Infrared Spectroscopy of Extreme Coordination: The Carbonyls of U~+ and UO_2~+

摘要

Uranium and uranium dioxide carbonyl cations produced by laser vaporization are studied with mass-selected ion infrared spectroscopy in the C-O stretching region. Dissociation patterns, spectra, and quantum chemical calculations establish that the fully coordinated ions are U(CO)_8~+ and UO_2(CO)_5~+, with D_(4d) square antiprism and D_(5h) pentagonal bipyramid structures. Back-bonding in U(CO)_8~+ causes a red-shifted CO stretch, but back-donation is inefficient for UO_2(CO)_5~+ producing a blue-shifted CO stretch characteristic of nonclassical carbonyls.