Elpasolite-type superstructures in inverse perovskite nitrides

We present a range of inverse perovskite nitrides with an elpasolite-type superstructure. (Ca3N0.682(9))Sn and (Ca3N0.559(7))Pb are variants of the previously described (Ca3N)Sn and (Ca3N)Pb which contain less nitrogen and crystallize in Fm3̄m. (Ba3N0.5)Sn and (Ba3N0.5)Pb resemble the previously reported perovskites (Ba3Nx)Sn and (Ba3Nx)Pb, but with both the superstructure and octahedral tilting, resulting in space group R3̄. (Ca3N0.77(2))Si, (Ca3N0.669(6))Ge, (Sr3N0.5)Ge and (Ba3N0.5)Ge all crystallize in P21/n. Among these, only (Ca3Nx)Ge has been previously described as (Ca3N)Ge. (Ca3N0.77(2))Si is notably the first compound in which mutually isolated N3− and Si4− ions coexist. There also exists a version with composition (Ca3N0.86(6))Si, which crystallizes in the cubic perovskite aristotype structure with space group Pm3̄m. Similarly, there are versions of (Sr3N0.5)Ge, (Ba3N0.5)Sn and (Ba3N0.5)Pb with elevated nitrogen contents, less strongly tilted octahedra and no apparent superstructure. Electronic structure calculations indicate a metallic nature of the title compounds, with rather narrow improper band gaps for the strontium and barium compounds.