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-1H-imidazole-3-oxide-1-oxyl (PyrNN) with [Co(hfac)2(H2O)2] (hfac = hexafluoroacetylacetonate) in n-heptane solvent (hep) with a small amount of bromoform (CHBr3 = bf) gives the 1D ferrimagnetic complex [Co(hfac)2PyrNN]n·0.5bf·0.5hep (Co-PyrNN·bf). 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 Δτ/kB = (365 ± 24) K. The compound is an isomorphous variant of a previously reported ambient unstable chain made by using chloroform (CHCl3 = cf), [Co(hfac)2PyrNN]n·0.5cf·0.5hep (Co-PyrNN·cf). This shows that the variation of a magnetically inactive lattice solvent can improve the stability of analogous, void space containing single-chain magnets.