B-containing molecular sieves crystallized in the presence of ethylenediamine. Part I: crystal structure of as-synthesized B-FER

Abstract

Hydrothermal treatment of an aqueous solution containing tetramethoxysilane, boric acid and ethylenediamine (EN) led to the crystallization of B-MFI (BOR-C) accompanied by small amounts of B-ferrierite (B-FER). Single crystal X-ray diffraction studies were performed on a platy B-FER crystal, with the unit cell dimensions a=18.512(2), b=13.865(1), c=7.317(1) Å, V=1877.9 Å 3, space group Immm. Framework incorporation of 6.5±0.5 B atoms/unit cell was evidenced with no extra-framework B species, in line with wavelength dispersive spectroscopy analysis of the B-FER crystals (6.5 B atoms/unit cell). Two crystallographically independent EN molecules were located with a total occupancy corresponding to 3.6 molecules/unit cell. Since the synthesis was performed in the absence of alkali metal ions, the EN molecules have to be in the dicationic form to compensate the negative framework charge or, at least, they interact with Brønsted protons forming N⋯H–O hydrogen bonds.