title: Zn2+ has a primary hydration sphere of five: IR action spectroscopy and theoretical studies of hydrated Zn2+ complexes in the gas phase.
abstract: Complexes of Zn(2+)(H(2)O)(n), where n = 6-12, are examined using infrared photodissociation (IRPD) spectroscopy, blackbody infrared radiative dissociation (BIRD), and theory. Geometry optimizations and frequency calculations are performed at the B3LYP/6-311+G(d,p) level along with single point energy calculations for relative energetics at the B3LYP, B3P86, and MP2(full) levels with a 6-311+G(2d,2p) basis set. The IRPD spectrum of Zn(2+)(H(2)O)(8) is most consistent with the calculated spectrum of the five-coordinate MP2(full) ground-state (GS) species. Results from larger complexes also point toward a coordination number of five, although contributions from six-coordinate species cannot be ruled out. For n = 6 and 7, comparisons of the individual IRPD spectra with calculated spectra are less conclusive. However, in combination with the BIRD and laser photodissociation kinetics as well as a comparison to hydrated Cu(2+) and Ca(2+), the presence of five-coordinate species with some contribution from six-coordinate species seems likely. Additionally, the BIRD rate constants show that Zn(2+)(H(2)O)(6) and Zn(2+)(H(2)O)(7) complexes are less stable than Zn(2+)(H(2)O)(8). This trend is consistent with previous work that demonstrates the enthalpic favorability of the charge separation process forming singly charged hydrated metal hydroxide and protonated water complexes versus loss of a water molecule for complexes of n ≤ 7. Overall, these results are most consistent with the lowest-energy structures calculated at the MP2(full) level of theory and disagree with those calculated at B3LYP and B3P86 levels.
authors.affiliation: Department of Chemistry, University of Utah, 315 Sourth 1400 East, Rm 2020, Salt Lake City, Utah 84112, United States.
authors.forename: Theresa E
authors.initials: TE
authors.lastname: Cooper
authors.forename: Jeremy T
authors.initials: JT
authors.lastname: O'Brien
authors.forename: Evan R
authors.initials: ER
authors.lastname: Williams
authors.forename: P B
authors.initials: PB
authors.lastname: Armentrout
mesh_terms: D005740:Gases / Q000737:chemistry*; D007700:Kinetics; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D014867:Water / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D005740:Gases; D014867:Water; D015032:Zinc