Spectroscopic Studies of Cationic h5-Cyclopentadienyl Iron Carbonyl Derivatives

Abstract
Mössbauer, 13C nuclear magnetic resonance and infrared spectroscopic studies of a series of cationic iron compounds of the type [(h5-C5H5)Fe(CO)2L]+X (L = CO, CH3CN, C2H4, (C6H5)3P, C5H4N; X = PF6, BF4) are described. The Mössbauer center shifts indicate that the σ donor plus π acceptor ability (σ + π) of these ligands increases in the order CH3CN ≤ C2H4 < C5H5N < (C6H5)3P < CO < CS. The positive 57Fe quadrupole splittings strongly suggest that the sign of the quadrupole splittings for the isovalent and isoelectronic Mn and Re compounds are also positive. The correlation between carbonyl infrared force constants and 13C carbonyl shieldings is discussed in relation to a similar correlation previously reported in the literature for a series of neutral complexes (h5-C5H5)Fe(CO)2Y, where Y is an anionic ligand.
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