Structure of a methylamine sorption complex of fully dehydrated Cd2+-exchanged zeolite X, ∣Cd46(CH3NH2)16∣[Si100Al92O384]-FAU

The structure of a methylamine sorption complex of fully dehydrated, fully Cd2+-exchanged zeolite X, ∣Cd46(CH3NH2)16∣[Si100Al92O384]-FAU (a = 24.863(4) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3¯ at 21(1) °C. An aqueous exchange solution 0.05 M in Cd2+ was allowed to flow past the crystal for 5 days. The crystal was then dehydrated at 480 °C and 2 × 10−6 Torr for 2 days (colorless), and exposed to 160 Torr of methylamine gas at 21(1) °C for 2 h (yellow). Diffraction data were then gathered in this atmosphere and were refined using all data to the final error indices (based upon the 524 reflections for which Fo > 4σ(Fo)) of R1 = 0.069 and wR2 = 0.200. In this structure, Cd2+ ions occupy three crystallographic sites. The octahedral sites I at the centers of the hexagonal prisms are filled with 16 Cd2+ ions per unit cell (Cd–O = 2.369(8) Å). The remaining 30 Cd2+ ions are located at two non-equivalent sites II with occupancies of 14 and 16. The 16 methylamine molecules per unit cell lie in the supercage where each interacts with one of the latter 16 site-II Cd2+ ions: N–Cd = 2.11(8) Å. The imprecisely determined N–C bond length, 1.49(22) Å, agrees with that in gaseous methylamine, 1.474 Å. The positions of the hydrogen atoms were calculated. It appears that one of the amino hydrogen atoms hydrogen bonds to a 6-ring oxygen, and that the other forms a bifurcated hydrogen bond to this and another 6-ring oxygen. The methyl group is not involved in hydrogen bonding.