2 research outputs found
Mixed aza-thia crowns containing the 1,10-phenanthroline sub-unit. Substitution reactions in [NiL(MeCN)][BF4]2 L = 2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane
The substitution reactions of the co-ordinated acetonitrile molecule in [NiL(MeCN)][BF4]2 1 (L = 2,5,8-trithia-
[9](2,9)-1,10-phenanthrolinophane) with different anionic and neutral ligands L9 [Cl2, Br2, I2, CN2, SCN2, H2O,
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 8C. The complex cations [NiL(L9)](2 2 n)1 (n = 0 for neutral and 1 for anionic ligands) have also been isolated in
the solid state, mainly as BF4
2 salts and the compounds [NiL(H2O)][ClO4]2?H2O, [NiL(Cl)]Cl?H2O, [NiL(SCN)]-
BF4?MeNO2, [NiL(eseu)][BF4]2 and [NiL(py)][BF4]2 have been characterized by X-ray diffraction studies. In these
complexes a distorted octahedral geometry is achieved at the NiII with five sites occupied by the macrocyclic ligand
L and the sixth by the appropriate ligand L9. The electrochemistry of all the prepared compounds has been studied
by cyclic voltammetry. In particular the reductive cyclic voltammetry of 1 in acetonitrile shows a quasi-reversible
one-electron reduction wave near 1E2¯
1 = 21.0 V vs. Fc/Fc1. Electrochemical reduction by controlled-potential
electrolysis at this potential in the presence of the axial ligand PMe3 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 [NiIL]1
species