Rotational spectra and molecular structures of organometallic and organic molecules

Understanding the nature of chemical bonds constitutes a major theme of this thesis. This thesis investigates the gas phase rotational spectra, electronic charge distributions and molecular structures of organometallic and organic molecules, using high-resolution pulsed beam Fourier transform microwave spectroscopy (PBFTMS) and computational methods. High-resolution rotational spectra and structural parameters were obtained for the following organometallic molecules in the singlet electronic state, including three symmetric and five asymmetric top complexes: C₅H₅Nb(CO)₄, CH₃Mn(CO)₅, MnRe(CO)₁₀, C₅H₅Mo(CO)₃H, C₅H₅W(CO)₃H, C₅H₅NiC₃H₅, C5H₄(CH₃)FeC₅H₅ and (C₅H₄(CH₃))₂Fe. High-resolution rotational spectra and structural parameters were obtained for three organic molecules in the singlet electronic state: ortho-benzyne (C₆H₄) and the keto-enol tautomers, 2-hydroxypyridine and 2-pyridone (C₅H₅NO). In addition to the tautomeric forms, pure rotational spectra of the H-bonded dimer, 2-hydroxypyridine:2-pyridinone, were also obtained. These detailed spectral investigations yielded novel and useful information about the molecular properties of these molecules. Primarily, these results provided information regarding chemical bonding, vibrational ground state structures, structural isomers, conformational behavior, metal-hydrogen bonding and electronic charge distributions. Density functional theory (DFT) and ab-initio calculations were carried out in conjunction with the experiments, providing additional insights into further understanding the equilibrium structures, structural isomers and the electric field gradient distributions for these molecules

π\pi -π\pi and CH-π\pi DISPERSION INTERACTIONS IN THE N2_2-C5_5H5_5N AND CH4_4-C5_5H5_5N DIMERS

Author Institution: Department of Chemistry, University of Alberta, Edmonton, T6G 2G2, CanadaWe will discuss the results of our high resolution spectroscopic studies of the dinitrogen-pyridine (N$_2$-C$_5$H$_5$N) and methane-pyridine (CH$_4$-C$_5$H$_5$N) dimers. The two dimers represent simple binary van der Waals systems that are good prototypes for studying the weak $\pi$-$\pi$ and CH-$\pi$ bonds involving polar and non-polar aromatic molcules. The pyridine molecule is of great interest because many of its derivatives are prevalently found in plants and microorganisms. Our preliminary results show that the dimers adopt T-shaped configurations. The N$_2$ lies perpendicularly to the aromatic plane with its center of mass closes to the $c$-inertial axis of the free pyridine molecule; similarly, the CH$_4$ molecule in CH$_4$-C$_5$H$_5$N sits above the aromatic plane. These are the only configurations presently observed for both dimers in our experiments. The talk will focus on the rotational spectra and structural properties of these dimers

THE ROTATION SPECTRA OF METHYL MANGANESE PENTACARBONYL COMPLEX.aCOMPLEX.^{a}

$^{a}$Supported by THE NATIONAL SCIENCE FOUNDATIONAuthor Institution: Department of Chemistry, University of ArizonaMethyl manganese pentacarbonyl is an important organometallics complex used for modeling migration/insertion reactions. We have obtained the microwave spectrum of methyl manganese pentacarbonyl complex over a range of 5-10 GHz using a Fourier-transformed microwave spectrometer. The observed hyperfine splittings is well resolved for the transitions in 7 GHz range. We are analyzing quadrupole and rotational constants to obtain information on the electronic structure and molecular structure

ROTATIONAL SPECTRA AND HYPERFINE STRUCTURE FOR A TITANIUM SANDWICH COMPLEX, C5_5H5_5TiC7_7H7_7

{Supported by THE NATIONAL SCIENCE FOUNDATION CHE0304969Author Institution: Department of Chemistry, University of Arizona, Tucson, AZ 85721\begin{wrapfigure}[9]{R}{4CM} \vspace{-0.6cm} \hspace*{-0.1cm} \epsfig{file=cpti8.eps} \end{wrapfigure} Microwave spectroscopy measurements and density functional theory calculations are reported for the cyclopentadienylcycloheptatrienyltitanium complex, C$_5$H$_5$TiC$_7$H$_7$. This appears to be the first microwave work on a complex containing the cycloheptatrienyl ligand. Rotational transition frequencies for this symmetric-top complex were measured in the 4-13 GHz range using a Flygare-Balle-type pulsed beam spectrometer. The spectroscopic constants obtained for the normal isotopomer are B= 771.78907(38), D$_J$= 0.0000295(41), and D$_{JK}$= 0.001584(73) MHz. The quadrupole hyperfine splittings for C$_5$H$_5$$^{48}$TiC$_7$H$_7$ were clearly observed, and eQq$_{aa}$= 18.432(90) MHz. Analysis of the rotational constants indicates that bond lengths in the gas phase are about 0.02\AA\ longer than those reported for the solid-state X-ray structure. The calculated Ti-C bond lengths are shorter for the C$_7$H$_7$ ligand (r(Ti-C)=2.21\AA) than for the C$_5$H$_5$ ligand (r(Ti-C)=2.34\AA), and the C$_7$H$_7$ H atoms are displaced 0.15\AA\ out of the C7 plane, toward the Ti atom