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Antiperovskite Structure with Ternary Tetrathiafulvalenium Salts Construction Distortion and Antiferromagnetic Ordering.

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The use of anionic ligation seems essential for
achieving positive cooperativities so that the occurrence of a
positive charge in the structure through the first metal cation
is carefully avoided.
Received: June 26, 1991 [Z 4749 IE]
German version: Angen. Chem. 103 (1991)1513
CAS Registry numbers:
6, 137003-64-6;6 (M = K'), 137003-65-7;7 (M = Na+), 137003-66-8;8
(M = K'), 137003-67-9;8 (M = Na'), 137003-68-0;
HO(CH,CH,O),H, 1122,3-bis(benzyl27-6;2,3-bis(benzyloxy)-l-(bromomethyl)benzene, 8 1464-85-9;
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[3] Scheparrr et al. developed an idea of self-assembling ionophores and reported the complexation of two different cations in the assembly: a) A. Schepartz, J. P. McDevitt. J. Am. Chem. Soc. If1 (1989)5976.Cocomplexation of
a neutral guest and an electrophilic cation immobilized in the macrocycle
was reported by Reinhoudt et al.: b) C. J. van Staveren, D. E. Fenton, D. N.
Reinhoudt, J. van Eerden, S. Harkema, ibid. 109 (1987)3456;c) C. J. van
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[4]a) K.N. Raymond, T. J. MacMurry, T. M. Garrett, Pure Appl. Chem. 60
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Chem. 103 (1991)75;Angew. Chem. Int. Ed. Engl. 30 (1991)85.
[S] a) J. Rebek, Jr., J. D. Trend, R. V. Wattley, S. J. Chakravosti, J. Am. Chem.
Sor. fO1 (1979)4333;b) J. Rebek, Jr., R. V. Wattley, ibid. 102 (1980)4853;
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102 (1980)7398: d) Angew. Chem. 93 (1981)584; Angew. Chem. Int. Ed.
€ng/. 20 (1981)605;e) J. Rebek, Jr., L. Marshall, J. Am. Chem. SOC.I05
(1983)6668;f ) J. Rebek, Jr., ibid. 107 (1985) 7481; g) T. Nabeshima, T.
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Luis, A. M. Costero, M. I. Burguete, J. Rebek, Jr.. J. Am. Chem. Sor. If0
Antiperovskite Structure with Ternary
TetrathiafulvaleniumSalts: Construction,
Distortion, and Antiferromagnetic Ordering **
By Patrick Batail,* Carine Livage, Stuart S. P . Parkin,
Claude Coulon, James D . Martin, and Enric Canadell
Our present ability to rationally design and prepare molecular solids within a predicted structure type is still in its
Dr. P. Batail, Dr. C. Livage
Laboratoire de Physique des Solides Associe au CNRS
Universite de Paris-Sud
F-91405Orsay (France)
Dr. S. S . P. Parkin
IBM Research Division, Almaden Research Center
San Jose, CA 95120 (USA)
Dr. C. Coulon
Centre de Recherche Paul Pascal, CNRS
Avenue Dr. Schweitzer, F-33600Pessac (France)
Dr. J. D. Martin, Dr. E. Canadell
Laboratoire de Chimie Theorique Associe au CNRS
Universiti de Paris-Sud
[**I This work was supported by the Ministere de la Recherche et de la Technologie (The "Ingenierie Moleculaire" Program and Research Fellowship
to C . L.), the Centre National de la Recherche Scientifique (France), and
the National Science Foundation Office of International Programs (postdoctoral fellowship for J.D.W.We thank P. Auban for her contribution to
the ESR experiments.
