A Cobalt Pyrenylnitronylnitroxide Single- Chain Magnet with High Coercivity and Record Blocking Temperature

Coordination of a [Co(hfac)(2)] moiety (hfac=hexafluoroacetylacetonate) with a nitronylnitroxide radical linked to bulky, rigid pyrene (PyrNN) gives a helical 1:1 chain complex, in which both oxygen atoms of the radical NO. groups are bonded to Co-II ions with strong antiferromagnetic exchange. The complex shows single-chain magnet (SCM) behavior with frequency-dependent magnetic susceptibility, field-cooled and zero-field-cooled susceptibility divergence with a high blocking temperature of around 14K (a record among SCMs), and hysteresis with a very large coercivity of 32kOe at 8K. The magnetic behavior is partly related to good chain isolation induced by the large pyrene units. Two magnetic relaxation processes have been observed, a slower one attributable to longer, and a faster one attributable to short chains. No evidence of magnetic ordering has been found.