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Electric-arc produced as-prepared single-walled carbon nanotube (AP-SWNT) films have been purified by a selective oxidation process. The purification is monitored by near-infrared (NIR) spectroscopy, which gives a quantitative estimate of relative purities. This technique also gives an estimate of the change in relative amounts of SWNTs and amorphous carbon impurities after each purification step, thereby providing accurate and selective control over the oxidation process. Oxidation was carried out by reaction in flowing oxygen at different temperatures and for different durations of time; the purity was evaluated after each oxidation step and compared to the starting as-prepared film. The purities and amounts of SWNTs and carbonaceous impurities were monitored as a function of oxidation temperature and time. Optimization of the process allowed a 3-fold improvement in the AP-SWNT purity with almost quantitative retention of the SWNT portion of the sample. A purification efficiency is defined, which is exp...

The nature of single-walled carbon nanotube (SWNT)−solvent interaction that is responsible for the stabilization of ultrasonicated dispersions was investigated using various techniques. It was found that the sonochemical decomposition and polymerization of o-dichlorobenzene (ODCB) is necessary for the stabilization of SWNTs in ODCB. The rate of decomposition of ODCB was shown to be dependent on the shape of the sonication vessel. The decomposition products of sonicated ODCB interact irreversibly with SWNTs. Under similar sonication conditions, N,N-dimethylformamide (DMF) did not induce discernible modification of the near-infrared spectrum of the dispersed SWNTs.

We report the crystal structure of a spiro-bis(1,9-disubstituted-phenalenyl)boron cation ( 2 + ) and by comparison with the structures of a series of radicals we conclude that the changes in bond lengths in the radicals compared to those of the corresponding cation can be qualitatively predicted by the sign of the partial bond order of the singly occupied molecular orbital (SOMO), which contains the additional electron. By use of this information, we can analyse the structures of the π-dimer radicals 1 and 2 and ascertain the location of the unpaired electron in these compounds. Where these radicals exist as paramagnetic π-dimers (high-temperature regime), the unpaired electrons reside mainly in the phenalenyl units not directly involved in the π-dimer interaction. At low temperatures, where the diamagnetic π-dimers exist, the electrons localise in the phenalenyl units directly involved in the π-dimer, but there still exists some degree of delocalisation of the electrons to the other halves of the molecules. We postulate that the increase in delocalisation of the unpaired electrons is related to the increase of the conductivity by about two orders of magnitude as the electrons spin pair.

We report the pressure dependence for the radial (omega R) and tangential (omega T) band frequencies in debundled single-walled carbon nanotubes (SWNTs) derived from laser-synthesized SWNT bundles. As previously described, a chemical procedure was used to prepare debundled SWNTs from as-prepared, large SWNT bundles. The normalized pressure coefficient for omega R in the debundled sample was compared with the corresponding value in the bundled sample to quantify the strength of van der Waals interactions between tubes in these nanotube materials. Furthermore, the pressure dependences for the radial (omega R) and tangential (omega T) band frequencies in debundled tubes were also compared with corresponding dependences predicted for isolated SWNTs, obtained with generalized tight binding molecular dynamic (GTBMD) simulations described in our previous work. The results presented here collectively suggest that the van der Waals interaction is still strong in the debundled sample studied here, which contained predominantly small bundles of SWNTs rather than isolated tubes.

We report a rapid, quantitative procedure for the evaluation of the carbonaceous purity of bulk quantities of as-prepared single-walled carbon nanotube (SWNT) soot by the utilization of solution-phase near-IR spectroscopy. The procedure starts with two steps of homogenization followed by solution/dispersion spectroscopy of a representative part of the bulk sample. The purity is evaluated against a reference sample by utilizing the region of the second interband transition (S22) for semiconducting SWNTs. The procedure is found to be capable of reliably analyzing the carbonaceous purity of a 10-g batch of SWNTs produced by the electric arc discharge method to within 3%.

A new class of phenalenyl-based neutral radical molecular conductors has recently been reported; a distinctive feature of these molecular solids is the absence of the well-defined conducting pathway(s) that are characteristic of the organic charge- transfer salts. These radicals do not stack in the solid state, and the requisite carbon- carbon contacts are all larger than the sum of the van der Waals distances. Magnetic susceptibility measurements show that these compounds usually exist as isolated free radicals with one spin per molecule (at least over some temperature range), apparently supporting the idea that there is little interaction between the molecules in the solid state. Nevertheless, these radicals show the highest conductivity (RT 0.05 S/cm) of any neutral organic solid and the conduction mechanism is at present unresolved. In this article we report a structurally related radical with a resistivity five orders of magnitude higher than that of the previously reported radicals. We analyze the crystallographic and electronic structure of this solid in detail and point out some of the challenges that remain in relating structure, magnetism, and conductivity in this new class of organic solids. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 853- 865, 2003

