Organic ion-radical salts having the electrical properties of metals and elements having a layer containing these salts are disclosed. The salts are salts of a chalcogenated tetracene donor compound and an electron acceptor compound wherein the ratio of donor compound to acceptor compound is from about 3:1 to about 1.5:1. These salts have a resistivity less than about 10.sup.-2 ohm-cm at 295.degree. K. The salts are further characterized by a resistivity that decreases with decreasing temperature. A vapor phase process for preparing these organic metals is also disclosed. The process comprises the steps of: PA1 1. forming a first vapor comprising the chalcogenated tetracene compound; PA1 2. forming a second vapor comprising the electron acceptor compound; and PA1 3. reacting the first vapor with the second vapor at a temperature of about 75.degree. C to about 300.degree. C in a substantially inert atmosphere.

FIELD OF THE INVENTION 
This invention relates to novel organic materials and to a process for 
their preparation. More particularly, this invention relates to 
chalcogenated tetracene ion-radical salts having metallic electrical 
properties. 
DISCUSSION OF THE PRIOR ART 
Many organic compounds are known to have semiconducting properties. These 
compounds characteristically have a conductivity in the range of 10.sup.2 
to 10.sup.-9 (ohm-cm).sup.-1. Recently, several organic compounds have 
been discovered which have higher conductivity. These compounds are 
considered to be metals or metal-like in that they have a conductivity 
greater than 10.sup.2 (ohm-cm).sup.-1 and further because their 
conductivity increases with decreasing temperature. In a typical 
semiconductor, the concentration of electrons and hence conductivity is 
dependent on the presence of thermally excited electrons. Thus, the 
conductivity in a semiconductor decreases with decreasing temperature 
according to a Boltzmann-type relationship. The resistivity of an ordinary 
semiconductor compound may be described by the formula: 
EQU .rho. = .rho..sub.o exp (E.sub.a /kT) 
where .rho. is the resistivity; .rho..sub.o is a constant; E.sub.a is the 
activation energy required to free an electron; k is Boltzmann's constant; 
and T is the absolute temperature (see U.S. Pat. No. 3,433,165). By 
contrast, a metal depends on the presence of delocalized electrons for 
conductivity and therefore, the conductivity increases with decreasing 
temperature as the electrical resistance due to scattering of electrons by 
lattice vibrations is decreased. 
The general requirements for the design and synthesis of organic metals are 
set forth by Garito and Heeger in Accounts of Chemical Research, 7,232 
(1974). If the unpaired electrons delocalize over all the electron sites 
in the compound, the compound attains a metallic state. If, on the other 
hand, the electrons localize on individual sites the compound may be an 
insulator or at best a semiconductor. To attain the metallic state Garito 
and Heeger set forth three basic criteria: 
1. THE EXISTENCE OF UNPAIRED ELECTRONS; 
2. A UNIFORM CRYSTAL STRUCTURE; AND 
3. RELATIVELY WEAK ELECTRON-ELECTRON REPULSIVE INTERACTIONS. In spite of 
these general guidelines, it is extremely difficult to predict in advance 
which compounds are going to have metallic properties. The second criteria 
is the most difficult to achieve because of the unpredictability of the 
crystalline structure of organic compounds. For example, compounds of 
N-methylphenazinium-tetracyanoquinodimethane can exist as two structures 
which differ only in the location of the ion radicals within the structure 
(L. B. Coleman, S. K. Khanna, A. F. Garito, A. J. Heeger and B. Morosin, 
Physics Letters, 42A, (1), 15 (1972). The conductivity of these two 
compounds, which are stoichiometrically identical, may differ by as much 
as six orders of magnitude. 
There are only a limited number of organic compounds which are known to 
have the electrical properties of a metal. These compounds are ion-radical 
salts. The term "ion-radical salt" as used herein refers to a complex of 
an electron donating species and an electron accepting species in which 
the species are in an ionized form in the ground state of the complex. 
Ion-radical salts are also known in the art as "dative-type 
charge-transfer salts" and sometimes simply "charge-transfer salts". These 
compounds are formed by the transfer of electrons between a donor compound 
and an acceptor compound. 
