A homoleptic Ag^III complex stabilized by succinimidate ligands

Herein, the first example of a homoleptic Ag^III complex stabilized by a monodentate N-donor ligand is presented. Na₂[S₂O₈] oxidizes the linear Ag^I complex, Na[Ag(succ)₂] (1^Na), to form a square planar argentate(iii) ion, [Ag(succ)₄]^-, which crystallizes with a polymeric chain-structure, M[Ag(succ)₄] (2^M), when treated with alkali metal sulfate M₂SO₄ (M = K, Rb, Cs). A mixed-valent Robin-Day class I system, [(H₂O)Ag][Ag(succ)₄] (2^Ag), forms in the absence of K⁺/Rb⁺/Cs⁺ ion. Diamagnetic 2^Cs displays a succinimide C[double bond, length as m-dash]O stretching frequency at higher energy than does the isoelectronic Pd^II complex, [(H₂O)Na]₂[Pd(succ)₄] (3^Na). Moreover, 2^Cs displays UV-vis absorptions that are more intense and occur at lower energy than those in 3^Na. The electron-deficient nature of 2^Cs is further evident from its ability to oxidize water to O₂. From ¹⁰⁹Ag magic-angle spinning NMR studies, a highly deshielded Ag^III environment in 2^Cs (2080 ppm) relative to the Ag^I starting material 1^Na (492 ppm) is observed.