Preparation of molecule-based magnets from metal thiocyanate complexes

The study of magnetism has enabled many technological applications that are ubiquitous in our daily life. Presently, most of the magnetic applications use metal/metal oxide magnets, which are readily available. In the last few decades, research has focused on a new class of magnetic materials, molecule-based magnets. This class of materials has diverse physical and chemical properties, which can be controlled by synthetic methods. Utilizing a variety of metals and ligands, researchers can control and fine tune various aspects of these magnetic materials, such as structural connections and possibly magnetic properties. Tetracyanoethylene (TCNE) is widely used in the preparation of molecule-based magnets due to its unique electronic and connectivity properties. TCNE has multiple binding sites, which gives it a diverse range of structural connectivity. Also, TCNE can be reduced easily to form a radical anion, which facilitates spin communication between metal centers allowing isolation of magnetically ordered systems such as V(TCNE)2 (a room temperature molecule-based magnet). M-TCNE magnets are prepared from solvated MII complexes or a metal carbonyl and TCNE in dichloromethane. The reaction involves the oxidation of the MII to MIII and the reduction of TCNE. More coordinating solvents used to prepare TCNE molecule-based magnets facilitate the dimerization of the radical TCNE, which does not allow for long-range ordering. The work presented herein will show the synthesis of MII thiocyanate complexes and their reaction with TCNE radical anion to yield M(TCNE)[C4(CN)8]1/2, which is obtained through ligand substitution between TCNE and thiocyanate.;The development of new MII thiocyanate complexes through MII(NCMe)x(BF4)2 (x = 4, 6) in acetone, acetonitrile, and tetrahydrofuran will be the focus of Chapter 2. Also, in Chapter 2, structural and magnetic characterization will be discussed. Few of the metal thiocyanate complexes exhibit antiferromagnetic ordering at temperatures ranging from 8 to 50 K. Next the use of iron, manganese, and cobalt thiocyanate complexes for the preparation of M(TCNE)[C4(CN) 8]1/2 will be presented in Chapter 3. In Chapter 4, the effects of acetone and acetonitrile in the preparation of M-TCNE systems will be presented and structural and magnetic properties will be discussed. Mixed metal molecule-based magnets of the composition of M'xM''1-x (TCNE)[C4(CN)8]1/2 (M', M'' = Fe, Mn, Co) will be explored in Chapter 5. The metal composition ratios, coercive field, and critical temperature (T c) will be considered. Chapter 6 will cover some concluding remarks and some future directions towards the design and synthesis of new molecule-based magnets.