Synthesis and characterization of pentagonal-bipyramidal mercury(II) complexes with 2,6-diacetylpyridine bis(2′-pyridylhydrazone). X-Ray structure of [2,6-diacetylpyridine bis(2′-pyridylhydrazone)]mercury(II) tetrachloromercurate(II)

Abstract

The ligand 2,6-diacetylpyridine bis(2′-pyridylhydrazone)(H₂dapp) reacts in ethanol with HgCl₂ or Hg(ClO₄)₂·3H₂O to give the charged species [Hg(H₂dapp)][HgCl₄](1) or [Hg(H₂dapp)(H₂O)₂][ClO₄]₂(2) respectively. Starting from HgCl₂ in the presence of perchlorate ions the mixed chloro–aqua complex [Hg(H₂dapp)Cl(H₂O)][ClO₄](3) is obtained. Complexes (1), (2), and (3) can be deprotonated to the neutral species [Hg(dapp)](4) under basic conditions. The complexes have been characterized by a number of physicochemical measurements including the X-ray analysis of (1). Crystals of (1) are monoclinic, space group P2₁/n, with unit-cell dimensions a= 12.271(5), b= 15.948(6), c= 12.703(6)Å, β= 109.06(3)°, and Z= 4. The structure has been solved from three dimensional counter data by Patterson and Fourier methods and refined by full-matrix least squares to R 0.040 for 2 654 observed reflections. The packing can be described either as consisting of infinite chains of alternating pentagonal planar [Hg(H₂dapp)]²⁺ cations and tetrahedral [HgCl₄]^2– anions running along b or as infinite chains of µ-Cl-connected pentagonal bipyramidal (pbp) and tetrahedral Hg complexes. In the pbp co-ordination around the metal atom the five basal positions are occupied by five N atoms of the polydentate ligand and the two apical positions by two Cl atoms belonging to the tetrahedral anions. The five-co-ordinate ligand is not planar, and its general form is that of a flattened helix.