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 H -imidazole-3-oxide-1-oxyl (PyrNN) with [Co(hfac) 2 (H 2 O) 2 ] (hfac = hexafluoroacetylacetonate) in n- heptane solvent ( hep ) with a small amount of bromoform (CHBr 3 = bf ) gives the 1D ferrimagnetic complex [Co(hfac) 2 PyrNN] n ·0.5 bf ·0.5 hep ( 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 Δ τ / k B = (365 ± 24) K. The compound is an isomorphous variant of a previously reported ambient unstable chain made by using chloroform (CHCl 3 = cf ), [Co(hfac) 2 PyrNN] n ·0.5 cf ·0.5 hep (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.