Synthesis and Structure Determination of a New Microporous Zeolite with Large Cavities Connected by Small Pores Manuel Herna ́ ndez-Rodríguez, Jose L. Jorda ́ , Fernando Rey,* and Avelino Corma* Instituto de Tecnología Química (UPV-CSIC), Universidad Polite ́ cnica de Valencia - Consejo Superior de Investigaciones Científicas, Av. de los Naranjos s/n, 46022 Valencia, Spain * S Supporting Information ABSTRACT: A new small-pore germanosilicate zeolite, named as ITQ-49, has been synthesized using a new ditetraalkylphosphonium dication as an organic structure- directing agent, and its structure has been solved by direct methods applied to the powder X-ray diffraction pattern of the calcined solid. This new zeolite crystallizes in the space group Immm with cell parameters a = 19.6007(8) Å, b = 18.3274(7) Å, and c = 16.5335(6) Å. The pore topology of ITQ-49 consists of large, nonspherical cavities that are connected to each other through small eight-membered- ring windows, resulting in a unidirectional small-pore zeolite that has a relatively large adsorption capacity. Also, ITQ-49 contains double four-membered-ring units where Ge is preferentially located, and fluoride anions are placed inside these units. Z eolites are crystalline microporous materials, mainly constituted by oxides of silicon and/or other elements (e.g., Al, B, Ti, Ge, Sn) in tetrahedral coordination. The well- defined size and distribution of the structural channels in each different zeolitic framework type confer to these materials multiple applications in processes such as gas adsorption, separation, catalysis, and encapsulation or controlled release of molecules, among others, some of them with industrial applications. 1-9 This is the major force for studying novel methods for the preparation of new zeolitic structures, since it would give the possibility of obtaining tailored materials with the most appropriate channel system for each specific application. To date, up to 201 different zeolitic structures have been accepted by the International Zeolite Association, 10 and this number is still increasing. To obtain novel structures, several approaches have been attempted. The incorporation of fluoride anions replacing hydroxyl anions as the silica-mobilizing agent in the synthesis gel has been found very often to drive the reaction toward the formation of double four-membered-ring (D4R) units in the zeolites obtained under those conditions. 11-21 In the same way, the isomorphic substitution of Si with Ge presents a stronger directing effect, favoring the formation of not only the D4R units 20-30 but also the previously elusive double three- membered-ring (D3R) units, 29,30 opening the doors to new families of zeolites. Nonetheless, the most important approach for obtaining new zeolites is the use of tetraalkylammonium organic cations, which in the zeolite field are generally called organic structure-directing agents (OSDAs). 20,21,31 Recently, the employment of P-containing OSDAs such as tetraalkylphosphonium and phosphazene cations instead of the tetraalkylammonium cations typically used for zeolite syntheses has been described. These uncommon OSDAs have given several new extra-large-, large-, and medium-pore zeolitic structures. 30,32-35 To date, however, no small-pore zeolites have been synthesized using tetraalkylphosphonium as the OSDA. In this report, we describe the synthesis and crystal structure of ITQ-49, a new small-pore zeolite containing large non- spherical cavities accessible by a one-directional system of eight- membered-ring (8R) channels, that has been synthesized using ditetraalkylphosphonium dications [obtained from butane-1,4- diylbis(tri-tert-butylphosphonium) hydroxide] as the OSDA along with Ge and F - as inorganic structure directing agents (ISDAs). Details of the synthesis are described in the Supporting Information (SI). Elemental analysis of the as-made zeolite ITQ-49, as well as 13 C and 31 P magic-angle-spinning (MAS) NMR spectroscopy (see the SI) indicated that the OSDA dications remain intact within the zeolitic channels, with their positive charges being balanced by the fluoride ions, which are located in the small D4R cages, as indicated by the presence of resonance bands at -9 and -20 ppm in the 19 F MAS NMR spectrum of the as- made material 22,36 (see the SI). Chemical analysis showed a Si/ Ge ratio of 4.7, very similar to that used in the synthesis gel. The phosphorus content corresponds to a (Si + Ge)/P ratio of 21.6 in the as-made material as well as in the final calcined solid. This indicates that the P-containing OSDA gives rise to the formation of phosphate-like species during calcination, instead of volatile phosphines as occur in zeolites with larger pore apertures. These phosphate-like species were further identified by means of 31 P MAS NMR spectroscopy (see the SI). Scanning electron microscopy indicated an average crystal size of ∼0.2 μm, precluding structure determination using single- crystal X-ray diffraction. Powder X-ray diffraction (PXRD) data were collected on a PANalytical X’Pert PRO diffractometer in the Bragg-Brentano geometry using Cu Kα radiation, as described in the SI. Prior to the measurement, in order to remove all of the organic content, the sample was calcined in situ at 923 K for 5 h under a continuous flow of dry air in an Anton Parr XRK-900 reaction chamber attached to the diffractometer. Received: June 20, 2012 Published: August 1, 2012 Communication pubs.acs.org/JACS © 2012 American Chemical Society 13232 dx.doi.org/10.1021/ja306013k | J. Am. Chem. Soc. 2012, 134, 13232-13235