Synthesis of new donor/acceptor eta(5)-cyclopentadienyl and eta(5)-indenyliron(II) complexes with p-benzonitrile derivatives. Crystal structures of [Fe(eta(5)-C5H5)(CO)(P(OC6H5)(3))(p-NCC6H4NO2)][BF4]center dot CH2Cl2 and [Fe(eta(5)-C9H7)(CO)(P(OC6H5)(3))(p-NCC6H4NO2)][BF4]

New complexes of the type [Fe(eta (5)-Cp or Ind)(L)(L ')(p -NCR)][BF4] (L, L ' = CO, P(OC6H5)(3), P(CH5)(3); R = C6H4N(CH3)(2). C6H4NO2, (E)-C(H)=C(H) C6H4NO2, (E)-C(H)=C(H)C6H4N(CH3)(2)) have been synthesised and characterise d. Spectroscopic data were analysed in order to evaluate the tuning of the electronic density at the metal centre and the extension of the pi -delocal isation on the molecule, due to the presence of coligands with different ac ceptor/donor abilities. The structures of two complexes [Fe(eta (5)-C5H5)(C O)(P(OC6H5)(3))(P-NCC6H4NO2)][BF4] and [Fe(eta (5)-C9H7)(CO)(P(OC6H5)(3))(P -NCC6H4NO2)][BF4] were determined by X-ray crystallographic analysis. The c ompounds crystallised in the centrosymmetric space groups P (1) over bar an d P2(1)/n, respectively. Bond distances within the nitrile ligand are discu ssed in order to evaluate the nature of iron-nitrile bonding in these compl exes. (C) 2001 Elsevier Science B.V. All rights reserved.