Crystal Structure of ITQ-26, a 3D Framework with Extra-Large Pores

ITQ-26 was synthesized via the fluoride procedure using 1,3-bis-(triethylphosphoniummethyl)-benzene as the structure-directing agent. The unit cell and space group were initially determined from electron diffraction experiments on individual tilted microcrystals, using material that had been sectioned by ultramicrotomy. The material crystallizes in space group I4/mmm, where after refining against synchrotron powder data (λ = 0.8714 Å), a = 26.7769(8) and c = 13.2505(5) Å. Integrated electron diffraction intensities (hk0 + 0kl) were assigned phases with the program MICE to yield electrostatic potential maps with the first informative view of the microporous framework. As a constraint for subsequent phasing trials of the powder data with FOCUS, one useful solution was found after 500 000 trials, conforming to the electron crystallographic determination. The final model, refined by Rietveld methods, comprises 7 unique T-sites forming a framework with a straight 12-MR channel along [001]. Two other 12-MR channels are tilted with respect to this one. The T-site density is 14.3 T/1000 A3.