Ferrocenyl Dithiophosphonate Stabilized Heterobimetallic (Co ^II /Fe ^II , Ni ^II /Fe ^II , and Cu ^I /Fe ^II ) Complexes: Synthesis, Characterization, Luminescence, and Electrochemical Beha

Ferrocenyl dithiophosphonate metal-based molecular compounds are infrequent with untapped potential in electrocatalysis and luminescence. A stoichiometric reaction of late 3d metal(II) (Co, Ni, Cu) salts with ferrocenyl dithiophosphonate NH₄[S₂P(<i>O</i>^<i>n</i><i>Pr</i>)Fc] in a 1:2 ratio produces mononuclear [M{S₂P(<i>O</i>^<i>n</i><i>Pr</i>)Fc}₂] {M = Co^II (<b>1</b>), Ni^II (2)} complexes and a tetranuclear [Cu₄{S₂P(<i>O</i>^<i>n</i><i>Pr</i>)Fc}₄] (<b>3</b>) {Fc = Fe(η⁵-C₅H₄)(η⁵-C₅H₅)} cluster. The distinct core of <b>3</b> compared to <b>1</b> and <b>2</b> indicates that NH₄[S₂P(<i>O</i>^<i>n</i><i>Pr</i>)Fc] first serves as a sacrificial reductant and subsequently stabilizes the Cu(I) cluster. Heterometallic species (<b>1</b>-<b>3</b>) were characterized by NMR (¹H, ³¹P), FT-IR, TGA, UV-visible spectroscopy, ESI-MS, XPS, and single-crystal X-ray diffraction. Ligand [S₂P(<i>O</i>^<i>n</i><i>Pr</i>)Fc]^- stabilized the redox-derived tetrahedral Cu^I core of <b>3</b> and the M(II)-centered square (MS₄) frame in <b>1</b> and <b>2</b> through (η³; μ¹, μ²) and (η; μ¹, μ¹) bonding patterns, respectively. The irreversible single wave voltammogram indicated nonuniform electrochemical behavior of <b>1</b>-<b>3</b>. TD-DFT indicates MLCT and weak LLCT in isostructural <b>1</b>-<b>2</b> and <b>3m</b> [Cu^II{S₂P(<i>O</i>^<i>n</i><i>Pr</i>)Fc}₂], while <b>3</b> exhibits multielectron transitions with two types of MLCT. Third-order decay confirms singlet fluorescence, and multiple electronic transitions in <b>3</b> enhance its photoluminescence (27.5% QY) relative to <b>1</b>-<b>2</b>, correlating the isostructural and different nuclearity features of late 3d metals with their physical and electrochemical properties.