Crystal structure and vibrational spectroscopic studies of the complexes [HgX(NO3)(C5H5N)](X = Cl, Br or I)
Abstract
The structure of the complexes [HgX(NO3)(py)](py = pyridine, X = Cl or Br) have been determined by single-crystal X-ray diffraction analysis. Both complexes crystallize in the orthorhombic space group Pnam with one-half of the formula unit comprising the asymmetric unit of the structure. The mercury atom environments are dominated by close associations with the halide and pyridine nitrogen atoms in a quasi-linear array with nitrate oxygen contacts about the mercury in a ‘plane’ normal to N–Hg–X. The structural parameters for the N–Hg–X units are Hg–X 2.261(6) and 2.379(3), Hg–N 2.04(2) and 2.08(2)Å and N–Hg–X 177.0(5) and 176.1(4)° for X = Cl or Br respectively. The nitrate moieties link the mercury atoms in a two-dimensional polymeric array. The mean nearest-neighbour Hg ⋯ O distances in the two compounds are 2.99 and 3.02 Å respectively. The infrared and Raman spectra yield ν(HgX) 359 and 264 cm–1(IR, Raman), ν(HgN) 160 and 158 cm–1(Raman) for X = Cl or Br respectively. For the corresponding X = I compound the vibrational spectra suggest the presence of [Hg(py)2]2+ and molecular HgI2 units in the solid, the latter giving rise to bands due to the symmetric and antisymmetric ν(HgI) modes at 154 (Raman) and 214 cm–1(IR) respectively. The vibrational spectra of the 4-methylpyridine (4Me-py) complexes [HgX(NO3)(4Me-py)](X = Cl, Br or I) suggest that these all contain [HgX(4Me-py)]+ units with ν(HgX) 343, 251 and 218 (IR, Raman), ν(HgN) 201, 187 and 162 cm–1(Raman) for X = Cl, Br or I respectively.