Coordination Versatility of Thiazolidinone-Based Ligands toward Ag ⁺ : Structural and Photophysical Insights

The reaction of the thiazolidinone-based ligands HAm4DHotaz, Am4Motaz, and Am4Eotaz with AgClO4 in a 1:1 molar ratio yields complexes of varying nuclearities depending on the Nthiazolidinone R-substituent. The unsubstituted HAm4DHotaz (R = H) affords the coordination polymer {[Ag(HAm4DHotaz)](ClO4)}n (1) whereas Am4Motaz (R = Me) and Am4Eotaz (R = Et) lead to the discrete mononuclear complexes [Ag(Am4Motaz)2](ClO4) (2) and [Ag(Am4Eotaz)2](ClO4)] (3), respectively, as the main products. From the corresponding mother liquors, small amounts of the coordination polymers {[Ag(Am4Motaz)(ClO4)]}n (4) and {[Ag2(Am4Eotaz)2(H2O)(ClO4)](ClO4)·H2O}n (5·H2O) were also obtained. In addition, the reaction of AgNO3 with Am4Eotaz in 1:1 or 0.5:1 molar ratio leads to [Ag(Am4Motaz)2](NO3)·H2O (6·H2O), while the mother liquors of the 0.5:1 experiment produced small amounts of the coordination polymer {[Ag2(Am4Motaz)3](NO3)2·H2O}n (7·H2O). X-ray diffraction analyses of all the complexes highlight the remarkable coordination versatility of these ligands, revealing five distinct binding modes, including the unprecedented tridentate μ2-κ2NN′:κ1N″ and μ2-κ1N:κ2N′S bridging motifs, as well as the two rarely reported modes μ2-κ2NN′:κ1S and μ2-κ3NN′S:κ1. In addition, photophysical studies also highlight a pronounced dependence of the emission properties on the Nthiazolidinone R-substituent. Notably, although Ag+ coordination quenches ligand-centered emission in all cases, [Ag(Am4Eotaz)2](ClO4)] (3) stands out as the only complex that remains emissive.