Electrochemical and spectral properties of hexacoordinate polypyridyl silicon complexes

Various salts of tetracationic tris(2,2′-bipyridine)silicon(IV) and bis(2,2′;6′,2″-terpyridine)silicon(IV) were synthesized by reaction of SiI4 with the appropriate ligand followed by metathesis reactions. The resulting salts exhibit multiple, chemically reversible one-electron reduction waves that are significantly shifted to less negative reduction potentials than the corresponding ruthenium analogs. The salts also exhibit anion dependent ion pair charge transfer bands throughout the visible spectrum. Weak, low energy emission is observed from Si(bipy)3Br4 and Si(terpy)2Br4 in the solid state at 77 K when the sample is excited in the ion pair charge transfer band.

Graphical abstractSalts of Si(bipy)34+ and Si(terpy)24+ have been synthesized and their electrochemical and spectra properties have been investigated. Both sets of species exhibit extensive reversible electrochemistry and intense anion dependent ion pair charge transfer bands throughout the visible spectrum.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► New Si(terpy)24+ salts have been synthesized and characterized. ► Both Si(bipy)34+ and Si(terpy)24+ have several stable oxidation states. ► Halide salts of Si(bipy)34+ and Si(terpy)24+ exhibit intense ion pair charge transfer bands.