Cs3LiZn2(WO4)4 and Rb3Li2Ga(MoO4)4: different filled derivatives of the cation‐deficient Cs6Zn5(MoO4)8 structure

• Published in: Acta crystallographica. Section C, Crystal structure communications Crystal structure communications, 2017-11, Vol.73 (11), p.946-952
• Main Authors: Solodovnikov, Sergey F., Solodovnikova, Zoya A., Zolotova, Evgeniya S., Kadyrova, Yulia M., Savina, Aleksandra A., Stefanovich, Sergey Yu, Khaikina, Elena G.
• Format: Article
• Language: English
• Subjects: Cations; Cesium; Chemical compounds; crystal chemistry; Crystal structure; Crystallography; Cubic lattice; Diffraction; filling vacancies; Gallium; Ions; Lattice vacancies; Lithium; Nonlinearity; Optical materials; Rubidium; Second harmonic generation; structural family; tetrahedral framework; Thermal stability; triple molybdate; triple tungstate; Zinc
• ISSN: 2053-2296; 0108-2701; 2053-2296; 1600-5759
• DOI: 10.1107/S205322961701378X

Two new compounds, namely cubic tricaesium lithium dizinc tetrakis(tetraoxotungstate), Cs3LiZn2(WO4)4, and tetragonal trirubidium dilithium gallium tetrakis(tetraoxomolybdate), Rb3Li2Ga(MoO4)4, belong to the structural family of Cs6Zn5(MoO4)8 (space group I3d, Z = 4), with a partially incomplete (Zn5/6□1/6) position. In Cs3LiZn2(WO4)4, this position is fully statistically occupied by (Zn2/3Li1/3), and in Rb3Li2Ga(MoO4)4, the 2Li + Ga atoms are completely ordered in two distinct sites of the space group I2d (Z = 4). In the same way, the crystallographically equivalent A+ cations (A = Cs, Rb) in Cs6Zn5(MoO4)8, Cs3LiZn2(WO4)4 and isostructural A3LiZn2(MoO4)4 and Cs3LiCo2(MoO4)4 are divided into two sites in Rb3Li2Ga(MoO4)4, as in other isostructural A3Li2R(MoO4)4 compounds (AR = TlAl, RbAl, CsAl, CsGa, CsFe). In the title structures, the WO4 and (Zn,Li)O4 or LiO4, GaO4 and MoO4 tetrahedra share corners to form open three‐dimensional frameworks with the caesium or rubidium ions occupying cuboctahedral cavities. The tetrahedral frameworks are related to that of mayenite 12CaO·7Al2O3 and isotypic compounds. Comparison of isostructural Cs3MZn2(MoO4)4 (M = Li, Na, Ag) and Cs6Zn5(MoO4)8 shows a decrease of the cubic lattice parameter and an increase in thermal stability with the filling of the vacancies by Li+ in the Zn position of the Cs6Zn5(MoO4)8 structure, while filling of the cation vacancies by larger Na+ or Ag+ ions plays a destabilizing role. The series A3Li2R(MoO4)4 shows second harmonic generation effects compatible with that of β′‐Gd2(MoO4)3 and may be considered as nonlinear optical materials with a modest nonlinearity. Cs3LiZn2(WO4)4 and Rb3Li2Ga(MoO4)4 represent two distinct series of filled derivatives of the cation‐deficient Cs6Zn5(MoO4)8 structure with three‐dimensional tetrahedral frameworks related to that of mayenite 12CaO·7Al2O3. The series of tetragonal A3Li2R(MoO4)4 compounds exhibits second harmonic generation effects compatible with that of β′‐Gd2(MoO4)3.