Structural studies of mercury(II) halide pyridine complexes [HgX₂(py)₂], X = Cl, Br, or I

The structures of the three title compounds have been determined by single-crystal X-ray diffraction methods at 295(1) K. For [HgCl₂(py)₂],(1), a redetermination, the cell is Monoclinic, space groupP2₁/n, with a = 17.726(7), b = 8.572(3), c = 3.910(2) Å, β = 92.00(4)°, and Z = 2. The structure is a chloride-bridged polymeric lattice of HgCl₄ square-planar entities [Hg-Cl 2.754(2) and 2.765(2) Å] with pyridine ligands filling the trans-octahedral sites about the mercury atom [Hg-N 2.266(6) Å]. For [HgBr₂(py)₂], (2), the cell is Orthorhombic, space group Pca2₁, with a = 18.023(5), b = 8.754(3), c = 8.592(3) Å, and Z = 4; the basic structural unit is the [HgBr₂(py)₂] molecule [Hg-Br 2.478(3) and 2.483(3) Å, Br-Hg-Br 141.2(1)°; Hg-N 2.38(2) and 2.39(2) Å, N-Hg-N 90.7(7)°, N-Hg-Br 102.5(5)-104.3(4)°]. For [HgI₂(py)₂], (3), the cell is also Orthorhombic, space group Pnma, with a = 14.545(7), b = 11.396(6), c = 8.510(5) Å, and Z = 4, the stuctural unit also being the [HgI₂(py)₂] molecule with similar geometry to that of (2); in particular, Hg-I 2.70(1) and 2.65(1) Å, I-Hg-I 141.7(4)°.