83005-95-2Relevant articles and documents
Influence of substituents in 1,10-phenanthroline on the structural and photophysical properties of W(CO)4(1,10-phenanthroline-type) complexes
Fernández, Mariano,Jara, Danilo H.,Pizarro, Nancy,Vega, Andrés
, (2021)
In this work, methyl and phenyl substituents were introduced in the 2,9- and 4,7-positions of the phen ligand in order to study its impact on the structural and photophysical properties of [W(CO)4(phen-type)] complexes [phen-type = 4,7-dimethyl-1,10-phenanthroline (4,7-DMPhen); 4,7-diphenyl-1,10-phenanthroline (BPhen), and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)]. Crystallographic analysis of these complexes allows to investigate the correlation between the geometrical parameters with their photophysical properties measured by steady-state and time-resolved spectroscopies. The (OC)eq–W–(CO)eq angle is the most significantly influenced geometrical parameter by the substituents, showing values of 92.5°, 90.2°, and 81.2° for [W(CO)4(4,7-DMPhen)], [W(CO)4(BPhen)], and [W(CO)4(BCP)], respectively. The smallest angle observed for [W(CO)4(BCP)] is attributed to a steric repulsion exerted by the methyl groups to the equatorial carbonyls. Remarkably, a smaller OCeq–W–COeq angle favors the High-Energy (HE) emission band, as evidenced in the photoluminescence (PL) spectra of [W(CO)4(BCP)]. Conversely, a greater angle favors the Low-Energy (LE) emission band, as observed in the PL spectra of [W(CO)4(4,7-DMPhen)] and [W(CO)4(BPhen)]. The PL lifetime of the LE emission band becomes shorter when decreasing the (OC)eq–W–(CO)eq angle. Furthermore, the absorption feature was affected by the 2,9-dimethyl substituents, showing greater contribution from the high-energy shoulder on the visible absorption band. This study shows that the perturbation of the (OC)eq–W–(CO)eq angle induced by the substituents in the phen ligand influences on the photophysical properties of [W(CO)4(phen-type)] complexes.
Photolysis of group 6 metal hexacarbonyl solutions containing diimine ligands. Spectral characterization and reaction kinetics of a photoproduced intermediate, monodentate M(CO)5(diimine)
Schadt, Mark J.,Lees, Alistair J.
, p. 672 - 677 (2008/10/08)
Electronic absorption spectra have been obtained immediately following the photolysis of M(CO)6 solutions containing diimine ligands (1,10-phenanthroline, 2,2′-bipyridine, 1,4-diazabutadiene, or their derivatives) with the use of a microprocessor-controlled diode-array UV-visible spectrophotometer. The time-dependent spectra illustrate rapid formation of a reaction intermediate that is assigned to be M(CO)5L, where L is a diimine ligand coordinated in a monodentate fashion. Monodentate M(CO)5L subsequently extrudes CO thermally via a first-order kinetic process to form stable M(CO)4L. No discernable M(CO)5L intermediates were observed when L = 1,10-phenanthroline (phen) or a phen derivative consistent with the rigid coplanar nature of these ligands. In contrast, the chelation of M(CO)5L complexes, where L = 2,2′-bipyridine, 1,4-diazabutadiene, or derivatives, proceeds with considerably slower reaction rates. The rate data are interpreted in terms of the stereochemistry of the monodentate intermediate. For a given ligand, the reaction rate decreases in the sequence Mo > Cr > W, analogous to the order of CO release in M(CO)6; this ordering suggests that the predominant barrier to chelation involves breaking of the M-C bond. Derived activation energy parameters indicate that the chelation reaction is enthalpy-controlled. The marked dependence of reaction rate on diimine and resulting negative activation entropy values imply that the chelation mechanism proceeds with a substantial associative component.
