Knowledge Bank

The symmetric-top rotational spectrum of the neutral argon-cyclopentadienyl thallium complex was measured using a Flygare-Balle-type Fourier transform microwave spectrometer. This appears to be the first rotational spectrum for a noble gas-organometallic complex. The rotational constants are $B$ = 372.45 MHz for Ar-C$5$H$\mathrm{5<mrow\; data-mjx-texclass="ORD">205</mrow>}$Tl and 373.35 MHz for Ar-C$5$H$\mathrm{5<mrow\; data-mjx-texclass="ORD">203</mrow>}$Tl isotopomers. D = 0.1 kHz and D = 0.4 kHz, indicating a fairly rigid structure. The argon atom is located on top of the cyclopentadienyl ring, on the a-axis of the C$5$H$5$Tl monomer, opposite the thallium atom. The separation distance between argon and the cyclopentadienyl ring is 3.56 \AA. The binding energy of Ar-C$5$H$5$Tl was estimated to be about 1-3 kJ mol$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ using low-level MP2 theory.