M. Thomas Jones

Synthetic, Structural, and Electrical Aspects of Molecular and Polymeric Selenium and Tellurium Materials

Abstract The physical and structural concepts concerning organochalcogen-based anisotropic organic metals are summarized, and the rationales which motivate synthetic activity in new selenium and tellurium materials are presented. An overview of our approach to new aromatic molecular and polymeric materials involving direct thermal reaction of new alkali chalcogenide reagents with unactivated aromatic halides is given, and recent applications to the synthesis of tetraselenonaphth-alene (TSeN) and new transition metal diselenolenes based on o-benzenediselenolate (bds) are noted. The crystal and molecular structures of TSeN and (nC4Hg)4N+ Ni(bds)2′ have been determined, as well as their electronic absorption and electron spin resonance spectra and cyclic voltammetric behavior. The reaction of cis-dichloroethylene and sodium diselenide leads to a polymer to which the repeat sequence ←Se-CH=CH-CH-CR-Se→ is assigned, based on elemental analysis and infrared spectrum.

An E.S.R. study of the ion pairs of the anion radicals of tetracyanoquinodimethan (TCNQ) and tetrafluorotetracyanoquinodimethan(TCNQF4) in solution

A comparative E.S.R. study of the potassium salts of the anion radicals of tetracyanoquinodimethan(TCNQ) and tetrafluorotetracyanoquinodimethan(TCNQF4) in dilute solutions of ether type solvents reveals that both anion radicals are ion paired. Careful measurements of the hyperfine splittings (hfs) as a function of temperature for both anions in solution show that the isotropic hfs are temperature and solvent dependent. Generally, at temperatures below room temperature, both anion radicals in solution display linewidth alternation phenomena which arise from modulation of the nitrogen and fluorine hfs in TCNQ and TCNQF4, respectively. In contrast, the isotropic g-values of both anion radicals in solution are independent of temperature and the solvents used in this study. The experimental evidence, molecular orbital calculations of the charge density distribution in the free anion radicals, calculations of the ion pair association energies for various K+/TCNQ- and K+/TCNQF4 structures and comparison of the c...

ESR and Theoretical Studies of Bis-Benzene-1, 2-Diselenolate Nickel and Related Complexes

Abstract ESR and theoretical studies of the transition metal complexes of [Co and Ni (Se2C6H4)2]− (n-C4H9)4N+ are reported and compared with closely related systems. Room temperature single crystal X-ray studies reveal the Nickel complex is orthorhombic. ESR studies of the polycrystalline powders of the Ni complex as a function of temperature from 108 K to room temperature show a series of spectral envelopes which can arise only from a paramagnetic site which possesses axial symmetry. At ca 160 K, there is an abrupt change in the value of the principal components of the anisotropic g-tensor of the Ni complex which is discussed. Low temperature ESR studies of polycrystalline samples of the ground state triplet Cobalt complex which is isomorphous with the Nickel complex reveal an orthorhombic g-tensor. From the field position of the half-field resonance, it is possible to calculate a mean separation, of the two electrons which make up the triplet state, of 4.3 (±0.5) A.

An E.S.R. study of some alkyl substituted benzene anion radicals : an experimental evaluation of the extent of vibronic interaction

E.S.R. studies of the proton hyperfine splitting in the anion radicals of benzene, toluene, ethylbenzene, iso-propylbenzene, t-butylbenzene, and p-xylene show that it is strongly dependent upon temperature. In the case of the monoalkylbenzenides there are two contributions to this observed temperature dependence. First, there is a rapid thermal averaging over two near-degenerate states which have different spin-density distributions. The energy separations between these two near-degenerate states have been measured for the above series of monoalkylbenzenides and are reported here. It is also possible to measure experimentally the spin-density distributions for the two states between which the averaging takes place. With this information one can obtain an experimental estimate of the extent of vibronic interaction which occurs in these systems. Such estimates are presented here and compared with those obtained theoretically. The second source of the strong temperature dependence of the proton hfs lies in t...

