Electronic and Photophysical Properties of a Heterometallic Ru(II)–Cu(I) Kuratowski Complex: Insights from Spectroscopy and Density Functional Theory Calculations

Polynuclear metal complexes offer tunable electronic properties that are valuable for photocatalysis and molecular electronics. Herein, the synthesis and characterization of a poly-heteronuclear Kuratowski complex, [Ru^IICu^I₄(Me₂bta)₆(PPh₃)₄] is presented. This complex is designed to investigate the electronic coupling between strongly reducing Cu(I) centers and a Ru(II) ion, mediated by a highly symmetric framework of triazolate ligands. Electrochemical studies reveal coupled redox behavior between Ru(II) and Cu(I), while UV–vis spectroscopy shows an overlapping Ru- and Cu-centered metal-to-ligand charge transfer (MLCT) band, redshifted in comparison to its {Ru^IIZn^II₄} analog. Despite this, fluorescence lifetime measurements indicate that ultrafast nonradiative relaxation limits electron transfer between the metal centers. Density functional theory (DFT) and time-dependent-DFT calculations confirm that ligand-field effects, rather than direct Ru–Cu interactions, drive the MLCT redshift. These observations offer tentative insights into excited-state dynamics and highlight design aspects for controlling electronic communication in polynuclear systems.