Reactions of Th and U Atoms with C2H2: Infrared Spectra and Relativistic Calculations of the Metallacyclopropene, Actinide Insertion, and Ethynyl Products

• Published in: Chemistry : a European journal 2006-11, Vol.12 (32), p.8324-8335
• Main Authors: Andrews, Lester, Kushto, Gary P., Marsden, Colin J.
• Format: Article
• Language: English
• Subjects: density functional calculations; IR spectroscopy; matrix isolation; thorium; uranium
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200600075

Reactions of laser‐ablated Th and U atoms with C2H2 during condensation with excess argon at 7 K give several new product species. The metallacyclopropene, inserted hydride, and actinide ethynyl are identified from isotopic frequencies and relativistic DFT calculations. The higher‐energy vinylidine isomer was not observed. These actinide metallacyclopropenes exhibit substantially stronger bonding interactions than found recently for the Pd and Pt metals. In the case of Th(C2H2) the argon matrix interaction is strong enough to reverse the computed order of states (MR‐CISD) in favor of a triplet ground state for the (Ar)n(Th(C2H2)) complex. The nature of the electronic interactions between various metal atoms and acetylene is compared and the origin of the particularly strong interaction for U and Th is traced to the higher energy of their 6d orbitals. The ThCCH and UCCH actinide ethynyl products are also observed and characterized by CC stretching modes 38±2 cm−1 lower than acetylene itself. Several new product species were obtained in reactions of laser‐ablated Th and U atoms with C2H2 during condensation with excess argon at 7 K. The metallacyclopropene, inserted hydride, and actinide ethynyl are identified from isotopic frequencies and relativistic DFT calculations.