Expanding the coordination chemistry of bismuth : synthesis and characterization of heavy pnictogen ligated 3d transition metal complexes




Cashman, Brenna Kelsey

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The coordination chemistry of the very heavy pnictogens, bismuth in particular, have been historically underdeveloped compared to the chemistry of their lighter congeners. Unlike nitrogen and phosphorous, among the most ubiquitous donor atoms in modern inorganic chemistry, bismuth is a poor σ donor with a relativistically contracted 6s lone pair. Additionally, bismuth’s weak bonds with carbon further complicate the design and synthesis of bismuth-based ligands. Despite these inherent challenges, bismuth’s status as the heaviest of the stable elements makes it an intriguing potential donor atom as the coordination of heavy elements to light, spin bearing centers can impart a number of benefits by increasing the spin-orbit coupling character of the spin center through the heavy atom effect. Unfortunately, the investigation of the effect in bismuth-bound transition metal centers has thus far been hindered by the fact that the known library of bismuth-ligated transition metal species is almost entirely dominated by diamagnetic, low-valent metal carbonyls.
The work described herein involves the expansion of the known chemistry of bismuth to include its ligation to paramagnetic 3d transition metal centers as well as the examination of influence of heavy pnictogen ligation on 3d magnetic centers. The reactivity of neutral, monodentate bismuth ligands with paramagnetic transition metal salts was investigated, resulting in the synthesis of an unusual bismuth “nano-square” which was characterized and the structural factors driving its formation were examined. To facilitate metal coordination, a set of anionic pnictogen-based ligands were designed and synthesized, and the resulting isostructural, isoelectronic series of pnictogen ligated paramagnetic cobalt(I) were synthesized. The electronic structure and magnetic properties of these cobalt centers featuring bonds to heavy pnictogens (As, Sb, Bi) were investigated through dc magnetometry and multi-reference quantum chemical calculations.



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