Quantum Chemistry Studies of Titanio- and Germanio-zeolites

We study the new properties acquired by a silica framework when Ti and Ge atoms are introduced into it. Some of the new properties can be explained by the great distortion caused in the framework after the Ti/Ge replaces the original Si atom. This depends on how the structure can accommodate the strain, so different structures are expected to yield different properties -such as Lewis acidity- depending on its flexibility. We use standard HF and DFT methods under Gaussian95 by using basis sets of different qualities such as 3-21G**, 6-31G, 6-311-G, 6-31G**, among others, and clusters of medium size. Also we intend to explore the reactivity of these clusters in reactions involving charge transfer.

Regarding Ge-zeolites, their interest comes not only from the heteroatom substitution and the new properties brought in, but also from the zeolite synthesis viewpoint. Introduction of Ge in the synthesis gel has led to the discovery of new structural types such as ASV, BEC, IWR, IWW and UTL among others, most of them containing double four rings as secondary building unit (one notable exception being PKU-9). This is important, also from the point of view that Ge stabilises low TOT angles in the structure, with the recognition that certain topologies are more prone than others to bear such low angles. A point raised by many researchers is whether low TOT angles are associated with preferential sizes of rings and this is a point we have addressed in recent research. A number of studies on this topic are underway.

Cluster used in the calculations with Ti-zeolites