Abstract: 

Extended metal atom chain complexes (EMAC) are 1-D arrangements of three or more metal atoms that often contain direct metal-metal bonds. EMAC that incorporate first-row transition metals can have unique magnetic behaviors arising from the combination of high spin metal centers with direct magnetic exchange. Many trimetallic EMACs are known, however they are almost exclusively supported by dipyridylamine (dpa) and take the form M3(dpa)4X2 where M = Cr, Mn, Co, Ni, or Cu and X is a halide or small monoanion. These complexes typically have low spin electronic configurations, a consequence of their moderate to strong M-M bonds and strong, tetragonal ligand fields. Therefore, a significant synthetic challenge exists to find ways to support M-M bonds that are low to moderate strength but also have low coordination numbers to promote formation of high spin complexes. A complex of this type can have large spin ground states and significant magnetic anisotropy, with potential application as single-molecule magnets.

 

This work utilizes the more sterically diverse 2,6-bis(trialkylamino)pyridine ligands to isolate EMACs with different coordination numbers and structures. For example, we have shown that both 2,6- bis(trimethylsilylamino)pyridine (H2LMe) and 2,6-bis(dimethylphenylsilylamino)pyridine (H2LPh) can support triiron EMACs. These two complexes are extremely unique, and remain the only two known EMAC of Fe(II) with Fe-Fe bonding. They are isostructural with a composition of Fe3L3, similar Fe-Fe bond lengths, a helical arrangements of ligands, and trigonal coordination about each Fe(II). Other complexes supported by this ligand family will be presented as well as their magnetic, electrochemical, and spectroscopic properties. Attempts to computationally model the respective orbital energy diagrams will also be discussed.