Synthesis, structural characterization and spectroscopic properties of cobalt complexes with the 2,6-bis(8′-quinolinyl)pyridine ligand

Coordination of the 2,6-bis(8′-quinolinyl)pyridine (bqp) ligand to a cobalt (Co) core and its influence to electron spin and configuration on the structures and properties of the resulting complexes has been investigated. The homoleptic complexes Co(mer-bqp-κ3N,N′,N″)]2+ (1) and [Co(mer-bqp-κ3N,N′,N″)]3+ (2) were prepared and characterized. X-ray structure determinations of complexes 1 and 2 revealed twisted, near-octahedral arrangements relative to the cobalt center. The magnetic data for 1 is typical of those for distorted octahedral (i.e., D4h symmetry) high-spin d7 species despite the near-ideal octahedral coordination of the bqp ligand around the Co(II) core. Electronic spectra for 1 and 2 have been investigated and assigned. Both complexes exhibit intense π–π∗bqp ligand centered transitions in the UV region and low intensity mixed charge transfer transitions in the visible region. Neither complex strongly absorbs in visible spectral region. The electrochemistry of these compounds has been studied and compared to that of similar cobalt terpyridine compounds. A metal-centered Co2+/3+ redox wave and ligand-based reduction processes were observed for 1 and 2 in acetonitrile. The metal-centered redox potentials were reversible with potentials more positive than comparable cobalt-terpyridine complexes. Density functional theory (DFT) calculations of the electronic and ground state properties are in good agreement with the experimental data.

Coordination of the 2,6-bis(8′-quinolinyl)pyridine (bqp) ligand to a cobalt (Co) core and its influence to electron spin and configuration on the structures and properties of the resulting complexes has been investigated.Figure optionsDownload as PowerPoint slide