A comprehensive study of the molecular vibrations in solid-state benzylic amide [2]catenane

Area of Science:

• * Molecular Spectroscopy
• * Computational Chemistry
• * Materials Science

Background:

• * Vibrational spectra interpretation is complex but crucial for understanding molecular structure.
• * Mechanically interlocked molecules, like catenanes, present unique structural and spectroscopic challenges.
• * Benzylic amide [2]catenane is a complex molecular solid with crimped mechanical bonds.

Purpose of the Study:

• * To record and assign the infrared (IR) spectrum of the benzylic amide [2]catenane.
• * To calculate and analyze all vibrational modes of the catenane crystal.
• * To compare experimental IR spectra with theoretical calculations and Raman spectroscopy.

Main Methods:

• * Quantum first-principles calculations for vibrational mode analysis.
• * Born effective charges approach to evaluate mode activity.
• * Detailed assignment of over 1000 normal modes in terms of internal coordinates.

Main Results:

• * Remarkable agreement between calculated and experimental IR spectra without empirical corrections.
• * Complete assignment of the vibrational spectrum, identifying key IR-active modes.
• * Comparison with Raman spectroscopy, exploring the rule of mutual exclusion.

Conclusions:

• * First-principles calculations accurately predict the IR spectrum of the benzylic amide [2]catenane.
• * The detailed normal mode analysis provides a thorough understanding of the molecular structure.
• * The study elucidates vibrational spectroscopy principles in complex, symmetric molecular systems.