Dipyridyl-Decorated Nitronyl Nitroxide-DyIII Single-Molecule Magnet with a Record Energy Barrier of 146 K.

A nitronyl nitroxide biradical with a capping N-donor group was discovered to improve single-molecule-magnet behavior of the Dy-biradical cluster, generating a magnetic reversal barrier of 146 K. As far as we know, the effective energy barrier of the Dy compound is largest in the nitronyl nitroxide 4f system by far.

Designing Multicoordinating Nitronyl Nitroxide Radical Toward Multinuclear Lanthanide Aggregates.

Profiting from a multicoordinating nitronyl nitroxide radical, i.e. a functionalized nitronyl nitroxide biradical ligand, a family of novel tetranuclear lanthanide complexes, formulated as [RE4(hfac)12(NITPhO-3Pybis)2] (RE = Gd 1, Tb 2, Dy 3, Ho 4, and Y 5; NITPhO-3Pybis = 5-(3-pyridinyloxy)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene; hfac = hexafluoroacetylacetonate) were successfully constructed and characterized. In these complexes, the designed functionalized nitronyl nitroxide biradical ligand functions as the chelating and/or bridging ligand to bind the lanthanide ions, resulting in tetranuclear octa-spin lanthanide complexes with a circle-shaped arrangement. Direct-current magnetic data show that antiferromagnetic interaction dominates in the Gd derivative, while ferromagnetic coupling plays a leading role in complex Y, in which the relevant magnetic exchange parameters were obtained through applicable magnetic models. Dynamic magnetic studies of Tb and Dy analogues exhibit apparent frequency-dependent out-of-phase signals, which are typical features for slow magnetic relaxation behavior. The values of Ueff and τ0 were obtained as follows: Ueff = 10.5 K and τ0 = 6.6 × 10-7 s for the Tb complex and Ueff = 5.2 K and τ0 = 2.5 × 10-6 s for the Dy compound. Intriguingly, the butterfly shaped hysteresis loop is found for the Tb analogue. Guided by fluorescence spectra, the representative peaks are identified for the Tb derivative.

Functionalized Nitronyl Nitroxide Biradicals for the Construction of 3d-4f Heterometallic Compounds.

Functionalized nitronyl nitroxide biradical ligands incorporating pyridine groups hold CoII and LnIII ions together, creating biradical-based 3d-4f tetranuclear complexes [Ln2Co2(hfac)10(NITPhPybis)2] [LnIII = Gd (1), Tb (2), Dy (3), and Ho (4); NITPhPybis = 5-(4-pyridyl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1 H-imidazol-2-yl)benzene; hfac = hexafluoroacetylacetonate]. These complexes have a centrosymmetric cyclic molecular structure in which two biradicals perform as tetradentate ligands to bind two CoII and two LnIII ions, resulting in a rare octaspin system. Direct-current (dc) magnetic susceptibility studies reveal that the strong antiferromagnetic CoII-NO magnetic exchange dominates the present magnetic system, while magnetic coupling of Gd-ON is ferromagnetic. Analysis of the magnetic data of the Gd complex allows us to determine the magnetic parameters through the appropriate magnetic model. Alternating-current (ac) magnetic susceptibility investigations indicate that 2 displays frequency-dependent out-of-phase signals under a zero dc field, while ac magnetic susceptibilities of 3 show field-induced frequency dependence, which is a typical feature of slow relaxation of the magnetization. Complexes 1-4 represent the first nitronyl nitroxide biradical-based 3d-4f compounds.

Lanthanide-radical single-molecule magnets: current status and future challenges.

In the field of molecular magnetism, the lanthanide-radical (Ln-Rad) method has become one of the most appealing tactics for introducing strong magnetic interactions and has spurred on the booming development of heterospin single-molecule magnets (SMMs). The article is a timely retrospect on the research progress of Ln-Rad heterospin systems and special attention is invested on low dimensional Ln-Rad compounds with SMM behavior, primarily concerning with nitrogen-based radicals, semiquinone and nitroxide radicals. Rational design, molecular structures, magnetic behaviors and magneto-structural correlations are highlighted. Meanwhile, particular attention is focused on the influence of exchange couplings on the dynamic magnetic properties, with the purpose of helping to guide the design of prospective radical-based Ln-SMMs.

Multifunctional properties of {CuLn} systems involving nitrogen-rich nitronyl nitroxide: single-molecule magnet behavior, luminescence, magnetocaloric effects and heat capacity.

A series of nitrogen-rich nitronyl nitroxide radical PPNIT (1)-based (PPNIT = 2-(1-(pyrazin-2-yl)-1H-pyrazole)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide) 3d-4f ring-shaped tetranuclear clusters [Ln2Cu2(hfac)10(PPNIT)2(H2O)2]·CHCl3 (LnIII = Gd 2, Tb 3, Dy 4; hfac = hexafiuoroacetylacetonate) with multifunctional properties were isolated. The magnetic behavior, luminescence and heat capacity of the 3d-4f complexes were investigated, displaying interesting multiple properties of the molecular materials. The Gd derivative shows a magnetocaloric effect with the maximum entropy change (-ΔSm) of 15.3 J kg-1 K-1 at 2 K for ΔH = 70 kOe. The Tb cluster exhibits spin glass behavior and the characteristic fluorescence emission of the TbIII ion, while the Dy cluster exhibits SMM behaviour, and the heat capacity has been investigated. Notably, in nitronyl nitroxide radical-metal systems, the investigation of diverse properties is still scarce so far. This work can pave the way towards the synthesis of multifunctional materials that combine SMM behavior, and optical or/and thermodynamic properties.

Improved single-chain-magnet behavior in a biradical-based nitronyl nitroxide-Cu-Dy chain.

A biradical with ferromagnetic intramolecular interaction was found to improve the SCM behavior of a nitronyl nitroxide-Cu-Dy chain, resulting in an energy barrier for magnetization reversal of 40 K.

Structural and Magnetic Properties of 2p-3d-4f Hetero-Tri-Spin Chains Comprising [{Cu(hfac)2 -Radical}2 ] Dimers and Ln(hfac)3 (hfac=hexafluoroacetylacetonate).

A new family of 2p-3d-4f hetero-tri-spin complexes [Ln(hfac)3 {Cu(hfac)2 (NIT-3 PyPh)}2 ] (Ln=Gd (1), Tb (2), Dy (3), Ho (4); NIT-3 PyPh=2-[4-(3-pyridinylmethoxy)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac=hexafluoroacetylacetonate) have been synthesized. Four complexes possess a 1D chain structure in which two radical ligands join two Cu(hfac)2 molecules to form a [{Cu(hfac)2 -rad)}2 ] dimer cycle and the dimer rings are linked by Ln(hfac)3 units. Magnetic studies show that ferromagnetic exchange couplings exist between the coordinated NO groups of radical ligands and metal ions. Field-induced slow relaxation of the magnetization was observed in the Tb and Dy compounds.