Deviations from ideal trigonal-bipyramidal geometry in the [HgCl5]3– anion: crystal structures of two complex salts

Abstract

A rhombohedral modification of [Cr(NH₃)₆][HgCl₅] has been prepared. The space group is Rc, with a= 7.521(1), c= 46.111(8)Å(hexagonal axes), and Z= 6. On the other hand, [Co(NH₃)₆][HgCl₅] is monoclinic, space group P2₁/m, with a= 8.444(1), b= 7.705(1), c= 11.357(2)Å, β= 107.70(1)°, and Z= 2. The crystal structures have been determined from 411 and 1 591 unique diffractometer-measured intensities respectively, and refined to final R indices of 0.041 and 0.049. Both contain mercury atoms in distorted trigonal-bipyramidal co-ordination, with short equatorial Hg–Cl bonds (2.417–2.431 Å) and very long axial Hg–Cl bonds (2.871–3.038 Å).