Polymorphic Alternating HNN−Cobalt(II) Chains Both Behaving as Single-Chain Magnets (HNN = 4,4,5,5-Tetramethylimidazolin-1-oxyl 3-Oxide)

Metal-radical alternating chains [Co(hfac)2HNN]n crystallized in two morphs containing repeating all-cis (alpha) and cis,cis,trans (beta) configurations with respect to the O(HNN)-Co-O(HNN) geometry (HNN = 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide). Both phases showed magnetization jumps with hysteresis at 2 K. The alpha phase has a relatively high activation energy of magnetization reorientation (193 K).