215
Electrically Conducting Metal Dithiolate-Perylene Complexes (15) A. R . Kazanjian and D. R. Horreli, Radiat. Effects, 13, 277 (1972). (16) For a good review of curium and its chemistry, see C. Keiiar, "The Chemistry of the Transuranium Elements," Verlag Chemie GmbH, Weinheim, West Germany, 1971, p 529. (17) H. J. Groh, R. T. Huntoon, C. S. Schlea, J. A. Smith, and F. H. Springer, Nucl. Applications, 1, 327 (1965). (18) J. T. Lowe, W. H . Hale, and D. F. Hallman, lnd. Eng. Chem., ProcessDes. Develop., 10, 136 (1971). (19) W. Davis, Jr., and H. J. deBruin, J. lnorg. Nucl. Chem., 26, 1069 (1964). (20) W. J. Kerrigan and R. S. Dorsett, J. lnorg. Nucl. Chem., 34, 3603 (1972). (21) C. Kellar, "The Chemistry of the Transuranium Elements," Veriag Chemie GmbH, Weinheim, West Germany, 1971, p 530. (22) W. F. Linke, "Solubilities of Inorganic and Metal Organic Compounds," 4th ed, Vol. 1, Van Nostrand, New York, N. Y., 1958, p 1078.
(23) W. F. Linke, "Solubilities of Inorganic and Metal Organic Compounds," 4th ed, Voi. 2, Van Nostrand, New York, N. y . , 1958, p 1229. (24) C. N. Trumbore and E. J. Hart, J. Phys. Chem., 63, 867 (19591. (25) M. V. Vladimirova and Z. V. Ershova, Proc. 2nd. All-Union Conf. Radiat. Chem., 166 (1962). (26) I. G. Draganic and Z. D. Draganic, "The Radiation Chemistry of Water," Academic Press, New York, N. Y., 1971, p 76. (27) J. M. Cleveland, "The Chemistry of Plutonium," Gordon and Breach, New York, N. Y., 1970, p 54. (28) R. W. Matthews, H. A. Mahiman, and T. J. Sworski, J. Phys. Chem., 76,2690 (1972). (29) M. Anbar, "Fundamental Processes in Radiation Chemistry," P. Ausloos, Ed., Interscience, New York, N. Y.,1968, p 660. (30) C. E. Burchill and I. S. Ginns, Can. J. Chem., 48, 1232 (1970). (31) C. E. Burchill and I. S. Ginns, Can. J. Chem., 48, 2628 (1970).
Electrically Conducting Metal Dithiolate-Perylene Complexes Luis Alcacer Laboratorio de Fisica e Engenharia Nucieares, Sacavem, Portugal
and August
H. Maki*
Department of Chemistry, University of California, Riverside, California 92502 (ReceivedAugust 29, 7973) Publication costs assisted by the National Science Foundation
We report on the preparation and some properties of a series of electrically conducting molecular complexes of the general formula (perylene)z[MS4C4(CN)4], with M = Ni, Cu, or Pd. Room temperature conductivities of the order of 50 (Q cm)-l were observed on single crystals of the nickel complex, and slightly lower values on the others. The high electrical conductivities are attributed to the existence of relatively wide energy bands associated with positively charged linear chains of perylene molecules. The complexes behave as simple intrinsic semiconductors over the temperature range investigated.
Molecular complexes such as the salts of tetracyanoquinodimethane, TCNQ,1-3 and some perylene-halogen comp l e ~ e sare ~ - known ~ to be highly conductive. In this paper, we wish to report on the preparation, characterization, and conductivity results of a series of molecular complexes of perylene, I, and several planar bis(maleonitriledithio1ene)-metal chelates, 11, M = Ni, Cu, or Pd,7 which exhibit electrical conductivities up to 50 (Q cm1-l at room temperature.
I
I1
Experimental Section and Results Preparation of the Complexes and Characterization. The complexes, of general formula (C20H12)2[M&C4(CN)4], M = Ni, Cu, or Pd were prepared by two different met hods.
