| The electronic band structure of a series of 1,2,3,5-diselenadiazolyl (1,2,3,5-DSDA) radicals has been investigated at the level of Extended Hückel Theory (EHT). Their electronic properties are correlated to the molecular packing arrangements in their solid state structures. In addition, the electronic band structure of a 1,3,2-selenathiazolyl (1,3,2-DSTA) 3:2 charge transfer salt has been determined, also at the EHT level. The results are correlated with the molecular orbitals of the triple decker dicationic radical molecular unit, which is the building block of the structure.;The magnetic properties of a series 1,3,2-dithiazolyl (1,3,2-DTA) radicals have been re-examined. Thermally-induced magnetic bistability has been observed for the pyrazinyl 1,3,2-DTA radical (PDTA). The solid state structure of PDTA has been determined above and below the phase transition using X-ray crystallography. A mechanism for phase interconversion to account for the observation of magnetic hysteresis in both PDTA and the related thiadiazolodithiazolyl radical TDTA is proposed. Based on this proposed mechanism, several novel 1,3,2-DTA radicals have been synthesized.;In addition to the bistability in heterocyclic radicals, the magnetic properties of a carbon centred radical have been investigated. The n-butyl substituted spirocyclic biphenalenyl radical exhibits a magnetic bistability just above room temperature. The solid state structure of this material has been determined for both the LT and HT phases by X-ray crystallography and a mechanism for phase interconversion has been proposed.;Two novel resonance-stabilized bis(1,2,3-dithiazolyl) (1,2,3-DTA) radicals containing a pyridine moiety have been prepared for investigation of their use as neutral radical conductors. The relationship between molecular architecture and solid state packing has been investigated in these materials by changing peripheral R groups. Both radicals, MeBPMe and PhBPMe, form slipped π-stacks, with graphitic intermolecular spacing along the stacking direction. The symmetry afforded to MeBPMe by the presence of two peripheral methyl groups, provided a linear arrangement of molecular stacks throughout the solid. In contrast, PhBPMe, with one methyl group and a phenyl group, packs in a pinwheel fashion that is unique for this class of radical. The three dimensional electronic band structures of both materials have been evaluated using EHT level calculations. |
