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 $C13$ 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 $rs$ 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.