Magneto-structural characterization of polynuclear complexes with supramolecular architectures
The thesis describes the supramolecular organization of homo- and heteropolynuclear complexes, containing different paramagnetic centers, going from d-block metal ions to combination of d-f spin carriers topologies. These polynuclear complexes have been structurally and spectroscopically characterized, and partly magnetostructural correlations have been performed. The synthesis of polynuclear complexes has been based on self-assembly and rational strategies. Iron(iii) aza-crown complexes have been isolated through self-assembly reaction between N-imidazol-2-yl-salicyloyl hydrazide and FeX3·xH2O salts in presence of pseudo-halide coligands. These complexes are characterized by antiferromagnetic coupling between the Fe(iii) centers. In addition, self-assembly of easy accessible Schiff base ligands and d-block metal salts led to homo-polynuclear d-complexes with the magnetic interaction varying from strong antiferromagnetic coupling between the paramagnetic centers to ferromagnetic interaction induced by accidental orthogonality of the magnetic orbitals associated to d-metal ions in partial-cubane structural core. The rational strategy approach is divided in two subcategories, namely the dendritic approach and ”complex-as-ligand” strategy. The dendritic approach is based upon C3-symmetric triaminoguanidine-Schiff base ligand derivatives which present three-fold tridentate coordination pockets. Hence, trinuclear Ni(ii)-complexes have been isolated, for which the influence of the anion as well as co-ligand in the supramolecular arrangement of the triad Ni(ii) core has been investigated. In addition, the re-organization of the trinuclear Ni(ii) complexes in presence of outer metal-salts led to self-assembled pentanuclear nickel(ii) complexes. All these complexes are characterized by antiferromagnetic interaction between the diazine-bridged Ni(ii) centers. The ”complex-as-ligand” strategy has yielded trinuclear CuII 2 CoII complexes and 1-D chain compounds based on d-f topology on going from oximate-copper precursor to compartmental salen-type-based Cu(ii) complex. The trinuclear CuII 2 CoII has a ferrimagnet-like behavior, whereas the Cu-Ln (Ln-lanthanide ion) coordination polymers show an antiferromagnetic interaction between constituting aramagnetic centers for lanthanide(iii) ions with less than half-fulfilled forbitals and ferromagnetic interaction when lanthanide ions with f>7 electronic configuration have been used. In addition, a less polydentate organic-bridge, i.e. salicylic acid has led to oligo-trinuclear Cu2Ln (Ln-lanthanide ion) complexes, but only for lanthanide ions comprising lanthanum to gadolinium ions.