Crystal structures of the NO and NO 2 sorption complexes of fully dehydrated fully Mn 2+-exchanged zeolite X (FAU)

Abstract

The crystal structures of the NO and NO 2 sorption complexes of fully dehydrated, fully Mn 2+-exchanged zeolite X, ∣Mn 46(16NO)∣[Si 100Al 92O 384]-FAU (crystal 1, a = 25.017(10) Å) and ∣Mn 46(28NO 2)∣[Si 100Al 92O 384]-FAU (crystal 2, a = 24.672(7) Å), have been determined by single-crystal X-ray diffraction techniques at 21(1) °C in the cubic space groups Fd 3 ¯ m and Fd 3 ¯ , respectively. Each crystal was prepared by ion exchange in a flowing stream of 0.05 M aqueous Mn(NO 3) 2 for 3 days, followed by dehydration at 500 °C and 2 × 10 −6 Torr for 2 days, and exposure to 100 Torr of NO or NO 2/N 2O 4 gas at 21(1) °C for 1.5 h. The structures were determined in these atmospheres and were refined using all data to the final error indices (based only on the 250 reflections for which F o > 4 σ( F o)) of R 1 = 0.059 and wR 2 = 0.206 for crystal 1; the corresponding values for crystal 2 are 347, 0.063, and 0.168. In crystal 1, Mn 2+ ions occupy four crystallographic sites: 15 are at the octahedral site I (at the centers of hexagonal prisms), 2 are at site I′, and the remaining 29 occupy two different sites II. Sixteen NO molecules lie in the supercage where each coordinates laterally to a Mn 2+ ion at one of the sites II (Mn–framework oxygens = 2.244(15), Mn–N = 2.31(3), Mn–O = 2.32(3) Å). The observed N–O bond length, 1.6(3) Å, does not differ significantly from that in NO gas, 1.15 Å. In crystal 2, the Mn 2+ ions also occupy four crystallographic sites: 14, 4, 20, and 8 are at sites I, I′, II, and III, respectively. Twenty-eight NO 2 molecules lie in the supercage; each coordinates either to a site-II or a site-III Mn 2+ ion (Mn–framework oxygens = 2.286(10)/2.41(6) Å, Mn–N = 2.27(7)/2.17(11) Å, N–O = 1.20(12), 1.10(10)/1.27(12), 1.21(13) Å, respectively). The latter four values agree with the N–O bond length in NO 2 gas, 1.193 Å.