A crystalline hybrid of paddlewheel copper(II) dimers and molecular rotors: Singlet-triplet dynamics revealed by variable-temperature proton spin-lattice relaxation

Article abstract of DOI:10.1002/zaac.201300622

We report on the synthesis and application of a 2 nm long, curved ditopic biscarboxylic ligand with a 1,4-bis(ethynyl)bicyclo[2.2.2]octane rotator core and an helical twist to the construction of an extended single-crystalline framework solid with paddlew

Full text of DOI:10.1002/zaac.201300622

ARTICLE
DOI: 10.1002/zaac.201300622
A Crystalline Hybrid of Paddlewheel Copper(II) Dimers and Molecular
Rotors: Singlet-triplet Dynamics Revealed by Variable-temperature Proton
Spin-lattice Relaxation
Guillaume Bastien,[a] Cyprien Lemouchi,[a] Pawel Wzietek,[b] Sergey Simonov,[c]
Leokadiya Zorina,[c] Antonio Rodríguez-Fortea,[d] Enric Canadell,[e] and
Patrick Batail*[a]
Dedicated to Professor C. N. R. Rao on the Occasion of His 80th Birthday
Keywords: Molecular rotors; Metal organic frameworks; NMR spectroscopy; Rotational barrier; Exchange coupling constant
Abstract. We report on the synthesis and application of a 2 nm long, experiments carried out on a static crystalline sample did not provide
curved ditopic biscarboxylic ligand with a 1,4-bis(ethynyl)bicyclo-
however a value of this rotational barrier because the relaxation proved
[2.2.2]octane rotator core and an helical twist to the construction of an to be dominated by the coupling of the moving protons to the elec-
extended single-crystalline framework solid with paddlewheel hinges,
[CuII]2[1,4-bis(carboxyphenyl ethynyl)bicyclo[2.2.2]octane]2(H2O)2 or
tronic spins of the CuII dimers. Remarkably, we reveal how the singlet-
triplet spin dynamics of non-interacting CuII dimers is elegantly char-
[CuII]2(bbcbco)2(H2O)2. The interconnection of interpenetrated square acterized by solid state NMR spectroscopic experiments yielding an
lattices involves short rotor–rotor H···H interactions (1.9 to 2.4 Å) such exchange coupling constant, Jexp = –365 K = –254 cm–1, in good
that the moving parts are expected to rub onto each other in the lattice
agreement with theoretical estimations and experimental data on re-
in a Brownian rotational motion with a calculated rotational barrier lated CuII dimer systems.
1
of 3.7 kcal·mol–1. Variable-temperature H spin-lattice relaxation (T1)
(BCO) core (Scheme 1) can rotate around its axis. With 1-
Introduction
pyridinediethynylbicyclo[2.2.2]octane,[3b] 1,4-bis(4Ј-pyridyl-
ethynyl)bicyclo[2.2.2]octane, and bis((4-(4-pyridyl)-ethynyl)-
bicyclo[2.2.2]oct-1-yl)buta-1,3-diyne,[3d] this is another rare
example of a ligand with a BCO rotator. It is also valuable on
account of its dynamic curved and helical shape, a property
linked to the torsional interconversion of the three blades of its
chiral helical core,[3d] illustrated herein in the single-crystalline
The design of functional ligands,[1] most notably di- and
polytopic carboxylates, is central to the development of hybrid
metal-organic constructs blessed with a huge variety of archi-
tectures and diverse degrees of densification.[2] Inspired by this
current formidable trust in materials chemistry, we report on
the synthesis of one such extended ditopic dicarboxylate li-
gand, H2bbcbco, whose 1,4-bis(ethynyl)bicyclo[2.2.2]octane
* Dr. P. Batail
E-Mail: patrick.batail@univ-angers.fr
[a] Laboratoire Moltech
Université d’Angers, CNRS
2 Boulevard Lavoisier
49045 Angers, France
[b] Laboratoire de Physique des Solides
Université de Paris-Sud, CNRS
91405 Orsay, France
[c] Institute of Solid State Physics
Russian Academy of Sciences
142432 Chernogolovka MD, Russia
[d] Departament de Química Física i Inorgànica
Universitat Rovira i Virgili
Marcel·lí Domingo s/n
43007 Tarragona, Spain
[e] Institut de Ciència de Materials de Barcelona (ICMAB-CSIC)
Campus de la UAB
Scheme 1. H2bcbco [bcbco2– = 1,4-bis(carboxylateethynyl) bicyclo-
[2.2.2]octane, formerly BABCO[3b]], BCO,[3] and synthetic scheme for
H2bbcbco [bbcbco2– = 1,4-bis(benzenecarboxylate ethynyl)bicyclo-
[2.2.2]octane].
