3366 (30) P. O'D. Offenhartz, 8. H. Offenhartz. and M. M. Fung, J. Am. Chem. SOC.,92, 2966 (1970). (31) J. M. Pratt. "inorganic Chemistry of Vitamin BI2". Academic Press, New York, N.Y., 1972, Section 2. (32) D. G. Brown, Prog. Inorg. Chem., 18, 177 (1973). (33) E. Bertele, H. Boos. J. D. Dunitz, F. Elsinger, A. Eschenmoser, I. Felner, H. P. Gribi, H. Gschwend, E. F. Meyer, M. Pesaro, and R. Scheffold. Angew. Chem., Int. Ed. €ng/., 3, 490 (1964). (34) I. D. Dicker, R. Grigg, A. W. Johnson, H. Pinnock, K. Richardson, and P. van den Broek, J. Chem. Soc. C,536 (1971). (35) Spectral data here and the spectra in Figure 6 (vide infra) are given in nanometers in order to facilitate direct comparison with published spectra, most of which are plotted in nanometers. Band intensities of synthetic Ni(li) corrins (not given) are qualitatively similar to those of 10 and 11. (36) V. B. Koppenhagen and J. J. Pfiffner, J. Bo/. Chem., 245, 5865 (1970);
248, 3075 (1971). (37) J. A. Hill, J. M. Pratt, and R. J. P. Williams, J. Chem. SOC., 5149 (1964). (38) R. A. Firth, H.A. 0. Hill, J. M. Pratt, R. G. Thorp, and R. J. P. Williams, J. Chem. SOC.A, 381 (1969). (39) V..E. Koppenhagen, F. Wagner, and J. J. Pfiffner, J. Bo/.Chem., 248, 7999 (1973). (40) No X-ray structural information is currently available for any of these complexes. In regard to phenyl substituent interaction with the conjugated ring, it is noted that the 4-phenyl-1,Pdithiolium cation, the initial prec ~ r s o rto~ all . ~ring systems in Figure 1, is entirely planar.'" (41) A. Hordvik and E. Sietten, Acta Chem. Scand., 20, 1874 (1966). (42) D. C. Hodgkin, Proc. R. SOC.,London, Ser. A, 288,294 (1965). (43) P. G. Lenhert, Proc. R. Soc., London, Ser. A, 303, 45 (1968). (44) E.G.dger. Z.Chem., 4, 437 (1964); 8, 30, 392, 470 (1968); Z.Anorg. AI@. Chem., 364, 177 (1969): C. J. Hipp and D. H.Busch, Inorg. Chem., 12,894 (1973): J. Chem. Soc., Chem. Commun., 737 (1972).
Lamellar Compounds of Graphite with Transition Metals. Graphite as a Ligand M. E. Vol'pin," Yu. N. Novikov, N. D. Lapkina, V. I. Kasatochkin, Yu. T. Struchkov, M. E. Kazakov, R. A. Stukan, V. A. Povitskij, Yu. S. Karimov, and A. V. Zvarikina Contribution from the Institute of Organo-Element Compounds and Institute of Chemical Physics, Academy of Sciences o f t h e USSR, Moscow, USSR. Received February 21, 1974
Abstract: Lamellar compounds of chromium, molybdenum, tungsten, iron, cobalt, nickel, manganese and copper with graphite were obtained and their structure, magnetic properties, and Mossbauer spectra were studied. Molybdenum was shown to form sandwich type x-complexes with graphite, similar to dibenzenemolybdenum, in which graphite acts as an aromatic n-ligand. Arguments were presented suggesting that in graphite compounds with iron, cobalt, and nickel some part of the metal forms weak complexes with graphite.
Carbon atoms in graphite are well known to be arranged in layers, and each layer is a regular hexagonal net of carbon atoms (Figure 1 ) . The C-C distances in a layer are 1.41 A which is close to the bond length in aromatic hydrocarbons. The interlayer spacing is equal to 3.35 A which corresponds to van der Waals interaction. Such difference in layer and interlayer bond types makes possible formation of lamellar compounds of graphite (LCG)-the products of insertion of different substances into the interlayer space. At present LCG with alkali a%d alkali earth metals, acids, halogens, and metal chlorides are The number of carbon layers of graphite per each layer of inserted substance in an LCG is usually called the stage of LCG (Figure 2). The bonding between an inserted substance and a carbon net of graphite depends on the compound inserted and is known to be of either charge transfer or van der Waals type. However, if a carbon net of graphite is considered as an infinite aromatic molecule, the formation of another type of LCG, namely, complexes of graphite with transition metals, could be expected. In these complexes the carbon net of graphite should act as a polynuclear aromatic ligand. In accordance with Sidgwick's rule, zero-valent metals of group VI (Cr, Mo, W ) form stable bis(arene) complexes. Thus, LCG with these metals can be expected to have a bis(arene) structure. Similar bisarenic complexes could also be expected for Mn(I), Fe(II), Co(III), etc. a-Complexes of allylic and olefinic types should be possible in the case of zero-valent Fe, Co, Ni, Mn, and Cu. Formation of such r-complexes would require localization of a certain number of bonds in the conjugated graphite system a t the expense of some resonance energy. However, this loss might be compensated Journal of the American Chemical Society
1 97:12 1 June
by the energy of complex formation. Actually examples are well known in which a metal atom breaks the conjugation system of benzene producing allylic complexes.I0 However, zero-valent metal L C G could c1 priori have another structure with only weak van der Waals interaction between metal atoms and graphite layers or that of the charge transfer complex type. The present paper deals with the synthesis of L C G with transition metals iron, cobalt, nickel, chromium, molybdenum, tungsten, manganese, and copper and with a study of their structure by X-rays, Mossbauer spectroscopy, and magnetic measurements. Transition metal LCG were prepared by reduction of the metal chloride L C G (FeC13, FeC12, CoC12, NiC12, MnC12, CuC12, MoCIs, WCl6, CrC13). Reduction by means of different reducing agents, hydrogen, sodium borohydride, lithium aluminum hydride, sodium in liquid ammonia, and aromatic anion-radicals (Li, N a , and K naphthalenide and diphenylide and sodium benzophenone ketyl), has been studied. Reduction of the FeC13 LCG by sodium i n liquid ammonia has been previously described by Klotz and Schneider;l reduction of FeC13 to Fe(0) is reported to take place. Later Knappwost and Metzi2-I4confirmed this result and studied magnetic properties of Fe LCG. According to their data iron is not chemically bonded to carbon nets of graphite in the compounds obtained.
