INVESTIGADORES
PARISE Alejandro Ruben
artículos
Título:
Role of Ruthenium Oxidation States in Ligand-to-Ligand Charge Transfer Processes
Autor/es:
CRISTINA LUJÁN RAMIREZ; CÉSAR NICOLÁS PEGORARO; OSCAR FILEVICH; ANDREA BRUTTOMESO; ROBERTO ETCHENIQUE; ALEJANDRO R. PARISE
Revista:
INORGANIC CHEMISTRY
Editorial:
AMER CHEMICAL SOC
Referencias:
Año: 2012 vol. 51 p. 1261 - 1268
ISSN:
0020-1669
Resumen:
We describe in this paper the properties of [RuII/III(bpy)2ClL]+1/+2 and [RuII/III(bpy)2L2]+2/+3. L = ditolyl-3-pyridylamine (dt3pya)
is a redox active ligand related to triarylamines, which is very
similar to 3-aminopyridine except for the reversible redox behavior. The
monosubstituted complex shows a metal-to-ligand charge-transfer (MLCT)
at 502 nm, and reversible waves in acetonitrile at E0(RuIII/II) = 1.07 V, E0(L+/0) = 1.46 V (NHE). The disubstituted complex shows an MLCT at 461 nm, a photorelease of dt3pya
with quantum yield of 0.11 at 473 nm, and two reversible one-electron
overlapped waves at 1.39 V associated with one of the ligands (1.37 V)
and RuIII/II (1.41 V). Further oxidation of the second ligand
at 1.80 V forms a 2,2′-bipiridine derivative, in an irreversible
reaction similar to dimerization of triphenylamine to yield
tetraphenylbenzidine. In the dioxidized state, the
spectroelectrochemistry of the disubstituted complex shows a
ligand-to-ligand charge transfer at 1425 nm, with a transition moment of
1.25 Å and an effective two-state coupling of 1200 cm1. No
charge transfer between ligands was observed when Ru was in a 2+
oxidation state. We propose that a superexchange process would be
involved in ligandmetalligand charge transfer, when ligands and metals
are engaged in complementary π interactions, as in metalligandmetal
complexes. Best orbital matching occurs when metallic donor fragments
are combined with acceptor ligands and vice versa. In our case, RuIII bridge (an acceptor) and two dt3pya (donors, one of them being oxidized) made the complex a RobinDay Class II system, while the RuII bridge (a donor, reduced) was not able to couple two dt3pya (also donors, one oxidized).