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An organic material composed of neutral free radicals based on the spirobiphenalenyl system exhibits a room temperature conductivity of 0.3 siemens per centimeter and a high-symmetry crystal structure. It displays the temperature-independent Pauli pararnagnetism characteristic of a metal with a magnetic susceptibility that implies a density of states at the Fermi level of 15.5 states per electron volt per mole. Extended Huckel calculations indicate that the solid is a three-dimensional organic metal with a band width of ~0.5 electron volts. However, the compound shows activated conductivity (activation energy, 0.054 electron volts) and an optical energy gap of 0.34 electron volts. We argue that these apparently contradictory properties are best resolved in terms of the resonating valence-bond ground state originally suggested by Pauling, but with the modifications introduced by Anderson., The familiar properties of inorganic metals, such as the inverse temperature dependence of their conductivity, are well understood in terms of band theory, in which valence electrons populate delocalized states [...]

The nature of single-walled carbon nanotube (SWNT) -solvent interaction, which is responsible for the stabilization of ultrasonicated dispersions, is investigated by various techniques. The degradation of SWNTs was observed under conditions that might be expected to remove covalent functionalities, and the chemical interaction of the sonopolymer with the SWNTs was found to be irreversible.

Research describing the crystallization and characterization of phenyl-based neutral radicals is presented. The paper shows that their conductivity rises on dimerization along with a change from paramagnetic to diamagnetic form.

Research describing the preparation and solid-state properties of peerchlorophenalenyl radicals is presented. The paper shows that the radical is a Mott-Hubbard insulator, owing to the narrow bandwidth resulting from isolation of molecules.

Research is presented describing the preparation, crystallization, and solid-state characterization, of a spiro-biphenalenyl radical which is monomeric in the solid state. Curie behaviour (1 spin per molecule) occurs throughout a 10-400 Kelvin temperature range.

A study was conducted on the design and synthesis of new heterocyclic radicals and radical ions. It presents the complete results of the synthesis of trans-4,4'-dichloro-1,1',2,2',3,3'-tetrathiadiazafulvalene (DC-TAF), and discusses the spin state problem pertaining to its electronic structure. It also describes the preparation and structural characterization of DC-TAF's 1:1 radical ion salts [DC-TAF][X], and reports on the measurements of transport property on [DC-TAF][ClO4].

A study was conducted to analyze the synthesis and properties of a neutral pi-radical molecular conductor. The PAR 273A electrochemical system was utilized to carry out cyclic voltammetry experiments. X-ray data were then determined on ENRAF-Nonius CAD-4 with monochromated MO K-alpha radiation. Moreover, magnetic data and variable-temperature single-crystal conductivity measurements were evaluated against the one-dimensional hopping mechanism for charge transport.

An investigation into the regiochemistry of addition to the fulleroid C61H2 by Zn(Cu) reduction and hydroboration was conducted. One major isomer is formed by hydroboration while two major isomers of C61H4 were formed by the reduction with Zn(Cu). The structures of the major isomers formed by reduction with Zn(Cu) were identified as 1,2-C6H4 and 3,4-C61H4. The regiochemistry observed in the formation of 1,2-C61H4 was the same regiochemistry seen in the further reactivity of azafulleroids.

A study was conducted on the redox, magnetic and structural characteristics of the heterocyclic radical 1,2,5-thiadiazolol[3,4-b]-1,3,2-dithiazolol[3,4-b]pyrazin-2-yl (TDP-DTA). TDP-DTA was prepared by the S3N3Cl3 treatment of 5,6-dithiolo-1,2,5-thiadiazolo[3,4-b]pyrazine and in vacuo fractional sublimation purification. The donor/acceptor characteristics and spin distributions of the radicals were observed to be highly sensitive to 4,5-substituents' nature.

Crystals of the heterocyclic diradical benzo-1,2:4,5-bis(1,3,2-dithiazolyl) (BBDTA) were grown and characterized. X-ray crystallographic analysis revealed that the compound consists of discrete, unassociated molecules that form slipped stacks along the x direction, with the molecular plane making an angle of 32.4 degrees to the x axis. Electron resonance spectrometry showed signals characteristic of partially associated materials and free diradicals. It was also indicated by ab initio calculations that there is a small separation between the triplet and singlet diradical states, measuring approximately 0.5 kcal/mol. Magnetic susceptibility measurements indicated that BBDTA is diamagnetic.

Bis(1,2,3,5-dithiadiazolyl) radicals (S2N2C)-X-(CN2S2) containing a heterocyclic bridging group X = piperazine,thiophene,bithiophene were prepared and characterized. The results indicated that piperazidine- and bithhiophene-bridged diradicals crystallize in the monoclinic space group P2(sub 1/n) and associate as cofacial dimers. The latter feature a herringbone stacking of close interdimer S-S interactions along the backbone.

