The broader goal of this project is to identify and characterize molecular complexes with the potential to undergo structural changes in condensed-phase environments. Our recent focus has been a series of N-donor - MX3R acceptors (M=Si, Ge; X=F, Cl; R=CH3, C6H5), which may also have potential for electro-mechanical applications. Initially, using computations and low-temperature infrared spectroscopy, we found that most of the complexes in this class were too weak for significant medium sensitivity. However, the germanium complexes, H3N–GeCl3CH3 and H3N–GeCl3C6H5, still exhibited the key signature of these effects; an extremely anharmonic Ge-N potential energy curve, with a long equilibrium distance and a slight energy rise toward the inner wall that is preferentially stabilized in bulk dielectric media. Another issue with these initial systems, however, was that the organic substituent preferred an equatorial site, whereas we sought an axial orientation for potential applications. Moving forward, we have embarked on a sequential, systematic study of related systems, using density functional theory to explore the impact of changes in the M, X, and R-substituents, in an effort to design a complex with the optimal strength and an axial coordination geometry. For one, we have found that the analogous Ti-containing systems (e.g., H3N–TiCl3CH3) are quite strong, in spite of organic substituent on the metal. This will provide flexibility for further alterations of the X and R substituents, in hopes of inducing axial coordination. We have also explored additional Ge-containing systems with electronegative R substituents (e.g., H3N–GeCl3CF3). The interactions in these systems are strengthened, and are also more favorable for axial coordination. In addition to the overall progress towards identifying a structurally-sensitive complex with the R in an axial binding site, the underlying design principles that manifest progress toward that end will also be discussed.

Optimizing the structural response in nitrogen donor: MX3R complexes

Macromolecular Chemistry: The Second Century

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