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Endo or Exo ? Structures of Gas‐Phase Alkali Metal Cation/Aromatic Half‐Belt Complexes
Author(s) -
Chen Yanyang,
JamiAlahmadi Yasaman,
Unikela Kiran Sagar,
Bodwell Graham J.,
Fridgen Travis D.
Publication year - 2018
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201800371
Subject(s) - chemistry , infrared multiphoton dissociation , fourier transform ion cyclotron resonance , dissociation (chemistry) , mass spectrum , molecule , population , infrared spectroscopy , ion , ionic bonding , alkali metal , infrared , bond dissociation energy , mass spectrometry , analytical chemistry (journal) , crystallography , organic chemistry , physics , demography , chromatography , sociology , optics
1,1,9,9‐Tetramethyl[9](2,11)teropyrenophane (TM9TP), a belt‐shaped molecule, has a sizable cavity that molecules or ions could occupy. In this study, the question of whether TM9TP forms gas‐phase ion‐molecule complexes with metal cations (K + , Rb + , Cs + ) situated inside or outside the TM9TP cavity was addressed using both experimental and computational methods. Complexes were trapped in a Fourier transform ion cyclotron resonance mass spectrometer and their structures were explored by some novel physical chemistry/mass spectrometry methods. Blackbody infrared radiative dissociation kinetics reveal two populations of ions, a fast dissociating fraction and a persistent fraction. Infrared multiphoton dissociation spectra (vibrational spectra) provide very strong evidence that the most abundant population is a complex where the metal cation is inside the TM9TP cavity, endo ‐TM9TP. Red‐shifted C−H stretching bands present in the gas‐phase vibrational spectra of these ionic complexes show that there is an interaction between the metal cation and bridge C−H bonds due to the cation sitting inside the cavity of TM9TP. B3LYP/6‐31+G(d,p) calculations showed the endo complexes to be the lowest in energy; about 60 kJ mol −1 more thermodynamically stable and more than 120 kJ mol −1 kinetically more stable than the exo complex.