Hydrogen bonding and exchange interactions in organic based magnetic materials

• Main Author: Taylor, Patrick S
• Language: ENG
• Published: ScholarWorks@UMass Amherst 2006
• Subjects: Organic chemistry
• Online Access: https://scholarworks.umass.edu/dissertations/AAI3216965

The work in this dissertation focused on two topics which are typically encountered in organic based magnetic materials: (1) the self-assembly of molecules in the solid state to provide viable interelectronic exchange pathways and (2) the use of spin density distribution and radical communication in high spin molecules to provide a better understanding of the interelectronic exchange pathways that are encountered in (1). To study the effects of crystal packing and exchange behavior in hydrogen bonded systems, compounds 5NNBIm, 6UrIN, 35diBu4HOPhNN, and 35diBu4HOPhIN were all synthesized and their solution and solid state properties were analyzed. Compound 5NNBIm, was synthesized and found exhibit antiferromagnetic interactions between spin units. The crystal structure revealed a water of molecule was incorporated into the structure, providing NH(imidazole)......O(H)H......:N(imidazole) chains of hydrogen bonds. The magnetic data was fit to 1D and 2D Heisenberg chain models for spin exchange, both of which gave excellent fits to the data. The crystal structure of 6UrIN, revealed a dimer structure which formed between two uracil portions of the molecule. The magnetic data was fit to a Bleaney-Bowers dimer model for spin pairing and showed overall antiferromagnetic interactions between spin units. The crystal structure of 35diBu4HOPhNN revealed extended hydrogen bonded chains formed between the phenolic OH and a NO of the nitronyl nitroxide portion of the molecule. The magnetic data was fit to a 1D Heisenberg model for exchange and showed strong antiferromagnetic interactions between spin units. Compound 35diBu4HOPhIN was found to have disorder in its crystal structure making the magnetic analysis very difficult. To study the effects of spin density distribution and radical communication in high spin molecules, compounds BTNIT, 5azaBABI, pNPhIN, mNPhIN, 35diBu4OPhNN, and 35diBu4OPhIN were synthesized and their solution state properties analyzed. Compounds BTNIT and 5azaBABI were prepared to determine what effect heteroatom substitution would have on the spin density distribution in BABI. Electron spin resonance (ESR) and computational results determined sulfur substitution in BTNIT played a significant role in increasing the spin density onto the benzenoid portion of the molecule, while nitrogen substitution in 5azaBABI did not significantly affect the spin density on the nitroxide portion of the molecule. The ground state spin multiplicities in compounds pNPhIN, mNPhIN, 35diBu4OPhNN, and 35diBu4OPhIN were all determined using ESR and/or theoretical computations. Heteroatom substitution, within the spin bearing portions of the molecule, was determined to reverse the expected ground state spin multiplicities that were expected based on traditional spin polarization and parity connectivity models.