Microhydration of the adamantane cation: intracluster proton transfer to solvent in [Ad(H₂O)_n=1–5]⁺ for n ≥ 3

Abstract

Radical cations of diamondoids are important intermediates in their functionalization reactions in polar solvents. To explore the role of the solvent at the molecular level, we characterize herein microhydrated radical...

Infrared spectrum of the 1-cyanoadamantane cation: evidence of hydrogen transfer and cage-opening upon ionization

“…30,32 This binding motif is confirmed by the measured redshift of 25 cm À1 for n acidic CH (from 2600 to 2575 cm À1 ) when switching the ligand from He to N 2 and its disappearance from this spectral range upon microhydration. [30][31][32] NBO analysis of CC(I) indicates that the acidic C6H proton has the highest positive partial charge of 353 me. Given that this behaviour is very similar to that of Ada + , it is likely that N 2 binding also occurs to the acidic proton for CC(I) of AdCN + .…”

“…For example, recent IRPD spectra of [Ada(H 2 O) n ] + revealed intracluster proton transfer (ICPT) of the acidic CH proton of Ada + to the (H 2 O) n solvent cluster at cluster sizes n Z 3. 31 As the CC(I) isomer of AdCN + has a similar CH acidity as Ada + , also only a few H 2 O ligands may be required to drive such an ICPT.…”

“…DFT calculations are performed at the dispersion-corrected (u)B3LYP-D3BJ/cc-pVTZ level to obtain geometries, energies, and IR spectra of various AdCN + isomers and their clusters. 53 This computational level has been shown to provide reliable results for related diamondoid cations and their clusters, 25,26,31,32,54 with the addition of Becke-Johnson damping to yield more accurate results for non-covalent bond distances and intramolecular dispersion interactions. Relative energies and binding energies (E e , D e ) are corrected for harmonic zero-point vibrational energies to yield E 0 and D 0 values.…”

“…25 Various studies of bare Ada using synchrotron VUV radiation and XUV femtosecond pulses reveal dissociative channels beginning with opening of the cage structure. [27][28][29] However, IRPD and electronic photodissociation (EPD) spectra of Ada + and its clusters generated in the same EI source as Ama + show no evidence of open-cage isomers, similar to the diamantane radical cation (C 14 H 20 + , Dia + ), 12,13,[30][31][32] indicating that reaction barriers are high for bare diamondoid cations. To test this hypothesis further, similar experiments with AdCN have been proposed to understand how electron-withdrawing functional groups influence the stability of diamondoid cage structures.…”