08193, Bellaterra, Spain
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201300622 or from the au-
thor.
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P. Batail et al.
ARTICLE
hybrid of the rotator ligand H2bbcbco (Scheme 1) and pad-
dlewheel [CuII2]2 hinges[4,5] anchored in the lattice. With its
moving part an inherent constituent of the framework, this ex-
ample complements the former MOF-5 rotor system with a
1,4-phenylenedicarboxylate ligand, where the phenyl ring is
flipping over two positions in the lattice with a barrier of 11
kcal·mol–1.[6]
By designing metal-organic amphidynamic crystals with
rapidly moving parts, whose rotational barrier may be as low
as 1.5 kcal·mol–1, for example, we intent to bring together in
the form of complex functional materials the fields of molecu-
lar machines[7] and amphidynamic solids[8] with the field of
multifunctional, eventually magnetic MOFs. By pursuing this
materials discovery initiative our idea is to design hybrid mag-
netic systems where the dielectric modulation inherent to the
rotor dynamics may be coupled to the response of the frame-
[9a,b,c,d]
work metal spins.[3c] There is a present surge in T1
T2
and
[9e,f]
NMR spectroscopy investigations of the motion of mo-
lecular species confined in the cavities of porous MOFs.[9]
Herein, variable-temperature 1H spin-lattice relaxation (T1) ex-
periments,[3,6,8,10,11,12] associated to calculations of rotational
barriers,[3c,3d,3e] were conducted to investigate both molecular
motion and spin dynamics[13] in the framework of a crystalline
hybrid material with rotator struts.
Results and Discussion
Once one disposes of 1,4-bis(ethynyl)bicyclo[2.2.2]octane
(BCO), the synthesis in good yields of the 1,4-bis(ethynyl
carboxylate)bicyclo[2.2.2]octane ligand, H2bbcbco is straight-
forward: a Sonogashira coupling of BCO and 4-iodomethyl-
benzoate affords the methylester 1, whose saponification
gives H2bbcbco. BCO is prepared in a 9-step sequence de-
scribed in published procedures.[3a,14] Bulky blue crystals of
[CuII]2(bbcbco)2(H2O)2 are obtained by slow diffusion in four
weeks. The compound formulation was determined by resolu-
tion of its crystal structure (orthorhombic unit cell, space group
Ccmb).
Figure 1. (a) Curvature of H2bbcbco and angle between the mean pla-
nes of the outer phenyl fragments. (b) A view of the distorted square
net motif; the values are for Cu–Cu–Cu angles. (c) Two interpenetrated
extended square nets; H···H rotor–rotor contacts at 2.310, 2.343 Å and
2.427 Å (black and white cylinders) connect the nets along c.
A Dicarboxylate Rotator Ligand with a Helical Twist
As exemplified in Figure 1a, the rotator has one equilibrium
position only in the 200 K structure, and H2bbcbco has a sig-
nificant curvature. It spans 2 nm, a rather significant extension
when compared to 1.1 nm for 1,4-bis(carboxylethynyl)bicy-
clo[2.2.2]octane (H2bcbco).[3c]
Figure 2). Altogether, the rotator ligand appears to have
adapted its curvature (Figure 1b) to the steric demand of the
interpenetration in a way reminiscent of the process revealed in
an adaptable peptide-based porous material.[15] Yet, the whole
framework is expected to respond to the rotational motion and
torsional mutations[3d] of the rotator ligand.
