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On the “orthorhombic form of C60” molecular crystals containing CS2
PHYSICAG
Physica C 184 (1991) 21-23 North-Holland
On the "orthorhombic form of C6o" Molecular crystals containing CS2 B. Morosin, P.P. Newcomer, R.J. Baughman, E.L. Venturini, D. Loy a n d J.E. Schirber Sandia National Laboratories, Albuquerque, NM 87185, USA Received 6 September ! 991 Revised manuscript received 2 October 1991
Crystals of orthorhombic symmetry obtained on evaporation of CS2 solutions of C6o contain solvent moleculesre.~herthan representing a new lower density form of pure C6o. Introduction of 12into the CS2 solutions yieldscrystalscontainingsolid solu-
tions, i.e. C6o"1.5(CS2,12). Bothtypes of crystals degraderapidly in X-ray radiation.
1. Introduction
We recently became aware of results by Kikuchi and coworkers [ 1 ] on crystals of C6o grown from CS2. T h e s e preliminary diffraction results appear to agree with those we had obtained with respect to symmetry, Pbnm, and our unit cell parameters (24.97(6), 25.52(3), and 9.98( 1 ) A for a, b and c, respectively; see comment below); however, not with respecl to our observed density (1.75 g/cc). Such crystals contain solvent molecules and are C6o" 1,5 CS2. Some 12 will replace part of the CS2 if it is introduced into the solutions. Most striking to us is the rapid radiation degradation of the crystals.
2. Experimental
We have grown crystals of C6o from CS2 solutions in the form of long black (brownish-black if very thin) laths up to 10 mm long (growth along the caxis) similar to those reported by Kikuchi and coworkers. The same crystal form is obtained if 12 is also dissolved in the solution forming solid solutions or alloys of the form C6o" 1.5 (CS2,12). For example, one preparation gave crystals with a = 2 5 . 0 0 ( 4 ) , b=25.90(4), c= 10.01 ( 1 ) A and measured density of 1.95 g/cc suggesting about 40% replacement of CS2 by 12 molecules. Such crystal surfaces are shiny and
remain so stored in semidarkness even at elevated temperatures. We have crystals which are more than 5 weeks old stored primarily in the dark at ambient as well as in a refrigerator which give excellent sharp X-ray photographs during the first few hours of irradiation. Energy dispersive X-ray analysis on selected crystals confirm the presence of S or S and I depending on the initial solution. Precession photographs as well as single crystal diffractometer data show the crystals belong to Pbnm symmetry as grown. Exposure to X-ray radiation induces significant damage with extended exposure. Thus, we have obtained lattice parameters employing the stronger, but lower two-theta reflections and have observed changes to such values upon several hours of exposure to the Mo Ka radiation. For example, employing "check" or standard reflections during data coilectio-, a crystal grown from pure CS2 showed no change w~th respect to the (002) reflection while the (501) lost an order of magnitude in its intensity over a 38 h time frame; similarly, an I2 containing alloy showed no change with respect to the (002) reflection while the ( i 32 ) degraded by an order of magnitude in 27 h. Cu Kct also appears to show a similar degradation of the crystal quality. It should be noted that our crystals grown slowly from toluene ( ~ 0.3 mm prism) of the cubic Fm3m form (a = 14.19 ( 1 ) ~, in agreement with others [ 2 ] ) show no such radiation damage to exposures of many days.
0921-4534/91/$03.50 © 1991 ElsevierScience PublishersB.V. All rights reserved.
22
B. Morosin et al. / On the orthorhombic form of C6o
Fig. I. Preces3ionphotographson a C60"1.5CS2crystal subjected to long term X-ray radiation during normal intensitydata collection. Top, hOI and Okl zones before data collection;bottom, identical zones followingdata collection. Note the similarityof the two bottom photos as the crystalapproaches tetragonalsymmetry. Precession photographs taken after such radiation damage show that the glide planes as well as the repeat distances normal to the c-axis undergo large changes (fig. 1); however, the c-direction remains intact explaining the reason why the (002) reflection remained essentially constant in the above data collections. Such radiation damaged crystals approach tetragonal symmetry. Both the pure CS2 and alloy crystals were examined for superconductivity using an RF induction coil down tG 4 K [ 3 ]. None of the crystals to date proved :o be superconducting. Low temperature (2.5-5.0 K) static magnetization data for a sample containing several C60"1.5CS2 crystals (2.1 mg total mass) show a paramagnetic signal varying as 1/T. After correc-
tion for the reported diamagnetism of C6o ( Z , , = - 2 6 0 cgs ppm [ 4 ] ) and of CS2 ( Z m = - 4 2 . 2 cgs ppm), the paramagnetic signal has a molar susceptibility Zm= 1.0× l0 -3 at 4.3 K and 1.7X 10 - 3 at 2.5 K. Assuming Curie behavior due to isolated spins of ~ with g = 2 , this paramagnetism corresponds to roughly 1 spin per 100 C6o" 1.5CS2 molecules. Efforts to detect these spins with room temperature electron paramagnetic resonance were unsuccessful.
