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Hg(II) halide complexes [HgCl₂] 2<b>L¹</b> [<b>L¹</b> = <i>N,N’</i>-bis(3-pyridyl)bicyclo(2,2,2,)oct-7-ene-2,3,5,6-tetracarboxylic diamide), <b>1</b>, [HgBr₂(<b>L¹</b>)]_n, <b>2</b>, [HgI₂(<b>L¹</b>)], <b>3</b>, [Hg₂X₄(<b>L²</b>)₂] [X = Cl, <b>4</b>, Br, <b>5</b>, and I, <b>6</b>; <b>L²</b> = <i>N,N’</i>-bis(4-pyridylmethyl)bicyclo(2,2,2,)oct-7-ene-2,3,5,6-tetracarboxylic diamide] and {[HgX₂(<b>L³</b>)]⋅H₂O}_n [X = Cl, <b>7</b>, Br, <b>8</b> and I, <b>9</b>; <b>L³</b> = 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 <b>1</b> are interlinked by the <b>L¹</b> ligands through Hg---N and Hg---O interactions, resulting in 1D supramolecular chains. Complex <b>2</b> shows 1D zigzag chains interlinked through the Br---Br interactions to form 1D looped supramolecular chains, while the mononuclear [HgI₂<b>L²</b>] molecules of <b>3</b> are interlinked through Hg---O and I---I interactions, forming 2D supramolecular layers. Complexes <b>4</b>–<b>6</b> are isomorphous dinuclear metallocycles, and <b>7</b>–<b>9</b> form isomorphous 1D zigzag chains. The roles of the ligand type and the halide anion in determining the structural diversity of <b>1</b>–<b>9</b> is discussed and the luminescent properties of <b>7</b>–<b>9</b> evaluated. Complexes <b>7</b>–<b>9</b> manifest stability in aqueous environments. Moreover, complexes <b>7</b> and <b>8</b> 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 <b>7</b> and <b>8</b>.