Sanders, Codi Anne (2016-08). Investigation of Magnetic Behavior: The Tuning of Spin-Transitions and Redox Properties in Pentanuclear Cyanide Architectures. Doctoral Dissertation.
Thesis
The critical need to miniaturize electronic devices has initiated a renaissance in the study of the electronic and magnetic properties of both discrete molecules and extended structures vis-a-vis their potential for high-density data storage devices, sensors, switches, displays and quantum computing. Researchers in molecular magnetism are focusing on the fundamental behavior of unusual paramagnetic molecules in an effort to rationally design those with improved properties which requires exquisite synthetic control. One strategy that is particularly successful is to use a linear bridging ligand, such as cyanide, that allows for predictive magnetic exchange between spin centers. The use of cyanometallates to bridge metal centers has led to interesting properties, including remnant magnetization above room temperature, spin-crossover (SCO), charge-transfer-induced-spin-transition (CTIST), photomagnetism and single molecule magnetic properties. The research described in this dissertation focuses on the synthesis of [Ru^III(CN)6]^3- and [Os^III(CN)6]^3- and their incorporation into discrete, pentanuclear molecules, referred to as trigonal bipyramids (TBPs). TBPs are modeled after the well-studied Prussian blue and its analogs (PBAs) and has a general formula of [M^II(tmphen)2]3[M'^III(CN)6]2 (M3M'2), which allows for six equivalent exchange interactions. TBPs are the largest homologous family of cyanide materials reported in literature and have been shown to mimic the behaviors exhibited by PBAs. The incorporation of the heavier Group VIII 4d and 5d hexacyanometallates into TBPs was undertaken to explore magnetic exchange through the CN- bridges which had been found to lead to interesting magnetic phenomena for the Fe analogs. The tools of IR spectroscopy, thermal gravimetric analysis, magnetometry, single X-ray crystallography and ^57Fe Mossbauer spectroscopy (when appropriate) have been used to characterize the TBPs discussed herein. The rich redox behavior in the new Co3Ru2 and Co3Os2 TBPs manifested itself in the irreversible metal-to-metal-charge-transfer event in the Co3Ru2 and the reversible CTIST in the Co3Os2 TBPs. The Co3Os2 TBP is one of a very small number of compounds to display CTIST and is only the second Co/Os cyanide compound to do so, preceded only by a Co3Os2 Prussian Blue analog from the Dunbar laboratories. A study of the first Fe/Ru cyanide compound to exhibit CTIST is discussed in regard to how the identity and amount of solvent in the Fe3Ru2 TBP effects the CTIST events. A final study was aimed at investigating how changes in the ?-? stacking interactions in the Fe3Co2 TBP affects the SCO behavior of the equatorial Fe^II metal centers.