Experiments and Results Starting Compounds. The starting compounds were MoCI5, FeC12, FeC13, CoC12, NiC12, MnC12, WCl6, CrC13, and CuC12 LCG of a definite stage and good regularity. 11, 1975
3367 Table I. The Identity Periods (I,) and Thicknesses of the Filled Layers (I,') of Metal Chloride LCG and Metal LCG Metal chloride LCG CIMC1,a FeC1, FeC1, COCI, coc1, MnCl, NiC1, CUCI, CUC1, MoC1, MoC1, MoCL a
9 18
7 13 9 6 6 12 21 34 42
Stage I I1 I I1 I I1 I I1 I1 I11 IV
ICC,
IC,
9.42 12.66 9.45 12.74 9.50 12.70 9.42 12.75 12.54 16.02 19.37
Metal LCG
Stage
IC, A
Fe Fe co co Mn Ni
I I1 I I1 I I1 I I1 I1 111 IV
5.9 9.5 5.8 9.3 5.8 9.3 5.8 9.3 7.3 10.4 13.7
9.42 9.31 9.45 9.39 9.50 9.35 9.42 9.40 9.19 9.32 9.32
Amount of carbon atom per 1 molecule of metal chloride.
AI, =
CU
Cu Mo Mo Mo
AIc, hb
I,', A 5.9 6.15 5.8 5.95 5.8 5.95 5.8 5.95 3.95 3.7 3.65
3.5 3.2 3.6 3.4 3.7 3.4 3.7 3.4 5.2 5.6 5.7
IC (MC1, LCG) - I , (M LCG). Table 11. The Products of Metal Chloride LCG Reduction by NaBH,, LiAIH, , and Na-NH,
T
~Ic
Initial metal chloride LCG FeC1, I stage
1 Figure 1. Structure of graphite
Compounds with MoC15, FeC13, and WCl6 were synthesized by Croft's8 and Rudorffs9 methods by heating graphite-metal salt mixtures in a sealed ampoule in an atmosphere of chlorine or argon or under vacuum. Conditions for the synthesis of these compounds of different stages and their dependence of the graphite's type were described earlier. I 5 I 6 Compounds of CoC12, NiCI2, MnC12, CuC12, and CrCI3 were prepared by chlorination of graphite and metal mixture. FeC12 LCG were obtained by reduction of FeC13 LCG by hydrogen a t 400°.'6 Compositions, stages, identity periods, and thicknesses of the filled layers of initial LCG with metal chlorides are given in Table I. Methods of Investigation. X-Ray studies have been performed both with a one-circle diffractometer "DRON-I" (Cu K a radiation, Ni filter) and with a Debye-Scherer camera (diameter 114 mm, Cu K a and Fe K a radiation). Results are given in Table I . Magnetic measurements have been performed with a magnetic balance by the Faraday method over the temperature range 4.2-300'K and in magnetic fields up to 7 kOe for Fe, Co, Ni, Mn, Cu, Mo, Cr, and W LCG. For some Fe LCG a hysteresis loop has been established at helium and room temperatures in weak fields. Mossbauer Spectra. Fe LCG under investigation served as absorbers in conventional Mossbauer transmission experiments. The absorbers have been molded in plexiglass cells without any binder. The weighed amounts of compounds have been used which gave the density in iron 10-15 mg/ cm2. Mossbauer spectra have been taken on an electrodynamic spectrometer with a multichannel analyzer in a constant acceleration regime, the spectrometer being calibrated with a - F e and sodium nitroprusside spectra a t 300'K. Samples have been studied a t 80 and 300'K, the external magnetic field of H = 20 kOe being normal to the y-quanta beam and applied a t 300'K. The field has been supplied by a permanent magnet system.17 Mossbauer spectra of cobalt LCG were studied on samples containing the 57C0 isotope by an emission Mossbauer spectroscopy method on an apparatus with the moving standard potassium ferrocyanide absorber a t room temperature. Isomeric shifts (IS) in this paper are given as related to sodium nitroprusside, a t 300'K. The L C G composition has Vol'pin et al.
