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, Li5Cu3.75P6 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.