Structural Diversity of Mercury(II) Halide Complexes Containing Bis-pyridyl-bis-amide with Bulky and Angular Backbones: Ligand Effect and Metal Sensing.

Hg(II) halide complexes [HgCl 2 ] 2 L 1 [ L 1 = N,N' -bis(3-pyridyl)bicyclo(2,2,2,)oct-7-ene-2,3,5,6-tetracarboxylic diamide), 1 , [HgBr 2 ( L 1 )] n , 2 , [HgI 2 ( L 1 )], 3 , [Hg 2 X 4 ( L 2 ) 2 ] [X = Cl, 4 , Br, 5 , and I, 6 ; L 2 = N,N' -bis(4-pyridylmethyl)bicyclo(2,2,2,)oct-7-ene-2,3,5,6-tetracarboxylic diamide] and {[HgX 2 ( L 3 )]⋅H 2 O} n [X = Cl, 7 , Br, 8 and I, 9 ; L 3 = 4,4'-oxybis(N-(pyridine-3-yl)benzamide)] are reported and structurally characterized using single-crystal X-ray diffraction analyses. The linear HgCl 2 units of complex 1 are interlinked by the L 1 ligands through Hg---N and Hg---O interactions, resulting in 1D supramolecular chains. Complex 2 shows 1D zigzag chains interlinked through the Br---Br interactions to form 1D looped supramolecular chains, while the mononuclear [HgI 2 L 2 ] molecules of 3 are interlinked through Hg---O and I---I interactions, forming 2D supramolecular layers. Complexes 4 - 6 are isomorphous dinuclear metallocycles, and 7 - 9 form isomorphous 1D zigzag chains. The roles of the ligand type and the halide anion in determining the structural diversity of 1 - 9 is discussed and the luminescent properties of 7 - 9 evaluated. Complexes 7 - 9 manifest stability in aqueous environments. Moreover, complexes 7 and 8 show good sensing towards Fe 3+ ions with low detection limits and good reusability up to five cycles, revealing that the Hg-X---Fe 3+ (X = Cl and Br) interaction may have an important role in determining the quenching effect of 7 and 8 .