The Synthesis, Characterization and Complex Forming Ability of Several - 2 Pyridylamine Ligands

Abstract

Several substituted tri-2-pyridylamines have been synthesised and their complexing potential with transition metal ions studied. The synthesis of 6-methyl-2-pyridyl-(2-pyridaymiln) amine (6mpdpa), 5-methyl-2-pyridy1-(2-pyridyl) amine (5mpdpa), 4-methy1-2-pyridyldi-(2-pyridyl) amine (4mpdpa), 5-nitro-2-pyridyldi-(2-pyridyl) amine (5npdpa) and tri-(4-methyl-2-pyridyl) amine (tri-4m-pyam) are discussed in terms of difficulties experienced and of modifications to the Wibaut and La Bastide synthesis for tri-(2-pyridyl) amine (tripyam). Attempts to prepare a pentapyridyl ligand [2,6 di(di-2-pyridylamine) pyridine ] are discussed together with a possible explanation for the failure to isolate the ligand under the conditions used. The infra red and nuclear magnetic resonance spectra of the pyridylamines were analysed and the effect of the substituent on absorption position was noted. Nuclear magnetic resonance data were used in an attempt to explain earlier observations by Watson and Mann for the protonation of tri-2-pyridylamine. Complexes of the above ligands were synthesised with iron (II), Cobalt (II), nickel (II), copper (II) and molybdenum(0). The infra red and electronic spectra of the nickel complexes and the Möissbauer spectra of the iron complexes were studied. The single absorption in the Mössbauer spectrum of [Fe(tripyam)2] (C104)2 is split for [Fe(5mpdpa) 2] (C104) 2 and [Fe(4mpdpa)2](C104)2 indicating that the metal ion is sensitive to the effect of the substituent present in one of the pyridine rings. The electronic spectra of the nickel complexes and the Mössbauer spectra of the iron complexes were analysed to determine the extents of σ and π bonding in the complexes. Isomeric complexes with copper(II) (e.g. [Cu(6mpdpa)2] (c104)2 and [ Cu(6mpdpa)2(C104)2]), were studied and data obtained analysed to determine the morphology of the complexes. Infra red, electron spin resonance and electronic spectra were analysed and a tetragonally distorted octahedral environment was suggested for complexes of the type [Cu(L)2](C104)2] where L = 6mpdpa and 4mpdpa. Complexes of the type L CuL2 (C104)2] where L = 6mpdpa, 4mpdpa and 5npdpa were considered to have a trans stereochemistry. The isotropic nature of several of the esr spectra presented the problem of determining whether a static or dynamic Jahn Teller distortion existed for the complexes concerned. Electron spin resonance studies were extended to cover related copper(II) systems, the ligands involved being di-2-pyridylamine and pyridine. An exploratory examination of complexes with cobalt(II) was undertaken, with an emphasis on magnetic behaviour, in an attempt to ascertain whether earlier observations for [Co(tripyam)2](C104)2 were common to the tri-2-pyridylamine type ligand in general. Data obtained suggested that the detailed behaviour of Co(tripyam)2(C104)2, which undergoes a change of spin multiplicity between 100°K and 200°K, was not general for the series. Although the new complexes with substituted tri-2-pyridylamines give room temperature magnetic moments remarkably close to the spin only value for 3 unpaired electrons, the Curie-Weiss Law is obeyed to 77ºK, the limit of the measurements. Finally, the use of physical techniques for studying structural variations in silver(II) complexes was considered. The techniques used were found to yield limited information.