Infrared Spectroscopy of Extreme Coordination: The Carbonyls of U⁺ and UO₂⁺

Abstract

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.

Infrared spectroscopy of mass-selected metal carbonyl cations

“…The dissociation energy of the n = 5 complex was determined to be 0.78 eV, indicating that the small amount of dissociation seen for this ion is likely the result of some multiphoton absorption. We see evidence for a small amount of this for several clusters, which is understandable because of the high IR absorption strength for these systems (computed to be in the range of 1000 km/mol) [47][48][49][50][51]. We see this same kind of photodissociation break-down behavior for all of the carbonyl complexes studied.…”

“…The details of the experiments described here have been reported previously [45][46][47][48][49][50][51][52][53]. Metal carbonyl cations of the form MðCOÞ þ n are produced in a pulsed nozzle laser vaporization source using the third harmonic of a pulsed Nd:YAG laser (355 nm; Spectra-Physics INDI-40).…”

“…The calculations on transition metals were performed using the B3LYP functional [62,63] as implemented in the pcGAMESS [64,65] or Gaussian03 [66] computational codes. Different basis sets were employed for different systems, as described in our original papers [45][46][47][48][49][50][51]. An important consideration throughout these studies is the spin configuration of the metal ground state and how it varies with the number of ligands present.…”

“…As another potential example of high carbonyl coordination numbers, we have explored the carbonyls of uranium and uranium oxide [50]. The coordination of actinide metals has important implications for energy and the environment, but the electronic structure and bonding in these systems present significant challenges for experiments and theory [2,80,81].…”

“…However, multi-metal atom cluster carbonyls have been studied by photodissociation with infrared free-electron lasers [41][42][43][44]. Recently we have studied the infrared spectroscopy of various metal cation-ligand complexes produced in the gas phase using a laser vaporization source and studied with mass-selected ion photodissociation spectroscopy [45][46][47][48][49][50][51]. The present article provides a review of this new work and the interesting insights gained from it.…”