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‘ ‘]terthiophene-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.