A. Wallace Cordes

Bio: A. Wallace Cordes is an academic researcher from University of Arkansas. The author has contributed to research in topics: Crystal structure & Ring (chemistry). The author has an hindex of 26, co-authored 66 publications receiving 1808 citations. Previous affiliations of A. Wallace Cordes include Indian Institute of Technology Kanpur & Florida State University College of Arts and Sciences.

Molecular Semiconductors from Bifunctional Dithia- and Diselenadiazolyl Radicals. Preparation and Solid-State Structural and Electronic Properties of 1,4-[(E2N2C)C6H4(CN2E2)] (E = S, Se)

Abstract: The reactions of 1,4-phenylenebis(N,N,N{prime}-tris(trimethylsilyl)amidine) with sulfur and selenium dichlorides yield, respectively, the 1,4-phenylenebis(dithiadiazolium) and bis(diselenadiazolium) dichlorides 1,4-((E{sub 2}N{sub 2}C)C{sub 6}H{sub 4}(CN{sub 2}E{sub 2}))Cl{sub 2} (E = S, Se). Reduction of these materials with triphenylantimony affords the corresponding diradical species 1,4-((E{sub 2}N{sub 2}C)C{sub 6}H{sub 4}(CN{sub 2}E{sub 2})), which can be purified by high vacuum sublimation. The crystal structures of 1,4-((E{sub 2}N{sub 2}C)C{sub 6}H{sub 4}(CN{sub 2}E{sub 2})) (E = S, Se) are both monoclinic, space group P2{sub 1}/n. The crystal packing consists of sheets of interleaved columns of weakly associated diradical units (dimers); the mean intradimer separation is 3.34/3.37 {angstrom} (E = S/Se). The sulfur compound is an insulator, but the selenium material has a room temperature pressed pellet resistivity of about 100 {Omega} cm. Magnetic susceptibility measurements show the solids to be predominantly diamagnetic with variable amounts of paramagnetic defects in the lattice. While the exact mechanism of conduction remains to be established, these systems represent the first structurally characterized conducting materials constructed from neutral molecular radicals.

Resonance-Stabilized 1,2,3-Dithiazolo-1,2,3-dithiazolyls as Neutral π-Radical Conductors

Abstract: 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 SS 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 Huckel 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

Playing with organic radicals as building blocks for functional molecular materials

Abstract: The literature has shown numerous contributions on the synthesis and physicochemical properties of persistent organic radicals but there are a lesser number of reports about their use as building blocks for obtaining molecular magnetic materials exhibiting an additional and useful physical property or function. These materials show promise for applications in spintronics as well as bistable memory devices and sensing materials. This critical review provides an up-to-date survey to this new generation of multifunctional magnetic materials. For this, a detailed revision of the most common families of persistent organic radicals—nitroxide, triphenylmethyl, verdazyl, phenalenyl, and dithiadiazolyl—so far reported will be presented, classified into three different sections: materials with magnetic, conducting and optical properties. An additional section reporting switchable materials based on these radicals is presented (257 references).

Reference Scales for the Characterization of Cationic Electrophiles and Neutral Nucleophiles

Abstract: Twenty-three diarylcarbenium ions and 38 π-systems (arenes, alkenes, allyl silanes and stannanes, silyl enol ethers, silyl ketene acetals, and enamines) have been defined as basis sets for establishing general reactivity scales for electrophiles and nucleophiles. The rate constants of 209 combinations of these benzhydrylium ions and π-nucleophiles, 85 of which are first presented in this article, have been subjected to a correlation analysis to determine the electrophilicity parameters E and the nucleophilicity parameters N and s as defined by the equation log k(20 °C) = s(N + E) (Mayr, H.; Patz, M. Angew. Chem., Int. Ed. Engl. 1994, 33, 938−957). Though the reactivity scales thus obtained cover more than 16 orders of magnitude, the individual rate constants are reproduced with a standard deviation of a factor of 1.19 (Table 1). It is shown that the reactivity parameters thus derived from the reactions of diarylcarbenium ions with π-nucleophiles (Figure 3) are also suitable for characterizing the nucleoph...