| This dissertation has focused on studying the electron spin dynamics in the quantum and classical limit and, most importantly, at the quantum-classical boundary. We have successfully used high frequency electron paramagnetic resonance (HF-EPR) techniques to characterize six paramagnetic materials with increasing number of unpaired electrons and molecular sizes. The samples studied are Mn2+-doped CdSe Quantum Dots (Mn:CdSe QDs), Na 20[Cu2Pd22PV12O60(OH) 8] (Cu2), Na12[X 2W18Cu3O66(H2O)3]·32H 2O (X = As, Sb) (Cu3), [Fe 7O4(O2CPh)11(dmem)2]·4MeCN (Fe7), [Mn7O4(pdpm)6(N 3)4](ClO4)2 (Mn7) and Na34[Mn19(OH)12(SiW10O 37)6]·115H2O (Mn19). Our results have illustrated that four samples including Mn:CdSe QDs, Cu2, Cu3 and Fe7 can be perfectly described with quantum mechanics while sample Mn19 behaves like a typical classical system. Most interestingly, sample Mn7 (S = 29/ 2) straddles the interface between the classical and quantum mechanical spin descriptions. Chapter 1 gives the motivation, overview and organization of this dissertation. Chapter 2 describes synthetic details of the materials studied, introduction of two HF-EPR spectrometers, as well as the computer simulation programs employed in this undertaking. Chapter 3 summarizes the HF-EPR studies of Mn:CdSe QDs, the first application of HF-EPR to magnetic QDs. Chapter 4 presents the structure and magnetic characterization of an octahedrally coordinated Cu(II) pair, a very rare bonding for Cu(II) ions. Chapter 5 reports the coherent manipulation of electron spins in an antiferromagnetically coupled spin triangle {Cu3} impregnated in free standing nanoporous silicon (NS) by using 240 GHz microwave pulses. Chapter 6 discusses continuous wave (cw) and pulsed HF-EPR measurements on an Fe-based magnetic cluster: Fe7. Chapter 7 describes the HF-EPR characterization of a high spin (S) compound, Mn7, whose properties straddle the interface between the classical and quantum mechanical spin descriptions. Chapter 8 reports the structure and magnetic properties of a novel, unique, discrete polyanion comprising a cationic, planar Mn19 assembly incorporated in a 60-tungsto-6-silicate. Finally, chapter 9 summarizes the major results and conclusions of this dissertation. |
