Structure-directing synthesis of two germanate cages featuring odd-member ring windows

Abstract

Zeolites and zeolite-like materials with unique pore structures have emerged as key functional materials in diverse fields such as the chemical industry, environmental protection, and energy, owing to their high selectivity, excellent catalytic performance, robust stability, and multifunctionality. In this study, two germanate compounds with distinct cage-like architectures were successfully synthesized through the rational design of rigid imidazole-based templates, specifically using 3-methyl-1-phenyl-1H-imidazol-3-ium and 3-propyl-1-phenyl-1H-imidazol-3-ium as organic structure-directing agents (SDAs). Single-crystal X-ray diffraction analysis reveals that the two germanates crystallize in the tetragonal I4/m and trigonal R space groups, respectively. Their frameworks are constructed from similar [4⁴3²] composite building units, which assemble into distinctive supercages via vertex-sharing, further stabilized by surrounding imidazolium cations. The supercage in germanate 1 features a 9 × 8-membered-ring (MR) pore aperture, whereas the cage in germanate 2 possesses a 10 × 9 × 7-MR pore window. Both germanates exhibit limited thermal stability, with germanate 2 beginning to decompose at 400 °C and germanate 1 at 350 °C.