84417-13-0Relevant academic research and scientific papers
Electronic absorption and emission spectra of dioxorhenium(V) complexes. Characterization of the luminescent 3Eg state
Winkler, Jay R.,Gray, Harry B.
, p. 346 - 355 (2008/10/08)
The low-temperature single-crystal-polarized electronic absorption spectra of three trans-dioxorhenium(V) ions, ReO2L4z (L = CN-, z = 3-; L = 1/2en, z = 1+; L = py, z = 1+), have been investigated. The spectra display up to four distinct band systems that exhibit vibrational progressions in a high-energy (750-800-cm-1) mode. The two lowest energy band systems (500-550 nm) are assigned to components of a 3Eg[b2g(xy)1e g(xz,yz)1 ← b2g(xy)2] excited state that is split by spin-orbit coupling interactions. The next higher energy band (400-450 nm) is assigned to the corresponding 1Eg state, whereas the fourth band (ca. 300 nm) must arise from a different one-electron excitation. Luminescence from at least two of the lowest energy 3Eg components in the cyanide and pyridine complexes has been detected, and the zero-field splitting between the two emitting states is 10-20 cm-1. At 5 K, only the lowest energy component is populated and the luminescence spectra from this state display progressions in a ca. 900-cm-1 mode that corresponds to the symmetric rhenium-oxygen stretching vibration. Franck-Condon analyses of the luminescence bands indicate distortions of 0.09 (1) and 0.07 (1) ? along each Re-O bond for the cyanide and pyridine complexes, respectively. The lower energy of the corresponding progressions in absorption and the π-antibonding character of the 3Eg state suggest that the excited-state distortion is an elongation. The luminescence spectrum of the pyridine complex also exhibits a progression in a 190-cm-1 mode indicative of a 0.03 (1) ? distortion along the symmetric Re-py stretching coordinate. The lifetime of the 3Eg state at room temperature varies from 10 to 300 μs in crystals and is about 10 μs for ReO2(py)4+ (and its substituted pyridine analogues) in aprotic solvents. The luminescence of these dioxorhenium species, however, is rather efficiently quenched by protic solvents such as water and alcohols.
