Crystal structure of zeolite X nickel(II) exchanged at pH 4.3 and partially dehydrated, Ni 2(NiOH) 35(Ni 4AlO 4) 2(H 3O) 46Si 101Al 91O 384

Abstract

Complete Ni 2+ exchange of a single crystal of zeolite X of composition Na 92Si 100Al 92O 384 per unit cell was attempted at 73°C with flowing aqueous 0.05 M NiCl 2 (pH=4.3 at 23°C). After partial dehydration at 23°C and ≈10 −3 Torr for two days, its structure, now of composition Ni 2(NiOH) 35(Ni 4AlO 4) 2(H 3O) 46Si 101Al 91O 384 per unit cell, was determined by X-ray diffraction techniques at 23°C (space group Fd 3 ̄ , a 0=24.788(5) Å). It was refined using all intensities; R 1=0.080 for the 236 reflections for which F o>4 σ( F o), and wR 2=0.187 using all 1138 unique reflections measured. At four crystallographic sites, 45 Ni 2+ ions were found per unit cell. Thirty of these are at two different site III′ positions. Twenty of those are close to the sides of 12-rings near O–Si–O sequences, where each coordinates octahedrally to two framework oxygens, to three water molecules which hydrogen bond to the zeolite framework, and to an OH − ion. The remaining 10 are near O–Al–O sequences; only three members of a likely octahedral coordination sphere could be found. In addition, two Ni 2+ ions are at site I, eight are at site I′, and five are at site II. Forty six H 3O + ions per unit cell, 24 at site II′ and 22 at site II, each hydrogen bond triply to six rings of the zeolite framework. Each of the 22 H 3O + ions also hydrogen bonds to a H 2O molecule that coordinates to a site III′ Ni 2+ ion. Six of the eight sodalite cages each contain four H 3O + ions at site II′; the remaining two each contains a tetrahedral orthoaluminate anion at its center. Each tetrahedral face of each orthoaluminate ion is centered by a site I′ Ni 2+ ion to give two Ni 4AlO 4 clusters. The five site II Ni 2+ ions each coordinate to a OH − ion. With 46 H 3O + ions per unit cell, the great tendency of hydrated Ni 2+ to hydrolyze within zeolite X is demonstrated. With a relatively weak single-crystal diffraction pattern, with dealumination of the zeolite framework, and with an apparent decrease in long-range Si/Al ordering likely due to the formation of antidomains, this crystal like others treated with hydrolyzing cations appears to have been damaged by Ni 2+ exchange and partial dehydration.