Interpenetrated Square Nets…
Paddlewheel CuII dimers[4,5] constitute the hinges of the
square nets in [CuII]2(bbcbco)2(H2O)2 (Figure 1b). Note the
distortion of the motif as a result of the curvature of the rotator
ligand. Densification of the crystalline space occurs upon inter-
penetration of four such distorted square nets (Figure 1c). The
…with Interacting Rotators: Rotor–Rotor H···H Interaction
and Rotational Barrier
The close proximity of the rotors belonging to neighboring
interpenetration creates strings of bicyclo[2.2.2]octane rotators square nets prompted us to evaluate the rotational barriers by
belonging to successive nets in close proximity (Figure 1c and means of density functional theory[16] (DFT) calculations ex-
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Hybrid of Paddlewheel Copper(II) Dimers and Molecular Rotors
Figure 2. Model used to simulate the rotor environment in the crystal.
Figure 3. Computed energy barrier for the rotational motion consider-
ing the environment in the crystal as fixed (empty circles) and optimiz-
ing the blades of the central and neighboring rotators (solid circles).
actly as in our previous investigation based on the inventory
of short H···H contacts.[3d] When the bicyclo[2.2.2]octane rotor
is considered alone, without the other rotors of the environ-
ment, the energy barrier for rotation is calculated to be only
0.1 kcal·mol–1.
found considering the fixed environment (Figure 3). A careful
inspection of the optimized structures shows that short H···H
contacts are not only found in the structures with the highest
energies. For example, for the arrangement with θ = 90°, the
two shortest contacts are 1.96 and 2.04 Å, even smaller than
for θ = 45°, but with the other contacts showing larger values.
Hence, the barrier does not only depend on the shortest con-
tacts but on the whole environment, that is, the dynamic con-
formation of all the rotator ligands in the environment re-
sponds in a co-operative manner to reach the lowest possible
energy barrier.
To simulate the rotation of the rotor in the crystal lattice we
have taken into consideration all nearest rotors in the environ-
ment that make short contacts with the central rotor (see Fig-
ure 2). Since the hydrogen atoms of the rotor do not make
short contacts with the static fragment of the molecules, we
have considered the reduced fragments shown in Figure 2, that
is, bicyclo[2.2.2]octane fragments saturated with hydrogen
atoms (“H”), to simulate the environment. Initially the three
rotator units simulating the environment were taken as fixed,
exactly as in the solid, and we have optimized the C and H
atoms of the three blades of the central rotor for each value of
the rotation angle. The initial H···H contacts that could be
smaller than 2.4 Å in some structures become even smaller due
to the fact that the optimized C–H distance (1.09 Å) is some-
1H Spin-Lattice Relaxation Dominated by Coupling of the
Moving Protons to the Electronic Spins of the CuII Dimers
The reciprocal 1H spin-lattice relaxation data, T1–1, between
what larger than the one observed in the X-ray structure 100 and 300 K are shown in Figure 4. The experiments were
(0.97 Å). Interestingly, the computed barrier for rotation does conducted on static crystalline samples at three fields, 1.29,
1
not exceed 4 kcal·mol–1 (Figure 3). The arrangement with the 3.09, and 4.92 Tesla, corresponding to H Larmor frequencies
highest energy, θ = 40°, shows two H···H contacts shorter than of 55, 132, and 210 MHz, respectively.
