MAGNETISM OF SELF-ASSEMBLED MONONUCLEAR AND TETRANUCLEAR SUPRAMOLECULAR NI2+ COMPLEXES

The magnetization of a novel supramolecular grid structure consisting of four bis(bipyridyl)-pyrimidine ligands and four Ni2+ ions and that of the mononuclear analogue Ni(terpy)(2) was measured. Magnetic anisot ropy was determined from investigations of powder as well as of crysta l samples. We provide evidence for an intramolecular antiferromagnetic coupling of the four Ni2+ spins of the tetranuclear species with J= - 8 K. The magnetization of the mononuclear complex is typical for a S=1 spin with zero field splitting. The magnetization of the tetranuclear grid is discussed in terms of the effective spin Hamiltonian appropri ate for Ni2+ ions including various higher order exchange terms. In pa rticular, significant indications for a biquadratic term of about J' = 0.5 K is found.