The passage of a current through a solid requires a pathway for the movement of electrons or holes. A new class of phenalenyl-based neutral radical molecular conductors has recently been reported; a distinctive feature of these molecular solids is the absence of any obvious conducting pathway(s). These radicals do not stack in the solid state, and the requisite carbon−carbon contacts are all larger than the sum of the van der Waals distances. Magnetic susceptibility measurements show that the first compound to be isolated behaves as a free radical with one spin per molecule, apparently supporting the idea that there is little interaction between the molecules in the solid state. Nevertheless, this radical shows the highest conductivity (σRT = 0.05 S/cm), of any neutral organic solid, and the conduction mechanism is presently unresolved. In the present study, we report a structurally related radical with a resistivity 4 orders of magnitude higher than that of the previously reported radicals. We analyze th...

Alkylation of the zwitterionic heterocycle 8-chloro-bis[1,2,3]dithiazolo[4,5-b:5',4'-e]pyridine (ClBP) with alkyl triflates affords 8-chloro-4-alkyl-4H-bis[1,2,3]dithiazolo[4,5-b:5',4'-e]pyridin-2-ium triflates [ClBPR][OTf] (R = Me, Et, Pr). Reduction of these salts with decamethylferrocene affords the corresponding ClBPR radicals as thermally stable crystalline solids. The radicals have been characterized in solution by cyclic voltammetry and EPR spectroscopy. Measured electrochemical cell potentials and computed (B3LYP/6-31G) gas-phase disproportionation enthalpies are consistent with a low on-site Coulombic barrier U to charge transfer in the solid state. The crystal structures of ClBPR (R = Me, Et, Pr) have been determined by X-ray crystallography (at 293 K). All three structures consist of slipped pi-stacks of undimerized radicals, with many close intermolecular S.S contacts. ClBPMe undergoes a phase transition at 93 K to a slightly modified slipped pi-stack arrangement, the structure of which has also been established crystallographically (at 25 K). Variable-temperature magnetic and conductivity measurements have been performed, and the results interpreted in light of extended Hückel band calculations. The room-temperature conductivities of ClBPR systems (sigma(RT) approximately 10(-)(5) to 10(-)(6) S cm(-)(1)), as well as the weak 1D ferromagnetism exhibited by ClBPMe, are interpreted in terms of weak intermolecular overlap along the pi-stacks. The latter is caused by slippage of the molecular plates, a feature necessitated by the steric size of the R and Cl groups on the pyridine ring.

The hydrofullerenes C(60)H(2) (1) and C(60)H(6) (2) have been prepared in (13)C-enriched form and 2D INADEQUATE NMR spectra were measured. These spectra have provided unambiguous (13)C assignments for 2, and nearly unambiguous assignments for 1. In both cases, the most downfield resonances are immediately adjacent to the sp(3) carbons, despite the fact that these carbons are the least pyramidalized carbons in the molecule. Typically, (13)C chemical shifts move downfield with increasing pyramidalization (THETA(p)), but in these systems there is no strong correlation between THETA(p) and delta. HF-GIAO calculations are able to predict the chemical shifts, but provide little chemical insight into the origin of these chemical shifts. London theory reveals a significant paramagnetic ring current in 1, a feature that helps explain the (1)H shifts in these compounds and may contribute to the (13)C chemical shifts as well.

Purification of single-walled carbon nanotubes by capillary electrophoresis (CE) is demonstrated. Real-time Raman spectroscopy of the separation process and single-wavelength UV/vis detection show the ability of CE to provide high-resolution separations of nanotube fractions with baseline separation. AFM images of collected fractions demonstrate that separations are based on tube length. The separation method is suggested to be based on alignment of the nanotubes along the separation field.

We report EHT calculations of the band electronic structure of substituted pentacene derivatives and the polymorphs of the parent compound. The results show that there are wide disparities among the bandwidths and electronic dimensionalities of these compounds. The parent pentacene polymorphs are 2-dimensional in their band electronic structure with moderate dispersions; the bandwidths in the 14.1 Å d-spacing polymorph are noticeably larger than for the 14.5 Å d-spacing polymorph, reported by Campbell. Whereas the parent pentacene polymorphs adopt the well-known herringbone packing, the new, substituted pentacenes are noticeably different in their solid state structures and this is reflected in the band electronic structures. TMS adopts a highly 1-dimensional structure that leads to a large bandwidth along the stacking direction; TIPS also adopts a stacked structure, but because the molecules are laterally interleaved in the fashion of bricks in a wall, this compound is strongly 2-dimensional.

