Urea-bridged diferrocene: structural, electrochemical, and spectroelectrochemical studies

Urea-bridged diferrocene derivatives N,N?-diferrocenylurea(1) and N,N?-dimethyl-N,N?-diferrocenylurea(2) were prepared and characterized. Single-crystal X-ray analysis shows that Compound 1 has a trans-trans linear conformation whereas Compound 2 has a trans-cis conformation. Both compounds display two consecutive redox couples with, respectively, E1/2 of +0.29 and +0.42 V vs. Ag/Ag Cl for 1 and +0.31 and +0.50 V for 2. Spectroelectrochemical studies show the presence of distinct intervalence charge transfer(IVCT) transitions for the one-electron-oxidized mixed-valent Compound 1+, with an estimated electronic coupling parameter of 190 cm?1. By contrast, the one-electron-oxidized Compound 2+ shows much weaker IVCT transitions.