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Title: Polymorphism and structural modification in some dithiadiazolyl radicals
Author: Clarke, C. S.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2006
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This thesis opens with a review and summary of the electronic, magnetic and structural properties of 1,2,3,5-dithiadiazolyl radicals, in the context of work presented in this thesis. Chapter 3 describes the synthesis and characterisation of a series of fluoro- and trifluoromethyl-substituted dithiadiazolyl radicals. The third chapter describes a novel synthetic methodology for the preparation of dithiadiazolyl radicals utilising the reaction of an organo-lithium salt (ArLi) with Me3SiNCNSiMe3 to generate the key amidinate derivate [ArC(NSiMe3)2]Li. This approach has been used to prepare two new dithiadiazolyl radicals bearing CF3 groups in the ortho-position which lead to monomeric radicals in the solid state; 2,4,6-(CF3)3C6H2CNSSN (21) and 2,6-(CF3)2C6H3CNSSN (22). Radical 21 is polymorphic and the magnetic behaviour of both phases has been measured indicating strong antiferromagnetic exchange between radicals in both cases (JI ~ -24 K). Preliminary single crystal EPR studies on 22 are presented. Chapter 4 describes the synthesis and preliminary physical studies on dithiadiazolyl radicals bearing long alkyl or perfluoroalkyl chains which may potentially exhibit liquid crystalline behaviour. Thermodynamic and EPR studies on CF3(CF2)6CNSSN are reported which shows a simple solid-liquid phase transition. In contrast n-C12H25C6H4CNSSN exhibits a more complex temperature dependent EPR spectrum suggestive of some pre-melting of the sample consistent with restricted molecular rotation. Chapter 5 describes the crystal structure of a fourth polymorph of C1CNSSN and an unusual co-crystal [2,4,6-(CF3)3C6H2CNSSN]4[C1CNSSN]C1 which was isolated during the synthesis of 21. Within the co-crystal the C1- anion acts as a template forming strong interactions to the disulfide bridge of each dithiadiazolyl ring.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available