Advances in the chemical vapor deposition (CVD) growth of graphene have made this material a very attractive candidate for a number of applications including transparent conductors, electronics, optoeletronics, biomedical devices and energy storage. The CVD method requires transfer of graphene on a desired substrate and this is most commonly accomplished with polymers. The removal of polymer carriers is achieved with organic solvents or thermal treatment which makes this approach inappropriate for application to plastic thin films such as polyethylene terephthalate substrates. An ultraclean graphene transfer method under mild conditions is highly desired. In this article, we report a naphthalene-assisted graphene transfer technique which provides a reliable route to residue-free transfer of graphene to both hard and flexible substrates. The quality of the transferred graphene was characterized with atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. Field effect transistors, based on the naphthalene-transfered graphene, were fabricated and characterized. This work has the potential to broaden the applications of CVD graphene in fields where ultraclean graphene and mild graphene transfer conditions are required.

Lithium-sulfur (Li-S) batteries are one of the most promising energy storage technologies because of the high theoretical capacity of sulfur as cathode. However, the high electrical resistivity of sulfur and the dissolution of lithium polysulfides into electrolytes are greatly limiting the performance of Li-S batteries. Interestingly, when the sulfur confinement size is smaller than 1 nm, different electrochemical behaviors and excellent cycle stabilities have been observed. However, the mechanism of sub-nano confinement of sulfur has not been investigated in details. Single-walled carbon nanotubes (SWCNTs) with their various pore size, uniform pore size distribution, and excellent electron conductivity are ideal hosts for studying the effect of different sulfur confinement sizes. In this study, we investigate the effect of sulfur confinement size by incorporating sulfur into both EA- (electric arc) and HiPco- (high-pressure carbon monoxide) SWCNTs with diameter of 1.55 ± 0.1 and 1.0 ± 0.2 nm, respectively. Interestingly, when sulfur is incorporated into HiPco-SWCNTs, the polymerized long chain sulfur molecules inside the tubes largely changes the Raman spectra. The giant Raman response from the sulfur provides an ideal opportunity to perform in situ studies on the lithiation-delithiation reactions of the confined sulfur. High-resolution TEM images confirm the chain structure of sulfur in EA- and HiPco-SWCNTs. Cyclic voltammetry and galvanostatic charge–discharge are performed by using different electrolytes, and sulfur in EA- and HiPco-SWCNTs show distinctively different electrochemical behaviors. In situ Raman spectra and ex situ XPS are measured during galvanostatic charge–discharge to investigate the lithiation-delithiation mechanism. A solid-state reaction mechanism was proposed when sulfur is in sub-nano confinement.

We report the crystallization of a subsitutionally doped organic conductor based on a host lattice composed of spiro-bis(phenalenyl)boron radicals. Co-crystallization of solutions of spiro-bis(9-oxidophenalenone)boron radical [PLY(O,O)]2B mixed with selected amounts of spiro-bis(9-oxidophenalenone)beryllium [PLY(O,O)]2Be leads to the formation of a series of solid-state solutions of composition [PLY(O,O)]2B(1-x)Be(x). The dopant molecules [PLY(O,O)]2Be serve to introduce holes into the lattice of spins provided by the [PLY(O,O)]2B radicals and lead to a systematic increase in the conductivity while decreasing the activation energy of the conduction process and leaving the solid-state structure relatively unperturbed. While the energies of the hole sites are expected to be high, the results are consistent with the interpretation of the electronic structure of [PLY(O,O)]2B in terms of the resonating valence bond model.

The formation of covalent bonds to single-walled carbon nanotube (SWNT) or graphene surfaces usually leads to a decrease in the electrical conductivity and mobility as a result of the structural rehybridization of the functionalized carbon atoms from sp(2) to sp(3). In the present study, we explore the effect of metal deposition on semiconducting (SC-) and metallic (MT-) SWNT thin films in the vicinity of the percolation threshold and we are able to clearly delineate the effects of weak physisorption, ionic chemisorption with charge transfer, and covalent hexahapto (η(6)) chemisorption on these percolating networks. The results support the idea that for those metals capable of forming bis-hexahapto-bonds, the generation of covalent (η(6)-SWNT)M(η(6)-SWNT) interconnects provides a conducting pathway in the SWNT films and establishes the transition metal bis-hexahapto organometallic bond as an electronically conjugating linkage between graphene surfaces.

Alterations in glial fibrillary acidic protein (GFAP) levels accompany the changes in the morphology and proliferation of astrocytes induced by colloidal solutes and films of carbon nanotubes (CNTs). To determine if GFAP is required for the effects of CNTs on astrocytes, we used astrocytes isolated from GFAP null mice. We find that selected astrocytic changes induced by CNTs are mediated by GFAP, i.e., perimeter, shape, and cell death for solutes, and proliferation for films.

