Vibrational signatures of diamondoid dimers with large intramolecular London dispersion interactions

Abstract

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 1.71Å. Attractive dispersion interactions caused by well-aligned intramolecular H· · · 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.

Long but Strong C−C Single Bonds: Challenges for Theory

“…The LD interactions between the first layers on each side gives 63 kcal mol −1 but the interaction between the outer layers is only 6 kcal mol −1 , that is, the C δ− ⋅⋅⋅H δ+ attraction between the inward fragments of the cages mainly contribute to the NCB. Through‐space interactions between hydrogen atoms led to the emergence of characteristic vibrational modes caused by LD [59] . Indeed, the largest LD‐induced frequency shift was observed for the inward directed C−H‐bond stretching vibrations at a frequency of about 3050 cm −1 in the Raman spectra [59] .…”

“…Through‐space interactions between hydrogen atoms led to the emergence of characteristic vibrational modes caused by LD [59] . Indeed, the largest LD‐induced frequency shift was observed for the inward directed C−H‐bond stretching vibrations at a frequency of about 3050 cm −1 in the Raman spectra [59] . These vibrations are absent in pristine diamondoids.…”

“…[59] Indeed, the largest LD-induced frequency shift was observed for the inward directed CÀ H-bond stretching vibrations at a frequency of about 3050 cm À 1 in the Raman spectra. [59] These vibrations are absent in pristine diamondoids.…”

Nanotechnology of diamondoids for the fabrication of nanostructured systems

“…By investigating the C-C-C bending or C-C stretching mode in the low-frequency region of the spectra, differentiation of the geometric properties of diamondoids has become possible and more assessable. The distinctive vibration modes also provide the necessary knowledge for further exploring the vibrational properties of different diamondoid derivatives [57,[72][73][74] and dimers [75,76].…”