Electronic and Magnetic Interactions in π-Stacked Bisthiadiazinyl Radicals

Abstract

The preparation of two bisthiadiazinyls (7, R1 = Me, Et; R2 = Cl, R3 = Ph), the first examples of a new class of resonance-stabilized heterocyclic thiazyl radical, are reported. Both radicals have been characterized in solution by EPR spectroscopy and cyclic voltammetry, which confirm highly delocalized spin distributions and low electrochemical cell potentials, features which augur well for the use of these materials as building blocks for neutral radical conductors. In the solid state, the radicals are undimerized, crystallizing in slipped pi-stack arrays which ensure the availability of electrons as potential charge carriers. However, despite these favorable electrochemical and structural properties, both materials exhibit low conductivities, with sigma(300K) < 10-7 S cm-1, a result which can be rationalized in terms of their EHT band electronic structures, which indicate that intermolecular interactions lateral to the pi-stacks are limited. The materials are thus very 1-D with low bandwidths, so that a Mott insulating state prevails. When R1 = Me, the intermolecular overlap along the pi-stacks is weak and the material is essentially paramagnetic. When R1 = Et, intermolecular pi-overlap is greater and variable-temperature magnetic susceptibility measurements indicate a strongly antiferromagnetically coupled system, the behavior of which has been modeled in terms of a molecular-field modified 1-D Heisenberg chain of S = 1/2 centers. Broken-symmetry DFT methods have been used to estimate the magnitude of individual exchange interactions within both structures.

Fluorescent Modular Boron Systems Based on NNN- and ONO-Tridentate Ligands: Self-Assembly and Cell Imaging

“…The residue was recrystallized from acetonitrile and gave a light brown solid in 57% (8.9 g) yield. The spectroscopic data are consistent with previously published data …”

“…The spectroscopic data are consistent with previously published data. 24 N,N′-(Pyridine-2,6-diyl)bis(4-methylbenzenecarboximidamide) (4b). This compound was prepared by modification of a literature procedure.…”

Sulfur monochloride in organic synthesis

“…81,82 Seven-membered dihydro-1,2,7-thiadiazepine 111a is a result of the unexpected dimerization of 4-nitro-substituted acetophenone oxime under the action of sulfur monochloride. 83 Analogous product 111b has been synthesized by the reaction of 2-acetylbenzofuran oxime under the same conditions (Scheme 56).…”

Oxygen, sulfur, selenium, tellurium and polonium

“…Unfortunately the bandwidth is also small and results in a conductivity s(300 K) less than 1 Â 10 À7 S cm À1 . 39 The generation of paramagnetic liquid crystals has been sought since this should lead to an enhanced magneto-optic effect. Kaszynski has reported a series of benzothiadiazinyl radicals this year which form a Smectic A liquid crystalline phase.…”