Mono- and dinuclear Hg(II) complexes of bis-(N-heterocyclic carbene) bridged with calixarene fragments: Synthesis, structure and sensing behavior

Mono- and dinuclear Hg(II) complexes of bis-(N-heterocyclic carbene) bridged with calixarene fragments, [HgL](PF6)2 (4a, 4b) and [Hg2L2](PF6)4 (5a, 5b), (L = bis{3-(N-1-naphthylmethyl-imidazol-2-ylidene)methyl-5-R-2-methoxyphenyl}methane, a: R = Me, b: R = t-Bu) were both obtained by treatment of corresponding bis-imidazolium salts with mercuric acetate. The structures of complexes 4a and 5a were established by X-ray diffraction. Mononuclear complex 4a displays a small rigid cavity consisting of a mercury cation and a bis-NHC ligand. Dinuclear complex 5a shows a 28-memebered metallamacrocycle formed by two mercury cations and two bis-NHC ligands. Short mercury–oxygen contacts are found between mercury cations and methoxy groups of ligands in 4a and 5a. Cation–π–arene interactions are present between mercury cations and naphthalene rings of ligands. Additionally, the fluorescent chemosensing behaviors of complex 5a with large cavity to diphenylacetylene, (E)-azobenzene and (E)-4,4′-azobispyridine were investigated.