–1
2 Å (1.85 and 1.98 Å) and one at 2.08 Å. On the other hand,
Note that T1 values for [CuII]2(bbcbco)2(H2O)2 are two
the shortest H···H contact for the arrangement with the lowest orders of magnitude larger than the contribution to the spin-
energy, θ = 10°, is 2.11 Å. lattice relaxation due to the dipolar proton-proton coupling
In view of these relatively short H···H contacts we deemed usually seen[3a,3c,3d,3e] in crystalline molecular rotors with bi-
necessary to check the influence of the assumption of a fixed cyclo[2.2.2]octane rotators. This is because, here, the relax-
environment in the calculated rotation barrier. We have recom- ation due to the moving protons is hidden by the relaxation
puted this barrier by re-optimizing the structure of the rotor due to the coupling to CuII S = ½ electronic spins. For exam-
with the environment, but now also allowing the blades of the ple, with a calculated barrier for the rotational motion of the
three neighboring rotors to relax. We observe that the C–H BCO rotators amounting to 3.7 kcal·mol–1 (1862 K), the 1H
–1
distances of these three rotors also increase, but the H···H con- T1 maximum in this experiment carried out at 210 MHz is
tacts do not shorten because the blades of the neighboring ro- expected to appear near room temperature with a value of the
–1
tors can now move so as to optimize (within the constraints) order of 10.[3] As shown in Figure 4, at this temperature, T1
the H···H distances. The shortest contacts in the arrangement values amount to about 103. Thus, one would require the data
with the highest energy, θ = 45°, are now 1.98 and 2.05 Å, to be obtained with a precision of at least 1% to be able to
whereas for the lowest-energy structure, θ = 0°, the shortest come up with a meaningful experimental identification of the
contacts are 2.16 and 2.19 Å. The estimated barrier thus ob- rotational barrier out of the overwhelming relaxation by the
tained, 3.7 kcal·mol–1, is surprisingly almost the same as that CuII electronic spins.
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P. Batail et al.
ARTICLE
(HS) state (S = 1) but is zero in the low spin (LS) state (S =
0). In this model we assume that τc, related to the electron-
spin correlation time in the HS state, is much shorter than the
average lifetime of the HS itself. In this limit it is easy to show
that the exact dynamics of the singlet-triplet excitations is not
relevant for the spectral shape of fluctuations in Equa-
tion (1).[18] Therefore, assuming that Equation (2) gives the re-
laxation in the HS state, the effective relaxation rate for the
singlet-triplet system is obtained taking Equation (2) weighted
by the population of the HS state:
(3)
where γHS is the fraction of sites populated in the triplet state:
(4)
It is instructive to give here the relation with the static mag-
netic susceptibility commonly used[19] to fit magnetization data
obtained by SQUID measurements. The latter may be written
as:
Figure 4. Variable temperature reciprocal spin lattice relaxation time
for [CuII]2(bbcbco)2(H2O)2 at three fields. Inset: electronic correlation
time determined from Equation (2).
We now propose a simple model for the spin-lattice relax-
ation T1 by CuII S = ½ electronic spins and show that 1/T1T
is, in this example, proportional to the electronic spin suscep-
tibility χ(T).
where χHS = C/T is the Curie-like behavior of the triplet state.
Therefore, considering that the temperature dependence of the
term involving τc in Equation (3) is negligible, χT and 1/T1 are
both proportional to γHS
:
1H Relaxation by Dipolar Coupling of the Nuclear Spin
with the CuII Electronic Spin
(5)
Hence, 1/T1T has been fitted in Figure 5 to this singlet-trip-
let law for [CuII2] spins to yield a gap of 365 K = 254 cm–1.
Our model is supported by the excellent quality of this fit.
The relaxation mechanism by dipolar coupling of nuclear
spins with a localized electronic spin has been considered in
the past in the context of materials containing paramagnetic
impurities.[17]
1
Just as for the case of the H relaxation due to Brownian
motion in amphidynamic solids, the relaxation rate is related
to the Fourier transform, taken at the nuclear frequency, of the
correlation function of the local magnetic field fluctuations
seen by the nuclei. If this local magnetic field is due to a local-
ized electronic spin S then:
(1)
If the dynamics of the fluctuations is characterized by a corre-
lation time τc, then we obtain:[17]
(2)
The correlation time τc can be determined by measuring the
relaxation rates at different frequencies, as shown in Figure 4.
However, the temperature dependence of T1 cannot be ex-
plained by Equation (2) because the calculated values of τc
(inset of Figure 4) yield a nearly temperature independent T1.
The reason for this is that in [CuII]2(bbcbco)2(H2O)2 we have
to take into account the two states of the system: the magnetic
Figure 5. Fit of the magnetic susceptibility (4.92 Tesla data) to the
singlet-triplet law [Equation (5)] for [CuII]2(bbcbco)2(H2O)2.
