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.

End-off bicompartmental ligands bearing a nitronyl-nitroxide arm have been designed for synthesizing various heterospin molecular systems. These ligands can selectively interact with 3d and 4f metal ions, leading to 2p-4f, 2p-3d, and 2p-3d-4f complexes. The magnetic properties of the 2p-4f and 2p-3d-4f complexes have been investigated and rationalized by theoretical calculations.

Two isostructural 1D complexes, [M(hfac)2NaphNN]n [M = Mn(II) (1) or Co(II) (2); NaphNN = 1-naphthyl nitronylnitroxide], were synthesized and exhibit very strong antiferromagnetic metal-radical exchange coupling. Compound 2 shows slow magnetic relaxation behavior with a high blocking temperature (TB ≈ 13.2 K) and a very high coercive field of 49 kOe at 4.0 K.

Coordination compounds containing three different spin carriers (2p, 3d, and 4f), with the general formula [M II Dy III (LH)-(hfac) 5 ] (M = Co, Ni, Mn, Zn), have been obtained using Mannich ligands decorated with a nitronyl−nitroxide fragment. The synthetic approach is general and leads to binuclear 3d−4f complexes, the two metal ions being bridged by one aminoxyl group and by one oxygen atom arising from a hfac − ligand. Triangular spin topology affords significant 2p−3d, 3d−4f, and 2p−4f exchange interactions. For the [Co II Dy III Rad] derivative obtained using a nitronyl−nitroxide chiral ligand, a high energy barrier (∼200 cm −1 ) and a slow relaxation behavior below 30 K were found and rationalized by ab initio calculations. The improvement of magnetic properties comes from the synergy of optimal single ions properties and exchange couplings contributions where the Co II −Rad interaction becomes the leading one. The role played by this interaction is clearly proved by the investigation of the magnetic properties of the [Zn II Dy III Rad] derivative, with a much lower energy barrier (12.7 cm −1 ) and by the lack of SMM behavior of the previously reported [Co II Dy III Rad] compound (Chem. Commun. 2017, 53, 6504), with a linear topology of spin carriers and a negligible Co II −Rad interaction.