The rotational spectrum and structure for the argon-cyclopentadienyl thallium van der Waals complex: Experimental and computational studies of noncovalent bonding in an organometallic π -complex

Chakree Tanjaroon, Adam M. Daly, Stephen G. Kukolich

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Abstract

The rotational spectrum of a noble gas-organometallic complex was measured using a pulse molecular beam Fourier transform microwave spectrometer. Rotational transitions for the neutral argon-cyclopentadienyl thallium weakly bound complex were measured in the 4-9 GHz range. Analysis of the spectrum showed that the complex is a prolate symmetric-top rotor with C5V symmetry. The experimentally determined molecular parameters for Ar- C 5H5 205Tl are B=372.4479 (3) MHz, D J=0.123 (2) kHz, and DJK =0.45 (2) kHz. For Ar-C 5H5 T 203 l, B=373.3478 (5) MHz, DJ=0.113 (3) kHz, and DJK=0.37 (3) kHz. Using a pseudodiatomic model with Lennard-Jones potential yields an approximate binding energy of 339 cm -1. The argon atom is located on the a -axis of the C 5H5Tl monomer, directly opposite from the thallium metal atom. The measured separation distance between argon and the cyclopentadienyl ring is R=3.56 Å. The overall size of the cluster is about 6 Å, measuring from argon to thallium. Relatively small DJ and DJK centrifugal distortion constants were observed for the complex, indicating that the structure of Ar- C5H5Tl is somewhat rigid. MP2 calculations were used to investigate the possible structures and binding energies of the argon-cyclopentadienyl thallium complex. Calculated, counterpoise corrected binding energies are evaluated at R=3.56 Å for Ar- C5H5Tl range from 334 to 418 cm-1. The experimental binding energy ε=339 cm-1 for Ar-C 5H5Tl falls within this range. The higher-level MP2/aug-cc-pVTZ-PP (thallium)/aug-cc-pVTZ(Ar, C, H) calculation with variable R yielded Re =3.46 Å and binding energy of 535 cm-1. Our estimated binding energy for argon-cyclopentadienyl thallium is very similar to the binding energy of argon-benzene. Calculations for the new van der Waals complexes, Ar (C5H5Tl)2 and (C 5H5Tl)2, have been obtained, providing further information on the structures and bonding properties of previously observed cyclopentadienyl thallium polymer chains. The calculated intermolecular distance RTl-Cp =3.05 Å for the (CpTl)2 chain subunit (Cp is cyclopentadienyl, C5H5) is slightly longer than the measured x-ray value RM-Cp (M=Tl) =2.75 Å. The x-ray distance RTl-Tl =5.5 Å for the chain structure is almost identical to the calculated R Tl-Tl =5.51 Å for the (C5H5Tl) 2 dimer.

Original languageEnglish (US)
Article number054305
JournalJournal of Chemical Physics
Volume129
Issue number5
DOIs
StatePublished - Aug 19 2008

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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