Au complexes with 5-S-alkylated-2-amino-1,3,4-thiadiazoles: from Au(III)-based ionic liquids to rare dinuclear Au(II) coordination compounds

Abstract The reaction of 5-amino-1,3,4-thiadiazole-2-thiols, S-modified with highly flexible trimethylsilylpropyl (H₂L 1 ) and n -hexyl (H₂L 2 ) groups, with HAuCl₄ afforded ionic salts of the type (H 3 L n ) (+) [AuCl 4 ] (-) (n = 1, 2). The structures of the resulting complexes were elucidated by single-crystal X-ray crystallography (SC-XRD) and/or spectroscopic analyses, whose results support their ionic nature. Based on their appearance and DSC data, (H 3 L 1 )[AuCl 4 ] melts at 55 °C, whereas (H 3 L 2 )[AuCl 4 ] is liquid at room temperature. The electroactive behavior of both cations and anions in such environments, as demonstrated by cyclic voltammetry for (H 3 L 2 )[AuCl 4 ], reflects their mobility and ability to participate in redox processes and is typical of ionic liquid electrolytes. Thus, these compounds show ionic liquid behavior at low temperatures. In the presence of water, rare dinuclear Au(II) complexes, [(HL n ) 2 Au 2 Cl 2 ], are formed, with a relatively short Au···Au distance, as demonstrated by crystallographic and additional analyses.