We report the response of the electrical conductivity of semiconducting single-walled carbon nanotube (SWNT) thin films on exposure to metal vapors of the early lanthanides under high vacuum conditions. We attribute the strongly enhanced conductivities observed on deposition of samarium and europium to charge transfer from the metals to the SWNT backbone, thereby leading to the first examples of mixed covalent-ionic bis-hexahapto bonds [(η(6)-SWNT)M(η(6)-SWNT), where M = Sm, Eu].

In this Perspective, we present an overview of recent fundamental studies on the nature of the interaction between individual metal atoms and metal clusters and the conjugated surfaces of graphene and carbon nanotube with a particular focus on the electronic structure and chemical bonding at the metal–graphene interface. We discuss the relevance of organometallic complexes of graphitic materials to the development of a fundamental understanding of these interactions and their application in atomtronics as atomic interconnects, high mobility organometallic transistor devices, high-frequency electronic devices, organometallic catalysis (hydrogen fuel generation by photocatalytic water splitting, fuel cells, hydrogenation), spintronics, memory devices, and the next generation energy devices. We touch on chemical vapor deposition (CVD) graphene grown on metals, the reactivity of its surface, and its use as a template for asymmetric graphene functionalization chemistry (ultrathin Janus discs). We highlight som...

Carbon nanotubes (CNTs) and graphene share a common structural element – they are both based on a periodic array of annelated benzene rings. While differing in dimensionality and curvature, they are sufficiently similar that both of them readily undergo hexahapto organometallic complexation reactions. The curvature and pyramidalization of the fullerenes are such that their organometallic chemistry is entirely distinct from that of the CNTs and graphene, and thus it is useful to review the behaviour of these three new carbon allotropes in parallel. Organometallic chemistry offers a new approach to the functionalization of the graphitic surfaces that are present in CNTs and graphene. The formation of bis-hexahapto–metal bonds between such surfaces electronically couples the π-systems in a process that we refer to as constructive rehybridization, which extends the dimensionality of the periodic π-electron systems present in CNTs and graphene.

The electronic structure of single-walled carbon nanotubes (SWNTs) is investigated by transmission spectroscopy of thin films. Hole-doping of SWNTs, as a result of purification, leads to free carrier absorption in the far-IR spectral range. Thermal cycling de-dopes SWNTs, transferring spectral weight from the far-IR to the interband transitions in the near-IR spectral range. After the nanotubes are de-doped, a diameter dependent peak in the far-IR is apparent at ∼100 cm-1, which we ascribe to a curvature induced energy gap in the DOS of nonarmchair metallic SWNTs.

The preparation and crystal structure of 5-cyanofuran-2-[1,2,3,5-diselenadiazolyl], [RCN(2)Se(2)] (R = 5-cyanofuran), is reported. Crystal data for C(6)H(2)ON(3)Se(2): monoclinic, space group P2(1), a = 7.1121(7), b= 20.541(2), c =20.923(2) A, beta = 99.785(1) degrees, Z = 16. The crystal structure consists of diselenadiazolyl pi-dimer stacks running parallel to the x direction; the asymmetric unit consists of four pi-dimer units. The dimers are aligned into snakelike ribbons along the y direction, with consecutive dimers linked by head-to-tail CN-Se contacts. Each pi-dimer stack is bordered by two out-of-register stacks, but most interstack Se-Se contacts lie outside the van der Waals separation. Along the pi-dimer stacks, the intradimer Se-Se distances range from 3.183(10) to 3.294(1) A, and the interdimer Se-Se distances range from 3.826(1) to 3.945(1) A. Like other pi-dimer stacked diselenadiazolyls, [C(6)H(2)ON(3)Se(2)](2) is diamagnetic over the temperature range 4-380K. Variable temperature single-crystal conductivity measurements reveal a room-temperature conductivity near 10(-5) S cm(-1) and provide a calculated band gap of 0.72 eV. The structural results and transport properties are interpreted in the light of Extended Hückel band structure calculations.

By use of solution phase mid-IR spectroscopy we are able to obtain an estimate for the ratio of the carbon atoms in the single-walled carbon nanotube (SWNT) backbone to the carbon atoms in the end-groups and at defect sites of the octadecylamido (ODA) functionalized soluble SWNTs (s-SWNT-CONH(CH2)17CH3). This analysis shows that the weight percentage of the octadecylamido functionality in the s-SWNTs is about 50%.