Modification of Stone's theory of g-factors for aromatic hydrocarbon free radicals to include quadratic terms

Abstract Stones theory for the g-factors of orbitally nondegenerate organic free radicals has been modified to include several important molecular orbital contributions which were omitted in the original derivation. Second-order terms in the Huckel eigenvalue λ have also been included. This leads to an expression of the form Δg = ′a + b′λ + c′λ2. Evaluation of the various molecular orbital parameters leads to the conclusion that both b′ and c′ should be negative. These results are in agreement with the limited amount of experimental data presently available from which the values b′ = −1.61 × 10−4and c′ = −4.85 × 10−5 have been derived.

The effect of field modulation amplitude and frequency upon the line shape analysis for unresolved hyperfine splitting

Abstract The use of magnetic field modulation amplitudes or frequencies which are too large with respect to the resonance line width lead to magnetic resonance line shape distortions. In this paper, the effect of modulation amplitude and frequency upon the magnetic resonance line shape and upon the recently discussed line shape analysis for the determination of unresolved hyperfine splitting are considered. Limits are suggested for both the experimental variables (field modulation amplitudes and frequencies) in terms of the observed line widths. The limits if observed will minimize line shape distortions and allow the use of the originally proposed line shape analysis. Attempts to modify the line shape analysis to include the effects of modulation frequency were not successful. The reasons for this lack of success are discussed. Experimental observations made upon dilute solutions of peroxylamine disulfonate confirm the results reported here.

An ESR study of ion pairing in solutions of the alkali metal salts of tetracyanoquinodimethan (TCNQ) and tetrafluorotetracyanoquinodimethan (TCNQF4)

ESR studies of the alkali metal salts of the anion radicals of tetracyanoquinodimethan (TCNQ) and tetrafluorotetracyanoquinodimethan (TCNQF4) in dilute solutions of ether type solvents reveal that solutions of salts of both anion radicals are ion paired. Quantitative measurements of the values of the hyperfine splittings (hfs) as a function of temperature for these salts in solution show that the isotropic hfs are temperature and solvent dependent. In contrast, the observed isotropic g-value for a given salt of either anion radical in solutions of the solvents studied is independent of temperature and solvent. However, there is a weak dependence of the isotropic g-value upon the alkali metal ion in the case of the heavier alkali metal ion salts, i.e., Cs/TCNQ, Rb/TCNQF4, and Cs/TCNQF4. The studies reported here (1) re-enforce an earlier report of ion pairing in solutions of the potassium salts of TCNQ and TCNQF4, (2) establish that ion pair formation occurs in the entire alkali metal TCNQ and TCNQF4 salt ...

Experimental and theoretical studies of transition metal dithiolate and diselenolate

Abstract The results of comparative physical (especially ESR) studies of bis-benzene-1,2-dithiolate(bdt) and bis-benzene-1,2-diselenolate(bds) transition metal complexes are presented and analyzed in terms of the molecular and electronic structures of these transition metal complexes. The results of Extended Huckel molecular orbital calculations are presented and discussed, also, as an aid toward developing a better and more complete understanding of the magnetic studies presented. These calculations provide such information as the order of the electronic energy levels, composition and symmetries of the molecular orbitals, the total charge density distribution within the molecular complexes, and the charge density distribution within the orbital(s) which contain the unpaired electron(s).

A comment on “ESR linewidth studies on naphthalene ion in low bulk dielectric constant media”

Abstract It is noted, if one uses the lineshape analysis for unresolved hyperfine splitting proposed by Jones et al. that one must be careful to avoid lineshape distortion from the magnetic field modulation amplitudes and frequencies used. At 100 kHz field modulation the lineshape distortion is significant for linewidths less than ≈ 350 mG and unresolved hyperfine splittings less than ≈ 70 mG.

New Synthetic Metal Precursors: Substituted Tetrathiotetracene and Related Compounds

The electron donor tetrathiotetracene (TTT), Fig. 1, forms charge transfer salts which, at room temperature, possess some of the highest electrical conductivities of any known synthetic metal1. For example, a conductivity of ca 103 S/cm is observed for (TTT)2I3 at room temperature. As the temperature of the complex is decreased, the conductivity increases until ca 35 K, at which point it decreases dramatically2. While not firmly established, it is believed that the latter behavior is the result of a Peierls transition, which allows alternating pairwise interactions to occur between adjacent TTT molecules and cations.