The synthesis and structure of Bi-7(3-), the only missing member of the family of heptanuclear pnictogen cluster anions Pn(7)(3-) (Pn = pnictogen, a group 15 element excluding the unique nitrogen), is reported. The new species is synthesized by oxidation of a solution of K5Bi4 by the solvent pyridine in the presence of (C6H6)Cr(CO)(3). The existence of the species in solution is confirmed by electrospray mass spectrometry, while its structure is elucidated by single-crystal X-ray diffraction in the compound [K(2,2,2-crypt)](3)Bi-7 center dot 2py (monoclinic, P21/n, a = 13.8739(13) angstrom, b = 24.878(2) angstrom, c = 26.401(2) angstrom, beta = 96.353(4)degrees, V = 9056.5(14) angstrom(3), Z = 4, and R1/wR2 = 0.0636/0.1390 for the observed data and 0.0901/0.1541 for all data).