Zero-Magnetic-Field Splitting in the Excited Triplet States of Octahedral Hexanuclear Molybdenum(II) Clusters: [{Mo6X8}(n-C3F7COO)6]2– (X = Cl, Br, or I)

Temperature (T)-dependent emission from [{Mo6X8}(n-C3F7COO)6]2– (X = Cl (1), Br (2), and I (3)) in optically transparent polyethyleneglycol dimethacrylate matrices were studied in 3 K < T < 300 K to elucidate the spectroscopic and photophysical properties of the clusters, in special reference to zero-magnetic-field splitting (zfs) in the lowest-energy excited triplet states (T1) of the clusters. The cluster complexes 1 and 2 showed the T-dependent emission characteristics similar to those of [{Mo6Cl8}Cl6]2–, while 3 exhibited emission properties different completely from those of 1 and 2. Such T-dependent emission characteristics of 1, 2, and 3 were explained successfully by the excited triplet state spin-sublevel (Φn, n = 1 – 4) model. The zfs energies between the lowest- (Φ1) and highest-energy spin-sublevels (Φ4), ΔE14, resulted by the first-order spin-orbit coupling, were evaluated to be 650, 720, and 1000 cm–1 for 1, 2, and 3, respectively. The emission spectra of 1, 2, and 3 in CH3CN at 298 K were r...