INVESTIGATION OF THE PHOTOCHEMICAL, ELECTROCHEMICAL, AND SPECTROELECTROCHEMICAL PROPERTIES OF AN IRIDIUM(III) RUTHENIUM(II) MIXED-METAL COMPLEX BRIDGED BY 2,3,5,6-TETRAKIS(2-PYRIDYL)PYRAZINE

The mixed-metal complex [(tpy)Ru(tpp)IrCl3]2+ and the model monometallic fragments [Ir(tPp)Cl3] and [Ru-(tpy)(tpp)]2+ have been prepared and their spectroscopic, electrochemical, and spectroelectrochemical properties studied (where tpp = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and tpy = 2,2':6',2''-terpyridine). This bimetallic system is the first example of a tpp-bridged mixed-metal complex. The combination of ruthenium, a good light absorber, with iridium, a catalytic metal center, into one molecule is of interest in intramolecular photosensitization schemes. The complex [Ir(tPP)Cl31 has been crystallized and its structure determined by X-my crystallographY. [Ir(tPP)Cl3] was found to crystallize in the monoclinic space group C2/c, with a = 8.745(2) angstrom, b = 21.215(5) angstrom, c = 17.734(4) angstrom, beta = 92.21(2)-degrees, V = 3288(i) angstrom3, Z = 4, d(x) = 1.68, and R = 0.0433. The iridium atom sits in a distorted octahedral environment with the three nitrogens of the tpp ligand and a chlorine atom defining the equatorial plane. The axial positions are occupied by chlorine atoms. All three compounds, [Ir(tpp)Cl3], [Ru(tpy)(tpp)]2+, and [(tpy)Ru-(tpp)IrCl3]2+, emit in fluid solution at room temperature, and the energy and lifetimes of these luminescences were determined. The mixed-metal system displays properties that are unique from either of the monometallic complexes with lower energy absorptions and emission, as well as more numerous electrochemical processes. The lowest energy absorption in the electronic spectrum of the bimetallic complex, [(tpy)Ru(tpp)IrCl3]2+, is an iridium-based transition, while the emissive state appears to be a ruthenium-based metal-to-bridging ligand charge-transfer state.