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Isothermal Magnetic Phase Transitions Controlled by Reversible ElectronIon Transfer Reactions.

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of the unit cell amounts to 7.0%. On anodic oxidation of
CuzCrzSe4the process is reversed and the starting material
(y = 0) is obtained again after a charge transfer of n = 2; the
same result is found on chemical oxidation, e.g. with Iz/
CH3CN leading to CuCrzSe4and (soluble) CuI.
Isothermal Magnetic Phase Transitions
Controlled by Reversible Electron/Ion
Transfer Reactions
By Robert Sch6llhorn* and Andreas Payer
One of the most intriguing aspects of the intercalation
chemistry of electronically conducting host lattices is the
possibility of reversibly modifying and controlling the physical properties of solid materials by chemical reactions at
ambient temperature."] So far, interest has focused mainly
on changes of electronic properties, superconductivity, optical properties and structural transitions with the reaction
state. We report here on the control of magnetic phase
transitions via reversible electron/ion transfer reactions at
300 K with copper selenospinels CullrCr2Se4 as the model
system. The process is correlated with the change in the
stoichiometric index y; at a critical concentration yc the
isothermal transition takes place according to the scheme
ferromagnetic state
Y < s<
paramagnetic state
(T= const.)
Prof. Dr. R. Schollhorn, DipLChem. A. Payer
lnstitut fur Anorganische und Analytische Chemie
der Technischen Universitat
Strasse des 17. Juni 135, D-1000 Berlin 12
Angen Chem. In: Ed Engl. 25 11986) No. 10
Spinel type structures formally provide an excess of vacant tetrahedral and octahedral lattice sites for the potential uptake and bulk transport of additional cations. In a
recent publication we have demonstrated that copper chalcogenospinels with appropriate electronic properties and
mobile Cue ions are, in principle, able to undergo topotactic redox reactions.IZ1Since the copper chromium selenospinel CuCr,Se4 exhibits metallic properties as well as ferromagnetic behavior at room t e m p e r a t ~ r e ~we
~ l investigated the electrochemical behavior of this compound in
aqueous and aprotic electrolyte solutions (Cue/CH3CN,
CuZe/H2O). Copper ions were found to be mobile in
CuCr,Se, and a chemical diffusion coefficient d(300 K)
= 5 x 10- I ' cm2 s - ' was measured. The selenospinel participates in reversible electron/ion transfer reactions according to Equations (a) and (b), which apply to the case of
C u e and Cu'@ electrolytes, respectively.
The potential/charge transfer diagram under dynamic
conditions (galvanostatic mode) as well as equilibrium potentials for the cathodic reduction of CuCr,Se4 in aqueous
Cu2@electrolyte are given in Figure la. An almost continuous change in potential is observed until the potential of
copper deposition where the solid state reaction has
reached its endpoint. The integral charge transfer value
thus obtained is n (eG/CuCrZSe,) = 2. For aqueous electrolytes containing CuZe ions the formal correlation between
n and the stoichiometric index y corresponds to y = n/2.
This was confirmed by analytical data, which agree perfectly with this correlation, i.e. no measurable side reactions appear and the intercalation of copper proceeds
quantitatively according to Equation (b). The X-ray data
(Fig. Ib) similarly indicate a one phase system with a continuous change in lattice parameters for the range 0 5 ~ 2 1 .
The products retain cubic symmetry with a = 10.57 A for
the terminal phase with y = 1 ; the total change in volume
Fig. 1. a) PotentiaVcharge transfer diagram lor the gdlvdnoatatic cathodic
reduction of CuCr2Se4(pressed polycrystaliine working electrodes, copper as
counter electrode and as reference electrode) to Cu, +,CrzSe4 in aqueous
electrolyte ( 0 . 5 ~CuS04+0.5 M HLSOI);charge transfer n(eo/CuCrLSe,);
y=stoichiometric index; nominal current density= I A/m2; open circles
refer to potentials measured under equilibrium conditions. b) Varlation of
cubic lattice constant a and Curie temperature T, with the stoichiometry y of
Cu,+,CrzSe,; the magnetic susceptibility was measured by means of a Faraday balance, 7,values were obtained from x - ' / T plots. Results obtained
for aqueous ( C u 2 @ / H 2 0and
) aprotic (Cu'/CHKN) electrolytes are identiCdl.
