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 [HgCl2] 2L(1) [L-1 = N,N'-bis(3-pyridyl)bicyclo(2,2,2,)oct-7-ene-2,3,5,6-tetracarboxylic diamide), 1, [HgBr2(L-1)](n), 2, [HgI2(L-1)], 3, [Hg2X4(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 {[HgX2(L-3)]center dot H2O}(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 HgCl2 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 [HgI2L2] 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 Fe3+ ions with low detection limits and good reusability up to five cycles, revealing that the Hg-X--Fe3+ (X = Cl and Br) interaction may have an important role in determining the quenching effect of 7 and 8.