Syntheses, properties and Mossbauer studies of mono- and di-nitrile phosphine complexes of iron(II).: Crystal structures of trans-[Fe(NCR)2(Et2PCH2CH2PEt2)2][BF4]2 (R = Me or CH2C6H4OMe-4)

Complexes trans-[FeL(NCR)(depe)(2)]Y-n (R = Me, Et, CH2C6H4OMe-4, C6H4OMe-4, C6H4Me-4, Ph, C6H4F-4 or C6H4NO2-4; depe = Et2PCH2CH2PEt2; Y = BF4 or BPh4; L = Br, n = 1 1; L = NCR, n = 2 2) have been prepared by treatment of trans-[FeBr2(depe)(2)] (in MeOH and in the presence of [NBu4][BF4] or Na[BPh4]) with a stoichiometric or a twofold molar amount of the appropriate organonitrile. Electronic, NMR and Mossbauer spectral as well as FAB mass spectrometric data are reported. Mossbauer partial isomer shift (p.i.s.) and partial quadrupole splitting (p.q.s.) parameters have been estimated for the nitrile ligands and rationalised, with the overall i.s. and q.s., in terms of pi- and sigma-electronic effects. The FAB MS fragmentation patterns are also proposed, and the crystal structures of 2 (R = Me or CH2C6H4OMe-4, Y = BF4) have been determined.