Flexibility and distortion of the collapsible framework of NAT topology: the crystal structure of H3O-natrolite
Stuckenschmidt, Elli; Joswig, Werner; Baur, Werner H.
published: Feb 22, 1996
manuscript accepted: Oct 8, 1995
manuscript received: May 12, 1995
ArtNo. ESP147050801010, Price: 29.00 €
Abstract As far as we knojw, this is the first instance that oxonium ions could be detected in a zeolite structure. A single crystal of H3O-natrolite was prepared by calcination of ammonium-natrolite. The space group C1121 is the same as for NH4-natrolite. The volume of the unit cell of H3O-natrolite (a = 17.912(6) Å, b = 18.474(4) Å, c = 6.542(2) γ = 90° , V = 2164.8(9)Å3) is slightly enlarged compared with NH4-natrolite (a = 17.899(2) Å, b - 18.390(2) Å, c = 6.529(1) Å, γ = 90°, V = 2149.1(8) Å3). The original single crystal of NH4-natrolite remained twinned during calcination (normal to  or ). The residual index after the refinement based on F2 is wR2 = 7.7% for 2919 F2obs. Starting with Na-natrolite, the distortion of the framework increases in NH4-natrolite and grows even stronger in H3O-natrolite. The hydrogen bonding to framework oxygen atoms from the oxonium ions leads to asymmetrical distortions of the tetrahedra with short Si-O distances (min. 1.580 Å) and relatively long Al-O distances (max. 1.769 Å). Hydrogen bonded oxygen atoms have, on average, smaller T-O-T angles (4.3°) than not-hydrogen bonded oxygen atoms of the framework.