Figure l b shows the change in Curie temperature T, of
the C U , + ~ C Tphases
~ S ~ ~as a function of composition in
the range 0 5 y I
1. With increasing copper content the critical temperature of the magnetic phase transition decreases
significantly from 432 K (y=0) to 175 K (y= 1). In the
course of the isothermal electrochemical reaction at 300 K
[Eq. (a), (b)] T, is attained at a critical composition
yc=0.52 (Fig. Ib) which is correlated with a transition
from the spin ordered ferromagnetic to the disordered paramagnetic state. The critical composition yc is itself of
course a function of the temperature at which the reaction
proceeds. The chemical reaction is reversible and can thus
be used to control the magnetic properties of the solid in
0 VCH Verlagsgeselkhaft rnbH, 0-6940 Weinheirn, 1986
0570-0833/86/1010-0905 $ 02.50/0
dependence of the reaction state. Systems of this type are
of potential interest for practical application; experiments
with permanent magnets in contact with a spring loaded
C u , +,Cr2Se4 working electrode demonstrated that, in principle, it is possible to construct a magnetic switch operated
isothermally by the chemical process under discussion.
Conversely, the latter arrangement represents a magnetic
sensor device for the reaction state of the chemical system.
The characteristic difference in reactivity direction between CuTi2S4[21and CuCr2Se4can be discussed qualitatively in terms of the relative stability in chalcogenospinel
lattices of the formal oxidation states of the transition metal ions involved. Since copper has the oxidation state + 1
in chal~ogenides,[~]
the compounds can be described in an
ionic model as mixed valence phases Cu@(Ti3@Ti4@)(S2"),
and C U @ ( C ~ ' @ C ~ ~ @ ) ( While
S ~ * " )CuTi2S4
can only be oxidized to Ti2S4,CuCr2Se4can only be reduced to Cu2Cr2Se4
under the conditions applied:
This can be explained reasonably well in terms of the
lower stability of Ti3@and the higher stability of Cr3@in
relation to the coexisting quadrivalent states in chalcogen
ligand fields.
The magnetic ordering in copper chalcogenospinels
CuCr2X4 has been interpreted in terms of Cr"'/Cr"' (superexchange) and Cr"'/Cr"'
interaction (double ex~ h a n g e ) . [ ~ "We
. ~ l attribute the significant decrease in T, of
C u l +$r2Se4 with increasing degree of conversion (y) to
the higher strength of ferromagnetic coupling of Cr"'/Crlv
as compared to Cr"'/Cr'''.[5c1
Extended studies of the related ferromagnetic chalcogenospinels CuCr2S4and CuCr2Te4revealed a behavior quite
similar to that o f the selenide. Current work is related to
the investigation of the influence of Lie intercalation in
these phases because of the strong difference in bond ionicity Cu/X and Li/X; the possibility of Lie insertion in
spinel type oxides and chalcogenides has been demonstrated in recent publication^.'^,^.^^
Received: May 12, 1986 [Z 1770 IE]
German version: Angew. Chem. 98 (1986) 895
CAS Registry number:
CuCr2Sea, 12140-05-5.
[I] R. Schollhorn, Angew. Chem. 92 (1980) 1015; Angew. Chem. lnr. Ed. Engl.
1Y (1980) 983; R. Schollhorn in J. L. Atwood, J. E. D. Davies, D. D.
