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.

Automated summary

This study reports the synthesis and structural characterization of various Hg(II) halide complexes using single-crystal X-ray diffraction analyses. The ligand type and halide anion were found to play important roles in determining the structural diversity of the complexes. The luminescent properties and stability of selected complexes were also evaluated.