FeC1, I1 stage
NiC1, I1 stage MoC1, I1 stage a
f-.Content, Reducing Solaeent vent T."C
70 -\ H
M U
34.4 35.8
14.25 15.4 10.5 12.1 9.8 17.6 16.2 9.6 9.4 17.5
Traces 6.8 6.0 1.6
19.0
1.7
NH,
25 100 25 66 -30 25 100 25 66 -30
52.7 54.0 48.15 48.35 51.1 54.3 54.2
2.14 2.6 1.1 3.73 0.4 0.5 1.3 1.7 1.4 1.4
NH,
-30
66.0
0.6
NaBH,
H,O
LiAlH,
THF
Na NaBH,
NH3 H,O
LiAIH,
THF
Na Na
B, AI, or N
C
Traces No 3.2 8.9 0.8
M = Fe, Ni, or Mo.
been determined by the spectra areas a t 80'K assuming the constancy off'. Reduction by Hydrogen. The metal chloride LCG were heated in hydrogen flow a t 300' for 4 hr; then the temperature was raised to 400-800" and the heating was continued. In all cases it was found that the metals leave the interlayer space of graphite and the samples obtained contain separate phases of the metal and of the graphite. An exception was the reduction of the MoCls LCG by H2 a t 250-400'. In this case the X-ray diffractograms show lines of the Mo LCG, besides those of metallic M o and free graphite. Reduction by Sodium Borohydride. Four grams of NaBH4 was dissolved in 200 ml of an aqueous or alcoholic solution of KOH and 1.5 g of metal chloride LCG was added on stirring in an argon flow. The reaction mixture was stirred a t room temperature or at reflux for 4 hr. The solid was washed with 10% HCI, water, acetone, and ether and dried a t 120' for 10 hr. The composition of resulting compounds is given in Table 11. Reduction by Lithium Aluminum Hydride. One gram of metal chloride L C G was added to 50 ml of a 10% solution of LiAIH4 in tetrahydrofuran (THF) in argon flow. The
/ Lamellar Compounds of Graphite with Transition Metals
3368 Table 111. The Products of Metal Chloride LCG Reduction by Lithium Diphenylide .-.
Metnl LCG
-
Stage
Way of r M e t a l content, % T treatment0 Analysis Magnetic data
~
F'e
I
Fe
I1
CO
I
Ni
I1
A
1.3
I1 I11 1v
B B B B B
21.0 21.8 19.1 16.1 22.4
A B A B A
B
M0 MO
MO
w
4.6 21.4 1.9 34.8 13.1 28.4
1.5 28.0 1.5 30.0 1.2 22.1 4.8 21.0 b C
d e
a Key: (A) reduced, washed with THF and dried under vacuum; (B) ;is in (.4)and then treated with ethanolic HCI, dried under vacu u m and heated a t 400-600". b Diamagnetic x = -0.96 X cgsrn/g. C Diamagnetic x = - 1.26 X cgsm/g. d Diamagnetic x = ~-1.49 X 10-6 cgsm/g. e Diamagnetic x = - 1 X 10-6 cgsm/g.
mixture was stirred for 4 hr a t room temperature (or a t reflux). The residue was filtered, washed with dry T H F , treated with 10% HCI, washed with water, and dried a t 120" for 10 hr. The composition of resulting compounds is given in Table 11. Reduction by Sodium in Liquid Ammonia. The suspension of 1 g of metal chloride LCG in I00 ml of liquid ammonia was added to 200 ml of a 0.04 M solution of sodium in liquid ammonia a t -70" in a dry argon flow. The mixture was stirred for 4 hr a t -70°, filtered off, and washed with liquid ammonia. The residue was divided into three parts. The first part was dried under vacuum a t room temperature; the second was treated with ethanol and dried a t 120' for 10 hr; the third part was treated in the same way as the second and then heated in hydrogen or argon flow a t 400-600'. The composition of resulting compounds is given in Table 11.
Reduction by Aromatic Anion-Radicals. Three grams of metal chloride LCG was added to 200 ml of a 0.1 M solution of anion-radical in T H F . The mixture was stirred for 2 hr at room temperature and left in the refrigerator for 3 days. The residue was then filtered off, washed with dry T I i F , and divided into three parts. The first part was dried under vacuum a t room temperature for 8 hr. The second part was treated with alcohol, boiled in a mixture of alcohol and 15% HCI ( l : l ) , and then dried under vacuum for 10 hr at 1 20". The third part was treated in the same way as the second and then heated in hydrogen or argon flow a t 400600'. The composition of resulting compounds is given in Table 111. Magnetic Properties of LCG with Metals. Magnetic properties of M o L C G have shown that all reduced compounds a r e diamagnetic (Table III), although the starting Mo
