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Catalytic Graphite-Intercalation with Alkali Metals in Solution.

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nents on going to the corresponding compounds of elements
of Groups V and IVrll. Heteropolar interactions are also
characteristic of the alkali and alkaline earth metal salts of
acids with complex anions (e.g. sulfates, phosphates, etc.),
and yet there is a lack of systematic studies on compounds
with complex anions with analogous metallic bonding components. We have now synthesized the compounds Sr3Si2As4
(1) and Sr3Ge2As4(2) which have a metallic luster but appear red by transmitted light when viewed as thin layers;
complete X-ray structure analysis on single crystals['] showed
them to contain networks of infinite chains which are to be
interpreted in this way (Figs. 1 and 2).
Received. November 8: 1979 [Z 490 LEI
German version: Angew Chem. Y2. 480 (1980)
[I] H. Schafer, B. Eisenmann, W Mdler, Angew. Chem. 85, 742 (1973); Angew.
Chem. Int. Ed. Engl. t2, 694 (1973).
[2] (1): monoclinic, space group C2/c, Z = 4 , a=920.5(4), b = 1683.2(5),
c=737.6(4) pm, @= 122.46(3j0; four circle diffractometer Sloe Stadi 4. 836
symmetry-independent reflections, R = 0.056.
(2): monoclinic. space group P2,/c, Z = 4 , 0=763.1(5), b = 1851.2(7).
c=743.9(5) pm, @ = 111.88(8)"; CAD 4 four-circle diffractomelers. 867 symmetry-independent reflections, R = 0.101. Solution by direct phase-determination methods [SHEL-X-76 program, G. M. Sheldrick (1976). unpuhlished]
Catalytic Graphite-Intercalation with Alkali Metals
in Solution[**]
By Hans- Friedrich Klein, Joachim Gross, and Jurgen 0.
Fig. 1 [Si,As:..],
anion in SriSi2As4( I J :
0 e As.
Fig. 2. [Ge2As:-], anion in Sr3GezAs4(21:
In the two novel compounds (1) and (2) the Si and Ge
atoms are surrounded tetrahedrally by three As atoms and
one neighbor of the same kind. Thus As3Si-SiAs3 and
As3Ge-GeAs3 units arise, which, in the case of the silicon
compound, are linked by shared edges (cf. Fig. 1) to form
one-dimensionally infinite chains. In contrast, the As3GeGeAs3 units in the germanium compound are joined together in such a way that all three As atoms of a GeAs3
group form bridges while only one As atom of the other
GeAs3 group contributes to the network; two As atoms are
still terminal (Fig. 2). In both cases, chain anions result
which are shown by their composition and the coordination
of their components (Zintl-Klemm conceptl']) to require description as (Si2Asz-), and (Ge2As:-),. The six negative
charges are compensated by three Sr2+ions.
Our results clearly show that transition from salts with
complex anions to ternary intermetallic compounds leads to
transitions in bonding similar to those demonstrated previously for numerous binary compounds['].
The catalysts used are monoolefintris(trialkylphosphane)cobalt(o) complexes which are reversibly reduced in
an apolar medium. A reduced form of the catalyst A[Co(olefin)(PR3)3]2151
transports the alkali metal through the hydrocarbon solution to the graphite where the cobalt(o) complex
is regenerated (Fig. 1). R is preferably methyl.
alkali metal
qraphi te
Fig. 1. Catalytic intercalation of graphite (A= K, Rb, Cs)
Stoichiometric amounts of the elements are heated to
1150 "C under argon in a corundum crucible in an evacuated
quartz bomb kept at that temperature for 1 h, and then
cooled at a rate of ca. 100 "C per hour. Crystalline platelets
can be broken out of the homogeneous reguli.
Angew. Chem. Int. Ed. Engl. 19 (1980) No. 6
Liquid or evaporated alkali metals A form stoichiometric
lamellar intercalation compounds AC, with graphite or
graphite-like samples of carbon. These compounds differ in
the number n of carbon planes between two layer vacancies
occupied by A (compounds of the n-th stage) and in the occupation of the interlayer vacancies.
When A = K, Rb, Cs, then x = 8, 24, 36, 48, 60 for compounds AC, of the 1st to 5th stage1'"],whereas other compositions were found for A = Li, Na, e. g. LiC6 and LiCI2for the
1st and 2nd stagellbl.
