). Data collections
were performed with APEX2 suite (BRUKER). Unit-cell parameters
refinement, integration and data reduction were carried out with
SAINT program (BRUKER). SADABS (BRUKER) was used for scaling
and multi-scan absorption corrections. In the WinGX suite of
programs35, the structures were solved with SIR9236 and
SUPERFLIPS37 programs respectively and refined by full-matrix least-
squares methods using using SHELXL-97 and SHELXL-1438. The
structures were deposited at the Cambridge Crystallographic Data
Centre with numbers CCDC 1052206 (1) and 1426776 (2) and can be
obtained free of charge via www.ccdc.cam.ac.uk.
(considering two MoVCuICuII and four isolated CuII centers), which
4
is relatively close to the observed value of 8.97 cm3.mol-1.K. On the
contrary, considering only a high spin state would lead to a
considerably higher χmT value.
DC magnetic susceptibility measurements were carried out on a
Quantum Design MPMS SQUID susceptometer equipped with a 7 T
magnet and operating in the range of temperature from 1.8 to
400 K. The powdered samples (10±50mg) were placed in a
diamagnetic sample holder and the measurements realised in a
1000 Oe applied field using the extraction technique. Before
analysis, the experimental susceptibility was corrected from
diamagnetism using Pascal constants.
Conclusion
In the present paper, two new high nuclearity photomagnetic
complexes [Mo6Cu14] (1) and [Mo3Cu4] (2) have been
synthesized and characterized. In particular, complex 1 shows
an impressive photomagnetic response with an almost
doubled χmT value recorded after irradiation and a relaxation
temperature as high as 230 K, which is not common for photo-
switchable [MoCux] complexes. Additional experiments were
Photomagnetic experiments were performed on grounded crystals
deposited on film. Irradiation was realized with a 405 nm laser
placed at approx. 2 cm from the samples. Samples were typically
irradiated at 10 K under a 1 kOe field for a few hours until
saturation of the signal was observed. The temperature was then
decreased to 2 K and magnetic data recorded on the heating mode
(under a 500 Oe or 1000 Oe field). To check the reversibility of the
conducted
on
analogue
compounds
based
on
octacyanotungstate precursors: [W6Cu14] and [W3Cu4],
showing only partial photo-transformation of the compounds,
probably caused by a too short lifetime of the excited states as
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second sample and results, considering a triclinViciewsyArmticmle Oentlrinye,
DOI: 10.1039/C6DT00743K
are reported herein. However, even if results are better than
process, the same workup was applied, then the compound was
kept a few hours at room temperature (typically 3 h) and the
magnetic data were recorded again in the 300 K – 2 K range.
the ones from the first dataset some residual density remains
which can be due to the very large solvent region. All non-
hydrogen atoms of the cation were refined anisotropically
while some solvent molecules were refined isotropically.
Hydrogen atoms were placed at calculated positions for tacn
ligands and acetonitrile molecules. No hydrogen atoms were
introduced for water molecules. The inside part of the complex
is highly disordered and we were not able to fully characterize
it. The sum of sof for Cu7/Cu7b was restrained to be equal to
1. Much information on the environment this copper atom is
still missing, as we were not able to model the residual density
located between two central copper atoms. We suppose they
are bridged with a O(H) atom but were not able, with SC-XRD,
to really confirm that hypothesis. Two solvent molecules,
located nearby the cation, were refined as a disorder of water
and acetonitrile. The perchlorate anion is disordered over two
orientations and undergoes restraints. Most of the final
residual density is located nearby metallic atoms. We also
notice a non-negligible amount of density in the large solvent
region.
EPR measurements were performed on a single crystal with a
standard X-band spectrometer and a 4–300 K variable temperature
cryostat under irradiation. EPR measurements were performed with
a Bruker ESP 300 spectrometer, at X Band frequency (9.5GHz). The
magnetic field modulation frequency was set at 100 kHz and the
modulation amplitude and the microwave power were both
adjusted to avoid saturation. The spectra were measured at
temperatures between 4 K and 300 K. The excitation of the samples
at low temperature was performed with laser sources at 405 and
488 nm.
