Sc5Pd4Si6 – crystal structure and 29Si/45Sc solid state MAS NMR spectroscopic investigations

Abstract

The silicide Sc₅Pd₄Si₆ was synthesized from the elements by arc-melting. Its structure was refined from single crystal X-ray diffractometer data: Immm, Li₅Cu_3.75P₆ type, a = 397.12(6), b = 945.4(1), c = 1314.4(2) pm, wR₂ = 0.0245, 578 F² values and 29 parameters. The palladium atoms have slightly distorted tetrahedral silicon coordination and a condensation of these PdSi₄ tetrahedra leads to a two-dimensional substructure which is condensed via Si₂ pairs (234 pm Si–Si), forming the [Pd₄Si₆]^δ− polyanionic network. The Sc₅Pd₄Si₆ structure contains three crystallographically independent scandium sites with coordinations Sc1@Pd₄Si₈Sc₆, Sc2@Pd₆Si₆Sc₃ and Sc3@Pd₄Si₆Sc₄. Sc₅Pd₄Si₆ is a Pauli paramagnet with a low susceptibility of 2.9(5) × 10⁻⁵ emu mol⁻¹ at room temperature. The ²⁹Si MAS-NMR spectrum confirms the presence of two crystallographically distinct sites in a 2 : 1 ratio. Likewise, the three crystallographic scandium sites are well-differentiated by three ⁴⁵Sc MAS NMR signals in the expected 2 : 2 : 1 ratio. Unambiguous assignments could be made based on the comparison of the nuclear electric quadrupolar coupling parameters with predicted values from WIEN2k calculations.