Solid state NMR spectroscopy as a probe of structure and bonding in the carbides Sc3TC4 (T = Co,Ni, Ru,Rh, Os,Ir)

Scandium transition metal carbides having the formula Sc₃TC₄ (T = Co, Ni, Ru, Rh, Os, Ir) have been structurally characterized by solid state ¹³C and ⁴⁵Sc nuclear magnetic resonance spectroscopy. In all the compounds investigated, well-resolved signals are observed for crystallographically distinct carbon and scandium sites, confirming the formation of superstructures in the Rh and Ir compounds at ambient temperature. ⁴⁵Sc NMR spectra are dominated by anisotropic broadening due to second-order quadrupolar perturbations. The nuclear electric quadrupolar coupling parameters (the coupling constant C_Q and the asymmetry parameter η) are generally found in good agreement with values calculated theoretically from the crystal structure using the WIEN2k program. Furthermore, the spectra reveal large isotropic resonance shift differences between inequivalent Sc sites in a given compound and between sites of the same type for different compounds. Altogether the results illustrate that ⁴⁵Sc NMR is a sensitive method for detecting isotropic and anisotropic local electron density variations in the Sc₃TC₄ family.