Synthesis and Characterization of Cs₅In₃As₄ with a Structure of Two Coexisting “Polymorphic” Forms of Different Dimensionality

The title compound was made by fusion of a stoichiometric mixture of the pure elements at 500 °C. The structure (monoclinic, P2₁/c, Z = 8, a = 17.037(6), b = 12.253(1), c = 18.105(4) Å, β = 117.24(2)°) is made of alternating one- and two-dimensional sections with the same composition of Cs₅In₃As₄, and can be considered as two coexisting polymorphic forms of the same compound. The chains and layers in these sections are made of repeating semicubane motifs of [In₃As₄]^5- that are connected to each other by In−As bonds in the chains, and by both In−As and In−In bonds in the layers. According to magnetic measurement and EHMO calculations, Cs₅In₃As₄ is a closed-shell compound that fulfills the Zintl concept.