X-ray photoelectron spectroscopy (XPS) has been used to investigate the surface chemical state of two carbon nanotube materials and determine the evidence of surface modification from a reaction with dichlorocarbene. Carbon and oxygen were the major elements observed on the surface of the pristine carbon nanotube produced by electric arc discharge. After reaction with dichlorocarbene, chlorine atoms amounting to about 1.6 at.% were detected and the peak position of Cl 2p was at 201.3 eV, which can be attributed to existence of organic chlorocarbons. A new intense peak addition to the peak at 285 eV for the elemental sp 2 and sp 3 carbon atoms appears at the binding energy of about 287.5 eV in the C 1s narrow scan spectrum. This binding energy is typical for C 1s ionization of sp 3 carbon in organic chlorocarbons. It was found that CC was the major carbon functional component in the surface modified carbon nanotube but other functional forms of carbon were also present such as CCl, CO, and OCO. With Ar + ion sputtering, the atomic percent concentration of chlorine decreased by 65%, the carbon concentration increased significantly and the oxygen surface concentration decreased from 20.7 to 5.5 at.%. The surface chemical treatment with dichlorocarbene has thus modified the surface of the carbon nanotube with localization of small amounts of chlorine atoms on the carbon surface without disrupting the single walled nanotube bundles.

We report the measurement of the acidic sites in three different samples of commercially available full-length purified single-walled carbon nanotubes (SWNTs) – as obtained from CarboLex (CLI), Carbon Solutions (CSI) and Tubes@Rice (TAR) – by simple acid–base titration methods. Titration of the purified SWNTs with NaOH and NaHCO3 solutions was used to determine the total percentage of acidic sites and carboxylic acid groups, respectively. The total percentage of acidic sites in full length purified SWNTs from TAR, CLI and CSI are about 1–3%.

We have measured the Raman spectrum of individual single walled carbon nanotubes in solution and compare it to that obtained from the same starting material where the tubes are present in ordered bundles or ropes. Interestingly, the radial mode frequencies for the tubes in solution are found to be approximately 10 cm (-1) higher than those observed for tubes in a rope, in apparent contradiction to lattice dynamics predictions. We suggest that there is no such contradiction, and propose that the upshift is due rather to a decreased energy spacing of the Van Hove singularities in isolated tubes over the spacings in a rope, thereby allowing the same laser excitation to excite different diameter tubes in these two samples.

We report the preparation, crystallization, and solid-state characterization of ethyl (3)- and butyl (4)-substituted spiro-biphenalenyl radicals. Both of these compounds are found to be conducting face-to-face pi-dimers in the solid state but with different room-temperature magnetic ground states. At room temperature, 4 exists as a diamagnetic pi-dimer (interplanar separation of approximately 3.1 A), whereas 3 is a paramagnetic pi-dimer (interplanar separation of approximately 3.3 A), and both compounds show phase transitions between the paramagnetic and diamagnetic forms. Electrical resistivity measurements of single crystals of 3 and 4 show that the transition from the high-temperature paramagnetic pi-dimer form to the low-temperature diamagnetic pi-dimer structure is accompanied by an increase in conductivity by about 2 orders of magnitude. This behavior is unprecedented and is very difficult to reconcile with the usual understanding of a Peierls dimerization, which inevitably leads to an insulating ground state. We tentatively assign the enhancement in the conductivity to a decrease in the on-site Coulombic correlation energy (U), as the dimers form a super-molecule with twice the amount of conjugation.

Full-length single-walled carbon nanotubes (SWNTs) were rendered soluble in common organic solvents by noncovalent (ionic) functionalization of the carboxylic acid groups present in the purified SWNTs. Atomic force microscopy (AFM) showed that the majority of the SWNTs ropes were exfoliated into small ropes (2−5 nm in diameter) and individual nanotubes with lengths of several micrometers during the dissolution process. The combination of multiwavelength laser excitation Raman scattering spectroscopy and solution-phase visible and near-infrared spectroscopies was used to characterize the library of SWNTs that is produced in current preparations. The average diameter of metallic nanotubes was found by Raman spectroscopy to be smaller than that of semiconducting nanotubes in the various types of full-length SWNT preparations. This observation sheds new light on the mechanism of SWNT formation.

The absorption properties of optical protein memories, comprised of Bacteriorhodopsin (BR) monolayer films, were studied for the first time to better understand the underlying read/write processes. We demonstrate that 755 nm light provides the greatest difference between the bR and Q photostates in 2D BR films. This implicates 755 nm as an optimal wavelength for probing the state of monolayer BR. A Cary 5000 spectrometer was used to observe state changes via absorption measurements following LED irradiation of BR coated samples.

Reduced fullerenes, the simplest covalent derivatives of the fullerene family of carbon allotropes, provide an excellent context for the study of the fundamental chemical reactivity of fullerenes. We have developed a general method for the formation of a number of these compounds. Using Zn(Cu) reduction, we have access to pure samples of several isomerically pure C 60 H n and C 70 H n species. We have completely assigned the 13 C NMR spectrum of C 60 H 6 and have assigned the majority of the resonances in C 60 H 2 .

