Zero-Field SMM Behavior Triggered by Magnetic Exchange Interactions and a Collinear Arrangement of Local Anisotropy Axes in a Linear Co Complex.

A new linear trinuclear Co(II) complex with a formula of [{Co(μ-L)}Co] has been prepared by self-assembly of Co(II) ions and the NO-tripodal Schiff base ligand HL, which is obtained from the condensation of 1,1,1-tris(aminomethyl)ethane and salicylaldehyde. Single X-ray diffraction shows that this compound is centrosymmetric with triple-phenolate bridging groups connecting neighboring Co(II) ions, leading to a paddle-wheel-like structure with a pseudo- axis lying in the Co-Co-Co direction. The Co(II) ions at both ends of the Co(II) molecule exhibit distorted trigonal prismatic CoNO geometry, whereas the Co(II) at the middle presents an elongated trigonal antiprismatic CoO geometry.

Pushing up the easy-axis magnetic anisotropy and relaxation times in trigonal prismatic Co mononuclear SMMs by molecular structure design.

The replacement of pyridine by 1-methyl-imidazol in the arms of a N-tripodal ligand allows preparing two new Co complexes with quasi-ideal triangular prismatic geometry, which behave as SIMs (Single Ion Magnets) at zero dc field with enhanced axial magnetic anisotropy, magnetic relaxation times and magnetic hysteresis.