Design, synthesis, and properties of a new class of building blocks for assembly of molecule-based magnets

In this work, mono and dianions of the tetrone 1 were proposed as discrete building blocks for assembly of molecular magnets.*; These anionic subunits are designed to form extended multidimensional structures upon complexation with metal rations. This particular framework also was chosen so that dianion 12− (or its derivatives) would possess a paramagnetic triplet as a ground state.; High quality ab-initio CASSCF(14, 12)/6-31+G* calculations showed that indeed the singlet-triplet gap of metal complexes of 1 2− is small and its sign and magnitude tongly depends on structural modifications. For example a 17.3 kcal/mol preference for a singlet is predicted for isolated 12− while the triplet state is preferred by 4.3 kcal/mol for the symmetrically coordinated complex 1(AlF₂)₂.*; Synthetic procedures leading to a family of neutral aryl substituted tetrones (2) has been developed and electrochemical studies have shown that they may be reversibly reduced in two successive one-electron processes to mono- and dianions.; These mono- and dianions have been generated on a preparative scale by reduction of the parent tetrones with alkali metals under anaerobic conditions. Solutions of anions were characterized by Vis-NIR, NMR and EPR spectroscopy. EPR of the anion radicals 2− reveals the high symmetry of the spin delocalisation. Spectroscopic studies of dianions were hampered by low solubility and aggregation phenomena and no definite answer concerning their ground spin states could be obtained.; Several attempts were made to grow single crystals of 2 − and 22− in order to probe the self-assembling properties of those species and to obtain definite answers concerning the ground state of the dianion. These attempts turned out to be successful only for alkali metal salts of the monoanion (t-Bu) ₈(MeO)₄2−. Its K + salt crystallized as 1-D chains with the expected bridging and chelating mode of coordination. The closely related Na+ salt, recently crystallized by Robert Gentner, shows a similar 1-D chain structure.; *Please refer to dissertation for diagrams.