Crystal structure of a new ternary molybdate in the Rb2MoO4-Eu2(MoO4)3-Hf(MoO4)2 system

A ternary salt system Rb2MoO4-Eu2(MoO4)3-Hf(MoO4)2 was studied in the subsolidus area by X-ray phase analysis. A novel ternary molybdate, Rb4.98Eu0.86Hf1.11(MoO4)6, formed in the system. The Rb4.98Eu0.86Hf1.11(MoO4)6 rubidium-europium-hafnium molybdate crystals were grown by solution-melt crystallization under the spontaneous nucleation conditions. The structure and composition of this compound were refined by single crystal X-ray diffraction (X8 APEX automated diffractometer, MoKα radiation, 1753 F(hkl), R = 0.0183). The crystals are trigonal, a = b = 10.7264(1) Å, c = 38.6130(8) Å, V = 3847.44(9) Å3, Z = 6, space group R\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$\bar 3$$ \end{document}c. The three-dimensional mixed framework of the structure comprises Mo tetrahedra and two types of octahedra, (Eu,Hf)O6 and HfO6. The large cavities of the framework include two types of the rubidium atom. The distribution of the Eu3+ and Hf4+ cations over two crystallographic positions was refined.