Lattice Solvent Engineering Improves the Stability of a Cobalt Pyrenylnitronylnitroxide Ferrimagnetic Chain.

Reaction of 2-(1'-pyrenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1-imidazole-3-oxide-1-oxyl (PyrNN) with [Co(hfac)(HO)] (hfac = hexafluoroacetylacetonate) in heptane solvent () with a small amount of bromoform (CHBr = ) gives the 1D ferrimagnetic complex [Co(hfac)PyrNN]·0.5·0.5 (). This chain exhibits slow magnetic relaxation with magnetic blocking below 13.4 K, presenting a magnetic hysteresis with high coercive field (51 kOe at 5.0 K) as a hard magnet. It also shows frequency-dependent behavior consistent with one dominant relaxation process with an activation barrier of Δ/ = (365 ± 24) K. The compound is an isomorphous variant of a previously reported ambient unstable chain made by using chloroform (CHCl = ), [Co(hfac)PyrNN]·0.5·0.5 (Co-·). This shows that the variation of a magnetically inactive lattice solvent can improve the stability of analogous, void space containing single-chain magnets.