4,4'-bis(1,2,3,5-dithiadiazolium) dichloride is produced in moderate yield by the condensation of oxamidrazone with sulfur dichloride in acetonitrile. The salt is then reduced by means of triphenylantimony to yield the diradical 4,4'-bis(1,2,3,5-dithiadiazolyl)(S2N2C-CN2S2). Studies show that this radical is disjoint and possesses a very small energy gap between the triplet and diradical singlet states regardless of the torsion angle about the central C-C bond.

The diamagnetic and paramagnetic ring currents present in the carbon allotropes, such as fullerenes and C60, considerably affect the magnetism of these molecules. In C60, the sigma-bond anisotropy causes the endohedral chemical shift. The ring currents are responsible for the chemical shift of the surface protons in C60. The study of magnetism shows the presence of pie-electrons moving in three dimensions.

An analysis of isomers of the higher fullerenes C76, C78, C84 by 3He NMR spectroscopy indicate the presence of at least five C78 isomers and nine C84 isomers. Each isomer produces a single, sharp, characteristic NMR peak resolved from the others. The high-pressure, high-temperature 3He labeling procedure applied to C60 and C70 is used in analysing the higher fullerenes.

The crystals of 1,3- and 1,4-((S2N2C)C6H4(CN2S2))(X) (X = I,Br) are prepared by the cosublimation of 1,3- and 1,4-benzene-bis(1,2,3,5-dithiadiazolyl) and iodine/bromine crystals. The weakly metallic character is confirmed by the magnetic susceptibility and conductivity. Perfect superimposed stacks with interannular spacing are observed in the iodide crystals. Transport properties are also covered for these salts.

Previous high-resolution electron microscopy (HREM) observations of the carbon nanotubes have led to a 'Russian doll' structural model that is based on hollow concentric cylinders capped at both ends. The structures of the carbon nanotubes and particles were characterized here by bulk physical and chemical property measurements. The individual nanostructure is as compressible as graphite in the c axis, and such nanostructures can be intercalated with potassium and rubidium, leading to a saturation composition of '[MC.sub.8]' These results are counter to expectations that are based on a Russian doll structure. HREM after intercalation with potassium and deintercalation indicates that individual nanoparticles are a 'paper-mache' of smaller graphite layers. Direct current magnetization and electron spin resonance measurements indicate that the electronic properties of the nanostructures are distinctly different from those of graphite. Although the nanostructures have distinct morphologies and electronic properties, they are highly defective and have a local structure similar to turbostratic graphite., Modification of the spark erosion technique (1, 2) for the synthesis of fullerenes has led to the discovery (3) and preparation of macroscopic quantities of carbon nanotubes (4). HREM images [...]

A study of the iodine-doped hexagonal phase of 1,2,3, 5-dithiadizolyl reveals P-type doping of a neutral radical. The molecular conductor maintains its basic structure during the doping process by the dopant filling a structural gap. Stoichiometry, cell repeat distance and Raman spectroscopic studies reveal the occurrence of polyiodide in the columnar cavity.

The products 1,2,3,5-dithia- and 1,2,3, 5-diselenadiazolium chloride were obtained when ECL2 (E = S, Se) reacted with N,N,N'-tris(trimethylsilyl)formamidine. X-ray diffraction helps derive the solid state structure of (HCN2S2)2, a cofacial dimer comprising stacked dimers, the asymmetric unit having three of them. Infrared intensities and vibrational frequencies of the sulfur radical have also been observed from experimental vibrational spectra which reveal rotational band envelopes.

The preparation and structural characterization of the 1,3,5-triazine-bridged tris(1,2,3,5-dithiadiazolyl) complex (N3C3(CN2S2)3) were described. The crystals belong to the monoclinic space group C2/c. The crystal structure consists of layers of interlocked dimers, and alternate layers are oriented in an antiparallel fashion. The packing of dimers leads to skewed stacking arrangement and a large number of close interdimer S- - -S contacts.

Van der Waals forces that bind [C.sub.60] molecular solids are found to be sufficient strong to allow the reproducible fabrication of free-standing [C.sub.60] membranes on (100) silicon wafers. Membranes, 2000 to 6000 angstroms thick, were fabricated by a modified silicon micro-machining process and were found to be smooth, flat, and mechanically robust. An important aspect of the silicon-compatible fabrication procedure is the demonstration that [C.sub.60] films can be uniformly and nondestructively thinned in a C[F.sub.4] plasma. Young's modulus and fracture strength measurements were made on membranes with areas larger than 6 millimeters by 7 millimeters. It may be possible to use [C.sub.60] membranes for physical property measurements and applications., The description of a simple technique to produce macroscopic amounts of [C.sub.60] molecules (1) has stimulated numerous investigations into how these molecules can be assembled into solid forms. Crystals (1-3) [...]

