Internal Dynamics in Halogen‐Bonded Adducts: A Rotational Study of Chlorotrifluoromethane–Formaldehyde

Abstract

The rotational spectra of two isotopologues of the 1:1 complex between chlorotrifluoromethane and formaldehyde have been recorded and analyzed by using Fourier-transform microwave spectroscopy. Only one rotamer was detected, with the two constituent molecules held together through a Cl⋅⋅⋅O halogen bond (R(Cl⋅⋅⋅O) = 3.048 Å). The dimer displays two simultaneous large-amplitude intramolecular motions. The internal rotation of formaldehyde around its symmetry axis (V2 = 28(5) cm(-1)) splits all the rotational transitions into two component lines with a relative intensity ratio of 1:3. On the other hand, the almost free internal rotation (V3 ≈ 2.5 cm(-1)) of the CF3 symmetric top increases the "rigid" value of the rotational constant A by almost one order of magnitude. In addition, all the transitions display a hyperfine structure due to the (35)Cl (or (37)Cl) nucleus quadrupole effects.

High-Resolution Spectroscopic Studies of Complexes Formed by Medium-Size Organic Molecules

“…These dynamic properties result in an extremely large value of the A rotational constant of the cluster. A similar result, related to almost free rotation of the CF 3 group, has been very recently reported, also for the CClF 3 –CH 2 O cluster, by MW spectroscopy …”

The Hydrogen Bond and Beyond: Perspectives for Rotational Investigations of Non‐Covalent Interactions

“…involving Cl⋅⋅⋅F, Cl⋅⋅⋅O, Cl⋅⋅⋅N, or Cl⋅⋅⋅C interactions. These dimers allowed discerning strong dynamical effects due to internal rotation within the dimers, together with structural information ( r 0 (Cl⋅⋅⋅F)=2.995, r 0 (Cl⋅⋅⋅O)=3.048, r 0 (Cl⋅⋅⋅N)=3.081–3.090 Å) and binding data (MP2 dissociation energies from −1.8 kJ mol −1 in CF 3 Cl⋅⋅⋅FCH 3 to −10.2 kJ mol −1 in CF 3 Cl⋅⋅⋅pyridine). Additionally, CF 3 I⋅⋅⋅B dimers were observed systematically to be stronger than the corresponding chlorine species, evidencing that heavier halogens exhibit stronger XBs …”

“…These investigations are mostly directed to 1) interrogate and differentiate the structures corresponding to the XBs/CBs/NBs/TBs, 2) evaluate the interaction energy in the context of other NCIs, and 3) contribute to establish the origin of the NCI forces. XBs are the most studied interactions in the gas phase,a si nitiated by Legon on dihalogens [44] and continued by as eries of chlorofluorocarbon heterodimers analyzed by Caminati et al involving Cl···F, [79] Cl···O, [80,81] Cl···N, [82] or Cl···C [83] interactions. These dimers allowed discerning strong dynamical effects due to internal rotation within the dimers, together with structurali nformation (r 0 (Cl···F) = 2.995 [79] , r 0 (Cl···O) = 3.048, [81] r 0 (Cl···N) = 3.081-3.090 [82] )a nd binding data (MP2 dissociation energies from À1.8 kJ mol À1 in CF 3 Cl···FCH 3 [79] to À10.2 kJ mol À1 in CF 3 Cl···pyridine [84] ).…”

“…XBs are the most studied interactions in the gas phase, as initiated by Legon on dihalogens and continued by a series of chlorofluorocarbon heterodimers analyzed by Caminati et al. involving Cl⋅⋅⋅F, Cl⋅⋅⋅O, Cl⋅⋅⋅N, or Cl⋅⋅⋅C interactions. These dimers allowed discerning strong dynamical effects due to internal rotation within the dimers, together with structural information ( r 0 (Cl⋅⋅⋅F)=2.995, r 0 (Cl⋅⋅⋅O)=3.048, r 0 (Cl⋅⋅⋅N)=3.081–3.090 Å) and binding data (MP2 dissociation energies from −1.8 kJ mol −1 in CF 3 Cl⋅⋅⋅FCH 3 to −10.2 kJ mol −1 in CF 3 Cl⋅⋅⋅pyridine).…”

Structure, Conformational Equilibria, and Weak Hydrogen Bonding in the CH2F2−CF3CH2F Dimer

“…For the complexes of water, the CÀH···O linkages exist in association with the OÀH···F-C [14,15] or the OÀH···ClÀC. [20][21][22][23][24] In some special cases when perhalogenated freons have p orbitals, lone pair···p linkages are favored. [15] The complex of formaldehyde and CH 2 ClF [18] presents a combination of CÀH···ClÀC and CÀH···O WHBs while CÀH···FÀC in cooperation with CÀH···O WHBs stabilize the complex of formaldehyde and CH 2 F 2 .…”