[ZnBi₄]^3– Pentagon in K₆ZnBi₅: Aromatic All-Metal Heterocycle

The first aromatic all-metal heterocycle, [ZnBi4]3–, found in the metallic salt, K6ZnBi5, has been synthesized and structurally characterized. The exactly planar [ZnBi4]3– pentagon with six π electrons coupled with multiply bonded Zn–Bi and Bi–Bi bonds, multicentered π-conjugated bonding, and negative nucleus-independent chemical shift values reveals its aromatic character. The metallic nature of K6ZnBi5 has been established by Pauli-type temperature-independent paramagnetism and theoretical analysis of the band structure and total/partial density of states.