Abstract
The reaction solution of triethylphosphine with MCl4 (M = V, Nb, Ta) has been reported to show electron paramagnetic resonance signals at both room temperature and low temperature. The axial behavior of the low temperature spectra was interpreted to be from the trans-MCl4 -2PEt3 while the room temperature spectra suggested a nondegenerate ground state. But from the ligand field theory, a trans arranged MCl4-PEt3 should have a degenerate E8 state. In the case of vanadium, this conflict was proved to be caused by a reaction product of vanadyl chloride and triethylphosphine that shows the reported EPR signals. The vanadyl chloride may result from the reaction of VCl4 with trace amount of water. The major products of VCl4 with various phospines were characterized crystallographically and it was found that the reduction of vanadium(IV) to vanadium(III) took place when VCl4 reacted with phosphines. The EPR spectra of niobium and tantalum systems have also been investigated and it is clear that, again, the reported spectra were not from MCl4 (PEt3)2 (M = Nb. Ta) samples. At this stage, no definite conclusion can be drawn on the identities of the impurities although there is evidence that oxide compounds are responsible for the EPR spectra. The second part of this research includes the synthesis and characterization of amidato-bridged dirhenium compounds. From reactions of Re2(OCCH3)4Cl2 with molten amide ligands, the corresponding amidato-bridged compounds can be formed. Four kinds of amides were used and the structures were determined by X-ray single crystal diffraction. NMR and UV-vis spectra were recorded. Three of these compounds have a cis arrangement of the Re2O4N4 core and the other has a trans coordination environment of the amidato ligands around the dirhenium centers. Compounds with cis geometry can react with water in the open air and for one compound the product has been proved to be converted to trans geometry. The trans compound is very stable toward water and oxygen.
Lu, Jian (1994). Reaction and EPR spectra of "MCl4.2PR3" (M=V, Nb, Ta) compounds and study of some amidato-bridged dirhenium compounds. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1551882.