Authors:	Kolanji, Kubandiran
Title:	Organic Radicals for Magnetic Materials through Controlling of Magnetic Exchange Interactions
Online publication date:	16-Jan-2019
Year of first publication:	2019
Language:	english
Abstract:	The thesis is mainly focused on design, synthesis, structural and magnetic studies of nitroxide free radicals connected with aromatic –conjugated systems. The nitronyl– and imino–nitroxide (NN, and IN) were selected as spin units because of their high stability, solubility, structural flexibility and multi-functionality among the building blocks known from literature. The thesis is separated in to five chapters. The chapter 1 is focused on the introduction, which contains basics of magnetism, molecular design, stable organic radical for magnetic materials, application of the organic radicals, and magnetic exchange interactions. Our main aim of the chapters 2 and 3 are the design and synthesis of the novel weakly antiferromagnetic (AFM) coupled spin–dimers for Bose–Einstein condensation (BEC) in the solid state organic magnetic materials. In chapter 2, the mixed phenyl and thiophene oligomers are selected for π–conjugated systems and nitronyl nitroxide (NN) is chosen as a spin unit. In chapter 3, planar π-bridge such as benzo[1,2–b:4,5–b']dithiophene derivatives were selected for π–conjugated systems with good π-stacking and substituted with nitronyl– and imino–nitroxides as spin units. The works mostly focused on examination of the spin–spin interaction between the spin centers, which can be related to the energy difference between singlet and the triplet state: EST = 2J. The exchange interactions were calculated by different DFT methods and upon using molar magnetic susceptibility measurements yielding χmol vs temperature T curves which were fitted to the Bleany–Blowers equation providing the experimental exchange interactions. In chapter 4, the mono NN substituted donor π–core such as 4-phenyl-4H-dithieno[3,2-b:2',3'-d]pyrrole (DTP–Ph) derivatives of the molecules were designed, and synthesized. Upon one electron oxidation, these molecules offered radical cationic high spin molecules with triplet ground state. The spin–spin of interaction between NN and radical cation were calculated by DFT. The last chapter 5, contains a collaboration with Dr. Pramod Bhatt, dealing with mono nitronyl–nitroxide (NN) of phenyl and thiophenyl radical which I synthesized as model compounds and compared for their coordination behavior to metal ions (Mn2 , Co2 ) and the resulting magnetic behaviors. The magnetic interactions of the NN and metal ions were studied by DFT and magnetic susceptibility. In all the chapters, all the new molecules were characterized by HRMS analysis, the diamagnetic molecules were characterized by NMR and the paramagnetic molecules by well resolved EPR spectra combined with simulation. The final compounds were investigated by optical spectroscopy and crystallized to obtain X–ray structures, which is very important for explaining their magnetic behavior (magneto structural correlation). Further, the bulk magnetic susceptibilities were examined by SQUID in cooperations.
DDC:	540 Chemie 540 Chemistry and allied sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-2813
URN:	urn:nbn:de:hebis:77-diss-1000025411
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Extent:	v, 199 Seiten
Appears in collections:	JGU-Publikationen