Hydrothermal synthesis and structure of ASU-14 topological framework by using ethylenediamine as a structure-directing agent

Abstract

A new germanate with interesting three-dimensional channels, [(H 2en) 2(en)][Ge 9O 18(OH) 4] (en=ethylenediamine), was synthesized from an aqueous solution containing GeO 2, pyridine, phosphate, hydrofluoric acid and en as a structure-directing agent (SDA). The colorless block-shaped crystals were obtained, and characterized by scanning electron microscopy, thermogravimetric analysis and X-ray powder diffraction analysis. The structure was determined by single crystal diffraction to be monoclinic, space group P2 1/n, a=9.963(2) Å, b=10.167(2) Å, c=13.032(3) Å, and β=90.11(3)°, and Z=2, V=1320.1(5) Å 3, R 1=0.0600 for the reflections with I>2 σ( I) and wR=0.1583. The three-dimensional structure has the same topological framework as the reported germanate ASU-14, which was originally synthesized with piperazine as an SDA, and is built up by GeO 4 tetrahedra, GeO 5 square pyramid and GeO 6 octahedra, connected to form interesting 10-membered rings along the crystallographic a-axis.