Organometallic nickel(II) complexes with substituted benzonitrile ligands. Synthesis, electrochemical studies and non-linear optical properties. The X-ray crystal structure of [Ni(η5-C5H5){P(C6H5)3}(NCC6H4NH2)][PF6]

Synthesis and Nonlinear Optical Properties of η5-Monocyclopentadienyliron(II) Acetylide Derivatives. X-ray Crystal Structures of [Fe(η5-C5H5)(DPPE)(p-C⋮CC6H4NO2)] and [Fe(η5-C5H5)(DPPE)((E)-p-C⋮CC6H4C(H)C(H)C6H4NO2)]

“…On the basis of a HOMO−LUMO correlation with the Fe II/III couple and nitro reduction, respectively, we also found that chain-lengthening leads to a decrease in the HOMO−LUMO gap. Therefore, we expect that compound [Fe(η 5 -C 5 H 5 )(DPPE)(( E )- p -C⋮CC 6 H 4 C(H)C(H)C 6 H 4 NO 2 )] ( 4 ) should give the highest β value in this family of compounds, in agreement with earlier studies. , …”

Synthesis and electrochemical studies of organometallic cobalt(III) complexes with substituted benzonitrile chromophores: NMR spectroscopic data as a probe on the second-order non-linear optical properties

“…This means a r-coordinated nitrile in which the overall N"C bond is strengthened upon coordination. The same behavior was found previously on [NiCpPPh 3 (p-NCR)[PF 6 ] derivatives [18] and seems to indicate the absence of p backdonation in these cobalt complexes, in opposite of that was found for the previously reported Fe(II) and Ru(II) analogs [7][8][9][10]. Accordingly, recent density functional theory (DFT) calculations on some of these cobalt complexes confirm that the ligand-metal interaction are p mainly and have no evidence of p back donation contribution [19].…”

“…In fact, as the electron donor character of the p-substituent in benzonitrile ligands increases, the Cp ring resonance shifts upfield, consistent with an increased electronic density on the Cp ring due to the increased electron density at the metal center. This effect was observed in similar nickel [18], iron [7,8] and ruthenium [9,20] complexes. In contrast to the effect observed for Cp ring, the phosphine signals are relatively insensitive to the nature of the aromatic nitrile.…”

“…The origin of the observed upfield shifts could be an effect of the change of the N"C anisotropy upon coordination. Moreover, an additional explanation can be found by assuming an electronic interaction of the protons with the counter ion, as observed before on Ru(II) [9] and Ni(II) [18] compounds. 13 C NMR data of this family of compounds confirm the evidence found for proton spectra.…”

“…As discussed above, the slope of the linear correlation between DCp (DCp = d Cp (p-substituted benzonitrile) À d Cp (benzonitrile)) and r p Hammett parameters of the nitrile substituents could give an insight of the electronic communicability between the nitrile ligands and the organometallic cobalt fragment. Comparison of the slope magnitude obtained from available spectroscopic data of related g 5 -monocyclopentadienyliron, ruthenium and nickel derivatives [7,8,16,18,20], show that the electronic communicability between the nitrile ligands and the organometallic fragments increases along the sequence Codppe < NiPPh 3 < Rudppe < Fediop < Fedppe. A similar trend was found for the first hyperpolarizabilities of complexes containing these organometallic fragments and p-NCC 6 H 4 NO 2 and p-NC(C 6 H 4 ) 2 NO 2 ligands [8,16].…”