Most of the known organic metals are based on tetracyanoquinodimethane 
(TCNQ) as the acceptor compound with tetrathiofulvalene (TTF), 
tetraselenofulvalene (TSF), hexamethylenetetraselenofulvalene (HMTSF) and 
other substituted TTF and TSF molecules as electron donor compounds. The 
TTF-TCNQ family of compounds suffer several disadvantages when used as 
conductors. Most importantly, TTF-type molecules are extremely difficult 
to synthesize. Thus, compounds of the TTF-type, having the required 
purity, are extremely expensive. Further, the known TTF-TCNQ type of 
compound is relatively unstable. For example, the ratio .rho.(60 
K)/.rho.(300 K) is observed to be a sensitive indicator of sample quality 
in TTF-TCNQ. Crystals of TTF-TCNQ measured several months after synthesis 
exhibit values of .rho.(60 K)/.rho.(300 K) considerably smaller than 
crystals measured immediately after synthesis, indicating instability of 
the material. 
Various tetracene-related compounds are known in the art. However, known 
compounds from this family are semiconductors rather than metals. In U.S. 
Pat. No. 3,403,165, Matsunaga describes semiconducting tetrathiotetracene 
compounds. Matsunaga describes the temperature dependence of the 
resistivity of his compounds as following the usual exponential 
relationship for semiconductor compounds described above. Of the compounds 
of Matsunaga, those demonstrating the lowest resistivities with highest 
thermal stabilities are represented by the formula: 
EQU [D].sub.3 [A].sub.n 
where the donor compound D is tetrathiotetracene and A is selected from 
o-chloranil, o-bromanil and o-iodanil and tetracyanoethylene. The integer 
n is defined as 1 except when A is tetracyanoethylene in which case n is 
2. The Matsunaga patent is directed to semiconductors and does not 
describe metallic compounds. 
In U.S. Pat. No. 3,629,158, E. A. Perez-Albuerne describes certain 
chalcogenated tetracene ion-radical salts. Again, all of these salts are 
semiconductor compounds and do not have the conductivity or the 
conductivity-temperature dependence of metals. The donor compound of 
Perez-Albuerne can be tetrathiotetracene and the electron acceptor 
compound can be any of a large number of anion-forming species. Other 
patents of Perez-Albuerne describing similar materials include U.S. Pat. 
Nos. 3,634,336 and 3,627,655. 
There is a great need for relatively stable, inexpensive organic compounds 
which have the electrical properties of metals. While several organic 
metals and numerous organic semiconductors are known in the art, at the 
present stage of development no organic compound has all of these desired 
properties. 
STATEMENT OF THE INVENTION 
I have found that certain ion-radical salts of a chalcogenated tetracene 
have the electrical properties of a metal when the molar ratio of 
chalcogenated tetracene to acceptor compound is in the range from about 
3:1 to about 1.5:1. Compounds of the invention have an electric 
resistivity at 295.degree. K that is less than about 10.sup.-2 ohm-cm. 
These compounds are further characterized in that their resistivity 
decreases with decreasing temperature according to the formula 
EQU .rho. = .rho..sub.o + CT.sup.2 
where .rho. is the resistivity, .rho..sub.o and C are constants which 
depend on the particular compound, and T is the absolute temperature. This 
form of the temperature dependence of the resistivity is characteristic of 
known organic metals (see S. Etemad, T. Penney, E. M. Engler, B. A. Scott 
and P. E. Seiden, Phys. Rev. Lett. 34 (12), 741 (1975) and S. N. Bloch et 
al, Phys. Rev. Lett. 34 (25) 1561 (1975)) and of transition metals at low 
temperatures (see N. V. Volkenshtein, V. P. Dyakina and V. E. Startsev, 
"Scattering Mechanisms of Conduction Electrons in Transition Metals at Low 
Temperatures", Phys. Stat. Sol. 657, 9, (1973)). Such a temperature 
dependence is predicted by theory for an electron-electron scattering (see 
C. Kittel, Introduction to Solid State Physics, 3rd. Ed., 238 (1966, J. 
Wiley, NY)). 
