Ternary silicides Sc3TSi3 (T = Ru, Rh, Ir, Pt) - Structure, chemical bonding, and solid state NMR

Harmening T, Mohr D, Eckert H, Alam AA, Matar SF, Pöttgen R

Abstract

New complex silicides Sc3TSi3 (T = Ru, Rh, Ir, Pt) were prepared by arc-melting of the elements. They crystallize with a new orthorhombic structure type, space group Pnma. The four structures were refined from single crystal diffractometer data: a = 1167.6(3), b = 398.20(9), c = 1026.9(2) pm, wR2 = 0.0559, 923 F2 values for Sc3RuSi 3, a = 1166.8(1), b = 401.85(5), c = 1019.7(1) pm, wR2 = 0.0355, 819 F2 values for Sc3RhSi3, a = 1160.7(2), b = 402.84(6), c = 1015.1(2) pm, wR2 = 0.0352, 905 F2 values for Sc3IrSi3, and a = 1166.3(1), b = 403.18(5), c = 1019.3(2) pm, wR2 = 0.0465, 917 F2 values for Sc 3PtSi3 with 44 variables per refinement. The Sc 3TSi3 structures contain complex three-dimensional [TSi3] polyanionic networks with slightly distorted tetrahedral silicon coordination of the transition metal atoms, e.g. 237-254 pm Ru-Si in Sc3RuSi3. The RuSi4tetrahedra share common corners along the short unit cell axis and these rows are connected by Si-Si bonds, leading to Si3 units (243- 244 pm Si-Si) within the [RuSi 3] polyanion. Ab initio electronic structure investigations point to dominating Ru-Si interactions and show strong electron localization around the Si3 units, underlining the polyanionic character. Significant differences in the 45Sc quadrupolar interaction strengths between the three distinct scandium sites in the Sc3TSi3 silicide were detected by lineshape analyses of field dependent 45Sc MAS as well as 2D TQMAS NMR spectroscopic data. By comparing the experimentally obtained quadrupole interaction parameters with theoretically calculated ones a site assignment of the equal intense signals is possible.