Structure and solvation of mercury(II) iodide, bromide, and chloride in pyridine solution; refinement of the crystal structure of di-iodobis(pyridine)mercury(II), [HgI2(py)2]

Abstract

The structure of the neutral mercury(II) halides in pyridine (py) solution has been studied by X-ray diffraction methods and vibrational spectroscopy. Pseudo-tetrahedral HgX₂(py)₂ species (X = I, Br, or Cl) are formed in solution with approximately C_2V symmetry. Relevant bond lengths are Hg–I 2.665(2), Hg–Br 2.497(2), and Hg–Cl 2.375(10)Å. The IHgI angle was found to be 143(2)° and BrHgBr 151(3)°, including estimated corrections for shrinkage effects. The two pyridine molecules have Hg–N distances of 2.43(2), 2.45(2), and 2.47(2)Å in the iodide, bromide, and chloride species, respectively. The crystal structure of [HgI₂(py)₂] has been refined to an R value of 0.031 for 744 observations. It consists of monomeric pseudo-tetrahedral [HgI₂(py)₂] species with Hg–I bond lengths of 2.664(1) and 2.668(1)Å and an IHgI angle of 142.7(1)°. The two pyridine ligands are related by a mirror plane which contains the HgI₂ entity. The Hg–N distance is 2.424(9)Å. Raman and i.r. spectra of the pyridine solutions and of the HgX₂(py)₂ solids are consistent with structural models based on the diffraction data.