In another aspect, I provide an element comprising a support having thereon 
a layer containing the chalcogenated tetracene metallic ion-radical salts 
of the invention. In still another aspect, I provide a novel vapor phase 
process for the preparation of these compounds which comprise the steps of 
1. forming a first vapor comprising the tetracene donor compound; 
2. forming a second vapor comprising the acceptor compound; and 
3. reacting the first vapor with the second vapor at a temperature of about 
75.degree. C to about 300.degree. C in a substantially inert atmosphere.

DETAILED DESCRIPTION OF THE INVENTION 
As mentioned above, the organic metal compounds of the present invention 
are chalcogenated tetracene ion-radical salts wherein the ratio of 
chalcogenated tetracene donor compound to electron acceptor compound is 
about 3:1 to about 1.5:1. The preferred ratio is 2:1. Chalcogenated 
tetracenes include tetrathiotetracene, tetraselenotetracene and 
tetratellurotetracene. 
The acceptor compound may be any of a wide variety of compounds which are 
capable of forming an ion-radical salt with a chalcogenated tetracene and 
which results in an organic compound whose resistivity decreases with 
decreasing temperature. Thus, the acceptor compound may be any element or 
compound having enough oxidizing power to produce the chalcogenated 
tetracene ion radical. Preferred acceptor compounds include halogen 
compounds, particularly iodine. 
Compositions of matter within the scope of the present invention include 
compounds having the formula: 
EQU (D.sub.x).sup.n.spsp.+ (A).sup.n.spsp.- 
wherein (D.sub.x).sup.n.spsp.+ is a chalcogenated tetracene complex cation 
selected from the group consisting of complex cations of 
tetrathiotetracene, tetraselenotetracene and tetratellurotetracene, and A 
is an anion selected from the group consisting of 
a. an inorganic anion selected from the group consisting of Br.sub.3.sup.-, 
I.sub.3.sup.-, F.sup.-, Cl.sup.-, Br.sup.-, I.sup.-, SCN.sup.-, nitrate, 
sulfate, phosphate, fluoroborate, ferricyanide, molybdate, tungstate and 
the like; and 
b. an organic anion derived from an organic acid selected from the group 
consisting of: an aliphatic monocarboxylic acid, an aliphatic dicarboxylic 
acid, an aliphatic polycarboxylic acid, an unsaturated carboxylic acid, an 
aromatic carboxylic acid, a sulfonic acid, a heterocyclic acid containing 
from 5 to 6 atoms in the heterocyclic nucleus and having at least one 
hetero atom selected from the group consisting of a nitrogen, oxygen or 
sulfur atom; a monohydric phenol, a polyhydric phenol and 
p-toluenesulfonate and the like. The above organic anions may also be 
attached to polymeric backbones. 
x represents the molar ratio of D to A and has a value between about 3:1 
and about 1.5:1 and is preferably about 2:1; 
n is an integer between 1 and 5 and is preferably one or two. 
The term "complex cation", represented by the symbol 
(D.sub.x).sup.n.spsp.+, is defined as a group of chalcogenated tetracene 
moieties (D) taken x times. To this group a positive charge of value 
n.sup.+ is balanced with one anion of charge n.sup.- to achieve charge 
neutrality. The values of n are restricted to integers but x may be 
integers or non-integers such that n.sup.+ and n.sup.- are balanced. 
The chalcogenated tetracene compounds are well known in the art and may be 
prepared by any of several processes. Particularly useful processes for 
preparing chalcogenated tetracene compounds are described in U.S. Pat. No. 
3,723,417 of E. A. Perez-Albuerne and in C. Marchalk, Bull. Soc. Chim, 
France, 19, 800 (1952). 
As mentioned previously, the term "organic metal" refers to organic 
compounds which behave as metals, that is, they are compounds which have 
an electrical conductivity greater than 10.sup.2 reciprocal ohm-cm at 
295.degree. K and whose conductivity increases with decreasing 
temperature. The organic metals of the present invention are further 
characterized in that their spin magnetic susceptibility is only very 
weakly dependent on temperature. The temperature independent spin magnetic 
susceptibility of the compounds of the present invention is attributed to 
delocalized electrons yielding the temperature independent Pauli spin 
paramagnetism that is a characteristic of a metal. By comparison, the spin 
magnetic susceptibility of a semiconductor compound such as described in 
the Perez-Albuerne patents and the Matsunaga patent increases with 
decreasing temperature as a result of the localization of the electrons. A 
discussion of the measurement of spin magnetic susceptibility may be found 
in C. Kittel, Introduction to Solid State Physics, (3rd Ed.) John Wiley, 
N.Y., (1966), p. 446, and J. M. Ziman, Principles of the Theory of Solids, 
Cambridge University Press, London, (1972) p. 332. 