(i) By electrolysis, in a manner similar to the synthesis of pyrene and perylene perchlorate.8 Controlled potential electrolysis a t +1.03 V us. sce of a 200 ml dichloromethane soluand 2 tion containing 1 mmol of (n-C4Hg)++N[MS4C4(CN)4] mmol of perylene after a few hours yielded needle crystals on the anode surface. They were then removed, washed with dichloromethane and pentane, and dried. (ii) By oxidation of perylene with iodine in the presence of (n-C4H9)4N[MS4C4(CN)4]according to the reaction
A dichloromethane solution containing 2 mmol of perylene was added to a solution of the same solvent containing 1 mmol of ( ~ Z - C ~ H ~ ) ~ N [ M S ~ C and ~ ( aC large N ) ~ ]excess of iodine. A portion of the solvent was slowly evaporated by gently heating and then let cool to room temperature. After 3-4 hr the complex was collected, washed, and dried. Elemental analyses for the nickel complex obtained by both methods gave the stoichiometry indicated above. As an example, the results obtained on a batch prepared by method ii are given. Calcd for ( C ~ O H & [ N ~ S ~ C ~ ( C N ) ~ ] : C, 68.33; H, 2.86; N, 6.64; S, 15.20. Found: C, 68.02; H, The Journal of Physical Chemistry, Vol. 78, No. 3, 1974
Luis Alcacer and August H. Maki
TABLE I: Conductivity Parameters
4b
c
Conductivity,
-
0; at20°
AE,
2-
Compound
(s2 cm)-l
eV
50 6 0.07
0 .lo2
0-
(C20H12)2(NiS4C4(CN)41 single crystal (C20H12)~[CuS4C4(CN)4] single crystal (CZoH12)z [PdS&a(CN)4]pellet
-
0.128 0.168
The dimensions of the unit cell were determined by X-ray diffraction methods for ( C ~ O H I ~ ) ~ [ C U S ~ C ~ ( C N ) ~ ] giving c = 4.06 A, l/a* = 15.11 A; lib* = 20.33 A; y* = 70.4"; with 1.5 formula units per unit cell, and a calculated -4 density of 1.61 in good agreement with a measured density of 1.62 f 0.01 using flotation methods. At least one of the axes is doubled and the unit cell contains a multiple of -6 three formula units. In the case of the nickel complex, due to the very small thickness of the needles, we could only estimate one of the axes to be 4.06 A as in the copper analog. -8 Electrical and Magnetic Properties in the Solid State. Electrical conductivities, using a four probe method, were 3 measured along the needle axis of single crystals of the -10 nickel and copper complexes and on a compressed pellet of the palladium complex. The samples were mounted on epoxy plates and the contacts were made with silver paint. The sample holder was placed in a copper can surrounded by a heating element. This was put in a stainless steel cylinder and placed in a liquid nitrogen cryostat. An Figure 1. Temperature dependence of the electrical conductivity: ( 1 ) ( C Z O H ~ Z ) Z N ~ S ~ C ~single ( C N ) ~crystal; , (2) (C20H12)2automatic arrangement was used which slowly increased CUS~C~(CN single ) ~ , crystal; (3) ( C ~ O H , ~ ) ~ P ~ S ~comC ~ ( C Nor) ~decreased , the temperature of the sample. A constant pressed pellet. current of order of 50 ,.LA was drawn through the sample while the voltage developed across the two sensing probes was being measured with a Cary vibrating reed electrome2.96; N, 6.57; S, 15.04. Method ii usually gave better ter, and plotted on an X-Y recorder against the output of yields but larger needles were obtained by i. The coma temperature-sensing copper-constantan thermocouple plexes are insoluble in most solvents, except nitrobenzene placed near the sample. Table I summarizes the results of and acetonitrile. However, they cannot be recrystallized the measurements of the conductivity parameters, accordfrom either because the perylene positive ion tends to deing to the usual relation u = uo exp(-AE/2kT). This is compose even in degassed solutions of highly purified solseen from Figure 1 to hold over the entire temperature vents. range investigated, viz. from 77 to 300 K. Quantitative measurements of the epr spectra also were Magnetic susceptibility measurements, using a Faraday used to characterize these complexes. For balance, gave a Curie-Weiss behavior for the nickel com(C20H&[NiS4C4( CN)4] the epr spectra obtained in a niplex, with e = -60 K and a magnetic moment of 2.2 BM. trobenzene solution yield the absorptions characteristic of The room temperature epr spectrum of this compound in (g = 2.063)? and the ionic species [NiS&(CN)4]the polycrystalline form shows a broad single line with a g (C2oH12)+ (g = 2.003).9 The integrated epr intensities of value of 2.012, the line width being of order of 600 G. In cation and anion signals corrected for the first-order decay the copper complex the resonance consists of a single line rate of the unstable cation radical were compared to those ~ ( C N )with ~ I . g = 2.020, 68-G wide at room temperature, which of a standard solution of ( ~ - C ~ H S ) ~ N [ N ~ S ~ C The narrows to 55 G at 77 K. The behavior of the magnetic intensities corresponded to one cation spin and one anion susceptibility and epr spectra as a function of temperaspin per formula weight of 869 f 40. This is in good agreeture of the palladium complex, also in the polycrystalline ment with the composition (C20H12)(C2oH12) form, suggests an exchange interaction between the