Synthesis and characterization of the new cyclosilicate hydrate (hexamethyleneimine)4•[Si8O16(OH)4]•12H2O

A new cyclosilicate hydrate with composition (C6H14N)(4)center dot[Si8O16(OH)(4)]center dot 12H(2)O was crystallized and the structure determined by single-crystal X-ray diffraction. The structure, described by the tetragonal space group I4(1)/a, with unit cell dimensions of a = 39.2150(2) angstrom and c = 14.1553(2) angstrom, contains columns of hydrogen-bonded cubic octamer silicate anions. The space between silicate columns holds hydrogen-bonded water and protonated hexamethyleneimine molecules compensating the negative charge of the silicate. The crystal water can be removed resulting in a rearrangement of the columns into ortho-rhombic symmetry. Removal of the organic moiety causes amorphisation. Flash evacuation results in a new microporous material with pore volumes typical of a zeolite. (C) 2009 Elsevier Inc. All rights reserved.