title: A cobalt pyrenylnitronylnitroxide single-chain magnet with high coercivity and record blocking temperature.
abstract: 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 14 K (a record among SCMs), and hysteresis with a very large coercivity of 32 kOe at 8 K. 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.
authors.affiliation: Instituto de Química, Universidade Federal Fluminense, Rio de Janeiro 24020-150 (Brazil). mariavaz@vm.uff.br.
authors.forename: Maria G F
authors.initials: MG
authors.lastname: Vaz
authors.forename: Rafael A Allão
authors.initials: RA
authors.lastname: Cassaro
authors.forename: Handan
authors.initials: H
authors.lastname: Akpinar
authors.forename: John A
authors.initials: JA
authors.lastname: Schlueter
authors.forename: Paul M
authors.initials: PM
authors.lastname: Lahti
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Novak
keywords: cobalt; hysteresis; magnetic properties; radicals; single-chain magnets