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. (C6H18N2). Ge2.2Nb0.8O6.8F1.2 (NGH-5) was synthesized from GeO2, Nb2O5, 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 NbO5F octahedra and GeO4 tetrahedra; the third is delimited by an 8-membered ring. Charge-balancing (C6H18N2)(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.