title: Infrared photodissociation spectroscopy of Co(+)(NH(3))(n) and Ni(+)(NH(3))(n): preference for tetrahedral or square-planar coordination.
abstract: Coordination structures of the Co(+)(NH(3))(n) and Ni(+)(NH(3))(n) ions are probed by infrared (IR) photodissociation spectroscopy with the aid of density functional theory (DFT) calculations. The IR spectra of N(2)-tagged Co(+)(NH(3))(n) (n = 1-4) exhibit two distinct bands assignable to the symmetric and antisymmetric NH stretches of the NH(3) molecules binding directly to Co(+). Size-dependent changes in the spectra of Co(+)(NH(3))(n) (n = 4-8) indicate that the first shell of Co(+) is filled with four NH(3) molecules and the resulting 4-coordinated structure forms the central core of further solvation. The spectra of Ni(+)(NH(3))(n) (n = 3-8) suggest that the coordination number of Ni(+) is also four, although a minor 3-coordinated isomer is identified for Ni(+)(NH(3))(4). Despite the same coordination number, the DFT calculations predict a distorted square-planar coordination for Ni(+)(NH(3))(4) and a distorted tetrahedral coordination for Co(+)(NH(3))(4). The coordination of Ni(+)(NH(3))(4) is explainable by using a simple model based on the geometry of a half-filled 3d orbital in Ni(+). This suggests that the Ni(+) ion gives priority to the minimization of the metal-ligand repulsion in accommodating four ligands in the first shell. On the other hand, the same model fails to explain the coordination of Co(+)(NH(3))(4). An interpretation for this is that the Co(+) ion gives priority to the minimization of the ligand-ligand repulsion.
authors: Department of Chemistry, Graduate School of Sciences, Kyushu University, Hakozaki, Fukuoka, 812-8581, Japan.
authors: Toshitaka
authors: T
authors: Imamura
authors: Kazuhiko
authors: K
authors: Ohashi
authors: Jun
authors: J
authors: Sasaki
authors: Kazuya
authors: K
authors: Inoue
authors: Kazuki
authors: K
authors: Furukawa
authors: Ken
authors: K
authors: Judai
authors: Nobuyuki
authors: N
authors: Nishi
authors: Hiroshi
authors: H
authors: Sekiya
mesh_terms: D000641:Ammonia / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D055668:Photochemical Processes; D013055:Spectrophotometry, Infrared / Q000379:methods
chemical_list: D056831:Coordination Complexes; D007477:Ions; D003035:Cobalt; D000641:Ammonia; D009532:Nickel