Cyanide Bridged Molecular Magnetic Materials with Anisotropic Transition Metal Ions: Investigation of Bistable Magnetic Phenomena

Abstract

The work presented herein focuses on the synthesis and characterization of new cyanide bridged molecular magnetic materials that form discrete molecules as well as three dimensional networks. This research is inspired by the recognition that the Prussian blue (PB) family exhibits a wide range of interesting magnetic properties such as photomagnetism, spin crossover, and high TC magnets owing to the presence of the cyanide bridge that promotes magnetic communication between adjacent metal spins. An underexplored facet of this research is the systematic development of the topic with anisotropic metal ions research that was undertaken as part of this dissertation. The resulting discoveries are materials that exhibit a wide range of bistable magnetic properties, including photomagnetism, long range magnetic ordering, SMM, and exchange-biased SMM behavior. New Prussian Blue analogs are presented in Chapter II of this thesis that are based on the nearly unexplored hexacyanoosmate(III) ion. A family of CoII PB derivatives of OsIII were found to exhibit photomagnetic and charge transfer induced spin transition (CTIST) behavior and a study of alkali metal cation dependence revealed marked differences in both the photomagnetic and CTIST properties, with the highest ordering temperature being observed for the K+ analog which exhibits a TC of 28.5 K. The phenomenon of linkage isomerism reported for PB analogs and other molecular materials that incorporate the [Cr(CN)6]3- ion wherein the CN ligand reverses its binding mode between the two metal centers was studied in detail as described in Chapter III. Small molecule models that incorporate [Cr(CN)6]3- and CoII ions were investigated by single crystal X-ray crystallography, magnetism, and solution IR studies and the data led to useful mechanistic information about the nature of the cyanide reversal process. The use of the anisotropic hexacyanoosmate(III) anion to form a trinuclear species with MnIII was undertaken in the study described in Chapter IV. The first SMM based on the hexacyanoosmate(III) ion was discovered and found to exhibit a very rare exchange biased SMM phenomena in one of its crystal forms. In Chapter V new building blocks with the pentadentate MPPA ligand are described which are ideally suited for the preparation of a range of model compounds of the dinuclear and trinuclear variety.