Verlagsgesellschafr mbH, W-6940 Weinheim. 1991
infancy.['] Here we report that a series of ternary tetrathiafulvalenium salts of large, divalent all-inorganic hexanuclear
molybdenum halides, formulated as (TTF'+),[(Y -)(Mo,X:,)]
(X = Y = CI; X = Br, Y = C1, Br, I), has been
electrochemically assembled and shown to actually adopt a
perovskite-type[21 structure. The latter features a unique
three-dimensional arrangement of tetrathiafulvalene (TTF)
cation radicals, located at the oxygen sites of the BaTiO,
prototypical structure. Thus, a rhombohedrally distorted
antiperovskite network is identified, in which, in all four
compounds, the unpaired K-electron spins ( S = l/2) for each
of the tetrathiafulvalenium HOMOS, centered at the vertices
of vertex-sharing {Y -(TTF'+),} octahedra, undergo sharp,
long-range antiferromagnetic ordering at roughly 6- 8 K. In
fact, the initial discovery that antiferromagnetic ordering
occurs in (TTF),[(CI)(Mo,CI,,)] 1 prompted the preparation of (TTF),[(Y)(Mo,Br,,)], Y = C1 (2), Br (3), and I (4)
with the two-fold anticipation that they would form the same
antiperovskite structure and indeed order antiferromagnetically.
These observations suggest that significant molecular information can be expressed and manipulated by substitution into
a predicted target structure in order to design highly ordered,
specialized three-dimensional molecular solids. These structures act as efficient receptors for halides with unique magnetic properties, very much along the same approach that
has proven so successful in solid state inorganic chemistry. In
this respect, such a unique family of compounds bridges the
gap between organic and inorganic materials: it is indeed a
novel simple structure type recognized[31in complex molecular solids in the CSC~,[~"I
NaC1,[4b. and CdCI, structures.[4d]
It is also suggested that the three-dimensional nature of the
perovskite structure has played a role in preventing the occurrence of the spin-Peierls transition commonly 0bserved1~1
in other cation radical salts, albeit of lower dimensionality,
thereby providing a particularly simple example of geometric control of the electronic structure in the solid state. An
exchange mechanism by direct, through-space coupling of
the organic spins inside the octahedron-unprecedented in
the molecular solid state-ould
be revealed by consideration of structural and antiferromagnetic resonance data
and MO calculations.
The electrochemical assembling of the units [Mo,Cl,,]' -,
TTF", and C1- was purposely attempted in order to
demonstrate that the formation of the perovskite framework
is a consequence of the divalent character of the large cluster
anion (site A). This assumption was based on recent evidence
that (a) such associations with the monovalent, isoelectronic,
and isostructural hexarheniate cluster anions [Re,Q,C19](Q = S, Se)r6] result in the formation of 2 : l binary phases
with discrete mixed-valence [(TTF);+] d i m e r ~ ; [ and
~ l (b)
that the monovalent rhenium cluster-based, paramagnetic
perovskite previously obtained by serendipity,[61was actually a disordered material with only a fraction of the monovalent anions on the A site. Indeed, we have shown that in the
latter phase, now formulated as {(TTF'+),(TTF)}((Cl-),){(Re,Se,CI~-)(Re,Se,C1,-)) one spin fails per TTF
octahedron and no antiferromagnetic ordering occurs.[71
Black, rhombohedrally-shaped single crystals of 1-4 were
grown on a platinum wire anode upon constant low current
density (1.3 KAcm-') oxidation of TTF (0.067 mmol) in anhydrous acetonitrile in the presence of equimolecular amounts
(0.045 mmol) of the tetrabutylammonium (TBA) salts of the
hexanuclear halomolybdatersl and of the appropriate halide.
The proportions and amounts of the two anionic components in the 30 mL electrochemical cells proved to be critical
for the formation of the proper 3 : 1 :1 stoichiometry. While
S 3.50+.2510
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 11
we have found no evidence so far of other ternary phases
with different stoichiometry, single crystals of a binary 11 :2
phase (for example, (TTF),.,(Mo,X,,), X = CI, Br) have
been identified, whose formation competes with that of the
3: 1 : 1 antiperovskite; more about this will be described separately. This binary phase was obtained earlier, independently
by us and by F ~ c h s , 'when
~ ~ the electrocrystallization was
conducted without TBA'Y - in the cells.
