A niobium-necked cluster [As3Nb(As3Sn3)]3− with aromatic Sn32−

We describe here the synthesis and characterization of a ternary cluster compound [As3Nb(As3Sn3)]3− (1), in which a niobium(V) atom is coordinated by an As33− triangle and a bowl-type As3Sn35− ligand. Cluster 1 was synthesized by dissolving K8NbSnAs5 (2) in the presence of [2.2.2]crypt in ethylenediamine solution, filtered and layered with toluene, then crystallized in the form of [K([2.2.2]crypt)]3[As3Nb(As3Sn3)]·en·tol. The flower-vase shaped compound 1 features a new structure type, rather different from the known Zintl phases. The stability and bonding of 1 are elucidated via extensive bonding analyses. The Sn3 ring is found to have σ-aromaticity featuring a delocalized Sn–Sn–Sn σ bond. Electronic structure calculations confirm the Nb(V) oxidation state and weak Nb–Sn and Sn–Sn bonding, in addition to the normal Nb–As and As–As bonds.