Molecular Engineering to Tune Functionality: The Case of Cl-Substituted [Fe(terpy)2]2+

In this paper, we first theoretically explored how substitution with a Cl atom at different positions of the terpyridine ligand affects the electronic structure of the [Fe(terpy)2]2+ complex. We found that besides the substitution at position 4′, the next most promising candidate to cause substantial electronic effects is that where the side pyridine ring is substituted at position 5 (β).

Therefore, next, we examined in detail the Fe(II) complexes of the 5-chloro and 5,5″-dichloro derivatives of terpy, theoretically and experimentally, to reveal how these substitutions modify the ground state properties and the lifetime of the excited quintet state in such complexes. In addition, we extend the investigation to the complexes of the analogously substituted derivatives of 4′-SMe-terpy. The substitution at position(s) 5 (and 5″) with Cl lowers the energy of the quintet state and increases its lifetime; the results on the 4′-SMe-substituted complexes show similar changes with these two substitutions, verifying that these effects are more or less additive.