The dielectric constant [Epsilon] and conductivity Σ of undoped [C.sub.60] single crystals have been measured as a function of temperature, 10 K < T < 330 K, and frequency, 0.2 kilohertz < f < 100 kilohertz. On cooling below the first-order structural phase transition at 260 K, a Debye-like relaxational contribution to the dielectric response is observed, which requires the presence of permanent electric dipoles. The relaxation rate is thermally activated with a broad distribution of energies centered at 270 millielectron volts. The existence of a dipole moment in [C.sub.60] is unexpected, because it is precluded by symmetry for the pure ordered cubic phase. These data suggest that the high degree of frozen-in orientation disorder of the [C.sub.60] molecules for the existence of electric dipolar activity., The discovery and synthesis of the icosahedral carbon molecule [C.sub.60] [1] and its subsequent crystallization [2] have stimulated great gravity directed toward understanding the static and dynamic properties of its [...]

Thetrifunctional radical 1,3,5-benzenetris(1,2,3,5-dithiadiazolyl) 4,4',4''- (1,3,5-benzenetriyl)tris(1,2,3,5-dithiadiazolyl) was prepared from 1,3,5-benzenetris(N,N,N'-tris(trimethylsilyl)carboxamidine). Structural determination revealed crystals of the complex to belong to the monoclinic space group P21/c. Crystals consist of triradical stacks packed in a pseudo-pinwheel manner with resulting in close S...S contacts. The structure adopted is stable. Higher temperatures are necessary for radical uncoupling butlead to and low sensitivity toward hysteretic magnetic behavior.

A study to isolate the solid-state structures of (Cyanophenyl)dithia- and (Cyanophenyl)diselenadiazolyl radicals was conducted. Condensation of either the free cyanobenzamidine or its N, N'-bis-(trimethylsilyl) lithium salt resulted in the formation of the 3- and 4- cyanophenyl-substituted dithia- and dithia- and diselenadiazolium cations. The solid-state structures are analyzed and described.

Raman, electron spin resonance and microwave loss-superconductivity studies showed that the doping of C60 films generated multiple phase boundaries that remained separate during the entire process. The application of potassium and rubidium dopants produced fullerene films with phases of the types A3C60 and A6C60, wherein the A3C60 phase exhibited superconductivity. Sodium metal also formed the two phases but cesium only produced the A6C60 phase. The doping process of these alkali metals failed to provide superconductivity with C70 films.

A new organic molecular conductor, based on a spiro-biphenalenyl neutral radical, simultaneously exhibits bistability in three physical channels: electrical, optical, and magnetic, in the paramagnetic state, the unpaired electrons are located in the exterior phenalenyl units of the dimer, whereas in the diamagnetic state the electrons migrate to the interior phenalenyl units and spin pair as a π-dimer. Against all expectations, the conductivity increases by two orders of magnitude in the diamagnetic state, and the band gap decreases. This type of multifunctional material has the potential to be used as the basis for new types of electronic devices, where multiple physical channels are used for writing, reading, and transferring information., The processing of information is based on the ability to control and retrieve changes in a particular physical property of a material, such as the electrical, magnetic, or optical response. [...]

Chemical reactions are usually considered to be processes that form and break bonds. This approach suits the analysis of isolated reactions processes, but does not give a general metric enabling ready comparisons between different chemical reactions. Hybridization is introduced as a unifying metric for structural progress in organic reactions, and reference to the Hammond postulate and electrocyclic reactions illustrates the usefulness of such an analysis.

Organic field-effect transistors have been developed that function as either n-channel or p-channel devices, depending on the gate bias. The two active materials are a-hexathienylene (α-6T) and [C.sub.60] The characteristics of these devices depend mainly on the molecular orbital energy levels and transport properties of α-6T and [C.sub.60] The observed effects are not unique to the two materials chosen and can be quite universal provided certain conditions are met. The device can be used as a building block to form low-cost, low-power complementary integrated circuits., Organic transistors have characteristics that make them attractive in applications such as large-area electronics, including low-cost deposition processes, compatibility with plastic substrates, and steadily improving performance. Thin-film transistors (TFFs) with [...]

Elemental carbon can be synthesized in a variety of geometrical forms, from three-dimensional extended structures (diamond) to finite molecules ([C.sub.60] fullerite). Results are presented here on the magnetic susceptibility of [...]

