The effect of metal centers on the electronic transitions of HOMO- and heteronuclear Ru(Ⅱ) and Os(Ⅱ) complexes with 2,3,5,6-tetrakis(2-pyridyl) pyrazine: A combined theoretical and experimental study

This study investigates the impact of the type and arrangement of metal centers on the electronic transitions of multimetallic complexes through a combined experimental and computational approach. At first, homo- and hetero-metallic [Mn(TPPZ)_n+1]²ⁿ⁺ complexes (M = Ru(Ⅱ) and Os(Ⅱ), TPPZ = 2,3,5,6-tetrakis(2-pyridyl)pyrazine, and n = 1 and 2) were synthesized and fully characterized. Then, density functional theory (DFT) and time-dependent DFT calculations were performed to explore the geometries, electronic structures, excited states, and spectroscopic properties of mono-, bi-, and trimetallic complexes. The comparison between experimental and computational spectra of mono- and bimetallic complexes showed excellent agreement, particularly in peak intensities and absorption energies. The visible region bands were attributed to metal-to-ligand charge-transfer (MLCT) transitions. This study offers insights into how the quantity, type, and arrangement of metal centers influence the frontier orbital energy levels and electronic spectra in homo- and heteronuclear complexes.