Chemistry of 2-(arylazo) phenolate complexes of osmium. Synthesis, structure and redox properties
Journal
Polyhedron
Journal Volume
18
Journal Issue
3-4
Pages
391-402
Date Issued
1998
Author(s)
Abstract
Reaction of five 2-(arylazo)phenol ligands (abbreviated in general as Hap-R, where H stands for the phenolic proton) with [OsII(bpy)2Br2] has afforded complexes of type [OsII(bpy)2(ap-R)]+ , which have been isolated as the perchlorate salts. The complexes are diamagnetic (low-spin d6, S = 0) and in acetonitrile solution shows several MLCT transitions in the visible region. Structure of the [Os(bpy)2(ap-Me))ClO4 complex has been determined by X-ray crystallography. The 2-(arylazo)phenolate anion is coordinated to osmium as a bidentate N,O-donor forming a five-membered chelate ring and the OsN5O coordination sphere is distorted octahedral. Cyclic voltammetry shows a reversible osmium(II)-osmium(III) oxidation in the range of 0.37-0.51 V vs SCE followed by an irreversible osmium(III)-osmium(IV) oxidation in the range of 1.36-1.50 V vs SCE. These oxidation potentials are sensitive to the electronic nature of the substituent R in the 2-(arylazo)phenolate ligands. Three one-electron reductions of the coordinated bpy ligands are also displayed on the negative side of SCE below - 1.0V. Chemical or electrochemical oxidation of the [OsII(bpy)2(ap-R)]ClO4 complexes affords brownish-yellow [OsIII(bpy)2(ap-R)]2+ species, which have been isolated as the perchlorate salts. These complexes are one-electron paramagnetic (low-spin d5, 5=1/2) and in acetonitrile solution show LMCT transitions in the visible region. Reduction of the brownish-yellow [OsIII(bpy)2(ap-R)](ClO4)2 complexes gives back the respective brown [OsII(bpy)2(ap-R)]C1O4 complexes. © 1999 Elsevier Science Ltd. All rights reserved.
Type
journal article