Determination of structural parameters for the half-sandwich compounds cyclopentadienyl thallium and cyclopentadienyl indium and indium quadrupole coupling for cyclopentadienyl indium using microwave spectroscopy

Microwave rotational transitions for J′←J=2←1 and 3←2 were measured in the 7-11 GHz range for three isotopomers of (C₅H₅)In. Similar transitions (up to J′←J=5←4) for eight isotopomers of (C₅H₅)Tl were measured in the 5-15 GHz range. The rotational constants of the most abundant isotopomers are B(Cp ²⁰³Tl)=1467.9730(11) MHz, B(Cp ²⁰⁵Tl) =1465.0723(14) MHz, B(Cp ¹¹³In)=1809.9785(30) MHz, and B(Cp ¹¹⁵In)=1800.8199(18) MHz (Cp=C₅H₅). The quadrupole coupling strengths for the indium compounds are eQq(Cp ¹¹³In)=-118.397(69) MHz and eQq(Cp ¹¹⁵In)=-119.981(31) MHz. Spectra for single-substitution ¹³C isotopomers were seen in natural abundance. Deuterated samples of CpTl were prepared to obtain spectra for deuterium-substituted isotopomers. Analysis of the spectra allowed the determination of the following structural parameters; for (C₅H₅)Tl, r(Tl-C₅) =2.413(3) Å, r(C-C)=1.421(10) Å, r(C-H)=1.082(9) Å and 〈C₅-H=0.9(2)° (C₅ represents the planar, 5-carbon ring of C₅H₅), and for (C₅H₅)In, r(In-C₅)=2.314(4) Å and r(C-C)=1.426(6) Å. A Kraitchman analysis was performed on the available isotopomers for comparison of r₀ and r_s values. Both structural analyses indicate that the hydrogen atoms in (C₅H₅)Tl are bent slightly out of the carbon plane away from the coordinated metal atom.