Gas Phase Dissociation Energies of Saturated AHn·+ Radical Cations and AHn Neutrals (A = Li-F, Na-Cl): Dehydrogenation, Deprotonation, and Formation of AHn-2·+ - H2 Complexes

Gil, A.; Bertran, J.*; Sodupe, M.* J. Am. Chem. Soc.; 2003, 125(24), 7461.

The dissociation energies corresponding to the two possible A−H cleavages of A (A = Li−F and Na−Cl) radical cations (loss of a H+ and loss of a H·) have been computed at the CCSD(T)/ 6-311++G(3df,2pd) level of theory and compared to those of their neutral precursors. Removing an electron from AHn decreases dramatically its deprotonation energy, especially for the A molecules (C and ), which become one of the most acidic species of the row, their acid character being only exceeded by FH·+ and ClH·+, respectively. However, dehydrogenation energies only decrease for the systems on the left side of the row (up to C and SiH4·+) for which the electron is removed from a A−H bonding orbital. Nevertheless, the loss of hydrogen is the more favorable cleavage in all cases except FH·+. Ionization of SiH4 leads to a Jahn−Teller distorted structure that corresponds to a Si − H2 complex. Other − η2H2 complexes in the doublet spin state have also been found to be stable for A = Be, Mg, Al, and P, the hydrogen molecule complexes being more stable than their corresponding radical cations, for Be, Mg, and Al.

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