Experimental Data and Theoretical Estimation of the
Exchange Coupling on Related CuII Dimer Systems
Let us note that the singlet-triplet gaps for tetrakisacetato
field due to the electronic spin only exists in the high spin and tetrakisbenzoato CuII dimers obtained with commonly
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Hybrid of Paddlewheel Copper(II) Dimers and Molecular Rotors
12.64 mmol) was added to the former three solids and the stirred mix-
ture was heated at 70 °C overnight. Progress of the reaction was moni-
tored by thin layer chromatography with 100% toluene as the eluent,
until completion in 24 h. Addition of a saturated ammonium chloride
aqueous solution was followed by extraction of the organic phase with
dichloromethane, washing with water, drying with anhydrous magne-
sium sulfate. Filtration and evaporation under reduced pressure af-
forded an orange solid. The latter was purified by silica gel chromatog-
raphy with 100% toluene as the eluent to yield an orange powder
(4,8 g, 11.25 mmol; yield 89%). Tfusion = 216 °C. C28H26O4: calcd. C
used techniques, i.e. fittings of the variable-temperature mag-
netic susceptibility data, are around –300 cm–1,[20] which sup-
port the value obtained with the H spin-lattice relaxation ex-
1
periments.
The Cu···Cu distance inside the paddlewheel CuII dimers is
2.617 Å. In the solid, two of these dimers potentially interact
through a relatively long Cu···Cu distance of 4.796 Å. DFT
calculations of the exchange coupling constants in CuII dimers
with the B3LYP functional[21] usually lead to values in good
agreement with experimental ones.[20] An analysis of the ex- 78.85; H 6.14; O 15.01%; found: C 79.13; H 6.07; O 14.14%. 1H
NMR (CDCl3, 300 MHz): δ = 7.95 [d, J = 8.7 Hz, 4 H, 4CH(Ph)],
7.43 [d, 4 H, J = 8.7 Hz, 4CH(Ph)], 3.90 [s, 6 H, 2CH3(CO2Me)], 1.90
[s, 12 H, 6CH2(BCO)]. 13C NMR (CDCl3, 300 MHz): δ = 166.62,
131.48, 129.32, 128.86, 128.87, 99.60, 80.29, 52.13, 31.62, 26.94 ppm
perimental vs. calculated values using these computational set-
tings for forty seven CuII dimers with different bridging li-
gands[20] (Figure S1, Supporting Information) led to the con-
clusion that the mean absolute relative error is 36%. We de-
cided to evaluate theoretically the value of the intradimer (J)
and interdimer (JЈ) exchange coupling constants. The calcula-
tions were carried out for an isolated tetramer with intra and
inter dimer distances as in the solid. Benzoate groups were
used as coordinating ligands, whereas a water molecule was
used as the apical ligand. The calculated values were J =
–331 cm–1 and JЈ = –0.1 cm–1. Thus it can be concluded that
(i) the spin system of the CuII dimers are non-interacting in
agreement with the Curie-like behavior of the high-spin triplet
state, as discussed above; and (ii) the computed intramolecular
coupling constant Jcal = –331 cm–1 compares well (relative er-
ror of 30%) and thus confirms the experimental value Jexp
= –254 cm–1 obtained by the fit of the reciprocal spin-lattice
relaxation data (Figure 5).
