Andrey Rogachev, Cornell University
Abstract:
Modern theoretical methods coupled with the continuously growing power of computers allow one to model structure and properties of different chemical system with remarkable accuracy and reliability. As my talk will show, judiciously applied, such tools can bring us much new information even about well-known molecules, and predict new properties and reactivity.
The talk will have three parts. The first one is devoted to the new and unexpected properties and features of two familiar systems, benzene and molecular diiodine. Prompted by an interest in the transformations of benzene under extreme pressure, we investigated all possible dimerizations of benzene molecules. Surprisingly, four new dimers were found, which were never even mentioned in literature. The stability (both kinetic and thermodynamic) of the new molecules was comprehensively explored. In a second study, a Janus-faced behavior of I2 as ligand for organometallic fragments was investigated. The direct connection between coordination mode and bonding nature (I2 playing the role of an acceptor or a donor) was established, and new complexes predicted.
The second domain explored is that of the reactivity and properties of unusual open- geodesic polyaromatic organic molecules, fullerene fragments or buckybowls, in their reaction with different organic, organometallic and inorganic species. The predictive power of calculations can be used here to create new molecules and/or tune properties of already know systems, in close interaction with experiment.
Highly accurate theoretical calculations applied to molecular magnets constitute the third domain of the talk. A prototypic system, {Cu2(O2CCH3)4·2H2O} was used as the primary model. Multireference perturbation theory, as one of the most accurate theoretical approaches at this time, was the workhorse for this study. A detailed theoretical analysis of the electronic structure of the system revealed the presence and importance of the direct coupling between magnetic centers for the proper description of its magnetic behavior. Moreover, in combination with high- angle X-ray diffraction technique, this approach allowed one to introduce a new type of weak chemical bonding – we call it the magnetic bond.