(V@Ge8As4) 3 and (Nb@Ge8As6) 3 : encapsulation of electron-poor transition metal atoms†

[K([2.2.2]crypt)]+ salts of [V@Ge8As4]3− and [Nb@Ge8As6]3− were obtained by extraction of quaternary phases with en/[2.2.2]crypt. The V–Ge–As anion is the first Zintl anion incorporating a (formal) V5+ cation, thus the smallest cation ever embedded within a main group (semi-)metal cage. It represents the second example of a novel 12-vertex cluster architecture. The bonding situation was elucidated by quantum chemistry, also allowing for a precise assignment of Ge vs. As atoms, being indistinguishable by X-ray diffraction.