Vibrational signatures of diamondoid dimers with large intramolecular London dispersion interactions

We analyze the vibrational properties of diamondoid compounds via Raman spectroscopy. The compounds are interconnected with carbon-carbon single bonds that exhibit exceptionally large bond lengths up to 1.71 angstrom. Attractive dispersion interactions caused by well-aligned intramolecular H center dot center dot center dot H contact surfaces determine the overall structures of the diamondoid derivatives. The strong van-der-Waals interactions alter the vibrational properties of the compounds in comparison to pristine diamondoids. Supported by dispersion-corrected density functional theory (DFT) computations, we analyze and explain their experimental Raman spectra with respect to unfunctionalized diamondoids. We find a new set of dispersion-induced vibrational modes comprising characteristic CH/CH2 vibrations with exceptionally high energies. Further, we find structure-induced dimer modes that are indicative of the size of the dimers. (C) 2019 Elsevier Ltd. All rights reserved.