A Multiply Bonded Trigonal-Planar Bismuth(III) Complex: Prodigious Lewis Acidity, Solvatochromism, Etherification, and Semiconducting Characteristics

The formation of a hitherto unknown 4-center, 6π–conjugated trigonal-planar complex, [Bi{Cr(CO)₅}₃]⁻ (1), is reported, in which the oxidation state of the Bi atom is +3, as evidenced by XAS, XPS, and DFT calculations. The Bi^III atom in 1 has dual donor and acceptor properties in its bonding mode. In contrast to the mild Lewis acidity of Bi^III, the central Bi in 1 functions as a prodigious Lewis acid site to exhibit strong affinity toward F⁻ ions, unique solvatochromic properties, intriguing etherification through the C−O bond cleavage of alcohols, and surprising semiconducting characteristics with an ultra-narrow optical band gap of 1.02 eV, which can be attributed to the intermolecular Bi⋅⋅⋅O and O⋅⋅⋅O interactions in the solid state. The tetrahedral Fe(CO)₄-adduct [{Fe(CO)₄}Bi{Cr(CO)₅}₃]³⁻ (1-Fe) allowed the selective demetallation to afford the isoelectronic multiply bonded BiCr₃-complex 1 and the BiCr₂Fe-complex, [Bi{Cr(CO)₅}₂{Fe(CO)₄}]⁻ (2), which may open a novel pathway for the design of the heterometal-incorporated trigonal-planar Bi-Cr complexes.