Coordination structures of the Co+(NH3)n and Ni+(NH3)n ions are probed by infrared (IR) photodissociation spectroscopy with the aid of density functional theory (DFT) calculations. The IR spectra of N2-tagged Co+(NH3)n (n = 1-4) exhibit two distinct bands assignable to the symmetric and antisymmetric NH stretches of the NH3 molecules binding directly to Co+. Size-dependent changes in the spectra of Co+(NH3)n (n = 4-8) indicate that the first shell of Co+ is filled with four NH3 molecules and the resulting 4-coordinated structure forms the central core of further solvation. The spectra of Ni+(NH3)n (n = 3-8) suggest that the coordination number of Ni+ is also four, although a minor 3-coordinated isomer is identified for Ni+(NH3)4. Despite the same coordination number, the DFT calculations predict a distorted square-planar coordination for Ni+(NH3)4 and a distorted tetrahedral coordination for Co+(NH3)4. The coordination of Ni+(NH3)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+(NH3)4. An interpretation for this is that the Co+ ion gives priority to the minimization of the ligand-ligand repulsion.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry