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Regularities in the bond dissociation enthalpies of molecules of types AB and BAB: Energetics of 10- and 16-valence electron ions of groups 13, 15, and 16


  • This article is dedicated to Leland C. Allen on the occasion of his 75th birthday.


For the quantitative and qualitative understanding of molecular energetics, contemporary calorimetric and mass spectrometric measurement techniques and correspondingly high-level quantum chemical calculational methodologies increasingly work in concert. For example, letting A and B be group 14 and 16 elements, respectively, for their 10-valence electron AB and 16-valence electron AB2 gas-phase diatomic and triatomic species, the bond enthalpy ratio 〈Dmath image(AB2)〉/Dmath image(AB) has been shown to remarkably constant, namely, 0.77 ± 0.02. In the current study we discuss the corresponding bond enthalpy ratio for the valence isoelectronic cations and anions, e.g., for the carcinogen [NO]+, explosive precursor [NO2]+, and discrete (monomeric, i.e., nonsalt containing) anions [BO2] and [AlO2]. From a combination of results taken from archival literature measurements and new quantum chemical calculations reported in this article, again roughly constant ratios are found. Numerically, these ratios are 0.66 ± 0.03 and 0.86 ± 0.02 for cations and anions, respectively. That the ratios increase in the order cation < neutral < anion is also explained in our study. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003