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44308-GB3
Synthesis and Photochemical Characterization of Hexacoordinate Silicon(diimine)3 Complexes
The goal of this project is to synthesize a library of hexacoordinate silicon complexes with multi-dentate polypyridyl ligands and to study their electronic and optical properties (Figure 1). During the first year we have focused on the synthesis and purification of several complexes, including Si(bipyridine)3(PF6)4, Si(phenanthroline)3(PF6)4, Si(terpyridine)2(PF6)4, and some heteroleptic complexes including Si(phen)2(OMe)2(PF6)4, Si(bipy)2(OMe)2(PF6)4. All the complexes were synthesized by melting SiI4 in excess ligand following the procedures of Kummer and coworkers (Z. Anorg. Allg. Chem. 1979, 459, 145-156). The iodide salts are generally soluble in water and the +4 cation is easily precipated out of aqueous solution upon the addition of NH4PF6.
SiI4 + excess bipy → [Si(bipy)3]I4
We are now beginning to study the interesting electronic and optical properties of these complexes. While the ubiquitous Ru(diimine)32+ complexes (e.g. Ru(bipy)32+) have been the subject of thousands of papers, due primarily to the well studied photochemical, photophysical, and electrochemical properties, the chemistry and properties of the corresponding silicon analogs such as Si(bipy)30 and Si(bipy)34+ have been the subject of very few studies. In the case of the Si(bipy)34+ cation, preliminary cyclic voltammetry experiments of the Si(bipy)3(PF6)4 salt in CH3CN solution indicate 3 reversible reduction peaks and a fourth peak that appears to indicate depositing of the Si(bipy)3 neutral compound on the electrode. CV of the Si(bipy)3Cl4 salt in water also appears to have three reversible reduction peaks. The electrochemistry of Si(phen)34+ and Si(terpy)24+ cations are providing similar results, although with Si(terpy)24+ the first four reduction peaks are reversible. We have also begun to measure the spectroscopic properties and the fluorescence and fluorescence lifetimes of the compounds. Most of the complexes exhibit fluorescence, and both the fluorescence and absorbance properties are very dependent upon the counter-ion and solvent.
