Synthesis and Characterization of Transition-Metal Zintl Phases:  Cs₂₄Nb₂In₁₂As₁₈ and Cs₁₃Nb₂In₆As₁₀ with Isolated Complex Anions

The title compounds were prepared by direct reaction of the corresponding elements at high temperature. Their structures were determined by single-crystal X-ray diffraction (Cs₂₄Nb₂In₁₂As₁₈, triclinic, P1̄, Z = 1, a = 9.519(4), b = 9.540(5), and c = 25.16(1) Å, α = 86.87(4), β = 87.20(4), and γ = 63.81(4)°; Cs₁₃Nb₂In₆As₁₀, triclinic, P1̄, Z = 1, a = 9.5564(5), b = 9.6288(5), and c = 13.9071(7) Å, α = 83.7911(8), β = 80.2973(8), and γ = 64.9796(8)°). Cs₂₄Nb₂In₁₂As₁₈ and Cs₁₃Nb₂In₆As₁₀ contain isolated anions of [Nb₂In₁₂As₁₈]^24- and [Nb₂In₆As₁₀]^13-, respectively. Each anion includes two cubane-like units made of one niobium, three indium, and four arsenic corners where a fifth arsenic atom completes the tetrahedral coordination at niobium, [(NbAs)In₃As₄]. In Cs₁₃Nb₂In₆As₁₀ these two units are connected via a direct In−In bond between two indium vertexes of the cubanes. In Cs₂₄Nb₂In₁₂As₁₈, on the other hand, the same two units are linked by a dimer made of semicubanes of [In₃As₄], i.e., a cubane with one missing vertex. Magnetic measurements show that Cs₂₄Nb₂In₁₂As₁₈ is diamagnetic, i.e., a d⁰ transition-metal Zintl phase, while Cs₁₃Nb₂In₆As₁₀ exhibits a Curie−Weiss behavior that corresponds to one unpaired electron.