The room temperature conductivity and other electrical properties of the 
compounds of the present invention can vary depending on the specific 
donor compound and acceptor compound. Typically, the conductivity of the 
compounds at 295.degree. K is in the range of about 10.sup.2 to about 
10.sup.4 reciprocal (ohm-cm).sup.-1, although higher conductivities are 
possible. Illustrative of the conductivity of these compounds is the 
conductivity of (tetrathiotetracene.sub.2).sup.+ (I.sub.3).sup.- which is 
about 1000 (ohm-cm).sup.-1 at 295.degree. K. The conductivity of this 
compound increases with decreasing temperature and is about 2700 
(ohm-cm).sup.-1 at 85.degree. K. 
As used herein, conductivity is measured on the single crystal of the 
compound using the four-probe method. The four-probe method is well known 
in the art and consists of attaching four electrodes to a single crystal 
of the compound whose conductivity is to be measured. Compounds grown by 
the vapor phase method such as described herein may be needle-like single 
crystals having a length of about 1 mm to about 4 mm, although other sizes 
may also be grown. An electrode is attached to either end of the 
needle-like crystal while two electrodes are attached near the middle of 
the crystal. The electrodes may be attached by any method known in the 
art. For example, a colloidal suspension of graphite in polystyrene may be 
"painted" on a portion of the crystal and a copper wire imbedded therein 
to form the electrode. Current is passed between the two end electrodes 
while the voltage drop is measured across the two middle electrodes. Using 
this method, the effect of the electrode resistance is greatly reduced. A 
discussion of the four-probe method as used herein may be found in Phys. 
Rev. B7, 2122 (1973). 
The compounds of the present invention may exist in several different 
forms. Large single crystals having anisotropic electrical conductivity 
and optical properties may be prepared. The compounds may also be in the 
form of powders or thin transparent films. Because of their high degree of 
optical anisotropy, these compounds may be useful in a variety of 
applications. An anisotropic single crystal or assembly of oriented 
microcrystals may be used in optical devices such as polarizers. Because 
of their high conductivity these compounds may be useful in a wide variety 
of applications. The powders may be coated in layers so as to serve as 
antistatic layers for photographic elements and the like. Thin films of 
the compounds of the present invention similarly may be used as antistatic 
layers for photographic elements. Thin films may also be used as 
conducting electrodes for electrophotographic elements, for photovoltaic 
devices and the like. These compounds are particularly useful because 
their electrical properties do not substantially change on extended 
exposure to ambient conditions. 
Therefore, because of these advantageous properties, another aspect of the 
present invention is an element comprising a support having thereon a 
layer containing the organic metals of the present invention. The organic 
metal may be directly deposited on the support in the form of a thin film 
by the vapor phase process of the present invention or the powder form of 
the compound may be dispersed in a binder which may then be coated on the 
support. 
When the organic metal is to be dispersed in a binder, the binder should be 
chosen so as not to affect the electrical properties of the organic metal. 
Any of a wide variety of film-forming materials are suitable. Suitable 
binders include: natural resins including gelatin, cellulose ester 
derivatives and the like; vinyl resins including polyvinyl esters, vinyl 
chloride and vinylidene chloride polymers, styrene polymers such as 
polystyrene and the like, methacrylic acid ester polymers, polyolefins, 
poly(vinyl acetals), poly(vinyl alcohol); polycondensates including 
polyesters, polyamides, ketone resins, phenolformaldehyde resins and the 
like; silicon resins; and alkyd resins such as styrene-alkyd resins, 
silicone-alkyd resins, soya-alkyd resins and the like. 
The organic metal is typically mixed with the binder and solvent to form 
the coating composition. The organic metal-binder-solvent coating 
composition is typically coated on the support and the solvent is 
evaporated leaving an organic metal-binder layer coated on the support. 
