Sc₅Pd₄Si₆– crystal structure and²⁹Si/⁴⁵Sc solid state MAS NMR spectroscopic investigations

Abstract

The silicide ScPdSi was synthesized from the elements by arc-melting. Its structure was refined from single crystal X-ray diffractometer data: Immm, LiCuP type, a = 397.12(6), b = 945.4(1), c = 1314.4(2) pm, wR = 0.0245, 578 F values and 29 parameters. The palladium atoms have slightly distorted tetrahedral silicon coordination and a condensation of these PdSi tetrahedra leads to a two-dimensional substructure which is condensed via Si pairs (234 pm Si-Si), forming the [PdSi] polyanionic network. The ScPdSi structure contains three crystallographically independent scandium sites with coordinations Sc1@PdSiSc, Sc2@PdSiSc and Sc3@PdSiSc. ScPdSi is a Pauli paramagnet with a low susceptibility of 2.9(5) × 10 emu mol at room temperature. The Si 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 threeSc 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.

(Pseudo)binary Antimonides: Insights on Local Ordering and Effective Charge Configurations from 121Sb MAS NMR and Mössbauer Spectroscopies

“…This is likely due to the large 121 Sb quadrupole moment that makes this spin- 5 / 2 nuclide very susceptible to local, structural asymmetries, resulting in strong quadrupolar interactions that extensively broaden the 121 Sb NMR transitions. Two experimental solid-state NMR techniques have primarily been employed to date, allowing researchers to determine information about the local coordination of 121 Sb: for larger quadrupolar coupling strengths ( C Q ≳ 2 MHz), 121 Sb static wide-line or magic-angle spinning (MAS) NMR spectra of only the central Zeeman transition are available. − However, when small to moderate quadrupolar couplings are present, as in the present study for the cubic binary antimonides, 121 Sb MAS NMR spectra containing all five Zeeman transitions (central and satellite Zeeman transitions) can be recorded. , Moreover, in partly disordered solids containing Sb, where distributions of quadrupolar couplings may arise, approximate statistical information about the degree of disorder in the sample has only been reported so far taking advantage of the line width of the central transition. , Herein, we introduce a new approach by comparison of the different 121 Sb NMR line intensities for the central- and satellite-transitions occurring for ordered and disordered cubic systems.…”

“…43,44 Moreover, in partly disordered solids containing Sb, where distributions of quadrupolar couplings may arise, approximate statistical information about the degree of disorder in the sample has only been reported so far taking advantage of the line width of the central transition. 43,45 Herein, we introduce a new approach by comparison of the different 121 Sb NMR line intensities for the central-and satellite-transitions occurring for ordered and disordered cubic systems.…”