The preparation of coordinating agents derived from aromatic diamines is of special interest since the use of nitrogen atoms for coordination to a single cation is directly related to their situation in ortho, meta or para positions. In the case of diaminetetramethylenecarboxylic acids or Schiff bases derived from o-phenylenediamines, the proximity of the nitrogen atoms permits their simultaneous coordination to the same metal cation, leading mainly to monomer species. Combined with the lesser basicity of the nitrogen atoms of the aromatic diamines, the o- phenylenediaminetetramethylene-carboxylic acids are good sequestering agents for some metal ions. Complexes derived from o-phenylenediamine Schiff bases provide new and interesting environment for M-C funcionalities. Iron(III) complexes with o- phenylenediamine Schiff bases may present spin-crossover. On the other hand, the ligands derived from m- or p-phenylenediamines can only coordinate one nitrogen atom to any one metal cation. The formation of species with excess of ligand (2:1 ligand:metal ratio), with excess of metal (1:2 ratio), and monomers (1:1 ratio) is now possible. Moreover, the special conformation of the ligands with nitrogen atoms in meta or para positions on the aromatic ring facilitates the formation of dimer complexes since the ligands act as a bridge. The dinuclear complexes of those ligands with paramagnetic ions may present magnetic coupling. With the nitrogen atoms in para position, polymer complexes are also possible since the ligand acts as a bridge.