Coordinating ability of ligands derived from phenylenediamines

The preparation of coordinating agents derived from aromatic diamines is of special interest since the use of nitrogen atoms for coordination to a sin gle cation is directly related to their situation in ortho, meta or para po sitions. In the case of diaminetetramethylenecarboxylic acids or Schiff bas es derived from o-phenylenediamines, the proximity of the nitrogen atoms pe rmits their simultaneous coordination to the same metal cation, leading mai nly to monomer species. Combined with the lesser basicity of the nitrogen a toms of the aromatic diamines, the o-phenylenediaminetetramethylene-carboxy lic acids are good sequestering agents for some metal ions. Complexes deriv ed from o-phenylenediamine Schiff bases provide new and interesting environ ment for M-C funcionalities. Iron(III) complexes with o-phenylenediamine Sc hiff bases may present spin-crossover. On the other hand, the ligands deriv ed 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 l igand:metal ratio), with excess of metal (1:2 ratio), and monomers (I:I rat io) is now possible. Moreover, the special conformation of the ligands with nitrogen atoms in meta or pam positions on the aromatic ring facilitates t he formation of dimer complexes since the ligands act as a bridge. The dinu clear complexes of those ligands with paramagnetic ions may present magneti c coupling. With the nitrogen atoms in para position, polymer complexes are also possible since the ligand acts as a bridge. (C) 1999 Elsevier Science S.A. All rights reserved.