3. Concluding remarks In summary, we conclude that the orthorhombic crystals formed by evaporation of solutions of C6o in
B. Morosin et al. / On the orthorhombic form of C6o
23
C S 2 a r e C6o" 1.5CS 2 rather than a new morphology of
References
~.rystalline C6o. The formation of C6o" 1.5 (CS2,I2) alloys is not surprising given that the molar volume for the two molecules, obtained from crystal data, are 82.9 A 3 and 85. l A 3 for CS2 and 12, respectively [ 5 ]. The shorter 2.66 A l - I separation compared with that for the sum of the linear S - C - S distances, 3.10 ~ , is offset by the larger Van der Waal contact distance for I compared with S. In either case, the overall length of these molecules are less than the c-axis length, determined by close contact of the C6o molecules stacked along that direction. The cell volume also agrees within experimental errors with the sum of the molar volume of the CS2 and the C6o molecules (employing those determined by the crystal structure of the two constituent materials) [ 5 ].
/ [ I ] K. Kikuchi, S. Suzuki, K. Saito, H. Shiromaru, I. Ikemoto, Y. Achiba, A. Zakhidov, A. Ugawa, K. lmaeda, H. Inokuchi and K. Yakushi, Proc. M2S-HTSC Ill, 22-26 July 1991, Kanazawa, Japan, Physica C 185-189 ( 1991 ) 415. [2] R.M. Fleming, (others) Mater. Res. Soc. Symp. Proc., in press; J. Ibers, ACA Toledo Meeting, 22-26 July 1991. [3] L.J. Azevedo, J.E. Schirber, J.M. Williams, MA. Beno and D.R. Stephens, Phys. Rev. B (1984) 1570. [4] R.C. Haddon, L.F. Schn~ meyer, J.V. Waszczak, S. H. Glarum, R. Tycko, G. Dabbagh, A.R. Kortan, A.J. Muller, A.M. Mujsce, M.J. Rosseinsky, S.M. Zahurak, A.V. Makhija, F.A. Thiel, K. Raghacachari, E. Cockayne and V. Elser, Nature 350 ( 1991 ) 46. [ 5 ] Crystal Data: Determinative Tables, eds. J.D.H. Donnay and H.M. Ondik, JCPDS ( 1973 ).
Physica C 184 (1991) 21-23 North-Holland
On the "orthorhombic form of C6o" Molecular crystals containing CS2 B. Morosin, P.P. Newcomer, R.J. Baughman, E.L. Venturini, D. Loy a n d J.E. Schirber Sandia National Laboratories, Albuquerque, NM 87185, USA Received 6 September ! 991 Revised manuscript received 2 October 1991
Crystals of orthorhombic symmetry obtained on evaporation of CS2 solutions of C6o contain solvent moleculesre.~herthan representing a new lower density form of pure C6o. Introduction of 12into the CS2 solutions yieldscrystalscontainingsolid solu-
tions, i.e. C6o"1.5(CS2,12). Bothtypes of crystals degraderapidly in X-ray radiation.
1. Introduction
We recently became aware of results by Kikuchi and coworkers [ 1 ] on crystals of C6o grown from CS2. T h e s e preliminary diffraction results appear to agree with those we had obtained with respect to symmetry, Pbnm, and our unit cell parameters (24.97(6), 25.52(3), and 9.98( 1 ) A for a, b and c, respectively; see comment below); however, not with respecl to our observed density (1.75 g/cc). Such crystals contain solvent molecules and are C6o" 1,5 CS2. Some 12 will replace part of the CS2 if it is introduced into the solutions. Most striking to us is the rapid radiation degradation of the crystals.
2. Experimental
We have grown crystals of C6o from CS2 solutions in the form of long black (brownish-black if very thin) laths up to 10 mm long (growth along the caxis) similar to those reported by Kikuchi and coworkers. The same crystal form is obtained if 12 is also dissolved in the solution forming solid solutions or alloys of the form C6o" 1.5 (CS2,12). For example, one preparation gave crystals with a = 2 5 . 0 0 ( 4 ) , b=25.90(4), c= 10.01 ( 1 ) A and measured density of 1.95 g/cc suggesting about 40% replacement of CS2 by 12 molecules. Such crystal surfaces are shiny and
remain so stored in semidarkness even at elevated temperatures. We have crystals which are more than 5 weeks old stored primarily in the dark at ambient as well as in a refrigerator which give excellent sharp X-ray photographs during the first few hours of irradiation. Energy dispersive X-ray analysis on selected crystals confirm the presence of S or S and I depending on the initial solution. Precession photographs as well as single crystal diffractometer data show the crystals belong to Pbnm symmetry as grown. Exposure to X-ray radiation induces significant damage with extended exposure. Thus, we have obtained lattice parameters employing the stronger, but lower two-theta reflections and have observed changes to such values upon several hours of exposure to the Mo Ka radiation. For example, employing "check" or standard reflections during data coilectio-, a crystal grown from pure CS2 showed no change w~th respect to the (002) reflection while the (501) lost an order of magnitude in its intensity over a 38 h time frame; similarly, an I2 containing alloy showed no change with respect to the (002) reflection while the ( i 32 ) degraded by an order of magnitude in 27 h. Cu Kct also appears to show a similar degradation of the crystal quality. It should be noted that our crystals grown slowly from toluene ( ~ 0.3 mm prism) of the cubic Fm3m form (a = 14.19 ( 1 ) ~, in agreement with others [ 2 ] ) show no such radiation damage to exposures of many days.
