Zeolite Structure Direction: Identification, Strength and Involvement of Weak CH...O Hydrogen Bonds

We demonstrate that weak CH...O hydrogen bonds (HBs) are important host-guest interactions in zeolite assemblies involving structure directing organocations. This type of HB is identified between alkyl groups of the organic structure directing agent (OSDA) and the silica framework in as-synthesized silicalite-1 of complex topology (MFI) using a combination of experimental and theoretical data obtained at low and room temperatures. The 28 weak CH...O HBs, evidenced along dynamics simulation at room temperature, represent 30 % of the energy of the Coulomb electrostatic interaction between OSDA and the zeolite framework. The strongest and most stable HB found here connects the OSDA to the [4(1)5(2)6(2)] cage containing F atoms and should contribute to preserve zeolite topology during crystal growth. An inspection of other as-synthesized zeolites of very different framework topology indicates that the directional CH...O HBs have to be considered when discussing zeolite structure directing phenomena.