A cobalt(ii)-nitronyl nitroxide single chain magnet with a record high blocking temperature and low coercivity

Abstract

Two one-dimensional coordination polymers were synthesized: [M(hfac)₂(9-PhentNIT)]_n, where M = Mn (1) or Co (2), hfac⁻ is hexafluoroacetylacetonato and 9-PhentNIT is a new stable nitronyl nitroxide organic radical, 2-(9-phenanthrenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. These two complexes are isomorphous and crystallized with metal ions coordinated by two aminoxyl groups, arising from two bridging 9-PhentNIT radicals and two hfac⁻ chelating ligands. The asymmetric unit has two independent metal(II) sites, resulting in two crystallographically independent chains. The investigation of their magnetic properties shows that both compounds form ferrimagnetic chains with strong antiferromagnetic coupling between S = 5/2 or 3/2 and 1/2 spin carriers. The anisotropic compound 2 shows the highest blocking temperature T_B = 15.5 K reported so far for a single chain magnet (SCM) and exhibits magnetic hysteresis with low coercivity up to 22 K. In addition, we found evidence for magnetic irreversibility and relaxation of a small portion of long chains up to about 50 K.