Chemistry of osmium phenolates. Synthesis, structure and redox properties
Journal
Polyhedron
Journal Volume
17
Journal Issue
13-14
Pages
2191-2197
Date Issued
1998
Author(s)
Abstract
The reaction of three phenolic ligands (viz. salicylaldehyde, Hsal; 2-hydroxyacetophenone, Hacp and 2-hydroxynaphthaldehyde, Hnap; generally abbreviated as HL, where H stands for the phenolic proton) with [Os(bpy)2Br2] has afforded complexes of type [Os(bpy)2(L)]+, 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 [OsII(bpy)2(sal)]ClO4 complex has been determined by X-ray crystallography. The salicylaldehydate anion is coordinated to osmium as a bidentate O,O-donor and the OsN4O2 coordination sphere is distorted octahedral. Cyclic voltammetry shows a reversible osmium(II)-osmium(III) oxidation in the range of 0.17-0.25 V vs SCE follwed by an irreversible osmium(III)-osmium(IV) oxidation in the range of 1.38-1.48 V vs SCE. Three one-electron reductions of the coordinated bpy ligands are also observed on the negative side of SCE (-1.49-2.08 V). Chemical or electrochemical oxidation of the [OsII(bpy)2(L)]ClO4 complex affords green [OsII(bpy)2(L)]2+ species, which have been isolated as the perchlorate salts. These complexes are one-electron paramagnetic (low-spin d5, S = 1/2) and in acetonitrile solution show LMCT transitions in the visible region. Reduction of the green [OsII(bpy)2(L)](ClO4)2 complexes gives back the respective brown [OsII(bpy)2(L)]ClO4 complexes. © 1998 Elsevier Science Ltd. All rights reserved.
Type
journal article