Elemental analyses were performed at the Service Central
d'Analyse in the CNRS center (Vernaison. France).
Syntheses of complexes.
[Mo6Cu14-tacn] (1):
[(Mo(CN)7)6{(μ-CN)(CuC6H15N3)12(CuOH)2}] (ClO4)2⋅xH2O (x~23).
Complex 1 was synthesized by the reaction of four equivalent of
[CuII(tacn)](ClO4)2 prepared in situ from Cu(ClO4)2.2H2O (0.24 mmol,
4 eq.) and tacn ligand (0.24 mmol, 4 eq.), with one equivalent of
K4[MoIV(CN)8].4H2O (0.06 mmol, 1 eq.) in a water/acetonitrile
mixture (v:v = 1:2). Slow evaporation of the blue solution afforded
purple crystals shaped as diamonds after a few days.
Acknowledgements
The research has been supported by the CNRS, UPMC (University
Pierre et Marie Curie), the French Ministry of Research, ANR Switch
(2010-Blan-712) and ANR E-storic (14-CE05-0002).
Yield: 15 %. IR (KBr): 2152, 2124, 1626, 1451, 1100, 1090, 916, 618.
Anal Calc for (Mo(CN)8)6(CuC6H15N3)12(Cu2(OH)2)(ClO4)2(H2O)23
(KClO4)2: Mo 11.09; Cu 17.15; C 27.77; H 4.43; N 22.68; Cl 2.73.
Found: Mo 10.76; Cu 17.3; C 28.05; N 22.84; H 4.37; Cl 2.93.
Notes and references
1
J. Ferrando-Soria, A. Fernandez, E. Moreno Pineda, S. A.
Varey, R. W. Adams, I. J. Vitorica-Yrezabal, F. Tuna, G. A.
Timco, C. A. Muryn, R. E. P. Winpenny, J. Am. Chem. Soc.,
2015, 137(24), 7644-7647 and references therein b) For an in-
depth discussion of the term cluster in inorganic chemistry,
see: M. H. Chisholm, Polyhedron, 1998, 17, 2773-3044.
a) J. M. Clemente-Juan, E. Coronado, Coord. Chem. Rev. 1999,
193(5), 361-394. b) L. M. C. Beltran, J. R. Long, Acc. Chem. Res.
2005, 38(4), 325-334.
a) O. Sato, J. Tao, Y. Z. Zhang, Angew. Chem. Int. Ed., 2007,
46(13), 2152-2187. b) A. Bleuzen, V. Marvaud, C. Mathonière,
B. Sieclucka, M. Verdaguer, Inorg. Chem., Forum article, 2009,
48(8), 3453-3466
[Mo3Cu4-Me3tacn] (2):
[(Mo(CN)7)3{(µ-CN)CuC9H21N3}4][CuC9H21N3]2(ClO4)2K2⋅ 20 H2O
Complex
2 was obtained following the same experimental
procedure, using Cu(ClO4)2•6H2O (0.24 mmol, 4 eq.) and Me3tacn
(1,4,7-trimethyl-1,4,7-triazacyclononane (0.24 mmol, 4 eq.) in the
same solvent (10 mL). The blue solution was stirred for a few
minutes before the addition of 30 mg of K4[Mo(CN)8]•2H2O
(0.06 mmol, 1 eq.) in 5 mL of the same solvent. The solution was
kept away from light and crystals (purple rods) were obtained
within a few days. The same synthesis can be achieved from other
copper salts (nitrate or chloride) but showed rapid degradation of
the crystals when kept out of the solution.
2
3
4
5
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Yield: 40 %. IR (KBr): 2153, 2123, 1639, 1461, 1080, 1009, 629. Anal
Calc for Mo3Cu6C78H166N42Cl2K2O28: Mo 9.39; Cu 12.44; C
30.94; N 19.74; H 5.09; Cl 3.47. Found: Mo 8.54; Cu 13.52; C 32.92;
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rhombohedral R symmetry of the system. However, crystal
structure solution was not convincing and the ligands capping
copper atoms were highly disordered. We then worked in P-1
space group, which lead to a lower R1 factor and no disorder
on the ligands. A second dataset was thus collected on a
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