The formation of AC, can also be accomplished in metallic reducing solutions, e. g. of A in liquid ammonia12"],by alkali metal salts of organic radical anions such as naphthalenesodium in ethersLZb],and by electrochemical reduction of
graphite in aprotic solutions of A' salts'2'].
However, these procedures require strongly polar solvents
which solvate A@and lead to ternary compounds A(solv),,C,
which are generally extremely labile.
Solvate-free alkali metal intercalation compounds have so
far only been accessible from the elements at elevated temperature, with intercalation usually being performed in high
vacuum from the vapor phase131.
We have now found a catalytic method of generating nonsolvated compounds KC8, RbCs, and CsCRfrom graphite141
in an apolar medium, at room temperature, and in short
reaction times [reaction (I)].
[*I Prof. Dr. H.-F. Klein, Dip1:Chem. J . Gross, Doz. Dr. J. 0. Besenhard
Anorganisch-chemisches lnstilut der Technischen Universitit Munchen
Lichtenbergstrasse 4. D-8046 Garching (Germany)
[**I This work was supported by the Fonds der Chemischen Induslrie
0 Verlag Chemie, GmbH, 6940 Weinheim, 1980
0570-0833/80/0606-491 $ 02.50/0
49 1
Chem. 277, 156 (1954); A. Schieede, N . Wellmann, Z . Phys. Chem. B 18, I
In polar solvents ternary compounds A(solv),C, are ex(1932); M . A. M . Boersma. Catal. Rev. 10, 243 (1974): b) D. Biifaud, A. Hepectedly formed according to eq. (1); this also provides the
roid, Carbon 17. 183 (1979). and references cited therein.
first one-step entry to such compounds solvated with ar[2] a) W. Riidorff, E. Schulre. 0. Rubisch, Z. Anorg. Allg. Chem. 282,232 (1955);
enes@I. Thus, reaction of HOPG (highly oriented pyrolytic
b) I. B. Rashkou. I . M . Panayotou, Y C. Shishkoua. Carbon 17. 103 (1979); c)
graphite) with excess potassium (10% C O ( C ~ H ~ ) ( P M
in ~ ~ ) ~ J. 0.Besenhard, ibid. 14, 111 (1976).
[3] A. Herold. Bull. SOC.Chim. Fr. 22, 999 (1955).
benzene, 8 d, 25 " c ) gave the C6H6-solvatedcompounds of
[4] Manufacturer: Kropfmiihl, Passau (Germany), RFL 99.5
the 1st and 2nd stage, for which the compositions
15) Structure of the catalytically active species: H:F. Klein. J. Gross, J. M . BasK(C6H6)yC24
and K ( C ~ H ~ ) , Cand
~ Rbasal spacings of 930 and
sei, 0. Schuberf. Z . Naturforsch. B 35, 614 (1980).
161 a) C. Merie, I. Rashkou. C. Mar, J. CoIe, Mater. Sci. Eng. 31. 39 (1977); b) L.
1260 pm, respectively, are given[6b'. For the 2nd stage, howBonneiain, P. Touzain, A . Hamwi, ibid. 31, 45 (1977).
ever, we found a basal spacing of only 1245 pml'l. Although
[7] For samples prepared in presence of air we obtained basal spacings of 1260the composition and X-ray diffraction data of the nonsol1270 pm.
vated and the solvated alkali metal-graphite compounds cor[8] J. 0.Besenhard. H . - F Kiein. J. Gross, H. Mohwaid, J. J. Nickl, Synth. Metals, in press.
respond to those reported in the literature, some of the properties of the catalytically generated species are modified:
On rigorous exclusion of air, KC8 forms lustrous golden
flakes. They swell on contact with benzene, turning black.
Nonstoichiometric Alkali Metal Titanium Sulfides
"High-temperature" KC8 has been described as inert towith
Channel Structure
wards this arene[6"1.During the synthesis of KC24 we observed that a small portion of the graphite flakes adopts a
By Robert Schollhorn, Wolfgang Schramm, and Dieter
golden sheen immediately after dissolution of the potassium,
while the major part appears unchanged.
