Three coordination compounds based on thiadiazole-carboxylate ligand: synthesis, crystal structures and photoluminescence properties

Three metal-organic coordination compounds, [Bi(atma)2(bipy)(NO3)(H2O)⋅2H2O]n (1), [Bi(atma)2(bipy)(fa)⋅2H2O]n (2) and Cu2(atma)2(pypd)2 (3) (Hatma = 2-(5-amino-1,2,4-thiadiazol-3-yl)-2-methoxyiminoacetic acid, bipy= 2,2′-bipyridine, Hfa = formic acid and Hpypd = 2-(1H-pyrazol-3-yl) pyridine), were synthesized under hydro/solvothermal conditions and characterized. Single-crystal structural determination reveals that compounds 1 and 2 feature chain architectures built up from mononuclear Bi motifs linked via NO3− and fa− anions, respectively, while compound 3 presents a pypd-bridged Cu2 dinuclear structure, in which atma− ligands act in a chelating fashion to coordinate with Cu2+ centers. The chain and dinuclear structures are further extended into layered architectures through hydrogen bonding interactions. Room-temperature solid-state fluorescence tests reveal that compounds 1–3 exhibit similar emission behaviors to the free Hatma ligand, demonstrating that their luminescence is primarily derived from intraligand charge transfer. The fluorescence chromaticity diagram confirms that their emission signals are located in the blue region.