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Oxidation of [Rh2(O2CEt)4(PR3)2] (R:  cy = cyclohexyl and Pri = iso-propyl) with ferrocenium ion gave stable salts of their cationic radicals. Their X-ray structures showed ca. 0.048 Å longer Rh−Rh and ca. 0.12 Å shorter Rh−P bonds than those of the diamagnetic neutral complexes. The pyramids of the phosphine ligands of these cationic complexes are more flattened than those of the neutral complexes. These observations and ESR data indicate that the σRhRh singly occupied molecular orbital (SOMO) of these complexes is extensively mixed with the phosphine lone-pair orbitals in the Rh−P σ antibonding phase. X-ray crystallographic structures of [Rh2(mhp)4]+ (mhp = anion of 2-hydroxy-6-methylpyridine) and [Rh2(form)4]+ (form = N,N‘-di-p-tolylformamidinate anion) showed that the removal of a δRhRh* electron results in 0.017−0.043 Å decreases of their Rh−Eq bond distances, where Eq is the ligation atom in the bridging ligand. These results are consistent with the delocalization of the δRhRh* orbital (the SOMO of these cationic radicals) onto the bridging ligands in the π antibonding phase. B3LYP DFT calculations of Rh2 4+ and Rh2 5+ model complexes reproduced the ligand dependence of the electron configuration of Rh2 5+ complexes and geometrical changes accompanying the ionization and showed that the relatively rigid arrangement of the bridging ligands retards the dependence of the Rh−Rh bond length on the electron configuration. Also, the spin population in [Rh2(O2CH)4(PH3)2]+ is extensively delocalized onto the axial ligands, that in [Rh2(HNCHNH)4]+ and [Rh2(HNCHO)4(H2O)2]+ moderately onto the bridging ligands and that in [Rh2(O2CH)4(H2O)2]+ rather localized on the metal atoms.

We have developed a remote scintillation detector using a CCD spectrometer and a red-emitting scintillator coupled with a 20 m optical fiber for ultra-high-dose conditions. Gamma rays were detected with a conventional deep-red-emitting ruby scintillator and Cs2HfI6, which is a novel material with 700 nm red emission and a high light output. The scintillators were irradiated with gamma rays from a 60Co source under an effective dose rate from ∼0.002 to ∼1 kSv h−1. The integrated area of the Cs2HfI6 emission spectra was larger than that of the ruby, and good linearity of the Cs2HfI6 signal as a function of dose rate was confirmed.