Abstract
A number of chelates of Al(III), Cr(III), Mn(II), Mn(III), Fe(III), Co(II), Co(III), Ni(II) and Cu(II) with the ligands tropolone, 3-bromotropolone and 4-methyltropolone, have been prepared. Some of these chelates have not previously been reported. Using visible, ultraviolet, infrared and mass spectroscopic techniques, the general spectroscopic properties of these chelates have been studied. The visible spectra of the Cr(III) chelates shows that the crystal field splitting caused by the ligands used here, is of the same order as that of acetylacetone. The IE spectra indicate that associated tropolonate chelates exhibit characteristic absorption bands in the 1590 cm[-1] region. Absorption bands also exist in the region 800 cm[-1] 900 cm[-1], which are characteristic of the coordinated ligands. The mass spectra show that fragmentation is predominantly due to loss of ligand molecules, but that significant proportions of fragments derived from the ligands, occur in association with the metal to give, in particular, metal phenolate and metal cyclopentadienyl entities. Two of the chelates were chosen for a more detailed structural investigation by single crystal, X-ray crystallographic analysis. The hydrated complex of nickel(II) with tropolone is dimeric and the hydrated complex of cobalt(II) with tropolone is a tetramer. These chelates are associated through tropolone oxygen atom bridges, and represent the first reported oxygen bridged structures with tropolone. It is apparent that the compact structure of the tropolone ligand is an important factor contributing toward their stability. The formation of a hydrogen bonded lattice with both of these chelates is facilitated by the presence of terminal water molecules, and by the compactness of tropolone. The spectroscopic data, together with the results obtained from the X-ray analyses, has been of further value toward proposing the structures of some other of the chelates studied.