1,5-Diamido-9,10-anthraquinone, a Centrosymmetric Redox-Active Bridge with Two Coupled β‑Ketiminato Chelate Functions: Symmetric and Asymmetric Diruthenium Complexes
journal contribution
posted on 2016-05-12, 12:18 authored by Mohd. Asif Ansari, Abhishek Mandal, Alexa Paretzki, Katharina Beyer, Jan Fiedler, Wolfgang Kaim, Goutam Kumar LahiriThe
dinuclear complexes {(μ-H2L)[Ru(bpy)2]2}(ClO4)2 ([3](ClO4)2), {(μ-H2L)[Ru(pap)2]2}(ClO4)2 ([4](ClO4)2), and the asymmetric [(bpy)2Ru(μ-H2L)Ru(pap)2](ClO4)2 ([5](ClO4)2) were synthesized via the mononuclear species [Ru(H3L)(bpy)2]ClO4 ([1]ClO4) and
[Ru(H3L)(pap)2]ClO4 ([2]ClO4), where H4L is the centrosymmetric
1,5-diamino-9,10-anthraquinone, bpy is 2,2′-bipyridine, and
pap is 2-phenylazopyridine. Electrochemistry of the structurally characterized
[1]ClO4, [2]ClO4,
[3](ClO4)2, [4](ClO4)2, and [5](ClO4)2 reveals multistep oxidation and reduction processes, which were
analyzed by electron paramagnetic resonance (EPR) of paramagnetic
intermediates and by UV–vis–NIR spectro-electrochemistry.
With support by time-dependent density functional theory (DFT) calculations
the redox processes could be assigned. Significant results include
the dimetal/bridging ligand mixed spin distribution in 33+ versus largely bridge-centered spin in 43+a result of the presence of RuII-stabilizig
pap coligands. In addition to the metal/ligand alternative for electron
transfer and spin location, the dinuclear systems allow for the observation
of ligand/ligand and metal/metal site differentiation within the multistep
redox series. DFT-supported EPR and NIR absorption spectroscopy of
the latter case revealed class II mixed-valence behavior of the oxidized
asymmetric system 53+ with about equal contributions
from a radical bridge formulation. In comparison to the analogues
with the deprotonated 1,4-diaminoanthraquinone isomer the centrosymmetric
H2L2– bridge shows anodically shifted
redox potentials and weaker electronic coupling between the chelate
sites.
