Dinuclear rhenium pyridazine complexes containing bridging chalcogenide anions : synthesis, characterization and computational study
Articolo
Data di Pubblicazione:
2017
Citazione:
Dinuclear rhenium pyridazine complexes containing bridging chalcogenide anions : synthesis, characterization and computational study / L. Veronese, E. Quartapelle Procopio, D. Maggioni, P. Mercandelli, M. Panigati. - In: NEW JOURNAL OF CHEMISTRY. - ISSN 1144-0546. - 41:19(2017), pp. 11268-11279. [10.1039/C7NJ02548C]
Abstract:
The synthesis of a series of neutral dinuclear rhenium complexes of the general formula [Re2(m-ER)2(CO)6-
(m-pydz)] (pydz = pyridazine; E = S, Se or Te; R = methyl or phenyl; the TeMe is not included) has been
carried out via new, either one-pot or two-step, procedures. The one-pot synthesis consists of
the oxidative addition of RE–ER across the Re–Re bond of [Re2(CO)10], in the presence of 1 equivalent of
pyridazine, and affords the corresponding dinuclear complexes in high yields (ca. 85%). Furthermore, a
general two-step procedure has been carried out, which involves the synthesis of heterocubane-like
[Re4(m3-ER)4(CO)12] molecules and their reaction with pyridazine, quantitatively affording the corresponding
dinuclear species through a symmetric [2+2] fragmentation pathway. The molecular structure of the
complexes has been elucidated by single crystal XRD analysis, and TD-DFT calculations predicted
the existence of conformers differing in the orientation of the chalcogen substituents with respect to the
pyridazine ligand. The relative stabilities and the activation barriers for the interconversion have been
calculated, observing a regular trend that has been rationalized depending on the hybridization of the
chalcogen atom. Variable temperature NMR studies experimentally confirmed the theoretical prediction,
showing, in solution, two conformers with different relative amounts and different interconversion rates
between them, depending on the chalcogen nature. From the electrochemical point of view the S, Se and
Te complexes display a bi-electronic reversible oxidation peak, differently from the two mono-electronic
irreversible oxidation peaks previously observed for the O derivatives. Moreover, a progressive narrowing
of the HOMO–LUMO gap on going from O to Te, arising from the increase of the HOMO level, has been
observed. This is in line with the decreasing electron-withdrawing strength of the chalcogenide bridging
ligand, so that the energy gap for the telluride derivative is 1.64 eV, the smallest value in the whole family
of the di-rhenium pyridazine complexes. The spectroscopic HOMO–LUMO gap parallels this trend, with a
significant red-shift of the metal-to-ligand charge transfer absorption, making the telluride complex highly
promising as a photosensitizer in the field of solar energy conversion. In agreement with the narrow
HOMO–LUMO gap, no photoluminescence has been observed upon optical excitation.
Tipologia IRIS:
01 - Articolo su periodico
Elenco autori:
L. Veronese, E. Quartapelle Procopio, D. Maggioni, P. Mercandelli, M. Panigati
Link alla scheda completa:
Link al Full Text: