Infrared photodissociation spectra of mass selected homoleptic nickel carbonyl cluster cations in the gas phase

Abstract

Infrared spectra of mass-selected homoleptic nickel carbonyl cluster cations including dinuclear Ni₂(CO)₇⁺ and Ni₂(CO)₈⁺, trinuclear Ni₃(CO)₉⁺ and tetranuclear Ni₄(CO)₁₁⁺ are measured via infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The structures are established by comparison of the experimental spectra with simulated spectra derived from density functional calculations. The Ni₂(CO)₇⁺ cation is characterized to have an unbridged asymmetric (OC)₄Ni–Ni(CO)₃⁺ structure with a Ni–Ni single bond. The Ni₂(CO)₈⁺ cation has a Ni–Ni half-bonded D_3d structure with both nickel centers exhibiting an 18-electron configuration. The trinuclear Ni₃(CO)₉⁺ cluster cation is determined to have an open chain like (OC)₄Ni–NiCO–Ni(CO)₄ structure. The tetranuclear Ni₄(CO)₁₁⁺ cluster cation is determined to have a tetrahedral structure with two-center and three-center bridge-bonded carbonyl units. These nickel carbonyl cluster cations all involve trigonal pyramid like Ni(CO)₄ building blocks that satisfy the 18-electron configuration of the nickel centers.