Theoretical studies on the magnetic bistability of dinickel complex tuned by azide.

The magnetic-structural correlation in magnetic switchable dinickel(II) complex [LNi2(N3)3] (L- is a pyrazolate-based compartmental ligand) has been investigated on the basis of various unrestricted density functional theory (UDFT) combined with the broken symmetry (BS) approach. The calculated exchange coupling constants were in good agreement with experimental result by using the PBE0 method with LANL2DZ basis set. The antiferromagnetic interaction between the Ni(II) ions is mainly due to the large energy difference of the singly occupied molecular orbitals (SOMOs), and the p orbital overlap for nitrogen atoms on azido and the pyrazolate bridge groups. The analysis of the spin density distribution reveals that both the spin polarization and spin delocalization contribute to the antiferromagnetic interaction. Furthermore, the bistable magnetic behavior for this system (strong antiferromagnetic interaction in low-temperature phase and the week antiferromagnetic in high-temperature phase) results from the change of the Ni-NNN-Ni dihedral angle (tau) in mu1,3-N3. The increase of tau is the key role in decreasing the SOMOs energy difference and weakening the antiferromagnetic interaction. Therefore, the abrupt modulation of the magnitude of M-NNN-M dihedral angle tau in the binuclear-azide complex by external perturbations provides new possibilities for the design of molecular magnetic switching devices.