Mercury Complexes with Unusually High Coordination Numbers. Damon Parrish and M. E. Kastner, Department of Chemistry, Bucknell University, Lewisburg PA 17837 and Deborah C. Bebout, Kathleen T. Crahan and Jonathan C. Trinidad, Department of Chemistry, College of William and Mary, Williamsburg, VA 23187-8795.

Mercury(II) ions most frequently form two-coordinate, linear complexes or four-coordinate, tetrahedral complexes. Complexes with higher coordination numbers are rare. A series of mercury(II) complexes with polydentate pyridyl ligands have been characterized by single-crystal X-ray diffraction. These unusual structures include:

a) Bis-tris[(2-pyridyl)methyl]aminemercury(II) perchlorate, in which the two tetradentate ligands form an eight coordinate mercury(II) complex cation. The coordination sphere is that of a distorted cube. (Space Group P2₁/n, Z = 2).

b) Tris[(2-pyridyl)methyl]aminechloromercury(II) tetrachloromercurate(II), in which the tetradentate ligand and a chloride ion form two, crystallographically unique, five-coordinate cations. The tetrachloromercurate anion is essentially tetrahedral.

c) Bis-bis[(2-pyridyl)methyl]aminemercury(II) perchlorate, in which the two tridentate ligands form a distorted trigonal prism. The perchlorate anion packs such that the coordination approaches the seven-coordinate edge-capped trigonal prism.

d) Tris[(2-methylpyridyl)methyl]aminedichloromercury(II) in which only three of the four pyridyl groups coordinate to the mercury(II) ion, and together with two chloride ions form a five-coordinate complex.