Variable temperature /sup 31/P and /sup 19/F NMR studies of Fe(CO)/sub 3/(PF/sub 3/)/sub 2/ and Fe(CO)/sub 2/(PF/sub 3/)/sub 3/
/sup 31/P and /sup 19/F NMR spectra for the compounds Fe(CO)/sub 3/(PF/sub 3/)/sub 2/ and Fe(CO)/sub 2/(PF/sub 3/)/sub 3/ were studied in the temperature range +25 degreeC down to -100 degreeC. The four spin--spin coupling constants /sup 1/J/sub PF/, /sup 3/J/sub PFprime/, /sup 2/J/sub PPprime/, and /sup 4/J/sub FFprime/ were evaluated as a function of temperature. Owing to the fast intramolecular exchange of axial with equatorial ligand groups in these compounds, the observed spectra are time-averaged. The magnitude of the observed time-averaged /sup 2/J/sub PPprime/ coupling constant can be accounted for by the experimentally determined mole fractions for the various isomers and the trans, cis and vicinal phosphorus--phosphorus coupling constants /sup 2/J/sup t r a n s//sub PPprime/, /sup 2/J/sup c i s//sub PPprime/ and /sup 2/J/sup v i c i n a l//sub PPprime/, respectively. An angular correlation of the phosphorus--phosphorus coupling constant is attempted. These results are compared to variable temperature ir and /sup 13/C NMR studies of these compounds. The usefulness of studying ir or Raman spectra in addition to the NMR spectra for certain nonrigid molecules which fall in the ''very fast exchange'' category where no temperature coalescence of NMR spectral lines can be observed, is demonstrated. The simultaneous fitting of both the time-averaged NMR spectra on the one hand and the separate ir spectra on the other is the best way to study such molecules. 151
- Research Organization:
- Department of Chemistry, Florida State University, Tallahassee, Florida 32306
- OSTI ID:
- 7112900
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 66:11
- Country of Publication:
- United States
- Language:
- English
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ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBONYLS
NUCLEAR MAGNETIC RESONANCE
FLUORINE COMPOUNDS
IRON COMPOUNDS
PHOSPHORUS COMPOUNDS
CHEMICAL SHIFT
RELAXATION
TEMPERATURE DEPENDENCE
HALOGEN COMPOUNDS
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RESONANCE
TRANSITION ELEMENT COMPOUNDS
400201* - Chemical & Physicochemical Properties