Adsorption of CO 2 and N 2 , both as single components and as binary mixtures, in three zeolites with identical chemical composition but differing pore structures (silicalite, ITQ-3, and ITQ-7) was studied using atomistic simulations. These three zeolites preferentially adsorb CO 2 over N 2 during both single-component and mixture adsorption. The CO 2 /N 2 selectivities observed in the three siliceous zeolites vary strongly as the adsorbent's crystal structure changes, with the selectivity in ITQ-3 being the largest. Our studies indicate that the different electric fields present inside zeolites with different crystal structures but identical chemical composition play an important role in the observed adsorption capacities and selectivities. The accuracy of the ideal absorbed solution theory in predicting the behavior of CO 2 /N 2 mixtures in silica zeolites based on single component adsorption data was also tested; this theory performs quite accurately for these adsorbed mixtures.

Diffusion of CO 2 and N 2 , both as single components and as binary mixtures, in three zeolites with identical chemical composition but differing pore structuresssilicalite, ITQ-3, and ITQ-7swas studied using atomistic simulations. In all materials CO 2 diffuses slower than N 2 , but otherwise the behavior of these gases within ITQ-7 and silicalite is quite different than within ITQ-3. In ITQ-7 and silicalite, the loading dependence of diffusion is very similar for CO 2 and N 2 ; the apparent activation energies for diffusion of each adsorbate are similar in the two materials, and the diffusion properties of adsorbed mixtures can easily be understood. In contrast, none of these are true within ITQ-3. Free energy and potential energy profiles are used to uncover the roots of these differences. The preferential sites of adsorption for CO 2 and N 2 are the same within ITQ-7 and silicalite but not within ITQ-3. In ITQ-3, CO 2 molecules preferentially adsorb in the windows that separate the material's cages, whereas for N 2 this is the site of the largest barrier to diffusion. As a consequence, CO 2 hinders N 2 diffusion very effectively. Our analysis suggests that this behavior might be common for adsorbates that interact strongly with a material that has narrow windows between cages.

In 1919, Perucca reported anomalous optical rotatory dispersion from chiral NaClO(3) crystals that were colored by having been grown from a solution containing an equilibrium racemic mixture of a triarylmethane dye (Perucca, E. Nuovo Cimento 1919, 18, 112-154). Perucca's chiroptical observations are apparently consistent with a resolution of the propeller-shaped dye molecules by NaClO(3) crystals. This implies that Perucca achieved the first enantioselective adsorption of a racemic mixture on an inorganic crystal, providing evidence of the resolution of a triarylmethyl propeller compound lacking bulky ortho substituents. Following the earlier report, NaClO(3) crystals dyed with aniline blue are described herein. The rich linear optical properties of (001), (110), and (111) sections of these mixed crystals are described via their absorbance spectra in polarized light as well as images related to linear dichroism, linear birefringence, circular dichroism, and anomalous circular extinction. The linear dichroism fixes the transition electric dipole moments in the aromatic plane with respect to the growth faces of the NaClO(3) cubes. Likewise, circular dichroism measurements of four orientations of aniline blue in NaClO(3) fix a bisignate tensor with respect to the crystal growth faces. Electronic transition moments and circular dichroism tensors were computed ab initio for aniline blue. These calculations, in conjunction with the crystal-optical properties, establish a consistent mixed-crystal model. The nature of the circular extinction depends upon the crystallographic direction along which the crystals are examined. Along 100, the crystals evidence circular dichroism. Along 110, the crystals evidence mainly anomalous circular extinction. These two properties, while measured by the differential transmission of left and right circularly polarized light, are easily distinguished in their transformation properties with respect to reorientations of the sample plates. Circular dichroism is symmetric with respect to the wave vector, whereas anomalous circular extinction is antisymmetric. Analysis of Perucca's raw data reveals that he was observing a convolution of linear and circular optical properties. The relatively large circular dichroism should in principle establish the absolute configuration of the propeller-shaped molecules associated with d- or l-NaClO(3) crystals. However, this determination was not as straightforward as it appeared at the outset. In the solid state, unlike in solution, a strong chiroptical response is not in and of itself evidence of enantiomeric resolution. It is shown how it is possible to have a poor resolution-even an equal population of P and M propellers-within a given chiral NaClO(3) crystal and still have a large circular dichroism.