title: Weakly coordinating anions: crystallographic and NQR studies of halogen-metal bonding in silver, thallium, sodium, and potassium halomethanesulfonates.
abstract: 35Cl, (79,81)Br, and (127)I NQR (nuclear quadrupole resonance) spectroscopy in conjunction with X-ray crystallography is potentially one of the best ways of characterizing secondary bonding of metal cations such as Ag(+) to halogen donor atoms on the surfaces of very weakly coordinating anions. We have determined the X-ray crystal structure of Ag(O(3)SCH(2)Cl) (a = 13.241(3) A; b = 7.544(2) A; c = 4.925(2) A; orthorhombic; space group Pnma; Z = 4) and compared it with the known structure of Ag(O(3)SCH(2)Br) (Charbonnier, F.; Faure, R.; Loiseleur, H. Acta Crystallogr., Sect. B 1978, 34, 3598-3601). The halogen atom in each is apical (three-coordinate), being weakly coordinated to two silver ions. (127)I NQR studies on Ag(O(3)SCH(2)I) show the expected NQR consequences of three-coordination of iodine: substantially reduced NQR frequencies nu(1) and nu(2) and a fairly small NQR asymmetry parameter eta. The reduction of the halogen NQR frequency of the coordinating halogen atom in Ag(O(3)SCH(2)X) becomes more substantial in the series X = Cl < Br < I, indicating that the coordination to Ag(+) strengthens in this series, as expected from hard-soft acid-base principles. The numbers of electrons donated by the organic iodine atom to Ag(+) have been estimated; these indicate that the bonding to the cation is weak but not insignificant. We have not found any evidence for the bonding of these organohalogen atoms to another soft-acid metal ion, thallium. A scheme for recycling of thallium halide wastes is included.
authors.affiliation: National Center for Applications of NQR Spectroscopy in Inorganic Chemistry, Department of Chemistry, Middle Tennessee State University, Murfreesboro 37132, USA. wulfsberg@mtsu.edu
authors.forename: Gary
authors.initials: G
authors.lastname: Wulfsberg
authors.forename: Katherine D
authors.initials: KD
authors.lastname: Parks
authors.forename: Richard
authors.initials: R
authors.lastname: Rutherford
authors.forename: Debra Jones
authors.initials: DJ
authors.lastname: Jackson
authors.forename: Frank E
authors.initials: FE
authors.lastname: Jones
authors.forename: Dana
authors.initials: D
authors.lastname: Derrick
authors.forename: William
authors.initials: W
authors.lastname: Ilsley
authors.forename: Steven H
authors.initials: SH
authors.lastname: Strauss
authors.forename: Susie M
authors.initials: SM
authors.lastname: Miller
authors.forename: Oren P
authors.initials: OP
authors.lastname: Anderson
authors.forename: T A
authors.initials: TA
authors.lastname: Babushkina
authors.forename: S I
authors.initials: SI
authors.lastname: Gushchin
authors.forename: E A
authors.initials: EA
authors.lastname: Kravchenko
authors.forename: V G
authors.initials: VG
authors.lastname: Morgunov