The first structural characterisation of a heterocyclic free radical in all phases has been achieved. 4,5-Bis(trifluoromethyl)-1,3,2-dithiazol-2-yl, [CF3CSNSCCF3]˙ 4d, a 7π radical, was prepared quantitatively on reduction of [4d][AsF6] with various reducing agents. It is a blue gas over a green paramagnetic liquid [19F NMR δ −59.7], which freezes to a diamagnetic black-green solid. There is a remarkably large volume increase on melting implying that the liquid consists of discrete monomeric radicals, and consistently there is no tendency to dimerise in CCl3F solution and the vibrational spectra attributable to the monomer are essentially identical in all phases. The thermodynamic properties obtained for the vapourisation, sublimation and melting processes are very similar to those of related diamagnetic materials. 4d is remarkably thermochemically robust giving decomposition products identical to those from photochemical decomposition, a quantitative mixture of CF3CSSCCF3 (and its oligomers) and CF3CNSNCCF3. The reaction chemistry is described. The crystal structure shows radical 4d to be a planar heterocyclic ring which associates in the solid as a diamagnetic tetramer. The structure of the gaseous monomer determined by electron diffraction is very similar to that in the solid phase. Comprehensive physical measurements were made including the UV-visible spectra of the bright blue solutions, variable temperature magnetic susceptibility and quantitative variable temperature ESR spectra both of which confirm a phase change from a diamagnetic solid to a paramagnetic liquid on melting, the vibrational spectra, and the photoelectron spectrum of the gaseous free radical. A study of the behavior of RCSNSCR˙ (R = H, CH3 or CF3) given by the reduction of RCSNSCR+ on increase of concentrations of radical is reported, including the isolation of HCSNSCCF3˙ at low temperature. The experimental and calculated [UMPW1PW91/6-31+G*] structures of 4d are in good agreement. These and related calculations also support the interpretation of the vibrational and photoelectron spectra, and the thermodynamic properties of 4d, as well as provide possible explanations for the relative stabilities of RCSNSCR˙, and imply that the weak intramolecular interactions in 4d in the solid state are largely ionic Sδ+⋯Nδ− interactions.

We report the preparation, crystallization, and solid-state characterization of a spiro-biphenalenyl radical. The crystal structure shows that the radical is monomeric in the solid state and withou...

Reductive coupling of 4,5-dichloro-1,2,3-dithiazolylium chloride yields trans-4,4‘-dichloro-1,1‘,2,2‘,3,3‘-tetrathiadiazafulvalene (DC-TAF), the first example of this heterofulvalene system. Ab initio molecular orbital (B3LYP/6-31G**) calculations on prototypal TAF confirm that the closed shell 1Ag state lies 22 kcal mol-1 below the 3Bu diradical triplet. Cyclic voltammetry on DC-TAF reveals two reversible oxidation waves at 0.80 and 1.25 V (in CH3CN, reference SCE). The ESR signal (g = 2.0117) of the radical cation [DC-TAF]+ (in SO2(l)) exhibits a five-line hyperfine coupling pattern with aN = 0.096 mT. DC-TAF forms a series of 1:1 radical ion salts [DC-TAF][X] by electrooxidation in the presence of tetrahedral counterions (X- = BF4-, ClO4-, FSO3-). The crystal structures of these salts are isomorphous, monoclinic space group P21/n, and consist of one-dimensional ladder-like arrays of [DC-TAF]+ radical cations bridged by S- - -S contacts ranging from 3.5 to 3.7 A. Variable-temperature conductivity and ma...

The problem of resolving molecular components of the electronic structure of complex, organic solids with respect to their chemical and orbital character has been approached using soft X-ray absorption (SXA) and soft X-ray emission (SXE) spectroscopy. These techniques are powerful probes of the site and angular-momentum resolved partial density of states (PDOS) for both occupied and unoccupied states. Therefore these spectroscopies are particularly suited for an analysis of the density of states of multi-atomic, complex materials as the ET-based organic conductors, allowing site-specific electronic structure to be measured. We present a preliminary picture of the electronic structure of κ-ET 2 Cu(SCN) 2 and κ-ET 2 Cu[N(CN) 2 ]Br as measured by SXE and SXA performed at the C1s and N1s core levels.

