On the porous silicate HPM-5

HPM-5, a porous aluminosilicate with an intricate and so far unsolved structure, has been synthesized by using 1,2,3-trimethylimidazolium in hydroxide medium in the absence of fluoride anions. It consistently displays an ill-defined XRD pattern with broad and overlapped reflections and contains a large concentration of defects, as evidenced by IR and Si MAS NMR spectroscopy. H MAS NMR spectroscopy confirmed the existence of highly deshielded protons (δ = –11.6 ppm) assigned to hydrogen atoms in relatively strong Si–O–H···O–Si hydrogen bonds (O···O distance ≈ 2.64 Å) The calcined material shows limited microporosity (0.07–0.09 cm g). The results of a high-resolution transmission electron microscopy study suggest HPM-5 may be far more complicated than “standard” layered zeolites and may consist of low-density layers profusely decorated by holes. The resulting lace-like layers may be too unstable to withstand reactions characteristic of more conventional layered materials (both delamination and expansion by silylation); although the derivatives show an increase in the specific surface area, the layers are apparently disassembled and, at most, only ribbons remain.The authors acknowledge financial support from the Spanish Ministry of Science and Competitiveness (Projects MAT2012‐31759 and MAT2015‐71117‐R) and from the National Creative Research Initiative Program (2012R1A3A2048833) through the National Research Foundation of Korea. We also thank A. Valera for technical help (FESEM and EDS). A. M. acknowledges the European Union Seventh Framework Programme under Grant Agreement No. 312483‐ESTEEM2 (Integrated Infrastructure Initiative‐I)