A cobalt(II)-nitronyl nitroxide single chain magnet with record blocking temperature and low coercivity.

Abstract

Two one-dimensional coordination polymers were synthesized: [M(hfac)2(9-PhentNIT)]n, where MII= Mn (1) or Co (2), hfac- is hexafluoroacetylacetonato and 9-PhentNIT is a new stable nitronyl nitroxide organic radical 2-(9-Phenantrenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (9-PhentNIT). These two complexes are isomorphous and crystallized with the metal ions coordinated by two aminoxyl groups, arising from two bridging 9-PhentNIT radical and two hfac- chelating ligands. The asymmetric unit has two independent metal(II) sites, resulting in two crystallographically independent chains. The investigation of the magnetic properties shows that both compounds are 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 TB = 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 of magnetic irreversibility and relaxation of a small portion of long chains up to about 50 K.