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.