MacNicol (Eds.): Inclusion Compounds, Vol. I , Academic Press, New
York 1984, p. 249; M. S. Whittingham, A. J. Jacobson: Intercalation
Chemistry, Academic Press, New York 1982; F. A. Levy: In/ercalated
Layered Material.7. Reidel, Dordrecht 1979.
[2] R. Schollhorn, A. Payer, Angew. Chem. 97 (1985) 5 7 ; Angew. Chem. Int.
Ed. Engl. 24 (1985) 67.
[3] 1.Kanomata, H. Ido, J. Phys. Soc. Jpn. 36 (1974) 1322.
141 J. C. W. Folmer, F. Jellinek, J . Less-Common Mer. 76 (1980) 153.
[ 5 ] a ) J. B Goodenough, J. Phys. Chem. Solids 30 (1969) 261; b) R. J. Bouchard, P. A. Russo, A. Wold, lnorg. Chem. 4 (1965) 685; c) F. K. Lotgering, G. H. A. M. van der Steen, Solid Srare Commun. 9 (1971) 1741.
[ 6 ] J. H. Goodenough, M. M. Thackeray, W. 1. F. David, P. G. Bruce, Reu.
Chim Miner. 21 (1984) 435.
17) S Sinha, D. W. Murphy, Solid S / a / e Ionics 20 (1986) 81.
0 VCH Verlagsgesellscl~afimbH D-6Y40 Wernheim. 1986
a New Route to C,,H,, Isomers**
By Rolf Gleiter,* Horst Zirnmerrnunn, and
Worfrarn Sunder
1, which is of interest as a precursor of tricycl0[]deca-3,5,9-triene
2, and its derivatives undergo unexpected rearrangements,
which have allowed us to isolate several C l o H l oisomers,
some of them previously unknown. Starting from 3,s-cyclodecadiene- 1,6-dione bisethyleneacetal 3, accessible in
good yields from 1,4,5,S-tetrahydronaphthalene,"]it is possible to synthesize the ketone 4 in three steps (oxidation
with rn-chloroperbenzoic acid (rn-CPBA), reaction with
PhSeSePh and then with H 2 0 2according to the Sharpless
method,[21and oxidation with CrO,; Scheme 1). Irradiation
of 4 affords only 5 (the other possible regioisomer, 6, was
not detected).
0 0
u 3
Scheme I . Synthesis of 1. a) m-CPBA, CH2CI2.b) PhzSe2, NaBH4, nBuOH,
I Z O T , 24 h. c) H202.tetrahydrofuran (THF), O T , 20 h. d) CrO,, pyridine. e)
hv, H,CCN, O T , 7 h. f ) NaBH,, D O H . g) TsCI, pyridine. h) 1.5-DiazabicycIo[4.3.0]non-5-ene, H,CCN, 7 0 T , 12 h. i) TsOH, H20/acetone. j) LiAIH,,
Et20. k) (PhO),PCH,I, hexamethylphosphoric triamide, 8 0 T , 4 h. I) 1 N
HCI, THF, 24 h.
The structure of the photoproduct was established from
the 'H-NMR spectrum and by comparison with the specderivatives
troscopic data for tricycl0[5.3.0.O~~~]decane
whose structures are known.''] Reduction of the carbonyl
group in 5 to the hydroxyl group, subsequent H 2 0 elimination, and acetal cleavage afford the ketone 7, from
which, in an analogous series of reactions, 1 is obtained.
Prof. Dr. R. Gleiter, DiplLChem. H. Zimmermann, Dr W. Sander
Institut fur Organische Chemie der Universitat
Im Neuenheimer Feld 270, D-6900 Heidelberg (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie, and BASF AG. W . S. thanks the Studienstiftung des Deutschen Volkes for a fellowship. We thank Prof. J.
Dabrowski, DipLChem. M . Hauck. and Dr. P. Kunzelmann for their
help in recording and interpreting the NMR spectra.
0570-0833/86/1010-0906 ?
Angew. Chem. lnr. Ed. Engl. 25 (1986) No. 10
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