Synthesis, Structure, and Properties of a Three-Dimensional Open-Framework Niobium Fluorogermanate (NGH-5)

The low-temperature hydrothermal synthesis and crystal structure of a new open-framework niobium germanate phase is reported. (C 6 H 18 N 2 )·Ge 2.2 Nb 0.8 O 6.8 F 1.2 (NGH-5) was synthesized from GeO 2, Nb 2 O 5, and HF (aq) by using 1,4- trans -diaminocyclohexane (1,4-DACH) as an organic structure directing agent. The structure of NGH-5 was determined ab initio by using powder X-ray diffraction techniques and consists of a negatively charged three-dimensional Nb/Ge/O/F framework containing three orthogonal channel systems. Two of the channels are delimited by 10-membered rings of NbO 5 F octahedra and GeO 4 tetrahedra; the third is delimited by an 8-membered ring. Charge-balancing (C 6 H 18 N 2 ) 2+ cations are encapsulated within the framework and are located at the center of the 10-membered ring channels. The NGH-5 framework is characterized by a low framework density and is closely related to the recently reported zirconium germanate ASU-15.