The reduction of binary transition metal chalcogenides
M,X, in alkali metal halide melts represents a suitable techCO(C~H~)(PM
in ~pentane,
5 d, 25°C) are all the flakes
nique for the preparation of ternary chalcogenides A,M,X,
uniformly dark blue and have the same basal spacing. Equa(A = alkali metal, M =transition metal, X = S, Se, Te)[']. In a
tion (2) describes the overall reaction. The cobalt complex
study on the Ti/S system we observed the formation of the
also catalyzes equilibration between phases of different deternary sulfide KO3Ti3S4,which crystallizes in a structure
grees of intercalation.
type not described so far for the alkali metal titanium sulfides. Reduction of TiS2 in a KCl melt at 1300 K with potassium metal (TiS2:K = 1 :1.7) leads to formation of a solid
K +
phase consisting of gray, needle-shaped crystals with a mepentane. 4 d, 2S°C
[cxl pentane, 1 d, 2SoC+
tallic luster; analytical data correspond to a ratio K/Ti/
S = 0.3/3/4. Direct reduction of TiSz with K in titanium vessels at 1300 K yields the same compound, which, however, is
The reaction mechanism was confirmed by X-ray powder
contaminated by additional phases. Guinier powder diadiagrams for nonsolvated K, Rb, and Cs compounds: After
grams and Weissenberg single crystal photographs showed
short reaction times only the compounds of the 1st stage
Ko3Ti3S4to be hexagonal (a=950.5, c=341.4 pm, 2=2).
(AC,) were generally observed along with unchanged graphThe structure was determined from automatic diffractometer
ite. On prolonged reaction times compounds of higher stages
data (MoK,, 590 symmetry independent reflections, space
could be prepared with appropriate quantities of potassium.
group P6,/m(CZh). There are two different sulfur positions
Thus, intercalation according to reaction (1) is kinetically
in the unit cell; Ti and S(2) atoms occupy the position 6 h,
controlled. Nucleation of the AC, phases appears to be the
whereas the S(l) atoms occupy the positions 2(c) (for posirate determining step. In contrast, electrochemical intercalational parameters see Table 1). With Ti and S parameters
tion is thermodynamically controlled, i. e. the reaction proonly the structure model gave an agreement factor of
ceeds starting from graphite via higher stages to the 1st stage
R = 0.081. In a subsequent difference Fourier synthesis maxias the final
ma could be detected on the positions 2a (0, 0, 1/4) and 2b
The unusual reactivity of catalytically generated KC8 is
(0, 0, 0). With the assumption of a statistical distribution of
probably attributable to disorder effects. In general, solid
K' on these positions R showed a minimum at 0.30(5) K/
state reactions performed at room temperature lead to less
Ti3S4;the agreement factor was R = 0.065.
ordered, and hence frequently more "active" products than
high temperature reactions.
Table 1. Positional parameters of Ti and S atoms in K,,,Ti,S,.
Catalytic intercalation in solution permits the first transformation of highly oriented carbon fibers into good electriX
cal conductors by conversion into KC,'*'.
Preliminary experiments have shown that solution interTI
1 /4
calation of alkali metals can also be accomplished with metal
chalcogenides having layer structures (MoS2,WS2). Catalytic
reductions with Li are also feasible. Thus gray antimony (1.7
(10 ml), 48 h,
g, 1% C O ( C ~ H , ) ( P M ~in~ )tetrahydrofuran
The structure can be described in terms of distorted TiS6
25 "C) quantitatively yields the cubic low-temperature phase
octahedra joining common faces and edges to form a threeP-Li,Sb. The potential of these highly reducing solutions is
dimensional framework which is characterized by wide
estimated at 2.5-3 V.
channels parallel to the hexagonal c axis which are incom-
Received: December 1 I . 1979 [Z 482 IE]
German version: Angew. Chem. 92,476 (1980)
CAS Registry numbers:
KC,. 12081-88-8; RbCx. 12193-29-2; CsC8, 12079-66-2 Co(CIH4)(PMeA
111 a) W. Rudorff, Adv. Inorg. Chem. Radiochem. 1. 224 (1959); G. R . Hennig,
Progr. Inorg. Chem. I, 125 (1959); W . Riidor/f, E. Schulze. Z . Anorg. Allg
0 Verlag Chemie, GmbH. 6940 Weinheim, 1980
pletely occupied by potassium atoms (Fig. 1). The Ti atoms
are displaced from the center of the TiSh octahedra so that
[*) Prof. Dr. R. Schollhorn, Dipl.-Chem. W. Schramm. Pnv.-Doz. Dr. D.
Anorganisch-chemisches lnstitut der Universitat
Gievenbecker Weg 9, D-4400 Munster (Germany)
0570-0833/80/0606-492 $ 02.50/0
Angew. Chem. I n i . Ed. Engl. 19 (1980) No. 6
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graphite, solutions, metali, intercalation, catalytic, alkali
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