Luminescent Mixed Ligand Rhodium (III) Complexes
Elise G. Megehee, Department of Chemistry, St. John’s College of Liberal Arts and Sciences
Stephanie Ovalles, and Daniel Amarante, St. John’s College of Liberal Arts and Sciences Students
Abstract
Rhodium polypyridyl complexes are of interest because they exhibit visible to near infrared emission upon excitation with visible or ultraviolet light and as such are candidates for photochemical or electrochemical reaction catalysts, as models of photosynthetic reaction center, as energy and electron transfer agents, as emissive DNA labels, and photochemical DNA cleavage agents. While some of the rhodium complexes are known, their published syntheses are difficult and require extensive purification. We have developed two new, general synthetic methods that allow easy preparation of pure complexes in high yields. We have demonstrated that [Rh(NN)2(OTf)2]OTf and [Rh(tpy)(OTf)3] {where NN = 2,2'-bipyridine (bpy) and 4,4'-dimethyl-2,2'-bipyridine(dmbpy), OTf = trifluoromethansulfonate, and tpy = 2:2',6':2"-terpyridine} are versatile precursors to a wide variety of mixed ligand complexes in high yields. Over the past year we have characterized thirteen complexes of the form [Rh(bpy)2(NN)][PF6]3, {where NN = assorted substituted bipyridine and phenanthroline ligands} five of the form [Rh(bpy)2(SS)][PF6]n {where SS = 1,1’-dithiolates and dialkyldithiocarbamates},and six of complexes of the form [Rh(tpy)(NNN)] {where NNN = various substituted terpyridines}. In addition, we have synthesized and purified ten new compounds of the form [Rh(dmbpy)2(NN)][PF6]3. We have characterized each of these compounds by 1H NMR, 13C NMR, and elemental analysis and are currently studying their electronic properties.