The Impact of Schiff Base Backbone Rigidity on Electronic Structure of Axially coordinated Co(III) Complexes: A DFT Study of Salen vs. Salophen complexes

Cobalt coordination complexes of tetradentate Schiff base ligands represent a versatile class of compounds with applications ranging from catalysis to biomimetics and medicinal chemistry. Cobalt(III) complexes of Salen (H۲Salen = N,N’-bis(salicylidene)-۱,۲-ethylenediamine) and Salophen (H۲Salophen = N,N’-bis(salicylidene)-۱,۲-phenylenediamine) with labile axial amines mimic certain aspects of vitamin B۱۲. Moreover, cobalt(III) complexes with Salen and Salophen ligands have extensively studied in search of synthetic oxygen carriers. It should be noted that the equatorial Schiff base ligand could critically affect the electronic structure of the Co(III) complex. In this research work, the molecular and electronic structures of free gaseous [CoIII(Salen)(py)۲]+ and [CoIII(Salophen)(py)۲]+ (py = pyridine) are studied by density functional theory (DFT) method. The calculated HOMO and LUMO are the molecular π orbital of the Salen ligand and the antibonding σ*(Ligand―Co(dz۲)) molecular orbital, respectively. In comparison, the HOMO and LUMO for [CoIII(Salophen)(py)۲]+ are Salophen π and π* molecular orbitals. In addition, the electronic absorption spectra of the complexes are investigated by time-dependent density functional theory (TDDFT) method and are discussed based on the calculated electronic structures.

کلیدواژه ها:

Co(III) complex ، Schiff base ، Electronic Structure ، DFT