Structural Variations in Complex Sodium Thorium Arsenates

Three new sodium thorium arsenates, Na 5 Th 4 (AsO 4 ) 7 ( 1 ), Na 5 Th(AsO 4 ) 3 ( 2 ), and Na 4 Th(As 2 O 7 ) 2 ( 3 ) were synthesized via a high temperature route and their structures and optical properties were studied. Compound 1 adopts a three‐dimensional structure that consists of tetrameric fundamental building blocks (FBBs) [Th 4 (AsO 4 ) 7 ] 5– , which are constructed by ThO 8 and ThO 9 polyhedra. The structures of 2 and 3 are based on open frameworks with channels running along the a or c axes, respectively, which are occupied by Na cations. Structural relations between the structures of 2 and 3 have been discussed regarding their composition. In contrast to the other two compounds, the arsenate anions in the structure of 2 play role of bridging ligands and do not connect more than two Th atoms. Owing to this, the underlying net of this compound contains only Th nodes has a lon topology. The Raman spectra of 1 and 2 contain similar peaks due to As–O vibrations of AsO 4 groups, while the Raman spectrum of 3 differs significantly owing to the presence of As–O–As bridging group in As 2 O 7 4– anions.