Interplay of Bonding and Geometry of the Adsorption Complexes of Light Alkanes within Cationic Faujasites. Combined Spectroscopic and Computational Study

On the structure of superbasic (MgO)n sites solvated in a faujasite zeolite

Theory and experiment reveal the structure of magnesium oxide nanoclusters in a superbasic faujasite zeolite.

The effect of the zeolite pore size on the Lewis acid strength of extra-framework cations

The catalytic activity and the adsorption properties of zeolites depend on their topology and composition. For a better understanding of the structure-activity relationship it is advantageous to focus just on one of these parameters. Zeolites synthesized recently by the ADOR protocol offer a new possibility to investigate the effect of the channel diameter on the adsorption and catalytic properties of zeolites: UTL, OKO, and PCR zeolites consist of the same dense 2D layers (IPC-1P) that are connected with different linkers (D4R, S4R, O-atom, respectively) resulting in the channel systems of different sizes (14R × 12R, 12R × 10R, 10R × 8R, respectively). Consequently, extra-framework cation sites compensating charge of framework Al located in these dense 2D layers (channel-wall sites) are the same in all three zeolites. Therefore, the effect of the zeolite channel size on the Lewis properties of the cationic sites can be investigated independent of other factors determining the quality of Lewis sites. UTL, OKO, and PCR and pillared 2D IPC-1PI materials were prepared in Li-form and their properties were studied by a combination of experimental and theoretical methods. Qualitatively different conclusions are drawn for Li(+) located at the channel-wall sites and at the intersection sites (Li(+) located at the intersection of two zeolite channels): the Lewis acid strength of Li(+) at intersection sites is larger than that at channel-wall sites. The Lewis acid strength of Li(+) at channel-wall sites increases with decreasing channel size. When intersecting channels are small (10R × 8R in PCR) the intersection Li(+) sites are no longer stable and Li(+) is preferentially located at the channel-wall sites. Last but not least, the increase in adsorption heats with the decreasing channel size (due to enlarged dispersion contribution) is clearly demonstrated.

Probing Ionic Crystals by the Invariom Approach: An Electron Density Study of Guanidinium Chloride and Carbonate

A comparative study of two guanidinium salts, chloride and carbonate, is carried out to test the performance of the invariom approach for ionic crystals. Although treating them as formed by isolated ions with no charge transfer between them, the invariom approach provides features of interionic contacts that are amazingly similar to those obtained from conventional charge density analysis of high-resolution X-ray diffraction data, thus emerging as an easy way towards reliable description of chemical bonding peculiarities in ionic crystals.

Extremely long Cu···O contact as a possible pathway for magnetic interactions in Na2Cu(CO3)2

Chemical binding in a mixed copper sodium carbonate Na2Cu(CO3)2, a layered material showing ferromagnetic intralayer exchange and weak antiferromagnetic interlayer coupling, was examined within the topological analysis of experimental (from high-resolution X-ray diffraction) and theoretical (from periodic quantum chemical calculations) electron density functions in its crystal. Together with modeling of a superexchange pathway within the LSDA and DFT+U approach, the results obtained reveal a very weak Cu···O interaction (0.5 kcal/mol worth) between the copper-carbonate layers that is nevertheless stabilizing (bonding) and may serve as a possible pathway for antiferromagnetic interactions.