A molecular approach to nanoscale magnetic materials: New iron and manganese clusters from the use of pyridyl alcohols

This work focuses on the preparation and characterization of polynuclear iron and manganese clusters as new nanoscale magnetic materials. Non-carboxylate FeIII cluster chemistry has been explored in the presence of the bidentate N,O ligand, the anion of 2-hydroxymethylpyridine (hmp -), and it has proven to be a useful route to new FeIII clusters spanning Fe4 and Fe6 nuclearities and topologies that are both very rare. Of these, the Fe6 complex displayed a counterintuitive S = 3 ground state spin value, and it was rationalized by semiemperical theoretical calculations using ZILSH methods.;A non-carboxylate approach for FeIII cluster synthesis was further explored in the presence of the tridentate O,N,O group, 2,6-pyridinedimethanol (pdmH2), and it has led to the isolation of new Fe8 non-carboxylate cluster products with an unprecedented topology, and with an S = 0 ground state spin. The reactivity of these Fe 8 clusters was explored, and this revealed that they transform to an Fe18 product under mild hydrolysis. The Fe18 product shows an unprecedented metal topology and an S = 4 ground state spin, and is the highest nuclearity non-carboxylate FeIII cluster discovered to date. Apart from the non-carboxylate FeIII chemistry, the reactions of pdmH2 in the presence of carboxylate were also explored, and led to the isolation of a new Fe9 product with a prototypical structure, and with a ground state spin of 5/2. The combined results demonstrate the versatility of pdmH2 to give new high nuclearity products, and show that the presence and absence of carboxylates can have a marked effect on the obtained products.;In the development of new synthetic routes to polynuclear metal clusters, the choice of the ligands has always been a key issue. In order to provide a new ligand design strategy for the isolation of novel clusters, the introduction of two bulky phenyl or methyl groups onto the CH2 group of hmpH was investigated. The use of diphenyl-hmpH (dphmpH) has led to the isolation of Mn4, Mn6, and Mn11 products with very rare or prototypical structures, and with S = 0, 3, and 5/2 ground state spin values, respectively. These clusters are distinctly different from those obtained previously with hmpH itself, and it is also seen that dphmp- prefers to bind as a bidentate chelate, disfavoring the bridging modes favored by hmp-. It was concluded that the two phenyl groups had almost completely removed the ability of the alkoxide O atom to bridge, and thus dphmp- primarily functions as a bidentate chelate. This was rationalized as a combination of the steric bulk of the two phenyl groups, as well as their electron-withdrawing effect on the O atom. The less-bulky dimethyl-hmpH (dmhmpH) was then employed in order to switch back on the bridging modes as a result of both the smaller size of methyl groups and their electron-donating rather than electron-withdrawing character, while still hopefully providing sufficient steric differences with hmp- to lead to new products.;As an expansion of this ligand design strategy, a potentially tridentate ligand phenyldipyridine-2-ylmethanol (pdpmH), in which one phenyl and one pyridyl groups were added onto the CH2 unit of hmpH, was employed and successfully led to novel Mn4 and Mn7 clusters. Interestingly, the potentially tridentate ligand pdpmH mainly acts as a bidentate ligand. The reluctance of pdpm- to serve as a tridentate ligand is found to be due to the nearby steric bulk of the phenyl and pyridyl groups. Magnetochemical characterization revealed that the Mn4 and Mn 7 have ground state spin values of S = 0 and 29/2, respectively. The combined results demonstrate the usefulness and potential of a ligand design strategy in the synthesis of a variety of new metal clusters. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html) (Abstract shortened by UMI.)...