Synthesis of 4Ј,4Ј-(Bicyclo[2,2,2]octane-1,4-diylbis(ethyne-2,1-di-
yl)dibenzoic Acid (H2bbcbco): In a 500 mL flask, a degassed 40 mL
aqueous solution containing LiOH (1,42 g, 59.30 mmol) was added to
a dioxane solution (250 mL) of 1 (2,51 g, 5.89 mmol) giving a whitish
mixture stirred overnight at room temperature. The progress of the
reaction was monitored by thin layer chromatography (eluent: 100%
CH2Cl2). In the advent that the reaction was not complete after 24 h,
an additional 50 mL degassed aqueous LiOH solution (1 g,
41.75 mmol) was added and stirred, typically reaching completion in
4 more hours. The reaction product was precipitated off the solution
upon addition of a 300 mL 1 m aqueous HCl solution. The solid resi-
due was successively washed in water, CH2Cl2, and three times in
ethyl ether. The product was dried to yield a beige powder (2.1 g,
5.27 mmol, yield 90%). Tfusion Ͼ 320 °C. C26H22O4 : calcd. C 78.37;
H 5.57; O 16.06%; found: C 77.37; H 5.81; O 15.83%. 1H NMR
([D6]DMSO, 300 MHz): δ = 7.90 [d, J = 8.4 Hz, 4 H, 4CH(Ph)], 7.46
[d, 4 H, J = 8.4 Hz, 4CH(Ph)], 1.85 [s, 12 H, 6CH2(BCO)]. 13C NMR
([D6]DMSO, 125 MHz): δ = 166.78, 131.45, 129.91, 129.48, 127.40,
99.67, 80.06, 37.11, 26.54 ppm.
Conclusions
The synthesis of a 2 nm long, curved dicarboxylate rotator
rod with bicyclo[2.2.2]octane core and an helical twist was
illustrated in a crystalline hybrid of paddlewheel CuII dimers.
Because the connections between interpenetrated, extended
distorted square nets involve infinite strings of short rotor–
rotor H···H interactions, the rotators rub onto each other with
a calculated rotational barrier of less than 4 kcal·mol–1. How-
[CuII]2(bbcbco)2(H2O)2:
1,4-bis(Carboxyphenylethynyl)bicyclo-
[2.2.2]octane (H2bbcbco) (1.83 mg, 4.60.10–3 mmol) was dissolved in
dimethylformamide (750 μL). Afterwards ethanol (750 μL) was added
to give a clear solution, which was slowly added to a solution of
Cu(NO3)2·6H2O (20 mg, 8.60 10–2 mmol) in water (500 μL), yielding
a biphasic solution. The latter is left standing for 4 weeks. Bulky blue
crystals were harvested and filtered. No degradation of the crystals
occured after several months standing out of their mother solution.
1
ever, the H spin-lattice relaxation T1 due to the moving pro-
tons is hidden by the two orders of magnitude larger relaxation
due to the coupling to the electronic spins of the singlet-triplet
CuII dimer system. A simple model for the spin-lattice relax-
ation by CuII S = ½ electronic spins is proposed, which shows
that 1/T1T is, in this example, proportional to the electronic
spin susceptibility χ(T). An excellent fit of the relaxation data
to this model yield an intradimer exchange coupling constant
J of 365 K = 254 cm–1 in good agreement with theoretical esti-
mations and experimental data on related CuII dimer systems.
X-ray Structure Analysis of [CuII]2(bbcbco)2(H2O)2: Crystal data:
C52H44O10Cu2,
M = a =
955.95 g·mol–1, orthorhombic, Ccmb,
26.892(2), b = 32.267(4), c = 12.317(1) Å, V = 10688(2) Å3, Z = 8,
Dcalc = 1.188 g cm–3, μ = 8.47 cm–1, F(000) = 3952, T = 200(2) K,
2Θmax = 28.0°, reflections measured 63665, unique reflections 6488
(Rint = 0.0702), reflections with I Ͼ 2σ(I) = 4642, parameters refined
305, R1 = 0.0666, wR2 = 0.1557, GOF = 1.025. Single crystal X-
ray diffraction data were collected with a Bruker Nonius KappaCCD
diffractometer with monochromatized Mo-Kα radiation (λ
=
0.71073 Å, graphite monochromator, combined φ/ω-scans). Empirical
absorption correction of experimental intensities was applied using the
SADABS program.[22] The structure was solved by a direct method
followed by Fourier syntheses and refined by a full-matrix least-
squares method using the SHELX-97 programs.[23] All non-hydrogen
atoms were refined in an anisotropic approximation. The positions of
hydrogen atoms were calculated with Uiso(H) = 1.2 Ueq(C). The struc-
Experimental Section
Synthesis of Dimethyl 4Ј,4Ј-(Bicyclo[2,2,2]octane-1,4-diylbis-
(ethyne-2,1-diyl) Dibenzoate (BCO(PhCO2Me)2) (1): [Pd0(PPh3)4]
(1 g, 0.87 mmol), methyl 4-iodobenzoate 98% (8,3 g, 31.7 mmol), and
CuI (200 mg, 1.05 mmol) were introduced in a one-liter flask and ture contains strongly disordered solvent molecules (mixture of di-
placed in an inert argon atmosphere. A triethylamine solution methylformamide, ethanol, and water), which could not be localized
(500 mL) of 1,4-bis(ethynyl)bicyclo[2.2.2]octane (BCO, 2 g, appropriately and their contribution into electronic density was sub-
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P. Batail et al.
