Add a Pinch of Tetrel: The Transformation of a Centrosymmetric Metal into a Nonsymmorphic and Chiral Semiconductor

Centrosymmetric skutterudite RhP₃ was converted to a nonsymmorphic and chiral compound RhSi_0.3 P_2.7 (space group P2₁ 2₁ 2₁ ) by means of partial replacement of Si for P. The structure, determined by a combination of X-ray crystallography and solid state ³¹ P NMR, exhibits branched polyanionic P/Si chains that are unique among metal phosphides. A driving force to stabilize the locally noncentrosymmetric cis-RhSi₂ P₄ and fac-RhSi₃ P₃ fragments is π-electron back-donation between the Rh t_2g -type orbitals and the unoccupied antibonding Si/P orbitals, which is more effective for Si than for P. In situ studies and total energy calculations revealed the metastable nature of RhSi_0.3 P_2.7 . Electronic structure calculations predicted centrosymmetric cubic RhP₃ to be metallic which was confirmed by transport properties measurements. In contrast, the electronic structure for chiral orthorhombic RhSi_0.3 P_2.7 contained a bandgap, and this compound was shown to be a narrow gap semiconductor.