We have introduced hybridization as the unifying metric for the degree of structural progress in organic reaction processes. In the present paper we show how the hybridization metric may be applied to other atoms in the reacting molecule to provide information on bond- making and bond-breaking and the degree of concertedness in chemical reactions. The study of chemical reactions is probably the most important facet of chemistry. Considering the maturity of the subject, it is surprising to find that there has been no universal scale for the progress of chemical reactions that allows comparisons to be drawn even among those reactions that simply involve the formation and cleavage of carbon-carbon bonds. Most previous attempts to quantify reaction progress have relied on some function of the interatomic distances that suffer a significant change during the chemical transformation; while this approach is suitable for controlling the position of a structure on the potential surface, it is less useful as an indicator. We have recently introduced hybridization (with scaling based on the pyramidalization angle), as the general metric for reaction progress and as the universal reaction coordinate of the chemical reaction (1). In most cases it is possible to associate an ideal initial and final hybridization with the atoms that are involved in the bond forming and breaking in chemical reaction processes, and together these provide well defined boundary conditions for the reaction metric (Fig. 1). The most common reaction processes involve conversions among sp 2 and sp 3 hybrids in the reacting atoms. By use of the p-orbital axis vector (POAV) analysis it is possible to solve analytically for the intermediate hybridizations (2,3), and thus a general metric may be obtained for almost any organic reaction process. The hybridization metric is structurally based, and is valid for the reactants, products, transition states and intermediates of many organic reaction processes. By adopting this reaction metric, it is possible for the first time, to apply the Hammond postulate in a quantitative manner across a variety of reactions (1).

The problem of resolving molecular components of the electronic structure of complex, organic solids with respect to their chemical and orbital character has been approached using core-level photon spectroscopies. Specifically, the bulk C 2poccupied and unoccupied partial densities of states (PDOS) of the organic superconductorsκ-ET2Cu(SCN)2andκ-ET2Cu[N(CN)2]Br were measured using a combination of high-resolution soft X-ray absorption (SXA) and soft X-ray emission (SXE). The PDOS was also calculated using a tight binding model, and the measured spectra compared directly to that predicted by the calculations. The emission and absorption spectra from both materials were found to be quite similar, reflecting mostly contributions from the common conductive ET layers. The presence of two nonequivalent carbon sites of the ET molecule was identified in the SXA spectra. Contributions from theπandσstates were identified in the emission spectra. The occupied C 2pbandwidth was found to be approximately 17eV. An observed dependence of the SXE spectra on the excitation energy is partly accounted for by a simple model that considers the presence of the two nonequivalent ET carbon sites. We also find evidence in the SXE spectra for a high degree of localization in the lowest unoccupied states.

The synthesis and solid-state characterization of the heterocyclic π-radical 1,2,5-thiadiazolo[3,4-b]-1,2,3-dithiazolo[3,4-b]pyrazin-2-yl, 1,2,3-TDTA, is described. The ESR spectrum of 1,2,3-TDTA (in CH2Cl2, 293 K, g = 2.009) confirms a highly delocalized spin distribution, with observable hyperfine coupling to all five nitrogen atoms of the tricyclic molecule (aN = 0.514, 0.343, 0.109, 0.051, and 0.045 mT). While chemical and electrochemical oxidation (E1/2(ox) = 1.14 V vs SCE) of 1,2,3-TDTA requires relatively harsh conditions, reduction is extremely facile (E1/2(red) = 0.15 V vs SCE). More importantly both the observed cell potential Ecell and computed (MNDO) gas-phase enthalpy ΔHdisp for the disproportionation of this and other 1,2,3-dithiazolyls are significantly lower than those observed for their 1,3,2-isomers. Crystals of 1,2,3-TDTA are monoclinic P21/n, with a = 6.6749(16) A, b = 11.7178(14) A, c = 8.6148(14) A, β = 103.297(16)°, and Z = 4. The crystal structure consists of slipped stacks of head...

We report EPR studies on pristine, purified, shortened and soluble SWNTs in various solution phases. Some of these samples give rise to strong, sharp EPR signals, and this technique is useful for monitoring the presence of SWNTs in aqueous and organic solvents. The soluble SWNTs carry about 1 unpaired electron per 10000 carbon atoms and give a free electron g-value.

The presence of two disulfide groups in the tetrathiophenalenyl radical TTPLY leads to a highly delocalized spin distribution and the lowest cell potential ever observed for a monofunctional phenalenyl derivative. While the heteroatom substituents successfully block C-C bond formation, TTPLY nonetheless associates in the solid state to afford the hypervalent S-S-bonded dimer (TTPLY)2.

This article reports the first investigation into the regiochemistry of addition to the fulleroid C61H2 by Zn(Cu) reduction and hydroboration. Two major isomers of C61H4 are formed by the reduction with Zn(Cu) while only one major isomer is formed by hydroboration. The structures of the major isomers formed by reduction with Zn(Cu) were identified as 1,2-C61H4 and 3,4-C61H4. The 1,2-C61H4 isomer is the only dominant isomer formed by hydroboration with no indications of the 3,4-C61H4 isomer being formed. The regiochemistry observed in the formation of 1,2-C61H4 is the same regiochemistry seen in the further reactivity of azafulleroids (C60NR). Strain energies (calculated at the B3LYP-6-31G* level of theory) show that the relief of strain is greater for the hydrogenation of the fulleroid C61H2 than it is for the hydrogenation of C60 itself. This indicates that the twisted, anti-Bredt's rule, double bonds of the fulleroid are a source of greater localized strain than the pyramidalization of the carbons in th...

