Spectroscopic Studies of Cationic <i>h</i>⁵-Cyclopentadienyl Iron Carbonyl Derivatives

Abstract

Mössbauer, 13 C nuclear magnetic resonance and infrared spectroscopic studies of a series of cationic iron compounds of the type [(h 5 -C 5 H 5 )Fe(CO) 2 L] + X − (L = CO, CH 3 CN, C 2 H 4 , (C 6 H 5 ) 3 P, C 5 H 4 N; X = PF 6 − , BF 4 − ) are described. The Mössbauer center shifts indicate that the σ donor plus π acceptor ability (σ + π) of these ligands increases in the order CH 3 CN ≤ C 2 H 4 &lt; C 5 H 5 N &lt; (C 6 H 5 ) 3 P &lt; CO &lt; CS. The positive 57 Fe 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 13 C carbonyl shieldings is discussed in relation to a similar correlation previously reported in the literature for a series of neutral complexes (h 5 -C 5 H 5 )Fe(CO) 2 Y, where Y is an anionic ligand.