Vibrational center-ligand couplings in transition metal complexes

Area of Science:

• Computational Chemistry
• Molecular Vibrational Spectroscopy
• Quantum Chemistry

Background:

• Vibrational analysis of large molecules is computationally challenging.
• The mode-tracking principle offers a method for direct quantum chemical calculation of specific molecular vibrations.
• Understanding the interplay between ligand spheres and core structures is crucial for complex molecules.

Purpose of the Study:

• To demonstrate the feasibility of mode-tracking for large, complex molecular systems.
• To investigate the secondary effects of a phosphine ligand sphere on the vibrations of an embedded gold-carbon core.
• To quantify the coupling between the outer ligand sphere and the inner core of the [(Ph(3)PAu)(6)C](2+) cluster.

Main Methods:

• Direct quantum chemical calculation using the mode-tracking principle.
• Generation of local vibrations for the octahedral [Au(6)C] core.
• Analysis of long-range couplings between core vibrations and the phosphine ligand sphere.
• Convergence of mode-tracking refinement to obtain exact normal modes.

Main Results:

• The mode-tracking principle was successfully applied to the large [(Ph(3)PAu)(6)C](2+) complex.
• Secondary effects of the 18 phenyl groups on the [Au(6)C] core vibrations were investigated.
• Coupling between the ligand sphere and the core was quantified by changes in vibrational frequencies and atomic motions.
• Vibrational frequencies of the [Au(6)C] core were predicted to split due to symmetry breaking.

Conclusions:

• Mode-tracking is a viable method for vibrational analysis of very large molecules.
• The study quantifies how the periphery of a large molecule influences its local vibrations.
• This work provides the first set of predicted vibrational frequencies for the [(Ph(3)PAu)(6)C](2+) gold cluster using first-principles methods.