The compounds, which crystallize in the space group R3
(Table 1) are isostructural. Their structure,[101shown in Figure 1 a, emphasizes the analogy with the classical representation of the cubic perovskite-cage (Fig. 1b). Attention is thus
drawn to the three-dimensional framework of vertex-sharing
((TTF'+),Y - } octahedra, with the divalent inorganic cluster
anion encapsulated in the organic cage. Both the center of
Table 1 . Crystallographic and magnetic data for compounds 1-4
N [a1
R, [b]
c [cl
L a x
Y =c1
Y =I
- 14.6
- 16.7
- 11.5
- 12.1
[a] N = number of the observed intensities, corrected for absorption such that
I t 30(I). [b] R and R, are the residuals for the structure factors and their
weighted sum, respectively. [c] The observed Curie constants Care given in cgs
units per mol TTF (in SI units this is 3.75 .IT-* K); the calculated value is
0.3723 emu. mol-' for S = 112 and g = 2.
Fig. 1 . a) Structural organizationof the antiperovskites 1-4. b) The cubic perovskite structure. c) Binding geometry within the {(TTF),tY-J octahedra (see
text). In all figures the unique 3-axis direction of the R3 unit cell is indicated.
Angen. Cliem. l n f . Ed. Engl. 30 (1991) No. 11
the cage and that of the cluster anion are located at the origin
of rhombohedral unit cells (Table 1); the discrete halide ion
is found at the center of the unit cell and the TTF" ions at
the middle of the faces.
The analysis of the crystal structures reveals a set of six
symmetry-equivalent, short S-Y contacts (Table 1). These
might be primarily responsible for the binding geometry inside the octahedral motif, since the orientation of the TTF"
ions on their lattice site is such as to satisfy quasilinear CSs+ . . .Y . . . '+S-C electrostatic interactions across the central halide ion (Fig. 1c). Therefore, the small rhombohedral
distortions in the unit cell would specifically reflect the offset
between the former direction of optimum, long range Coulomb forces'' and that of the unit-cell translational symmetry vector linking the centroids of the TTF ions. This is a
novel type of geometrical distortion for the perovskite structure, since the quadratic, rhombohedra], and orthorhombic
distortions commonly observed in inorganic compounds result rather from the mismatch between the metal-oxygen
and the metal-halide bond lengths.1121
We then observe that this novel distortion of the perovskite
structure demonstrated in this series of isostructural salts allows for a striking crystallographic expression of the anisotropic shape and binding capabilities of their common organic
component when assembled with essentially spherical inorganic counterparts. A macroscopic manifestation of this
molecular shape-selective binding symmetry is to be found in
the actual rhombohedral habit of the single crystals.
The TTF" centers are 6.754 (%axis related) and 8.272 A
(for 1) to 6.984 and 8.521 A (4) apart along the edges of the
{Y-(TTF'+),} octahedra. This is another remarkable feature of this three-dimensional network of organic cation radicals, given the propensity of such planar aromatic cations to
overlap and favor electron delocalization along one-dimensional stacks of closely spaced molecules (3.47 A). As expected then, the compounds 1-4 are insulating.
As follows from the temperature dependence of their static
magnetic susceptibilities, the compounds are paramagnetic
down to low temperatures (as shown for example for 3 in
Fig. 2). Above 50 K, the data obey the Curie-Weiss law, and
the observed and calculated Curie constants and effective
magnetic moments (Table 1) are in excellent agreement with
the assumption of one spin per TTF molecule. The data also
reveal (Fig. 2) that the susceptibility of each compound goes
through a maximum at the temperatures T,,, given in
Table 1. The magnetic susceptibilities were measured at var-
Verlagsgesellschaft mbH, W-6940 Weinheim, 1991
8 3.50t.25/0
0 OlLl
Fig. 2. Temperature dependence of the specific magnetic susceptibilities (in cgs
units) measured directly on some single crystals of 3 using a SQUID susceptometer. The solid lines represent the fit of the data to x = xo + C(T + @ ) - I . The
observed Curie constants and Weiss temperatures for 1-4 are given in Table 1 .