The solvent is chosen so that the binder is soluble therein. Typical 
solvents include alcohols including aliphatic alcohols, aromatic alcohols, 
polyhydric alcohols, substituted alcohols, ketones, chlorinated 
hydrocarbons, aromatic hydrocarbons, organic carboxylic acids, substituted 
carboxylic acids, lower dialkylsulfoxides and water. Mixtures of these 
solvents may also be used. Preferred solvents are alcohols, ketones, 
chlorinated solvents, water, and the like. 
In preparing the elements of the present invention using the organic metal 
with a binder, useful results are obtained wherein the organic metal is 
present in an amount equal to at least about 10 weight percent of the 
coated layer. The upper limit for the amount of organic metal present 
varies widely. The organic metal may comprise up to about 100 weight 
percent of the coated layer. A preferred weight range for the organic 
metal is from about 20 weight percent to about 90 weight percent. Coated 
thickness of the organic metal-binder layer on the support can vary 
widely. Typically, the dry coating has a thickness of about 0.05 .mu.m to 
about 5 .mu.m, however, coatings having a thickness outside of this range 
are also useful. A preferred range for the thickness of the layers of the 
present invention comprising a binder is about 0.1 .mu.m to about 1 .mu.m. 
Because of the high conductivity of the compounds of the present 
invention, thin films (binderless films generally formed in situ) can be 
thin enough to be essentially transparent and still provide useful 
conductivity. Typically, the thin films have a thickness range of about 
0.005 .mu.m to about 5 .mu.m, however, coatings outside of this range are 
also useful. The preferred range of the coating thickness of the thin 
films is from about 0.01 .mu.m to about 1 .mu.m. 
The organic metal-containing layers may be coated on any of a wide variety 
of suitable substrates. Illustrative substrates include fibers, films, 
glass, paper, metals and the like. 
As mentioned previously, the elements of the present invention are useful 
in preparing a wide variety of articles of manufacture. For example, one 
such use is in anti-static photographic film elements comprising an inert 
film support (which may carry a subbing layer to improve adhesion), a 
conducting layer containing one of the organic metals described herein and 
a silver halide emulsion layer which is sensitive to electromagnetic 
radiation. These layers can be arranged having the conducting layer and 
the emulsion layer on each side of the support, and also both layers can 
be on the same side, with either one on top of the other. In some cases, 
it is desirable to include additional layers of insulating polymer which 
can be incorporated into the element, either below, between or above any 
of the above-mentioned layers. 
Another use is in anti-static magnetic tape, comprising the same 
arrangement of layers as in the above-described photographic film element, 
with the exception that the photographic emulsion is replaced by a 
suitable layer of magnetic material. 
A further use is in a direct electron recording film element comprising an 
inert insulating film support (which may carry a subbing layer to improve 
adhesion), a conducting layer containing one of the organic metals 
described herein and a layer of a silver halide emulsion which is 
sensitive to electron beams. In this case, both layers are placed on one 
side of the support with either one on top of the other. Also, additional 
layers of insulating polymer may be incorporated, as in the preceding 
elements, to provide particular advantages such as improvement of 
adhesion, elimination of undesirable changes in the electron-sensitivity 
of the emulsion, etc. 
A fourth use is in electrophotographic elements, comprising a conducting 
layer which contains one of the organic metals described herein. The 
conducting layer is coated on an inert support, and on top of the 
conducting layer is a second layer containing a photoconductor. Additional 
thin layers of insulating polymers may also be included in this case, as 
in the preceding elements, which may be located below, between or on top 
of the conducting and photoconductive layers. 
Another use is in the preparation of optically transparent conducting 
elements. These elements have a conducting layer containing an organic 
metal described herein applied to an insulating inert support. The 
thickness of the conductive layer is such that the resultant optical 
density is not more than about 0.5 in the spectral range from 400 to 700 
nm. Such an element is used in the manufacture of anti-static windows for 
electronic instruments; anti-static lenses for cameras; and other optical 
devices; transparent heating panels; photographic products; etc. 
Static-free woven goods also can contain the organic metals described 
herein. Fibers containing the organic metal can be incorporated in woven 
goods as the sole component or mixed with non-conducting fibers. 