The fullerene [C.sub.60] can be converted into two different structures by high pressure and temperature. They are metastable and revert to pristine [C.sub.60] on reheating to 300°C at ambient pressure. For synthesis temperatures between 300° and 400°C and pressures of 5 gigapascals, a nominal face-centered-cubic structure is produced with a lattice parameter a, = 13.6 angstroms. When treated at 500°to 800°C at the same pressure, [C.sub.60] transforms into a rhombohedral structure with hexagonal lattice parameters of [a.sub.o] = 9.22 angstroms and co = 24.6 angstroms. The intermolecular distance is small enough that a chemical bond can form, in accord with the reduced solubility of the pressure-induced phases. infrared, Raman, and nuclear magnetic resonance studies show a drastic reduction of icosahedral symmetry, as might occur if the [C.sub.60] molecules are linked., Although [C.sub.60] molecules are extremely stable at ambient conditions, nonhydrostatic compression induces a transformation of [C.sub.60] to diamond (1) or unknown structures above 15 GPa (2-4). Light irradiation is also [...]

A new molecular conductor relies on hole doped and electron doped charge transfer for carrier creation. The conductor has energy bands which are created from single-dimensional stacks of neutral pi-radicals. This enables conduction by the transfer of electrons from the conduction band which precedes the doping by an acceptor. The new conductor has a molecular formula of 1,4-phenylene-bis(dithiadiazolyl) diradical 1, 4-((S2N2C)C6H4(CN2S2)).

The alkali-metal fulleride Na2CsC60 is a f.c.c. superconductor with and a value of 14.132 angstroms and a transition temperature (Tc) of 10.5 K. Since cations can occupy the octahedral site of the fulleride, attempts were made to introduce molecular ammonia (NH3) to Na2CsC60. Ammonia was introduced by exposing the sample to 380 torr of NH3 gas distilled from a sodium/liquid-ammonia solution through a vacuum manifold. Introduction of the ion resulted in an increase in a to 14.473 angstroms and an increase in Tc to 29.6K.

Superconductivity has previously been discovered for compounds in which an alkali metal is intercalated with the C(sub 60) fulleride molecule. All such materials have had face-centered cubic crystal structure, but a body-centered cubic phase may be formed by intercalating fulleride with barium. This molecule is also superconducting, and has a ratio of six barium atoms to one fulleride. This ratio gives a different external coordination number for the fulleride than previous superconductors, suggesting that some intrinsic property of the fulleride is responsible for the superconductive mechanism.

The temperature- and concentration-dependent resistivities of annealed [Ca.sub.x][C.sub.60] and [Sr.sub.x][C.sub.60] films were measured near room temperature. Resistivity minima were observed at x = 2 and 5. The resistivities of these films were [rho.sub.min] 1 ohm-centimeter for x = 2 and [rho.sub.min] [10.sup.-2] ohm-centimeter for x = 5. This latter value is comparable to the resistivities found in similar experiments on [K.sub.3][C.sub.60] films. There is a maximum in the resistivity between x = 2 and 3, and another at x 7. The conductivity is activated over the whole range of compositions, and the activation energy scales with the logarithm of the resistivity. The results suggest that the conductivity and superconductivity observed in [Ca.sub.5][C.sub.60] are associated with the population of bands derived from the [t.sub.1g] level of [C.sub.60]., Solid [C.sub.60] and [C.sub.70] undergo doping with alkali metals to produce conductors[1]. For A = K or Rb, the [A.sub.3][C.sub.60] phases are superconductors[2-5]. It has been shown that Ca intercalates [...]

The room temperature Raman spectra of the intramolecular modes between 100 [cm.sup.-1] and 2000 [cm.sup.-1] are reported for alkali-metal doped [A.sub.x.C.sub.60] films. For A + K, Rb, and Cs, phase separation is observed with the spectra of [C.sub.60], [K.sub.3.C.sub.60], [K.sub.6.C.sub.60], [Rb.sub.3.C.sub.60], [Rb.sub.6.C.sub.60], and [Cs.sub.6.C.sub.60] phases reported. The x = 3 phases show only three Raman active modes: two of [A.sub.g] symmetry and only the lowest frequency [H.sub.g] mode. The other [H.sub.g] modes regain intensity in the x = 6 films, with several mode splittings observed. For A = Na, such phase separation is not clearly observed, and reduced mode shifts are interpreted as due to incomplete charge transfer in these films., CONDUCTING [1] AND SUPERCONDUCTING [2] compounds of [A.sub.x.C.sub.60] (0 [is less than or =] x [is less than or =] 6) have recently been prepared by intercalating alkali metals (A) [...]

THE DISCOVERY OF NEW METHODS of synthesis of fullerene carbon molecules [1] has led to a proliferation of studies of the properties of solid [C.sub.60] [2-6]. Most of these studies [...]

A novel approach toward development of advanced chemical sensors based on chemically functionalized single-walled carbon nanotubes (SWNTs) is demonstrated. P2-SWNTs exposed to 100 ppm NH3 exhibit a behavior, which is typical of pristine SWNTs.