The inset shows that Tmax
is independent of the field strength. o = 1 kOe. =
2 kOe, = 5 kOe, = 50 kOe. x in emug-'.
ious field strengths from 50 kOe (3.98 x 10, Am-') down to
1 kOe, and T,,, values were found to be independant of the
field. A typical example is given for 3, between 5 and 40 K,
in the insert of Figure 2. These indications of anisotropic
antiferromagnetic (AF) fluctuations suggest the possibility
of A F ordering at lower temperature.
This assumption was suppported by single-crystal electron
spin resonance (ESR) experiments showing in each case that
the narrow single line observed in the paramagnetic regime,
with Lorentzian shape and isotropic characteristics typical of
TTF" spins,['31abruptly vanishes in a few tenths of a degree
at NCel temperatures (T,) lower than T,,, (Table 1). Finally,
the observation of antiferromagnetic resonances (AFMR) below TNdefinitely confirms the existence of magnetic ordering.
So far we have only incomplete information on the mechanism of the magnetic interaction. A classical d e ~ c r i p t i o n ~ ' ~ ]
of the perovskite structure requires, however, that 1-4 are
built up by the stacking of pseudo-close-packed (TTF"),(Mo6X:4) layers which form octahedral holes occupied by
the discrete halide ions Y-. Owing to the rhombohedra1
distortion there is only one such stacking direction in the
structure, that is the layers of organic spins are stacked along
the unique threefold inversion axis. The most likely interactions are either the two through-space interactions symbolized by the arrows in Figure Ic, or the indirect trans-coupling across the halide at the center of the octahedron.
Extended Huckel-type
demonstrate that the
latter coupling is extremely weak. Remarkably, the strongest
interaction is between the TTF ions related by symmetry by
the %axis (solid arrow in Fig. lc). These interactions
( 5 x lo-* eV in 2) are about three times stronger than those
between the TTF ions not related by symmetry (dashed arrow in Fig. 1 c) and indeed thirteen times stronger than the
indirect trans-coupling. This would suggest that most of the
magnetic interaction might occur by direct exchange between spins of successive layers.
The quantitative analysis of the AFMR rotation patterns
provides information on the magnetic anisotropy.[' 6 ] The
AFMR spectrum is complex and composed of several narrow lines, the origin of which will be discussed in a separate
paper. However, the evolution of the mean position of the
spectrum as a function of the field orientation for 1-4 is
reminiscent of the room temperature crystal structure symmetry. That is, we find that the single 3-axis, actually the
0 VCH Verlagsgesellschafi mbH,
W-6940 Weinheim, 1991
short diagonal of the crystals, is the magnetic hard axis. In
addition there exists an easy plane, that is the spin-flop field
vanishes (HsF= 0). These results agree with the absence of
any sizeable field dependence of the magnetic susceptibility
below TN.Thus, with this approximation, we are left with
only one adjustable parameter to describe the anisotropy of
the system, that is, H + = hQ+/p,.['6al Preliminary estimations yield an H + field strength on the order of 5 kG, a value
similar to those found previously for other TTF-based
charge transfer salts.[' 6b1 This convincingly supports the hypothesis that the magnetic anisotropy has the same origin,
i.e. is due to magnetic dipolar interaction^.["^
Altogether, the structural analysis and molecular orbital
calculations are consistent with the ESR and AFMR experiments and favor a direct exchange mechanism for the antiferromagnetic ordering. Thus, the strength and anisotropy
of the magnetic interaction are expected to be very sensitive
to even small modifications of the {(TTF'+),Y - } octahedral
geometry. The electrochemical assembling of three components associated with the control of the site location of the
molecular ions, allows for many substitutions in these series
of compounds. One possible aim is the synthesis of a related
molecular equivalent of the K,NiF4-type of structure, particularly with the prospect of the occurrence of two-dimensional magnetic ordering reminiscent of the antiferromagnetic
phase of La,CuO,;['sl this would require the stabilization of
single perovskite layers, which might be achieved by decoupling the (TTF), octahedra either by alloying with unsymmetrical TTF ions or by using bulkier divalent cluster anions. Such possibilities are being explored.
