Crystal structure of R3Si1.75Se7 (R – 1.5 Y + 1.5 La)

Highlights: • The crystal structure of the La_1.5Y_1.5Si_1.75Se₇ compound was determined. • Si atoms have two valence states: +2 (octahedral coordination) and +4 (tetrahedral). • Si atoms in oxidation state +2 exhibit substantially ionic chemical bonding. The existence of the new quaternary compound R₃Si_1.75Se₇ (R – 1.5 Y + 1.5 La) was established. Its crystal structure was studied by X-ray powder method (space group P6₃, Pearson symbol h24–1.44, a = 1.05968(2) nm, c = 0.59995(2) nm, R_I = 0.0414). Rare-earth atoms in the structure of this compound are localized in trigonal prisms with two additional atoms, Si^IV atoms center tetrahedra, and Si^II atoms lie in octahedra. Quantum chemical simulation of separate fragments of the structure of this mixed selenosilicate (II, IV) was performed.