Weakly Coordinating Anions:  Crystallographic and NQR Studies of Halogen−Metal Bonding in Silver, Thallium, Sodium, and Potassium Halomethanesulfonates

• Published in: Inorganic chemistry 2002-04, Vol.41 (8), p.2032-2040
• Main Authors: Wulfsberg, Gary, Parks, Katherine D, Rutherford, Richard, Jackson, Debra Jones, Jones, Frank E, Derrick, Dana, Ilsley, William, Strauss, Steven H, Miller, Susie M, Anderson, Oren P, Babushkina, T. A, Gushchin, S. I, Kravchenko, E. A, Morgunov, V. G
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic010715i

35Cl, 79,81Br, and 127I 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(O3SCH2Cl) (a = 13.241(3) Å; b = 7.544(2) Å; c = 4.925(2) Å; orthorhombic; space group Pnma; Z = 4) and compared it with the known structure of Ag(O3SCH2Br) (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. 127I NQR studies on Ag(O3SCH2I) show the expected NQR consequences of three-coordination of iodine:  substantially reduced NQR frequencies ν1 and ν2 and a fairly small NQR asymmetry parameter η. The reduction of the halogen NQR frequency of the coordinating halogen atom in Ag(O3SCH2X) 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.