title: Coordination chemistry of mercury(II) in liquid and aqueous ammonia solution and the crystal structure of tetraamminemercury(II) perchlorate.
abstract: The ammonia solvated mercury(II) ion has been structurally characterized in solution by means of EXAFS, (199)Hg NMR, and Raman spectroscopy and in solid solvates by combining results from X-ray single crystal and powder diffraction, thermogravimetry, differential scanning calorimetry, EXAFS, and Raman spectroscopy. Crystalline tetraamminemercury(II) perchlorate, [Hg(NH3)4](ClO4)2, precipitates from both liquid ammonia and aqueous ammonia solution, containing tetraamminemercury(II) complexes. The orthorhombic space group ( Pnma) imposes C s symmetry on the tetraamminemercury(II) complexes, which is lost at a phase transition at about 220 K. The Hg-N bond distances are 2.175(14), 2.255(16), and 2 x 2.277(9) A, with a wide N-Hg-N angle between the two shortest Hg-N bonds, 122.1(7) degrees , at ambient temperature. A similar distorted tetrahedral coordination geometry is maintained in liquid ammonia and aqueous ammonia solutions with the mean Hg-N bond distances 2.225(12) and 2.226(6) A, respectively. When heated to 400 K the solid tetraamminemercury(II) perchlorate decomposes to diamminemercury(II) perchlorate, [Hg(NH3)2](ClO4)2, with the mean Hg-N bond distance 2.055(6) A in a linear N-Hg-N unit. The mercury atoms in the latter compound form a tetrahedral network, connected by perchlorate oxygen atoms, with the closest Hg...Hg distance being 3.420(3) A. The preferential solvation and coordination changes of the mercury(II) ion in aqueous ammonia, by varying the total NH 3:Hg(II) mole ratio from 0 to 130, were followed by (199)Hg NMR. Solid [Hg(NH 3)4](ClO4)2 precipitates while [Hg(H2O)6](2+) ions remain in solution at mole ratios below 3-4, while at high mole ratios, [Hg(NH3)4](2+) complexes dominate in solution. The principal bands in the vibrational spectrum of the [Hg(NH3)4](2+) complex have been assigned.
authors.affiliation: Department of Chemistry, Swedish University of Agricultural Sciences, PO Box 7015, SE-750 07 Uppsala, Sweden.
authors.forename: Kersti B
authors.initials: KB
authors.lastname: Nilsson
authors.forename: Mikhail
authors.initials: M
authors.lastname: Maliarik
authors.forename: Ingmar
authors.initials: I
authors.lastname: Persson
authors.forename: Andreas
authors.initials: A
authors.lastname: Fischer
authors.forename: Ann-Sofi
authors.initials: AS
authors.lastname: Ullström
authors.forename: Lars
authors.initials: L
authors.lastname: Eriksson
authors.forename: Magnus
authors.initials: M
authors.lastname: Sandström
mesh_terms: D000641:Ammonia / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D018360:Crystallography, X-Ray / Q000379:methods; D017669:Mercury Compounds / Q000737:chemistry*; D008958:Models, Molecular; D010472:Perchlorates / Q000737:chemistry*; D012996:Solutions; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D017669:Mercury Compounds; D010472:Perchlorates; D012996:Solutions; D000641:Ammonia; C494474:perchlorate