In electronic components, the organic metal can be applied to an insulating 
support and shaped in any desired way to give passive electronic 
components such as resistors or capacitors. Also, the organic metal can be 
incorporated as part of active components such as rectifiers or 
transistors. 
In another aspect of the present invention there is provided a novel 
process for the preparation of the chalcogenated tetracene compounds 
described herein. Using this process, chalcogenated tetracene ion-radical 
salts may be prepared easily and rapidly with high purity and sample 
quality. The process comprises the steps of 
1. forming a first vapor comprising a chalcogenated tetracene donor 
compound; 
2. forming a second vapor comprising an acceptor compound; and 
3. reacting the first vapor with the second vapor at a temperature of about 
75.degree. C to about 300.degree. C in a substantially inert atmosphere. 
Apparatus for carrying out the process of the present invention may take 
many forms. For example, a flow type reactor may be provided. In such an 
apparatus there is a first chamber containing the desired chalcogenated 
tetracene donor compound and a second chamber containing the desired 
acceptor compound. These chambers may be evacuated and separately brought 
to a temperature at which the compound therein forms a vapor. These vapors 
may be injected into a reaction chamber, either directly or by means of an 
inert carrier gas, where they react to form the desired product. 
DESCRIPTION OF FIG. 1 IN THE DRAWINGS 
A preferred process is carried out in a tube furnace shown in FIG. 1. In 
FIG. 1 there is shown a vacuum chamber 10 which is capable of being 
evacuated to very low pressures by vacuum pump 12. Vacuum chamber 10 is 
connected to vacuum pump 12 through valve 24. Typically, the vacuum 
chamber is evacuated to a pressure below the vapor pressure of the 
acceptor compound. Inside the vacuum chamber, there is a quartz boat 14 
containing the chalcogenated tetracene donor compound. Also in the vacuum 
chamber there are quartz collecting tubes 16. Heating means 18 surround 
the vacuum chamber so that the chamber may be heated to the reaction 
temperature. A receptacle 20 for the acceptor compound is connected to the 
vacuum chamber 10 through valve 22. The temperature of receptacle 20 may 
be controlled by means 26 so as to provide control of the vapor pressure 
of the acceptor compound within the apparatus. Depending on the vapor 
pressure characteristics of the acceptor compound, means 26 may be heating 
or cooling means. 
To form the compounds of the present invention using the apparatus 
described above, the vacuum chamber 10 and receptacle 20 are initially 
evacuated with both valves 22 and 24 open, whereupon valve 24 is closed. 
The vacuum chamber 10 is then heated by heating means 18 to a temperature 
above the sublimation point of the chalcogenated tetracene. If necessary, 
the temperature of receptacle 20 is adjusted so that there is sufficient 
vapor of the acceptor compound in vacuum chamber 10 to react with the 
chalcogenated tetracene. The desired product begins to form immediately on 
the walls of the vacuum chamber 10, the quartz collecting tubes 16 and in 
quartz boat 14. When the reaction is complete, that is when either all of 
the chalcogenated tetracene or the acceptor compound is consumed, the 
temperature of the vacuum chamber 10 is reduced, valve 22 is closed and 
valve 24 is opened. The apparatus is then reevacuated by vacuum pump 12 to 
remove excess acceptor compound. Thin films of the compounds of the 
present invention may also be formed using apparatus similar to that 
described in detail above. To produce a thin film, a suitable support is 
included in the vacuum chamber and the compound is deposited on the 
support. To promote the formation of thin films the support may be kept at 
a slightly lower temperature than the reactant temperature. Thus, thin 
films may be formed when the support is kept near a temperature of about 
150.degree. C to 200.degree. C when the reactants are at about 200.degree. 
C to 300.degree. C. 
The total pressure during the reaction step may vary over wide ranges. The 
total pressure may be adjusted by a suitable inert gas such as argon, 
nitrogen, helium, and the like. The total pressure may be from very low 
vacuum such as 10.sup.-5 torr and below up to atmospheric pressure. 
Typically, the rate of reaction decreases somewhat with increasing total 
pressure and the preferred range is therefore from about 10.sup.-5 torr to 
about 150 torr. As mentioned previously, reaction between the donor vapor 
and acceptor vapor occurs between about 75.degree. C to 300.degree. C. 
