Design, synthesis and characterization of paramagnetic complexes based on thiazyl radicals

Paramagnetic complexes based on the 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl radical as a bridging spin-bearing ligand have been exclusively studied in this thesis. The goal was to investigate the magnetic exchange interaction between transition metal ions and the radical ligand. We designed and synthesized transition metal complexes bridged by the 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl radical ligand with bis-bidentate N-coordination mode. The ligands and the complexes have been characterized by FT-IR, EPR, cyclic voltammetry, X-ray crystallography, etc. The SQUID (Superconducting Quantum Interference Devices) magnetometry measurements showed that the design goals were achieved. The complexes are the first bis-bidentate N-coordination compounds reported for a 1,2,3,5-dithiadiazolyl radical.;Complexes with bis-bidentate coordination modes provide a good platform for the study of intra-molecular magnetic exchange interaction. Two transition metal ions bridged by a spin bearing ligand construct a rigid geometry, and a direct consequence of this coordination mode is the direct exchange interaction between metal ions and radical. This results in the two metals being forced into ferromagnetic coupling with one another, in other words, an overall ferro- or ferri-magnetic coupling scheme. Therefore, regardless of the nature of the magnetic coupling between the ligand and the metal, an optimum total spin quantum number is always guaranteed.;Inter-molecular magnetic exchange interaction was also studied by coordinating only one metal ion to the 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl radical, leaving the remaining coordination site unoccupied. The complexes of this type of coordination, called herein mono-metal complexes, usually crystallize with dimerization of adjacent 1,2,3,5-dithiadiazolyl rings on neighboring complexes. Consequently, magnetic coupling of the ligand with a coordinated transition metal ion is not observed in the solid state. However, an unusual crystalline material consisting of mono-Mn complex packed in a "zigzag" structure was obtained, which has not been reported anywhere in the literature.;In this thesis a series of neutral radicals was prepared, among them 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl radical and 3,5-bipyridyl-1,2,4,6-thiatriazinyl radical were unknown prior to our research. The 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl radical has been fully investigated and coordinated to transition metal complexes. The designed objective has been achieved. We have also successfully synthesized the 3,5-bipyridyl-1,2,4,6-thiatriazinyl (TTA) radical. Due to this TTA radical's highly propensity to form the corresponding closed shell imine, perhaps from exposure to moisture, great effort has been taken to avoid moisture in every step of the processes. Difficulty working with this TTA radical has hindered the synthesis of its metal complexes to date.