Synthesis, Crystal Structure, and Magnetic Properties of R2Mg3SiPn6 (R = La, Ce; Pn = P, As)

Four new quaternary pnictides, R2Mg3SiPn6 (R = La, Ce; Pn = P, As), were synthesized via high-temperature solid-state reactions and gas-phase transport reactions with iodine. Their crystal structures were determined by single crystal X-ray diffraction. All four compounds are isostructural and crystallize in a new structure type in the orthorhombic space group Pnma (No. 62, Z = 4), Pearson symbol oP48. The crystal structures of R2Mg3SiPn6 are composed of two-dimensional puckered MgP3 layers, which are connected in a three-dimensional framework by P–P dimers and MgSiP4 double-tetrahedral chains. Rare-earth cations are encapsulated inside the channels of the framework running along [010]. Quantum-chemical calculations predict that La2Mg3SiP6 is an indirect narrow bandgap semiconductor. The Mg–P bonding in MgP4 tetrahedra and MgP6 octahedra was analyzed by means of crystal orbital Hamilton population (COHP) analysis. Magnetic characterization of Ce-containing compounds confirmed the trivalent nature of cerium...