Rate of reaction increases with increasing temperature and the preferred 
temperature range is from about 200.degree. C to 300.degree. C. 
As used herein, "substantially inert atmosphere" includes any atmosphere 
which is substantially free of compounds which will react with the donor 
compound, the acceptor compound or the organic metal. This criteria is of 
course met where the donor compound and acceptor compound are the only 
compounds present, i.e., the atmosphere is otherwise a vacuum. An 
atmosphere of an inert gas such as argon, nitrogen, helium and the like is 
also suitable. 
The following examples illustrate the invention: 
EXAMPLE 1 
Tetrathiotetracene was synthesized according to the procedure described in 
U.S. Pat. No. 3,723,417 and recrystallized from nitrobenzene. The 
tetrathiotetracene was further purified by two sublimations and was placed 
in a quartz boat located in the center of a tube furnace as described in 
FIG. 1. Solid iodine was placed in receptacle 20 while valve 24 was closed 
and valve 22 was open. The iodine was condensed with liquid nitrogen. 
Valve 24 was opened and the apparatus was evacuated by an oil diffusion 
pump 12 to 10.sup.-5 torr and valve 24 was closed. The tetrathiotetracene 
in the quartz boat 14 was heated to a temperature of 225.degree. C while 
the iodine receptacle 20 was maintained at room temperature. After the 
tetrathiotetracene and iodine were consumed, the oven was cooled to 
100.degree. C, valve 22 was closed and the apparatus was reevacuated by 
opening valve 24 and operating the vacuum pump 12. The crystals which had 
formed in the quartz boat and on the quartz collecting tube which had the 
composition (tetrathiotetracene.sub.2).sup.+ (I.sub.3).sup.- had well 
formed edges, smooth faces and a brilliant gold metallic luster. 
The direct current resistivity of the single crystals which were grown on 
the quartz collecting tubes 16 was measured along the axis having the 
highest conductivity using the four-probe technique described above. FIG. 
3 shows a plot of the ratio of the resistivity at a given temperature to 
the resistivity at room temperature versus the temperature in degrees 
Kelvin. The resistivity generally follows the expression: 
EQU resistivity = 0.27+(8.088 .times. 10.sup.-6)T.sup.2 
where T is temperature in degrees Kelvin. 
EXAMPLE 2 
This is a comparative example. 
The spin magnetic susceptibility of the (tetrathiotetracene.sub.2).sup.+ 
(I.sub.3).sup.- formed in Example 1 was measured as a function of 
temperature. Similarly, the spin magnetic susceptibility of 
(tetrathiotetracene).sub.1.14 (iodide) as described in U.S. Pat. No. 
3,629,158 was also measured as a function of temperature. FIG. 2 is a plot 
of that data. (Tetrathiotetracene).sub.1.14 (iodide) shows the 
characteristic spin magnetic susceptibility of a semiconductor. That is, 
the spin magnetic susceptibility increases with decreasing temperature. 
The spin magnetic susceptibility of (tetrathiotetracene.sub.2).sup.+ 
(I.sub.3).sup.- of the present invention is only slightly dependent on 
temperature and decreases with decreasing temperature which is 
characteristic of metallic compounds. 
EXAMPLE 3 
The resistance using the conventional four-probe technique of a crystal of 
(tetrathiotetracene.sub.2).sup.+ (I.sub.3).sup.- was measured one week 
after synthesis and found to be 910 (ohm-cm).sup.-1 at 290.degree. K and 
2800 (ohm-cm).sup.-1 at 85.degree. K. After 12 weeks of storage under 
ambient conditions, the resistance of the same crystal was again measured. 
It was found to be 910 (ohm-cm).sup.-1 at 290.degree. K and 2800 
(ohm-cm).sup.-1 at 85.degree. K. 
Thus, the metallic compounds of this invention are quite stable as compared 
to the TTF compounds described in Solid State Communications, 17, pp 
367-372, (1975). 
The invention has been described in detail with particular reference to 
certain preferred embodiments thereof, but it will be understood that 
variations and modifications can be effected within the spirit and scope 
of the invention.