Received: June 13, 1991 [Z 4700 IE]
German version: Angew. Chem. 103 (1991) 1508
[I] J. S. Miller, Adv. Muter. 2 (1990) 98.
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121 J. B. Goodenough, J. M. Longo in Lando/t-3ornstein-Tabellen
Springer, Berlin 1978, p. 126.
[3] An approach not unlike PuulMoore's perception ofstructural complexity:
P. B. Moore, Am. Miner. 74 (1989) 918-926. See also P. B. Moore, ibid. 71
(1986) 540; J. K. Burdett, Chem. Rev. 88 (1988) 3.
[4] a) L. Ouahab, P. Batail, C. Perrin, C. Garrigou-Lagrange, Muter. Res.
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Talham, J. Canciell, P. Batail, A. Collet, J. Lajzerowicz, Angew. Chem. 101
(1989) 1251 : Angebv. Chem. Int. Ed. Engl. 28 (1989) 1249; d) P. Batail, K.
Boubekeur, A. Davidson. M. Fourmigue, C. Lenoir, C. Livage, A. Penicaud in G. Saito, s. Kagoshima (Eds.): The Physics and Chemistry of
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[5] J. B. Torrance in D. Jerome, L. G. Caron (Eds.): Low dimensional Conductors andSuperronductors, NATO AS1 Ser. B155, (1987) 113.
[6] P. Batail, L. Ouahab, A. Penicaud, C. Lenoir, A. Perrin, C . R. Acad. Sci.
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171 K. Boubekeur, Dissertation, Universite de Rennes (1989).
[8] P. Nanelli, B. P. Block, Inorg. Synth. 12 (1970) 170.
[9] H. Fuchs. Disserlation, Universitat Munchen (1987).
[lo] Enraf-Nonius CAD-4F, (w-20) scans, Mo,., solution of structures by direct methods and Fourier synthesis. Further details of the crystal structure
investigations are available on request from the Fachinformationszentrum
Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH,
W-7514 Eggenstein-Leopoldshafen 2 (FRG), on quoting the depository
number CSD-55593, the names of the authors, and the journal citation.
1111 W. F. van Gunsteren, H. J. C. Berendsen, Angew. Chem. 102 (1990) 1020;
Angeu,. Chem. Int. Ed. Engl. 29 (1990) 992.
[12] R. A. Wheeler, M. H. Whangbo, T. Hughbanks, R. HofFmann, J. K. Burdett, T. A. Albright, J. Am. Chem. SOC.108 (1986) 2222.
1131 Y Tomkiewicz, A. R. Taranko, J. B. Torrance, Phys. Rev. BfS(1977) 101.
1141 A. F. Wells: Strucfural Inorganic Chemistry, Oxford University Press, Oxford, 1986, pp. 179-181.
[15] R. Hoffmann, .
Chem. Phys. 39 (1963) 1397. Our calculations use double6 typeorbitals: E. Clementi, C. Roetti, A(. Nucl. Data TabIesf4(1974) 177.
1161 a) T. Nagamiya, Prog. Theor. Phys. If (1954) 309; b) C. Coulon, R. Laversanne, J. Amiell, Physica B C (Amsterdam) 143 (1986) 425.
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0570-0833/9ljlfll-lSOO $3.50+.25/0
Angew. Chem. I n l . Ed. Engl. 30 (1991) N o . I1
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salt, structure, ternary, antiperovskite, distortion, ordering, tetrathiafulvalenium, construction, antiferromagnetic
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