Magnetism of self-assembled mono- and tetranuclear supramolecularNi2+complexes

Abstract

The magnetization of a novel supramolecular grid structure consisting of four bis(bipyridyl)-pyrimidine ligands and four ${\mathrm{Ni}}^{2+}$ ions and that of the mononuclear analogue ${\mathrm{Ni}\left(\mathrm{terpy}\right)\mathrm{}}_2$ was measured. Magnetic anisotropy was determined from investigations of powder as well as of crystal samples. We provide evidence for an intramolecular antiferromagnetic coupling of the four ${\mathrm{Ni}}^{2+}$ spins of the tetranuclear species with $J=-8\mathrm{K}.$ The magnetization of the mononuclear complex is typical for a $S=1\mathrm{}$ spin with zero field splitting. The magnetization of the tetranuclear grid is discussed in terms of the effective spin Hamiltonian appropriate for ${\mathrm{Ni}}^{2+}$ ions including various higher order exchange terms. In particular, significant indications for a biquadratic term of about $J^{\prime }=0.5\mathrm{}\mathrm{K}$ is found.