HYDROGEN BONDS DISTORT THE ALUMINOSILICATE FRAMEWORK OF AMMONIUM-NATROLITE

ABSTRACT Cation exchange of NH 4 for Na in natrolite yields an anhydrous NH 4 -natrolite, (NH 4 ) 2 Al 2 Si 3 O 10 . The symmetry is reduced from space group Fdd2 in the Na-formato P2 1 in the NH 4 -form. The angles T-O-T and the T-0 bonds of the framework are strongly distorted by the hydrogen bonds of the NH 4 -groups. The NAT framework of natrolite is collapsible, that is all angles T-O-T (the hinges between the rigid TO 4 , tetrahedra) change upon contraction or expansion in the same sense.