Electrochemical and structural properties of some 1,2,3,5 and 1,3,2,4 dithiadiazolylium salts and related compounds

Abstract

This work centres around the electrochemical and structural studies of 1,2,3,5 and 1,3,2,4 dithiadiazolylium salts and associated radical derivatives. Chapter one provides a brief history of sulphur nitrogen chemistry, in particular developments of 1,2,3,5 and 1,3,2,4 dithiadiazolyUum/ heterocyclic species. Also a quick outline of the pathways my research took are discussed. The following chapter is solely dedicated to the electrochemical investigations of (i) mono substituted aryl 1,2,3,4 and 1,3,2,4, (ii) di substituted aryl 1,2,3,4 and 1,3,2,4 and (iii) pyridyl 1,2,3,5 dithiadiazolylium salts and associated derivatives. This electrochemical process of interest involved the reduction of the 6π dithiadiazolylium cation going to the 7π radical. This was studied using a technique called Cyclic Voltammetry. Results from this survey revealed that all the derivatives studied were quasi-reversible to the same degree under these experimental conditions. The E(_pc/2) potentials of meta and Para derivatives were observed to increase with acceptor property of the substituent group attached. Using the relationship E(_pc/2) = σp, when the potentials of these derivatives were plotted against corresponding Hammett a values two excellent linear free energy relationships for both sets of derivatives were seen to exist. For the other systems this is not found to be so. Rationalisation of these responses are described by examination of electronic, solvent and steric factors of analogous benzoic acid and dithiadiazolylium/zolyl derivatives and how they compare with each other. Chapter three concentrates on the structural properties of dithiadiazolyls and discusses the potential of these types of derivatives to form conducting, charge transfer or magnetically interesting materials. The X-ray structures of the following compounds were obtained and are described in detail: pMeS-C(_6)H(_4)-CNSSN•, pF-C(_6)H(_4)-CNSSN•, pCF(_3)-C(_6)H(_4)-CNSSN•, pNO(_2)-C(_6)H(_4)-CNSSN•, mBr- C(_6)H(_4)-CNSSN•, mClpMe-C(_6)H(_4)-CNSSN•,| mC(_5)H(_4)N-CNSSN• and pC(_5)F(_4)N-CNSSN•. Comparisons of how these and similar dithiadiazolyl compounds pack with a view to rationalising packing trends, in order to molecular tailor materials for applications, is tackled as well. The forth chapter concerns the experimental details of this research and features information on technical procedures, synthetic routes and characterisation on the compounds examined. Finally chapter five attempts to bridge the results of the previous chapters all together.