anion [NiS4C*(CN)4]- (FW = 843.72). In the solid state the and cation spins as well as a nearly temperature indepencomplex (C~oH12)2+ is likely to be found. dent contribution to the susceptibility by the perylene Further epr measurements were made on solutions of molecular ions. the copper and palladium analogs and agreed, within exA detailed study of the magnetic properties of these perimental error, with the general formula complexes is in progress. (C2'OH12)(C20H12)+[MS4C4(CN)4]-, where M = Cu or Pd. In the same manner as above, the intensities corresponded Discussion to one cation spin and one anion spin per formula weight Based on the crystallographic data, electrical and magof 820 f 40 for the copper complex (FW = 848.6) and 930 netic properties, and on similarities between our comf 40 for the palladium complex (FW = 891.4). In the case pounds and other highly conductive complexes, such as of the copper complex, the monoanion was first reduced to the TCNQ salts,lOJl we suggest that the structure of the paramagnetic dinegative ion with p-phenylenediamine in both the standard and the sample. these perylene complexes consists of stacks of (C20H12)2+ -2
-
-
+-
The Journal of Physical Chemistry, Vol. 78, No. 3, 1974
Electrically Conducting Metal Dithiolate-Perylene Complexes complexes with the [M&C4(CN)4]- anions located between the columns. As far as the electrical conductivity goes, these complexes behave, over the investigated temperature range, like simple intrinsic semiconductors consisting of a filled valence band and empty conduction band at 0°K. In the limit of low electronic density, Le., when the Fermi-Dirac distribution function can be substituted by the Boltzmann distribution, taking the effective masses of electrons and holes to be equal and considering the most common case of acoustic mode phonon scattering giving a mobility proportional to ( k n - 3 ’ 2 , we have for the electrical conductivity u = uo exp( - E , / k T ) where Eg is half the band gap. As mentioned above, this expression is in good agreement with the observed conductivities. The applicability of the Curie-Weiss law to fit the magnetic susceptibility data for the nickel complex is certainly questionable. In solution we found two unpaired electrons, one in each ion, while in the solid, the magnetic moment calculated from x = C / ( T 60) is only 2.2 BM. This indicates strong interaction, either between the anion and cation or more likely within the cation system. The values of the effective magnetic moment calculated from the Curie law range from 2.01 BM a t room temperature to 1.66BM at 77 K. These properties are consistent with a band model if we assume a band system due to a perylene linear lattice, and a set of localized or short-range extended states due to the anion lattice. The perylene set of bands with a relatively wide conduction band is responsible for the high conductivity and would also account for the strong interaction predicted from the susceptibility data on the nickel complex and the Pauli-type contribution to the susceptibility observed in our samples of the palladium com-
+
217
plex.12 Such features of the band structure are associated with large overlap integrals between the molecular orbitals of neighboring perylene molecules. A related ionic complex of tetrathiotetracene (TIT) with nickel thiete, Ni[S4C4(CF3)4l1 (Nith), has been reported recently by Geiger.13 In contrast with the com(Nith)- has an extremely plexes reported here, (TIT)+ low electrical conductivity at room temperature [a (0 cm)-l].
-
Acknowledgment. The authors are indebted to Professor J. Kommandeur and Professor F. Gutman for many interesting discussions, as well as to Professor R. Wing for his help with the crystallographic data. This work was partly supported by a grant from the National Science Foundation (Grant No. GP 27298) for which we are grateful. References and Notes D. S. Acker, R. J. Harder, W. R. Hertler, W. Mahler, L. R. Melby, R. E. Benson, and W. E. Mochel, J. Amer. Chem. SOC., 82, 6408 (1960). R. G. Kepler, P. E. Bierstedt, and R. E. Merrifield, Phys. Rev. Lett., 5, 11 (1960). F. Gutman and L. E. Lyons, “Organic Semiconductors,” Wiley, New York, N. Y., 1967. T. Uchidaand H. Akamatu, Bull. Chem. SOC.Jap., 34, 1015 (1961). M. Labes, R. Seher, and M. Bose, J. Chem. Phys., 33,868 (1960). J. Komrnandeur and F. Hall, J. Chem. Phys., 34, 129 (1961). A. Davison, N. Edelstein, R. H. Holm, and A. H. Maki. Inorg. Chem., 2, 1227 (1963). T. C. Chiang, A. H. Reddoch, and D. F. Williams, J. Chem. Phys., 54,2051 (1971). T. C. Chiang and A. H. Reddoch, J. Chem. Phys., 52,1371 (1970). H. Kobayashi, Y. Olashi, F. Maruma, and Y. Saito, Acta Crystallogr., Sect. 5, 26, 459 (1970), and references therein. H. Kobayashi, F. Maruma, and Y. Saito, Acta Crystallogr., Sect. B, 27,373 (1971). A similar situation is reported for an arenchromium-TCNQ complex: A. V. Zvarykina, Y. S. Karimov, R. B. Ljubovsky, M. K. Makova, M. L. Khidekel, I. F. Shegolev, and E. B. Yagubsky, Mol. Cryst. Liq. Cryst., 11, 217 (1970). W.E. Geiger, Jr., J. Phys. Chem., 77, 1862 (1973).
The Journal of Physical Chemistry, Vol. 78. No. 3. 1974