We have subjected single-walled carbon nanotube materials (SWNTM's) to a variety of organic functionalization reactions. These reactions include radioactive photolabeling studies using diradical and nitrene sources, and treatment with dichlorocarbene and Birch reduction conditions. All of the reactions provide evidence for chemical attachment to the SWNTM's, but because of the impure nature of the staring materials, we are unable to ascertain the site of reaction. In the case of dichlorocarbene we are able to show the presence of chlorine in the SWNT bundles, but as a result of the large amount of amorphous carbon that is attached to the tube walls, we cannot distinguish between attachment of dichlorocarbene to the walls of the SWNT's and reaction with the amorphous carbon.

The reduction of 3He@C60 and 3He@C70 by lithium metal to give solutions of the corresponding hexaanions in THF-d8 has been achieved under gentle conditions, at subambient temperatures, without sonication, by capitalizing on the ability of corannulene (1) to serve as an efficient electron carrier between the lithium metal and the solid fullerenes, which are virtually insoluble in the reaction medium. The 3He inside the C60 hexaanion is found to be more strongly shielded (by nearly 20 ppm!) than any previously reported 3He in a fullerene [δ(3He@C606-) = −48.7 ppm, relative to dissolved 3He gas in the solution], whereas the 3He inside the C70 hexaanion is actually deshielded [δ(3He@C706-) = +8.3 ppm], resonating at nearly 15 ppm lower field than any previously reported 3He in a fullerene. These results stand in complete accord with earlier predictions that the magnetic properties of C60 and C70 would be altered dramatically, and in opposite directions, by reduction of the fullerenes to their hexaanions. The ...

Electroreduction of the 2,5-thiophene-bridged bis(1,2,3,5-diselenadiazolylium) salt [T-2,5-Se][SbF6]2 in acetonitrile, at a Pt wire and in the presence of iodine, affords a highly conductive ( sigma = 102 S cm-1 at 293 K) 1:1 charge-transfer (CT) salt [T-2,5-Se][I], the crystal structure of which has been determined by single-crystal X-ray diffraction. The crystals belong to the orthorhombic space group Fm2m, a = 3.544(2), b = 10.9808(16), c = 31.464(5) Å , V = 1224.5(7) Å 3. The structure consists of perfectly superimposed pi -stacks of molecular units bridged by columns of disordered iodines. This packing motif is similar to that of the related 1,3-benzene-bridged derivative [1,3-Se][I], but the lateral intermolecular Se···Se interactions linking adjacent pi -stacks are considerably shorter, indicative of a more isotropic electronic structure for [T-2,5-Se][I]. Magnetic susceptibility measurements on [T-2,5-Se][I] nonetheless indicate a phase transition to a diamagnetic state near 200 K, behaviour similar to that observed for [1,3-Se][I]. The electronic structures and transport properties of the two compounds are discussed in the light of extended Hückel band-structure calculations.Key words: diselenadiazolyl, diradical, charge-transfer salt, magnetic susceptibility, crystal structure.

Addition of benzyne to C70 results in four isomeric monoadducts (compounds 1a−d) in a 42:35:13:10 ratio as determined by 1H NMR. These compounds were separated by repeated passes through HPLC columns. The major isomer (1a) resulted from addition to the highly pyramidalized C1−C2 bond as shown by 13C NMR and UV/vis spectroscopy. The structure of the C1−C2 adduct (1a) was confirmed by X-ray crystallography. The second isomer (1b) was assigned as an adduct to the C5−C6 bond on the basis of 13C NMR and UV/vis spectroscopy. Compound 1c exhibited a 13C spectrum consistent with an adduct to the C7 and C8 positions. The presence of sp3 13C NMR resonances proved that the C7−C8 bond is still intact, making this the first identification of direct addition to a 5−6 ring fusion in a fullerene, and the first example of an adduct to a 5−6 ring fusion where the ring fusion bond remains intact. The fourth isomer (1d) displayed spectral data consistent with a compound with C1 symmetry and is assigned as an adduct to the C7...

The reactivity of the fullerenes is primarily a function of their strain, as measured by the pyramidalization angle or curvature of the conjugated carbon atoms. A consideration of the orientation of the π-orbitals shows that η2-complexation reactions lead to reaction products with the fullerenes that are very similar to those obtained from unstrained alkenes. Furthermore, a large amount of strain energy is released in this reaction, so it is clear just why this reaction is important in fullerene chemistry. On the other hand, it is shown that the π-orbitals of C60 are poorly oriented for overlap with an exohedral metal atom centered over the five- or six-membered rings, but well disposed for overlap with an endohedral metal atom centered under the five- or six-membered rings. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 139–143, 1998