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, l–Hg–I 141.7(4)°.