Synthesis and Characterization of Alkali-Metal Salts of 2,2′- and 2,4′-Bipyridyl Radicals and Dianions

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Abstract
The reaction of ethylenediamine (en) solutions of 2,2′- and 2,4′-bipyridine (bipy) with varying stoichiometric amounts of potassium and rubidium metal resulted in the isolation of compositionally pure solids containing the respective bipyridyl radical anions (2,2′- and 2,4′-bipy•−) and dianions (2,2′- and 2,4′-bipy2−). These species were structurally characterized by single-crystal X-ray diffraction in K(2,2′-bipy)(en) (1a), K4(2,2′-bipy)4(en)4 (1b), Rb2(2,2′-bipy)(en)2 (2), K(2,4′-bipy)(en) (3), K4(2,4′-bipy)2(en)3.5 (4), and Rb4(2,4′-bipy)2(en)3.5 (5). The crystallographic results obtained allow for interesting relationships to be drawn between the electronic structure of the bipyridyl moieties and metric structural data. Further characterization of the solids by means of powder X-ray diffraction, elemental analysis, electron paramagnetic resonance, and IR and Raman spectroscopy is also reported. These studies provide a comprehensive overview of the structural and spectroscopic properties of these often-cited yet elusive air- and moisture-sensitive species, helping to complement the existing data in the chemical literature.