This project is concerned with the structural properties of the pyridine-silicon tetrafluoride complex and several of its fluoropyridine analogs. The key issue is the extent to which they undergo structural changes in response to solvation by inert chemical environments (e.g., solid argon). These will be assessed using DFT computations and low-temperature IR spectroscopy. Prior studies obtained structure, vibrational frequencies, binding energies, and N-Si potential energy curves of the pyridine-silicon tetrafluoride complex using the M06/6-311+G (2df/2pd) level of theory. However, it is likely that medium effects were overlooked due to the deficiencies in the basis set. In this work, we are using larger basis sets (aug-cc-pVTZ and aug-cc-pVQZ) to resolve the theoretical deficiencies, and to obtain much-needed experimental data. First, we completed a method validation based on silicon tetrafluoride vibrational frequencies, since shifts in the Si-F stretching modes signal structural change for the complexes. We found that M06 and M062X had the lowest RMS error among nine DFT methods explored. Using these methods and basis sets, we obtained structures, frequencies, and binding energies for C₆H₅N–SiF₄, 3-FC₆H₄N–SiF₄, 3,5-F₂C₆H₃N–SiF₄ and 3,4,5-F₃C₆H₂N–SiF₄. Comparisons to experimental frequencies from argon and nitrogen matrices convey the extent of structural change that takes place in the inert media. Currently, we are scanning the N-Si potentials of these systems in the gas phase and in low-dielectric media. We will comment on the degree to which the predicted structural changes are consistent with those conveyed by the frequency shifts.

Figure: Pyridine-Silicon-Tetrafluoride in the optimal structure

Becca Adams

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