Far-infrared and NMR spectroscopic studies of organometallic compounds.
thesisposted on 19.11.2015, 08:46 by Zaid. Mahmood
Far-infrared and mid-infrared spectroscopy, mass spectrometry and 1H NMR spectroscopy of various isotopic combinations of (CH)3A1+(CH3)2A1H in the gas phase have been recorded to confirm the nature of mixed bridge compounds. IR studies have shown that the major constituent of a labile gas phase equilibrium mixture of trimethylalane and dimethylalane is the heteroleptic pentamethyldialane, Me2Al(uH)(uH)AlMe2. A partial normal coordinate analysis of the spectra of isotopic variants reveals that this predominance arises from a significant strengthening of the Al-H-Al bridging bond. IR and NMR studies lead to a similar conclusion for solutions of alane mixtures in toluene, and lend support for a ligand exchange mechanism involving singly bridged species. Solution mixtures of dimethylgallane and diethylgallane in toluene have been investigated using mass spectrometry and proton NMR spectroscopy. The mass spectrometric observations reveal the presence of dimeric and trimeric species. The NMR results confirm this conclusion, and further suggest that intramolecular exchange processes are fast even at 200 K, whereas intermolecular exchange is significant only abve 250 K. Vibrational spectra of C4H6Fe(CO)3, CpMn(CO)3 and MeCpMn(CO)3 have been measured in the vapour phase in the 500-10 cm-1 region using IR spectroscopy and an assignment is given. Low frequency vibrations were investigated in order to determine whether these provide any useful information on the structure and bonding in the aforementioned compounds. The vibrational spectra of XMn(CO)5 compounds (where X= CH3, H, CF3, Br, Cl) in the vapour phase have been studied in the far-infrared region. This study was carried out to ascertain the effect of the non-carbonyl ligand in XMn(CO)5 on the bonding in the Mn(CO)5 group. The number of v(MC) and s(MCO) modes active in the infrared in the gas phase was compared with the data available in the liquid phase in the same region and their frequencies were correlated where possible with the frequencies of the v(CO) modes. The overall aim of this work was to characterise the structure and interactions (intra- and intermolecular) in a variety of organometallics. Many of these compounds are important precursors in semiconductor fabrication.