No description available.

No description available.

No description available.

No description available.

A series of partially fluorinated 1,2,3,5-dithiadizolyl aryl derivatives was prepared, in order to examine the effects of the fluorinated substituents on the solid-state structure of these molecules. 3,5-(CF₃)₂(C₆H₃CNSSN and 3-CF₃C₆H₄CNSSN were synthesized, as well as nine isomers of CF₃FC₆H₃CNSSN. The crystal structures of seven of these derivatives are compared, and discussed in the light of their molecular electrostatic potential maps. 3-F-4-CF₃C₆H₃CNSSN was found to crystallize as an inclusion compound with nitrogen. The synthesis and characterisation of this inclusion compound is described, as well as the reactivity of 3-F-4-CF₃C₆H₃CNSSN to other small molecules (Ar, CO₂, O₂). Several fluorinated dithiadiazolyl derivatives were synthesized in order to investigate their physical properties. EPR studies on CF₃CNSSN were undertaken in order to further examine its known bistable nature. EPR studies on the novel dithiadiazolyl derivative, CF₃(CF₂)₆CNSSN are also described, and the possibility of this radical exhibiting a liquid crystalline phase is discussed. The synthesis and solid-state structure of novel monomeric dithiadiazolyl radical, (CF₃)₃C₆H₂CNSSN, is also described. During the course of these studies, the known dithiadiazolyl derivative, CICNSSN, was synthesized in three concomitant polymorphic forms. The solid-state structure of these compounds is described, and the competing interactions seen in the three forms are discussed in the light of the molecular electrostatic potential map and atomic partial charges of CICNSSN. A series of novel dithiatetrazocines, <i>p</i>-X₁C₆H₄C₂N₄S₂C₆H₄X₂ (X₁, X₂ = NO₂, Br) was synthesized and characterized in order to study the non-linear optical properties of the unsymmetric derivative. The solid-state structures of these three derivatives are described and rationalized using their molecular electrostatic potential maps.

Chapter Two details the design, synthesis and characterisation of some compounds of general formula <i>p</i>-DC₆F₄A-<i>p</i>’. Donor and acceptor groups are discussed both in the context of maximising the molecular NLO response, and in the context of the promotion of polar chain formation through supramolecular synthons. Of the ten compounds presented in this chapter, nine are noncentrosymmetric. Preliminary NLO measurements show that these nine compounds exhibit an appreciable SHG response. Semi-empirical calculations were performed on these and related systems to determine molecular hyperpolarisabilities.  Similar calculations were also used to draw Molecular Electrostatic potential maps for these compounds in an attempt to rationalise the observed packing. Chapter Three discusses some compounds of general formula DC₆F₄C₆F₄A. The synthetic difficulties associated with the preparation of these perfluorinated biphenyl derivatives are highlighted, and semi-empirical calculations are used to identify some idealised systems. The syntheses and crystal structures of some methoxy substituted derivatives are reported. Chapters Four and Five discuss some compounds in which donor-acceptor substituted rings are linked by delocalised spacer groups. The synthesis and characterisation of some donor-acceptor substituted aromatic Schiff base compounds is presented in Chapter Four, along with some initial calculations and NLO measurements. Chapter Five describes the design, synthesis and characterisation of some thiazyl chain compounds. UV measurements and preliminary calculations on some of these systems are also presented.

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 <i>ortho</i>-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 (<i>J</i><i>I ~ -</i>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 <i>n</i>-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.

No description available.

No description available.

No description available.