Fluorescence techniques have been used to identify humic substances, (e.g. aquatic fulvic acids from different origins). Synchronous scans have proven adequate for distinguishing detail and differentiating samples. As well, fluorescence has often been used to probe humic interactions with metals and xenobiotic organics. In this study, the fluorescence of a well-characterized material, Laurentian fulvic acid (LFA) was compared with that of a simple hydroquinone/quinone (H 2 Q/Q) model system. Synchronous fluorescence (room T) and laser-excited fluorescence experiments at 10°K were carried out to characterize the fluorophore. The synchronous fluorescence behavior of LFA displayed similarities to that of an equilibrated, aerated, H 2 Q/Q system, but only at higher pH. (Higher pH favours a shift of the redox equilibrium towards quinone.) In contrast, the spectra of LFA suggest the role of "quinone" groups, even at lower pH. A signif-
Aquatic Sciencesicant feature of these spectra is a lowest energy band. At low temperature this band was more selectively excited at 470 nm, but vibrationally resolved line narrowed spectra were not observed. Fluorescence lifetimes were very short compared to the laser pulse width of ca. 10 ns. Under the low T condition the spectra of LFA and the model are essentially identical. We suggest that the principal luminophore in LFA is a quinone-hydroquinone type, perhaps a charge transfer complex consistent with the absence of the fluorescence line-narrowing phenomenon. The spectra imply a lowest energy component of LFA emission from a fluorophore very similar to that of the simplest H 2 Q/Q. The significant similarities of the model system to LFA are underscored by striking parallels in the radicals in the two systems seen in well-resolved electron paramagnetic resonance (EPR) spectra that could be obtained at pH = 6.
The copper-catalyzed Click reaction of phenyl azide with ethynylphosphine oxides provides new P-substituted triazoles. With tris(ethynyl)phosphine oxide this route affords a versatile scorpionate ligand that coordinates to RhCl 3 as a tripodal N ligand. Upon reduction, the same ligand can act as a P donor to W(CO) 5 . Both coordination modes can be combined, giving access to a bimetallic Mo/W complex.
Novel transient phosphinidene complex Ph−PMo(CO)4PMe3, generated from a 7-phosphanorbornadiene precursor, adds to CC and C⋮C bonds to give Mo(CO)4PMe3-complexed phosphiranes
and phosphirenes. The cis-PMe3 ligand weakens the interaction between the molybdenum complex and
the three-membered ring. Under mild CO pressure the Mo(CO)4PMe3 transition metal group detaches
from the phosphorus center of the ring structure by selective CO substitution. The resulting byproduct
Mo(CO)5PMe3 can be reused in the synthesis of the phosphinidene precursor.
Intramolecular phosphinidene addition to the C==C bond of Mo-complexed, seven-membered phosphorus heterocycles affords three novel [(diphos)Mo(CO)(4)] complexes (18-20). The three bidentate phosphorus baskets differ in the composition of the seven-membered ring: one of the phosphorus atoms is flanked by CH(2), NCH(3), or O. The unsaturated tetrahydrophosphepine precursors are synthesized by either ring-closing metathesis (C and N derivatives) or by a cyclization sequence (O derivative). The crystal structures of the nitrogen- (19) and oxygen-containing (20) baskets have relatively small P-Mo-P angles of 76.240(13) degrees and 77.626(12) degrees , respectively, and complex 20 has slightly shortened Mo--P bond lengths.
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