title: Observation of a thermally accessible triplet state resulting from rotation around a main-group π bond.
abstract: We report the first direct spectroscopic observation by electron paramagnetic resonance (EPR) spectroscopy of a triplet diradical that is formed in a thermally induced rotation around a main-group π bond, that is, the SiSi double bond of tetrakis(di-tert-butylmethylsilyl)disilene (1). The highly twisted ground-state geometry of singlet 1 allows access to the perpendicular triplet diradical 2 at moderate temperatures of 350-410 K. DFT-calculated zero-field splitting (ZFS) parameters of 2 accurately reproduce the experimentally observed half-field transition. Experiment and theory suggest a thermal equilibrium between 1 and 2 with a very low singlet-triplet energy gap of only 7.3 kcal mol(-1) .
authors: Schulich Faculty of Chemistry and Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel).
authors: Arseni
authors: A
authors: Kostenko
authors: Schulich Faculty of Chemistry and Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel).
authors: Boris
authors: B
authors: Tumanskii
authors: Schulich Faculty of Chemistry and Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel).
authors: Miriam
authors: M
authors: Karni
authors: Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan).
authors: Shigeyoshi
authors: S
authors: Inoue
authors: Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan).
authors: Masaaki
authors: M
authors: Ichinohe
authors: Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571 (Japan). sekiguch@chem.tsukuba.ac.jp.
authors: Akira
authors: A
authors: Sekiguchi
authors: Schulich Faculty of Chemistry and Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa 32000 (Israel). apeloig@technion.ac.il.
authors: Yitzhak
authors: Y
authors: Apeloig
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D008958:Models, Molecular; D011789:Quantum Theory; D017655:Silicon Compounds / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
chemical_list: D017655:Silicon Compounds
keywords: EPR spectroscopy; density functional calculations; diradicals; disilenes; zero-field splitting parameters