[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.