How van der Waals bonds orient molecules in zeolites

Abstract

We show that weak bonds are responsible for the way a molecule is held in a zeolite, and for its reactivity.

IR Evidence that Secondary Interactions May Hamper H-Bonding at Protonic Sites in Zeolites

“…We ascribe these irregularities to the presence of walls surrounding the acidic site, with which relatively big molecules such as benzene (at variance with ethene and CO) may interact, not allowing the H-bonded adduct to assume the optimal conformation. H bonding is strongly sensitive to the geometry and is influenced by even small perturbations of the B···H distance or the O−H···B angle. , This explanation is in line with what was reported by Su and Barthomeuf, on the interaction of C−H groups of benzene with basic oxygens of the framework in faujasites, and with the very recent computational work by Kemner et al, showing that van der Waals interactions with walls orient ferrocene molecules in the cavities of NaY.…”

“…H bonding is strongly sensitive to the geometry and is influenced by even small perturbations of the B‚‚‚H distance or the O-H‚‚‚B angle. 1,2 This explanation is in line with what was reported by Su and Barthomeuf, on the interaction of C-H groups of benzene with basic oxygens of the framework in faujasites, 13 and with the very recent computational work by Kemner et al, 18 showing that van der Waals interactions with walls orient ferrocene molecules in the cavities of NaY.…”

The Nature and Catalytic Function of Cation Sites in Zeolites: a Computational Perspective

“…Whereas toluene and xylenes can only form π‐complexes with individual cations or form stacked aggregates at higher loadings, benzene becomes symmetrically aligned in the 12‐membered ring window of the supercage as a result of the formation of multiple van der Waals interactions between benzene C−H groups and the framework oxygens ,. Similarly, the specific alignment of ferrocene in NaY pores has been attributed to the concert effect of multiple weak van der Waals interactions between the cyclopentadienyl ligands and pore walls . These studies emphasize the importance of weak van der Waals interactions on adsorption and molecular recognition properties of zeolites.…”

“…[176c,177] Similarly, the specific alignment of ferrocene in NaY pores has been attributed to the concert effect of multiple weak van der Waals interactions between the cyclopentadienyl ligands and pore walls. [178] These studies emphasize the importance of weak van der Waals interactions on adsorption and molecular recognition properties of zeolites. Despite having small individual contribution, their cumulative power can be strong enough to not only define the preferred adsorption geometry but to even determine the catalytic performances of reactive ensembles inside the zeolite pores.…”

Structure, energy, vibrational spectrum, and Bader's analysis of π⋯H hydrogen bonds and H−δ⋯H+δdihydrogen bonds

“…With regard to the structure of 43, the formation of double interactions between the two molecules of hydrochloric acid directly aligned on the beryllium hydride demonstrates that H Àd can be an 'electronegative hydrogen'. 694 Although the electronic density value of 0.013 e a o À3 for both the (H Àd Á Á ÁH +d ) -( 43)-A and (H Àd Á Á ÁH +d ) -( 43)-B dihydrogen bonds are characteristic of van der Waals contacts (B10 À2 -10 À3 a o 3 ), 695,696 these interactions are essentially dihydrogen bonds. 472 Thereby, system 43 is thus formed by two dihydrogen bonds, which provide the formation of three proton donor centres: H Àd (H-Be) -( 43), H +d (H-Cl) -( 43 44)-B, H Àd (H-Be) -( 44), and H Àd (H-Be) -( 44).…”