Infrared Spectra and Structures of the Neutral and Charged CrCO₂ and Cr(CO₂)₂ Isomers in Solid Neon

Abstract

The reactions from codeposition of laser-ablated chromium atoms with carbon dioxide in excess neon are studied by infrared absorption spectroscopy. The species formed are identified by the effects of isotopic substitution on their infrared spectra. Density functional calculations are performed to support the spectral assignments and to interpret the geometric and electronic structures of the experimentally observed species. Besides the previously reported insertion products OCrCO and O₂Cr­(CO)₂, the one-to-one Cr­(CO₂) complex and the one-to-two Cr­(CO₂)₂ complex as well as the CrOCrCO and OCCrCO₃ complexes are also formed. The Cr­(CO₂) complex is characterized to be side-on η²-C,O-coordinated. The Cr­(CO₂)₂ complex is identified to involve a side-on η²-C,O-coordinated CO₂ and an end-on η¹-O-coordinated CO₂. OCCrCO₃ is a carbonate carbonyl complex predicted to have a planar structure with a η²-O,O-coordinated carbonate ligand. The CrOCrCO complex is predicted to be linear with a high-spin ground state. Besides the neutral molecules, charged species are also produced. The Cr­(CO₂)⁺ and Cr­(CO₂)₂⁺ cation complexes are characterized to have linear end-on η¹-O-coordinated structures with blue-shifted antisymmetric CO₂ stretching vibrational frequencies. The OCrCO^– anion is bent with the Cr–O and CO stretching frequencies red-shifted from those of OCrCO neutral molecule