Synthesis, structure solution, and characterization of the aluminosilicateMCM-61: the first aluminosilicate clathrate with 18-membered rings

The synthesis, structure solution, and characterization of the aluminosilic ate MCM-61 are described. MCM-61 is synthesized hydrothermally using 1,4,7, 10,13,16-hexaoxacyclooctadecane (18-Crown-6) in the presence of potassium c ations. The structure solution of MCM-61 shows that the material is a clath rate with a novel structure formed from [6(10)4(12)] polyhedral cages. The Rietveld refinement of synchrotron X-ray powder diffraction data of the as- synthesized material gives a space group assignment of R (3) over bar m (No . 166) with unit cell parameters a = 11.841 Angstrom and alpha = 93.29 degr ees, and agreement values of R-p = 5.33%, R-wp = 7.03%, and chi(2) = 0.43. The [6(10)4(12)] cages connect together to form large [6(20)4(6)] cages whi ch host the potassium-18-Crown-6 complex. These [6(20)4(6)] cages contain 1 8-membered rings, making MCM-61 the first aluminosilicate clathrate to poss ess cages bounded by 18-membered rings. The structure of MCM-61 suggests th at crown ethers may be useful molecules for the synthesis of extra-large po re zeolites. (C) 1999 Published by Elsevier Science B.V.