Mixed aza-thia crowns containing the 1, 10-phenanthroline subunit. Substitution reactions in [NiL(MeCN)][BF_4]_2 {L=2, 5, 8-trithia [9](2, 9)-1, 10-phenanthrolinophane}

摘要

The substitution reactions of the co-ordinated acetonitrile molecule in [NiL(MeCN)][BF_4]_2 1 (L=2, 5, 8-trithia [9](2, 9)-1, 10-phenanthrolinophane) with different anionic and neutral ligands L' [Cl~-, Br~-, I~-, CN~-, SCN~-, H_2O, pyridine (py), aniline (an), 1, 3-dimethyl-4-imidazoline-2-thione (etu) or 1, 3-dimethyl-4-imidazoline-2-selone (eseu)] have been studied by using electronic spectroscopy. While the reaction with all the anionic ligands is quantitative, for the neutral ones an equilibrium takes place; the corresponding equilibrium constants have been determined in MeCN at 25 deg C. The complex cations [NiL(L')]~((2-n)+)(n=0 for neutral and 1 for anionic ligands) have also been isolated in the solid state, mainly as BF_4~- salts and the compounds [NiL(H_2O)][ClO_4]_2 centre dot H_2O, [NiL(Cl)]Cl centre dot H_2O [NiL(SCN)]BF_4 centre dot MeNO_2, [NiL(eseu)][BF_4]_2 and [NiL(py)][BF_4]_2 have been characterized by X-ray diffraction studies. In these complexes a distorted octahedral geometry is achieved at the Ni~(II) with five sites occupied by the macrocyclic ligand L and the sixth by the appropriate ligand L'. The electrochemistry of all the prepared compounds has been studied by cyclic voltammetry. In particular the reductive cyclic voltmmetry of 1 in acetonitrile shows a quasi-reversible one-electron reduction wave near ~1E_(1/2)=-1.0 V vs. Fc/Fc~+. Electrochemical reduction by controlled-potential electrolysis at this potential in the presence of the axial ligand PMe_3 and investigation of the reduced product by ESR spectroscopy confirm the reduction process to be metal based and to correspond to the formation of the [Ni~IL]~+ species.