Spectroscopic and DFT assessment of bridging ligand effect on the structural and electronic properties of dinuclear iridium- and rhodium-based complexes

A series of chloro-, amido-, and methoxo-bridged dinuclear complexes of iridium(I) and rhodium(I) was synthesized, and their coordination properties were assessed. Density functional theory (DFT) calculations, and infrared and Raman spectroscopies were employed to examine the metal-olefin and metal-bridging group interactions. The outcome of these studies revealed that the nature of bridging ligands does influence the electronic properties of these metal complexes. They also revealed that the amido-bridged complexes exercised the least metal-olefin interaction, while the methoxo-bridged complexes exhibited the most. The p-character in the hybrid orbitals of olefinic carbons was calculated to increase upon coordination, and the extent of increase can be linked to the group electronegativity of bridging ligands. Vibrational spectroscopy, supported with theoretical DFT approach, was useful and found consistent in assessing the pi and combined (π + σ) metal-olefin interactions in these dinuclear complexes.