Structural Studies of Mercury(II) Halide Pyridine Complexes [HgX2(py)2], X = CI, 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 group P2,/n, with a = 17.726(7), b = 8.572(3), c = 3.910(2) A, beta = 92.00(4), and Z = 2. The structure is a chloride-bridged polymeric lattice of HgCI4 square-planar entities [Hg-CI 2.754(2) and 2.765(2) A] with pyridine ligands filling the trans-octahedral sites about the mercury atom [Hg-N 2.266(6) A]. 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) A, and Z = 4; the basic structural unit is the [HgBr2(py)2] molecule [Hg-Br 2.478(3) and 2.483(3) A, Br-Hg-Br 141.2(1); Hg-N 2.38(2) and 2.39(2) A, N-Hg-N 90.7(7), N-Hg-Br 102.5(5)-104.3(4)]. For [Hgl2(py)2], (3), the cell is also orthorhombic, space group Pnma, with a = 14.545(7), b = 11.396(6), c = 8.510(5) A, and Z = 4, the stuctural unit also being the [HgI2(py)2] molecule with similar geometry to that of (2); in particular, Hg-l 2.70(1) and 2.65(1) A, I-Hg-l 14l.7(4)