Molecular Electronic Structure and Energetics of the Isomers of Ti2H6

Ab initio calculations have been performed on five singlet and five triplet isomers which are minima on the two lowest potential energy surfaces of Ti2H6. We have used single-configuration ROHF as well as multiconfigurational methods, employing triple-ζ with polarization basis sets. Dynamic correlation effects are accounted for using second-order perturbation methods. Staggered and eclipsed C3v triple hydrogen bridged structures, which have been studied previously using single-determinant closed-shell reference wave functions, are shown to require a more sophisticated treatment. The remaining isomersCs triple hydrogen bridged, D2h double hydrogen bridged, and D4h quadruple hydrogen bridgedhave not previously been considered. The triplets are by definition diradical, and the singlets are found to possess largely diradical character. The D2h isomer may be thought of as the simplest model for dititanium(III) bridged compounds. It is found to be antiferromagnetic with a calculated isotropic exchange interaction of J = −250 cm-1 (singlet−triplet gap of 1.43 kcal/mol). All Ti2H6 isomers are predicted to be lower in energy than the separated monomers: 2TiH3. The lowest energy isomer is the triplet Cs structure with an exothermic dimerization energy of 56.4 kcal/mol on the classical ground-state potential energy surface. Disciplines Chemistry Comments Reprinted (adapted) with permission from Journal of the American Chemical Society 1120 (1998): 3846, doi:10.1021/ja973195s. Copyright 1998 American Chemical Society. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/chem_pubs/340 Molecular Electronic Structure and Energetics of the Isomers of Ti2H6 Simon P. Webb and Mark S. Gordon* Contribution from the Department of Chemistry, Iowa State UniVersity, Ames, Iowa 50011 ReceiVed September 11, 1997. ReVised Manuscript ReceiVed January 12, 1998 Abstract: Ab initio calculations have been performed on five singlet and five triplet isomers which are minima on the two lowest potential energy surfaces of Ti2H6. We have used single-configuration ROHF as well as multiconfigurational methods, employing triple-ú with polarization basis sets. Dynamic correlation effects are accounted for using second-order perturbation methods. Staggered and eclipsed C3V triple hydrogen bridged structures, which have been studied previously using single-determinant closed-shell reference wave functions, are shown to require a more sophisticated treatment. The remaining isomerssCs triple hydrogen bridged, D2h double hydrogen bridged, and D4h quadruple hydrogen bridgedshave not previously been considered. The triplets are by definition diradical, and the singlets are found to possess largely diradical character. The D2h isomer may be thought of as the simplest model for dititanium(III) bridged compounds. It is found to be antiferromagnetic with a calculated isotropic exchange interaction of J ) -250 cm-1 (singlet-triplet gap of 1.43 kcal/mol). All Ti2H6 isomers are predicted to be lower in energy than the separated monomers: 2TiH3. The lowest energy isomer is the triplet Cs structure with an exothermic dimerization energy of 56.4 kcal/mol on the classical ground-state potential energy surface. Ab initio calculations have been performed on five singlet and five triplet isomers which are minima on the two lowest potential energy surfaces of Ti2H6. We have used single-configuration ROHF as well as multiconfigurational methods, employing triple-ú with polarization basis sets. Dynamic correlation effects are accounted for using second-order perturbation methods. Staggered and eclipsed C3V triple hydrogen bridged structures, which have been studied previously using single-determinant closed-shell reference wave functions, are shown to require a more sophisticated treatment. The remaining isomerssCs triple hydrogen bridged, D2h double hydrogen bridged, and D4h quadruple hydrogen bridgedshave not previously been considered. The triplets are by definition diradical, and the singlets are found to possess largely diradical character. The D2h isomer may be thought of as the simplest model for dititanium(III) bridged compounds. It is found to be antiferromagnetic with a calculated isotropic exchange interaction of J ) -250 cm-1 (singlet-triplet gap of 1.43 kcal/mol). All Ti2H6 isomers are predicted to be lower in energy than the separated monomers: 2TiH3. The lowest energy isomer is the triplet Cs structure with an exothermic dimerization energy of 56.4 kcal/mol on the classical ground-state potential energy surface.