Structural And Photochemical Properties Of Zn(Ii) Phenanthroline-Derived Complexes: From Mononuclear To Bimetallic And Circular-Trimetallic Helicates

In the design of self-assembled compounds, small variations in the linkers connecting the coordinating moieties can produce large differences in the obtained structures. Here, we report three novel zinc(II) complexes with phenanthroline-derived ligands as building blocks (L-1-L-3): A mononuclear complex, a bimetallic helicate, and a trimetallic circular helicate. The evennumber spacer in L-2 promotes the formation of a bimetallic helicate stabilized by pi-pi interactions of adjacent phenanthrolines. The addition of an extra methylene in L-3 increases the distance between where the phenanthrolines can stack, and CH-pi noncovalent interactions give stability to the circular helicate. When irradiated at 308 nm in acetonitrile, long-lived excited states are formed with all three complexes, which are able to participate in oxidation of 2-propanol and in reduction of methylviologen, MV2+. While the overall behavior of the three complexes is similar, the bimetallic helicate is able to form a ground-state adduct with MV2+, while the trimer reaches the excited state to form an exciplex with MV2+.