Cubane with a handle: [[In(3)As(4)Nb]-As](7-) in Cs(7)NbIn(3)As(5).

Compared to the large number of main group Zintl compounds there are only a few that contain transition metals.[1] This is not surprising since the traditional definition of Zintl phases automatically excludes transition metals. However, many such compounds with transition metals can qualify for Zintl phases when a broader definition is used. The latter includes compounds of transition metals with filled or empty d shells, that is the late transition metals of the Ni, Cu, and Zn groups,[2] and the early transition elements of the Ti, V, and Cr groups at maximum formal oxidation states.[3] There are only two Zintl compounds containing a transition metal with partially filled d shell, both based on manganese, (AE)14MnPn11 (AE alkaline-earth metal, Pn pnictogen) and Sr21Mn4Sb18. Perhaps only they should be called true TMtransition metal Zintl phases∫ although the name is contradictory in itself. All but two of the d0 compounds contain isolated tetrahedra [MPn4] (M Nb, Ta, W, Ti).[5] The two exceptions are Na5HfAs3 with dimers of edge-sharing tetrahedra of [Hf2As6] and Rb5TaAs4Tl2 with [TaAs4] tetrahedra, where two Tl atoms bridge opposite edges, ( -Tl)[As2TaAs2]( -Tl)5 .[6] Here we report a new d0 transition metal Zintl phase, Cs7NbIn3As4, which contains an unprecedented anion, [{In3As4Nb} As]7 , a cubane made of three indium, four arsenic, and one niobium atom and a TMhandle∫ composed of an arsenic atom that is multiply bonded to the niobium corner. The title compound was initially made in an attempt to synthesize the recently reported Cs5In3As4 at temperatures higher than the original 500 C.[7] The reaction was carried out in niobium containers at 800 C, at which temperature the arsenic apparently attacked the container and formed the quaternary compound Cs7NbIn3As4. Later it was synthesized in high yield using the corresponding elements in stoichiometric ratio at the same temperature.[8] The overall structure of Cs7NbIn3As5 is quite simple and unremarkable,[9] an ionic assembly of isolated anions of [NbIn3As5] immersed in a TMsea∫ of cesium cations that screen them from each other (inter-anion dmin 5.009(4) ä). What is remarkable is the structure and bonding of the anion (Figure 1). Its geometry can be viewed in a few different ways. The more obvious approach is to recognize the cubane shape made of one Nb, three In, and four As atoms, [NbIn3As4], and its TMhandle∫ of a fifth arsenic atom attached to the niobium