Electronic and molecular structures of C-60-based polyanionic high-spin molecular clusters: Direct spin identification and electron spin transient nutation spectroscopy for high-spin chemistry

摘要

C-60-based polyanionic high-spin clusters (S = 1-3) in their ground state have been prepared by successive chemical reductions of pristine C-60 fullerene with potassium in the presence of dicyclohexano-18-crown-6-ether in solution. Intermolecular spin-triplet, quintet, and septet states arising from the C-60-based polyanionic molecular clusters have been generated at ambient temperature and identified by CW-ESR and pulse-ESR-based two-dimensional (2D) electron spin transient nutation (2D-ESTN) spectroscopy in organic rigid glasses, for the first time. Intermolecular exchange interactions between mono- and polyanionic C-60 fullerenes are ferromagnetic via bridging potassium metal cations. The molecular structures of the polyanionic high-spin C-60 clusters in solution have been proposed by a well-established phenomenological spin Hamiltonian approach in terms of the D-tensor-based calculations for the high-spin clusters. The findings of the C-60-based high-spin molecular clusters evidence the occurrence of an intramolecular triplet C-60 dianion in the ground state. Unequivocal spin identification for molecular high-spin entities by 2D-ESTN spectroscopy and its powerfulness have been illustrated, emphasizing that the 2D-ESTN spectroscopy is useful for mixtures of molecular species with different spin multiplicities, characterized by a small g-anisotropy, for which the powerfulness of advanced high-frequency ESR spectroscopy is hampered.