Emerging Trends in the Coordination Chemistry of Thiazolidinone-Containing Polydentate Ligands: Unconventional Binding Modes in Silver Complexes

This work presents an efficient and straightforward method for obtaining two previously described thiazolidinone-based ligands, HAm4DHotaz (N'-(4-oxothiazolidin-2-ylidene)picolino-hydrazonamide) and Am4Eotaz (N'-(3-ethyl-4-oxothiazol-idin-2-ylidene)picolinohydrazonamide), with high yield and purity. Moreover, the reactivity of these ligands toward different Ag+ salts has been explored, resulting in the isolation of four novel coordination complexes: two mononuclear species, [Ag(HAm4DHotaz)2](NO3)·H2O (1·H2O) and [Ag(Am4Eotaz)2](NO3) (2), and two tetranuclear compounds, [Ag4(Am4DHotaz)4]·8H2O (3·8H2O) and [Ag4(Am4Eotaz)4(NO3)2(H2O)](NO3)2·1.18H2O (4·1.18H2O). The crystal structures of 1·H2O, 2, 4·1.18H2O, and 3·3DMF, the latter obtained by recrystallization of [Ag4(Am4DHotaz)4]·8H2O in dimethylformamide, have been determined. Notably, in 4·1.18H2O, the thiazolidinone moiety shows the unprecedented bridging mode μ2-κ1S:κ1S. In addition, 3·3DMF represents a rare example of a thiazolidinone-containing complex featuring a μ2-κ1N:κ1S bridge. Moreover, across these complexes, the Am4Rotaz (R = DH or E) ligands display five hitherto unknown coordination modes. These ligands, and the auxiliary donors (present in 4·1.18H2O), provide different Ag+ coordination environments: AgN4 cores with a seesaw geometry in the mononuclear complexes, and AgN2, AgN2S, AgN4, AgN2OS, AgN2S3 or AgN2O2S3 cores with varied geometries in the tetranuclear ones. Furthermore, structures of the polynuclear species reveal significant argentophilic Ag···Ag interactions, which play a key role in directing the formation of the multinuclear frameworks.