0921-4534/91/$03.50 © 1991 ElsevierScience PublishersB.V. All rights reserved.
22
B. Morosin et al. / On the orthorhombic form of C6o
Fig. I. Preces3ionphotographson a C60"1.5CS2crystal subjected to long term X-ray radiation during normal intensitydata collection. Top, hOI and Okl zones before data collection;bottom, identical zones followingdata collection. Note the similarityof the two bottom photos as the crystalapproaches tetragonalsymmetry. Precession photographs taken after such radiation damage show that the glide planes as well as the repeat distances normal to the c-axis undergo large changes (fig. 1); however, the c-direction remains intact explaining the reason why the (002) reflection remained essentially constant in the above data collections. Such radiation damaged crystals approach tetragonal symmetry. Both the pure CS2 and alloy crystals were examined for superconductivity using an RF induction coil down tG 4 K [ 3 ]. None of the crystals to date proved :o be superconducting. Low temperature (2.5-5.0 K) static magnetization data for a sample containing several C60"1.5CS2 crystals (2.1 mg total mass) show a paramagnetic signal varying as 1/T. After correc-
tion for the reported diamagnetism of C6o ( Z , , = - 2 6 0 cgs ppm [ 4 ] ) and of CS2 ( Z m = - 4 2 . 2 cgs ppm), the paramagnetic signal has a molar susceptibility Zm= 1.0× l0 -3 at 4.3 K and 1.7X 10 - 3 at 2.5 K. Assuming Curie behavior due to isolated spins of ~ with g = 2 , this paramagnetism corresponds to roughly 1 spin per 100 C6o" 1.5CS2 molecules. Efforts to detect these spins with room temperature electron paramagnetic resonance were unsuccessful.
3. Concluding remarks In summary, we conclude that the orthorhombic crystals formed by evaporation of solutions of C6o in
B. Morosin et al. / On the orthorhombic form of C6o
23
C S 2 a r e C6o" 1.5CS 2 rather than a new morphology of
References
~.rystalline C6o. The formation of C6o" 1.5 (CS2,I2) alloys is not surprising given that the molar volume for the two molecules, obtained from crystal data, are 82.9 A 3 and 85. l A 3 for CS2 and 12, respectively [ 5 ]. The shorter 2.66 A l - I separation compared with that for the sum of the linear S - C - S distances, 3.10 ~ , is offset by the larger Van der Waal contact distance for I compared with S. In either case, the overall length of these molecules are less than the c-axis length, determined by close contact of the C6o molecules stacked along that direction. The cell volume also agrees within experimental errors with the sum of the molar volume of the CS2 and the C6o molecules (employing those determined by the crystal structure of the two constituent materials) [ 5 ].
/ [ I ] K. Kikuchi, S. Suzuki, K. Saito, H. Shiromaru, I. Ikemoto, Y. Achiba, A. Zakhidov, A. Ugawa, K. lmaeda, H. Inokuchi and K. Yakushi, Proc. M2S-HTSC Ill, 22-26 July 1991, Kanazawa, Japan, Physica C 185-189 ( 1991 ) 415. [2] R.M. Fleming, (others) Mater. Res. Soc. Symp. Proc., in press; J. Ibers, ACA Toledo Meeting, 22-26 July 1991. [3] L.J. Azevedo, J.E. Schirber, J.M. Williams, MA. Beno and D.R. Stephens, Phys. Rev. B (1984) 1570. [4] R.C. Haddon, L.F. Schn~ meyer, J.V. Waszczak, S. H. Glarum, R. Tycko, G. Dabbagh, A.R. Kortan, A.J. Muller, A.M. Mujsce, M.J. Rosseinsky, S.M. Zahurak, A.V. Makhija, F.A. Thiel, K. Raghacachari, E. Cockayne and V. Elser, Nature 350 ( 1991 ) 46. [ 5 ] Crystal Data: Determinative Tables, eds. J.D.H. Donnay and H.M. Ondik, JCPDS ( 1973 ).