Ferrocenyl Dithiophosphonate Ag(I) Complexes: Synthesis, Structures, Luminescence, and Electrocatalytic Water Splitting Tuned by Nuclearity and Ligands

The heterometallic Ag (I) /Fe (II) molecular electrocatalysts for hydrogen production were introduced here to recognize the mutual role of metallic nuclearity and ligand engineering. A series of ferrocenyl dithiophosphonate stabilized mononuclear Ag (PPh3) 2S2PFc (OR) where R = Me (1), Et (2), nPr (3), iPr (4), iAmyl (5) ; Fc = Fe (ɳ5-C5H4) (ɳ5-C5H5) and dinuclear Ag (PPh3) S2PFc (OR2 where R = Et (2a), and nPr (3a) complexes were synthesized and characterized by SCXRD, NMR (31P and 1H), ESI-MS, UV-Vis, and FT-IR spectroscopy. The comparative electrocatalytic HER behavior of 1-5 and 2a-3a showed effective current density of 1 mA/cm2 with overpotentials ranging from 772 to 991 mV, demonstrating the influence of extended and branched carbon chains in dithiophosphonates and metallic (mono-/di-) nuclearity, which correlates with documented tetra-nuclear Ag4 (S2PFc (OnPr) 4, 6. DFT study suggests the coordinated (μ1-S) site of ligands is the reactivity center and the adsorption energy of intermediate H*-SM varies with the engineering of ligand and nuclearity. A catalytic mechanism using mononuclear (1) and di-nuclear (2a) was proposed with the assistance of DFT. Each complex, being the first example of Ag (I) dithiophosphonates, exhibits intense photoluminescence with high quantum yields ranging from 33% to 67%. These results link the lower nuclearity structures to their physical and catalytic properties.