Gaseous Trihalogen Cations. Formation, Structure and Reactivity of Cl₃⁺ and Cl₂F⁺ Ions from a Joint ab Initio and FT-ICR Study

Abstract

Gaseous Cl3 + ions were obtained by two convenient routes, namely Cl+ transfer to chlorine from Cl2H+ or Cl2 .+ ions, whereas Cl2F+ was prepared upon fluorination of chlorine by XeF+. The structure and the stability of the trihalogen cations were investigated by reactive probing, utilizing FTICR mass spectrometry to survey their reactivity, in particular Cl+ transfer processes toward selected nucleophiles. The structure, relative stability, and dissociation enthalpies of Cl3 + and Cl2F+ were investigated by computational methods based on density functional theory up to the CCSD(T)/cc-pVQZ//B3LYP/6-311++G(3df, 3pd) level. The results show that an A1 singlet of C 2 v symmetry is the global minimum on the Cl3 + potential energy surface. Consistent with earlier results, the asymmetric bent [Cl−Cl−F]+, also an A1 singlet, is more stable by 44.3 kcal mol-1 at 298 K than the symmetric isomer of [Cl−F−Cl]+ connectivity. By combining theoretically computed dissociation enthalpies with available thermochemical data the heats of formation of Cl3 + and Cl2F+ cations, in their ground state, can be estimated to be 251.5 ± 5 and 245.0 ± 5 kcal mol-1 at 298 K. Comparison of the Cl+ and F+ binding energies to simple halogenated molecules shows an excellent linear correlation, which is not the case when the comparison is extended to the proton affinities. The different factors that influence the stability of protonated and halogenated adducts are briefly discussed.

Gaseous [H3C−Cl−Cl]+ Ions from the Reaction of Methane with Cl3+, the First Example of a New Dihalogenation Process: Formation and Characterization of CH3Cl2+ Isomers by Experimental and Theoretical Methods

“…Finally, from the H o f of 2 the dissociation into CH 3 Cl and Cl is endothermic by 98.1 AE 5 kcal mol À1 , comparable to the calculated value of 89.1 kcal mol À1 , which corresponds to the Cl affinity of the chlorine atom of CH 3 Cl. This Cl binding energy is higher than recently obtained for other chlorinated compounds, [9] probably reflecting the combined effects of the electron-rich chlorine atom and the electron-donating ability of the methyl group.…”

Gas-Phase Ion Chemistry of the Noble Gases: Recent Advances and Future Perspectives

“…In the last decade, mass spectrometric techniques and theoretical calculations have also been extensively employed to explore gas-phase reactions involving noblegas ions, especially cations. Surveyed here is, in particular, a group of ionic processes involving singly-charged xenon cations [219][220][221][222][223][224][225][226][227][228][229][230][231][232] and a series of bond-forming reactions involving doubly-charged cations. [233][234][235][236][237][238][239][240][241][242][243][244][245][246][247] The implications of these findings for the chemistry of certain xenon compounds observed in the condensed phases are also briefly examined.…”

“…10 These considerations stimulate interest for the gas-phase reactivity of XeF + , which was investigated in a series of strictly related experimental and theoretical studies. [219][220][221][222][223][224] The cation was generated from the EI of XeF 2…”

“…A formal transfer of F + was observed from the reaction between XeF + and Cl 2 . 224 The Cl 2 F + product has an asymmetric bent structure Cl-Cl-F + ( 1 A 1 ), that is more stable than the symmetric Cl-F-Cl + isomer by more than 167 kJ mol -1 . The Cl 3 + cation was also investigated and the comparison of the Cl + and F + binding energies to simple halogenated molecules showed an excellent linear correlation, which was not, however, the case when the comparison was extended to the PAs.…”

Heterocations in Superacid Systems

“…Raman spectra of the adducts AsF 5 -2ClF and BF 3 -2ClF have established that these compounds contain the unsymmetrical ClClF þ cation 805 and not the symmetrical ClFCl þ cation previously reported on the basis of the IR spectrum alone. 813 ClÀF bond strength in the ClClF þ cation is twice as strong as in cation ClFCl þ (41.6 kcal mol À1 versus 21.2 kcal mol À1 ). Theoretical calculations confirm that the ClClF þ cation is more stable by 43.0 kcal mol À1 [MP4(SDTQ)/6-311G(2df)//M3/6-311G(2df) þ ZPE level] 827 and 44.3 kcal mol À1 [CCSD(T)/cc-pVQZ level].…”