X-ray crystallographic studies on the self-condensation products of o-aminobenzaldehyde and anthranilic acid and of the metal complexes of some related tetra-azamacrocycles.
This Thesis describes X-ray crystallographic investigations on twelve compounds. The first three are the products of the acid condensation of ortho-aminobenzaldehyde, OAB, the so-called TAAB salts, based on the tetra-anhydro tetramer of OAB. Although known since 1926, their structures have remained controversial. Of the three salts, TAABH2(X)2, investigated, that of X = picrate was found to be ordered, whilst those of X = HSO4 and BF4 were disordered. The structure of the TAABH2 cation is saddle-shaped and based on a fused heptacyclic framework. In all the three salts the anion appears to be doubly hydrogen bonded to the cation, through hydrogen donors NH and CH. The results enable a controversy in the literature regarding the structures of these compounds to be resolved. The self-condensation products of anthranilic acid, AA, also somewhat controversial in nature, have been investigated. The formation of a trimeric, and minor yields of a tetrameric derivative, is confirmed. The crystal structures of the tetramer and of two solvates of the trimer (CHCI3 and CH3CN.H2O) were determined. These two compounds, also, have a fused heptacyclic double saddle-shape overall structure. Their structures are compared with those of the TAAB salts. Related types of hydrogen bonding are surveyed, and the results found in this Thesis are put in a wider context. The structure of the copper complex Cu(TAABH2 ) of reduced TAAB derivative TAABH4, a 16-membered tetra-azamacrocycle has been investigated. It, too, has an overall saddle-shape, but this is considerably flatter than those of the TAAB salts and AA derivatives. Two metal complexes (CuII and Felll) of a 14-membered tribenzotetra-azamacrocycle were investigated. In the case of the iron compound. X-ray crystallography showed that an unexpected, novel oxygenation reaction of the ethylene bridge had taken place to give an a,B-diketo group. The purpose-made copper diketo-analogue was examined for comparative purposes. This derivative, in contrast to that based on TAABH4 , has an almost square planar co-ordination around the copper atom. A compound, thought to have been the free parent ligand of these metal complexes, was also investigated. The data set was poor, but it could be shown that the compound was acyclic, contained an extra ortho-phenylene diamine residue, and was probably hydrogen bonded. The crystal structures of two metal complexes based on Cull and Felll of two dibrominated Schiff bases were investigated. The dibrominated copper salen derivative is monomeric, in contrast to the unbrominated compound, which is dimeric. The Felll derivative, like the earlier-mentioned oxidised tetra-azamacrocyclic iron derivative, has a dimeric structure, with the iron atoms linked by a p(?)-oxo-bridge. The structures of the three copper and two iron derivatives are discussed and compared. Three themes emerge from the twelve structures described in this Thesis: (i) the structural importance of hydrogen bonding, (ii) the inadequacy of a single valence bond formulation to explain the observed X-ray crystallographic results, and the need to invoke resonance forms, mainly ortho-quinonoid, and (iii) the versatile role of nitrogen in organic and metal organic heterocyclic structures.
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