Synthesis, single-crystal structure, and optical absorption of Rb2Th7Se15

The compound Rb2Th7Se15 has been synthesized by the solid-state reaction at 1273 K of Th, Rb2Se3, Se, and Ge, and its structure has been determined by single-crystal X-ray diffraction methods. Red crystals of Rb2Th7Se15 crystallize at 100(2) K with four formula units in a new structure type in the monoclinic space group C2h5−P21/c. The structure is three-dimensional and comprises Rb and Th atoms coordinated by Se atoms to form nine-, eight-, and seven-coordinate polyhedra. Infinite channels that contain Rb atoms are present. Crystals of Rb2Th7Se15 are red in color; an indirect band gap of 1.83 eV was derived from single-crystal optical measurements. - Graphical abstract: Structure of Rb2Th7Se15 viewed down the b-axis. Display Omitted - Highlights: • The new compound Rb2Th7Se15 was synthesized at 1273 K from the elements in the presence of Ge. • The structures of the two known Rb/Th/Se compounds, RbTh2Se6 and Rb2Th7Se15, differ markedly. • Optical measurements establish the band gap of Rb2Th7Se15 to be indirect with a value of 1.83 eV