(A(19)N(7))[In-4](2) (A = Ca, Sr) and (Ca4N)[In-2]: Synthesis, crystal structures, physical properties, and chemical bonding

Single phase powders of (A(19)N(7))[In-4](2) (A = Ca, Sr) and (Ca4N)[In-2] were prepared by reaction of melt beads of the metallic components with nitrogen. The crystal structure of (Ca19N7)[In-4](2) was refined based on neutron and X-ray powder diffraction data. The crystal structure of (Sr19N7)[In-4](2) was solved from the X-ray powder pattern. The structure refinements in combination with results from chemical analyses ascertain the compositions. The compounds (A(19)N(7))[In-4](2) (A = Ca, Sr) are isotypes of (Ca19N7)[Ag-4](2); (Ca19N7)[In-4](2) is probably identical to the earlier reported (Ca18.5N7)[In-4](2). The crystal structure of the isotypes (A(19)N(7))[In-4](2) (A = Ca, Sr; cubic, Fm3m, Ca: a = 1471.65(3) pm; Sr: a = 1561.0(1) pm) contains isolated [In-4] tetrahedra embedded in a framework of edge- and vertex-sharing (A(6)N) octahedra. Six of these octahedra are condensed by edge-sharing around one central A(2+) ion to form superoctahedra (A(19)N(6)) which are connected three-dimensionally via further octahedra by corner-sharing. The crystal structure of (Ca4N)[In-2] (tetragonal, I4(1)lamd, a = 491.14(4) pm, c = 2907.7(3) pm) consists of alternating layers of perovskite type stabs of vertex-sharing octahedra (Ca2Ca4/2N) and parallel arranged infinite zigzag chains (1)(infinity)[In-2]. In the sense of Zintl-type counting the compounds (A(2+))(19)(N3-)(7)[In2.125-)(4)](2) present an electron excess, (Ca2+)(4)(N3-)[(In2.5-)(2)] is electron deficient. Metallic properties are supported by electrical resistivity and magnetic susceptibility measurements. The analysis of the electronic structures gives evidence for the existence of homoatomic interactions In-In and significant heteroatomic metal-metal interactions Ca-In which favor the deviations of the title compounds from the (8-N) rule.