ARTICLE
tracted by PLATON/SQUEEZE procedure; four free cavities of 428 Å3
per unit cell, each containing 93 e, were found. The solvent molecules
participate as acceptor in hydrogen bonding with coordinated water
molecules.
Fortea, E. Canadell, P. Wzietek, P. Auban-Senzier, C. Pasquier, T.
Giamarchi, M. A. Garcia-Garibay, P. Batail, J. Am. Chem. Soc.
2012, 134, 7880–7891; d) C. Lemouchi, K. Iliopoulos, L. Zorina,
S. Simonov, P. Wzietek, T. Cauchy, A. Rodríguez-Fortea, E. Can-
adell, J. Kaleta, J. Michl, D. Gindre, M. Chrysos, P. Batail, J. Am.
Chem. Soc. 2013, 135, 9366–9376; e) G. Bastien, C. Lemouchi,
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opoulos, D. Gindre, M. Chrysos, P. Batail, CrystEngComm 2014,
16, 1241–1244.
Crystallographic data (excluding structure factors) for the structure in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the de-
pository number CCDC-973160 (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
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VT Proton Spin-Lattice Relaxation Time (1H T1) Experiments: Ex-
periments were carried out on static crystalline samples over a wide
range of temperatures (110–300 K). Wide-line 1H spectra were mea-
sured on a static crystalline sample at a 1H Larmor frequency of
210 MHz with a superconducting magnet operating at 4 Tesla using a
NMR spectrometer and probe built at Orsay. The probe is designed so
as to reduce spurious proton signals. Crystals were loaded into a small
glass tube (typically 1.2–1.6 mm in diameter, depending on the amount
1
of material available), on which the NMR coil was wounded. H sig-
nals were recorded using the FID following a π/2 pulse (typically 0.8–
1.5 μs) and spin-lattice relaxation was measured using the standard
saturation recovery sequence. For each T1 measurement we recorded
signals for 20 values of the relaxation delay between the saturating
comb and the measuring pulse.
Computational Details: DFT calculations for the rotational barriers
were performed as described previously[3c,3d] using the hybrid M06–
2X functional[24] and the 6-31G(d,p) basis set[25] as implemented in
the Gaussian09 package.[26] The DFT calculations of the exchange
coupling constants were carried out adopting the hybrid B3LYP func-
tional[21] using the Gaussian 09 code.[26] Basis sets of triple-ζ quality
for Cu and double-ζ quality for all other atoms were used.[27]
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Supporting Information (see footnote on the first page of this article):
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Acknowledgements
[8] a) B. Rodríguez-Molina, S. Perez-Estrada, M. A. Garcia-Garibay,
J. Am. Chem. Soc. 2013, 135, 10388–10395; b) B. Rodríguez-
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G. B. thanks the CNRS and the Région des Pays de la Loire for a PhD
grant. C. L. thanks the Région des Pays de la Loire for a Post-Doctoral
grant. Work at Angers was supported by the Region des Pays de la
Loire Grant MOVAMOL and the joint CNRS-Russian Federation
grants PICS 6028 and RFBR-CNRS 12–03–91059. Work in Bellaterra
and Tarragona was supported by the Spanish Ministerio de Economía y
Competitividad (Projects FIS2012–37549-C05–05, CTQ2011–29054-
C02–01, and CSD 2007–00041).
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Received: December 5, 2013
Published Online: March 25, 2014
Z. Anorg. Allg. Chem. 2014, 1127–1133
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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