Thermochemical Properties of Selenium Fluorides, Oxides, and Oxofluorides

Abstract

The bond dissociation energies (BDEs), fluoride and fluorocation affinities, and electron affinities of SeF(n) (n = 1-6), SeOF(n) (n = 0-4), and SeO(2)F(n) (n = 0-2) have been predicted with coupled cluster CCSD(T) theory extrapolated to the complete basis set limit. To achieve near chemical accuracy, additional corrections were added to the complete basis set binding energies based on frozen core coupled cluster theory energies. These included corrections for core-valence effects, scalar relativistic effects, for first-order atomic spin-orbit effects, and vibrational zero point energies. The adiabatic BDEs contain contributions from product reorganization energies and, therefore, can be much smaller than the diabatic BDEs and can vary over a wide range. For thermochemical calculations, the adiabatic values must be used, whereas for bond strength and kinetic considerations, the diabatic values should be used when only small displacements of the atoms without change of the geometry of the molecule are involved. The adiabatic Se-F BDEs of SeF(n) (n = 1-6) are SeF(6) = 90, SeF(5) = 27, SeF(4) = 93, SeF(3) = 61, SeF(2) = 86, and SeF = 76 kcal/mol, and the corresponding diabatic values are SeF(6) = 90, SeF(5) = 88, SeF(4) = 93, SeF(3) = 74, SeF(2) = 86, and SeF = 76 kcal/mol. The adiabatic Se-O BDEs of SeO(n) (n = 1-3), SeOF(n) (n = 1-4), and SeO(2)F(n) (n = 1,2) range from 23 to 107 kcal/mol, whereas the diabatic ones range from 62 to 154 kcal/mol. The adiabatic Se-F BDEs of SeOF(n) (n = 1-4) and SeO(2)F(n) (n = 1,2) range from 20 to 88 kcal/mol, whereas the diabatic ones range from 73 to 112 kcal/mol. The fluoride affinities of SeF(n), (n = 1-6), SeO(n), (n = 1-3), SeOF(n), (n = 1-4), and SeO(2)F(n) (n = 1,2) range from 15 to 121 kcal/mol, demonstrating that the Lewis acidity of these species covers the spectrum from very weak (SeF(6)) to very strong (SeO(3)) acids. The electron affinities which are a measure of the oxidizing power of a species, span a wide range from 1.56 eV in SeF(4) to 5.16 eV in SeF(5) and for the free radicals are much higher than for the neutral molecules. Another interesting feature of these molecules and ions stems from the fact that many of them possess both a Se free valence electron pair and a free unpaired valence electron, raising the questions of their preferred location and their influence on the Se-F and Se═O bond strengths.

Electronic Structure Predictions of the Energetic Properties of Tellurium Fluorides

“…This suggests that the experimental value is significantly in error. We note that there is a significant error in the value for Δ H f,298K (SeF 6 ) reported by Yost of −246.0 kcal/mol in contrast to our FPD value of −267.7 kcal/mol which is in good agreement with the more modern value of −267.18 kcal/mol at 298 K . The heats of formation of the ions TeF x + , x = 2, 3, 4, and 5 have been obtained from fragmentation of the valence electronic states of TeF 6 + studied by threshold photoelectron-photoion coincidence spectroscopy .…”

“…The heats of formation (which include spin–orbit effects) were used to calculate the adiabatic BDEs shown in Table . The tellurium species show the same alternation found for the fluorides of S and Se . TeF 5 is not very stable, so there is a large BDE for TeF 6 and a small BDE for TeF 5 .…”

“…The tellurium species show the same alternation found for the fluorides of S 130 and Se. 59 TeF 5 is not very stable, so there is a large BDE for TeF 6 and a small BDE for TeF 5 . The BDE for TeF 4 is larger than that for TeF 6 , and the remaining ones are smaller but still significant.…”

“…We have previously predicted reliable structural, spectroscopic, and thermodynamic information about selenium fluorides, oxides, and oxofluorides using the accurate computational chemistry Feller–Peterson–Dixon (FPD) composite method. − The FPD approach is based on correlated molecular orbital theory using coupled cluster methods at the CCSD­(T) level − extrapolated to the complete basis set (CBS) limit using the correlation consistent basis sets. − The recent design of systematically convergent, correlation consistent basis sets for the third, fourth, and fifth row main group and transition elements using relativistic effective core potentials − has been essential to the application of highly accurate thermodynamic predictions, and the continued development of basis sets to enable direct scalar relativistic corrections at the Douglas–Kroll–Hess level − will lead to even more accurate predictions by eliminating the pseudopotential error. In this work we have used the FPD approach to predict the heats of formation of TeF x from x = 1 to 6 together with the associated anions and cations.…”

“…− and F − . We have previously predicted 59 reliable structural, spectroscopic, and thermodynamic information about selenium fluorides, oxides, and oxofluorides using the accurate computational chemistry Feller−Peterson−Dixon (FPD) composite method. 60−63 The FPD approach is based on correlated molecular orbital theory using coupled cluster methods at the CCSD(T) level 64−67 extrapolated to the complete basis set (CBS) limit using the correlation consistent basis sets.…”