Bis(alkynyl) mercury(II) complexes of oligothiophenes and bithiazoles

A new class of binuclear mercury(II) bis(alkynyl) complexes containing oligothiophenes and bithiazoles as the central organic linkers are reported. The d¹⁰ mercury(II) complexes [R′HgC≡CRC≡CHgR′] (R = thiophene-2,5-diyl, [2,2′]bithiophene-5,5′-diyl, [2,2′:5′,2″]ter-thiophene-5,5″-diyl, 4,4′-di(tert-butyl)-2,2′-bithiazole-5,5′-diyl, 4,4′-di(p-methoxyphenylene)2,2′-bithiazole-5,5′-diyl; R′ = Me, Ph) were prepared in high yields by the dehydrohalogenation reaction of the appropriate mercury(II) chloride precursors with the diethynyl-functionalized oligothiophenes and bithiazoles under basic medium. Structural elucidation of these compounds was made by FTIR and NMR spectroscopies and FAB mass spectrometry. The solid-state molecular structures of [MeHgC≡CRC≡CHgMe] (R = thiophene-2,5-diyl, [2,2′]bithiophene-5,5′-diyl) established by X-ray crystallography reveal that a loose polymeric structure is formed in each case through weak intermolecular noncovalent Hg⋯Hg interactions. All the complexes have been demonstrated to exhibit rich absorption and luminescence behavior as a function of the number of thiophene rings as well as the electronic nature of the five-membered rings within the bridging ligand. With increasing thiophene content, the absorption and emission features are both red-shifted and the emission quantum yields are increased. In the presence of electron-withdrawing imine nitrogen atoms, the optical spectra for the bithiazole derivatives also show a significant bathochromic shift as compared to their bithienyl counterparts.