Single-Molecule Magnet Behavior in a Tb-Nitronyl Nitroxide Radical Network with [Tb(NIT)] Nodes.

Two rare two-dimensional Ln-radical networks, namely, [{Ln(tfa)}(NIT-4Py)] [Ln = Gd and Tb ; tfa = trifluoroacetylacetonato; and NIT-4Py = 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], have been successfully constructed and characterized. In these complexes, each NIT-4Py radical functions as a tridentate ligand to ligate three Ln ions, creating a 2D network with linear five-spin [Ln(NIT)] nodes. Ferromagnetic Ln-NO interactions govern the characteristic magnetic behavior of a finite spin system.

Tuning spin dynamics of binuclear Dy complexes using different nitroxide biradical derivatives.

By employing nitronyl/imino nitroxide biradicals, three Ln-Zn complexes, namely, [LnZn(hfac)(ImPhPyobis)] (Ln = Gd 1, Dy 2; hfac = hexafluoroacetylacetonate; ImPhPyobis = 5-(4-oxypyridinium-1-yl)-1,3-bis(1'-oxyl-4',4',5',5'-tetramethyl-4,5-hydro-1-imidazol-2-yl)benzene) and [DyZn(hfac)(NITPhPyobis)] 3 (NITPhPyobis = 5-(4-oxypyridinium-1-yl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1-imidazol-2-yl)benzene), have been successfully prepared. The three complexes possess {LnO} cores bridged by the oxygen atoms of the 4-oxypyridinium rings of the biradical ligands and one of the imino/nitronyl nitroxide groups of the biradical is coordinated to a Zn ion, then producing a centrosymmetric tetranuclear six-spin structure. The studies of spin dynamics indicate that complexes 2 and 3 exhibit distinct magnetic relaxation behaviors at zero dc field: complex 2 presents single relaxation with an effective energy barrier () of 69.

Magnetic relaxation in unique nitronyl nitroxide biradical-Ln-Cu chains with Ln-bis(NIT)-Cu-bis(NIT)-Ln units.

Utilizing a nitronyl nitroxide biradical NITPhPybis [5-(4-pyridyl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1-imidazol-2-yl)-benzene], a new family of isomorphic 2p-3d-4f chains {[LnCu(hfac)(NITPhPybis)]·CHCl} (hfac: hexafluoroacetylacetonate; Ln: Gd 1; Dy 2; Ho 3; Tb 4) have been successfully produced. In complexes 1-4, the NITPhPybis biradical chelates one Ln ion through its bis(NIT) moiety while the N donor of pyridine and another uncoordinated NO group of the biradical, respectively, bind one Cu ion, yielding a biradical-Ln-Cu 1D zigzag chain with a unique [Ln-bis(NIT)-Cu-bis(NIT)-Ln] structural motif. DC magnetic studies reveal that ferromagnetic exchanges dominate in these Cu-Ln-biradical chains, originating from the ferromagnetic Ln-NO and NO-Cu exchanges.

Cyclic [Cu-biRadical] Secondary Building Unit in 2p-3d and 2p-3d-4f Complexes: Crystal Structure and Magnetic Properties.

Employing the new nitronyl nitroxide biradical ligand biNIT-3Py-5-Ph (2-(5-phenyl-3-pyridyl)-bis(4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide)), a 16-spin Cu-radical complex, [Cu(biNIT-3Py-5-Ph)(hfac)] , and three 2p-3d-4f chain complexes, {[Ln(hfac)][Cu(hfac)](biNIT-3Py-5-Ph)} (Ln= Gd , Tb , Dy ; hfac = hexafluoroacetylacetonate), have been prepared and characterized. X-ray crystallographic analysis revealed in all derivatives a common cyclic [Cu-biNIT] secondary building unit in which two bi-NIT-3Py-5-Ph biradical ligands and two Cu ions are associated via the pyridine N atoms and NO units. For complex , two such units assemble with four additional Cu ions to form a discrete complex involving 16 = 1/2 spin centers.

Enhancing the Magnetization Blocking Energy of Biradical-Metal System by Merging Discrete Complexes into One-Dimensional Chains.

The reaction of nitronyl nitroxide biradical NITPhMeImbis [5-(2-methylimidazole)-1,3-bis(1-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)-benzene] with Ln(hfac)  ⋅ 2H O and Cu(hfac) (hfac=hexafluoroacetylacetonate), led to two series of 2p-3d-4f complexes, namely, nona-spin clusters, [Ln Cu (hfac) (NITPhMeImbis) ] (Ln=Gd 1, Dy 2), or one-dimensional chains [LnCu (hfac) (NITPhMeImbis)] (Ln=Y 3, Dy 4, Tb 5) depending on the temperature of the reaction. All five complexes contain a biradical-Ln unit in which the biradical chelates the Ln ion by the means of one aminoxyl (i. e.

Influence of the Coordinated Transition Metal Ion on Magnetic Relaxation of Lanthanide Based Complexes with Imino Nitroxide Biradical Ligands.

In spite of achievement of a lot of Ln-radical SMMs, how to improve magnetic behavior of Ln-radical system remains challenging. Here, two series of Ln-radical complexes have successfully been built using an imino nitroxide biradical, namely, [Ln (hfac) (ImPhPyobis) ] (Ln =Gd 1, Tb 2, Dy 3) and [Ln Cu (hfac) (ImPhPyobis) ] (Ln =Gd 4, Dy 5; hfac=hexafluoroacetylacetonate and ImPhPyobis=5-(4-oxypyridinium-1-yl)-1,3-bis(1'-oxyl-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene). For these biradical-metal complexes, two imino nitroxide biradicals bind two Ln(III) ions via their oxygen atoms coming from 4-oxypyridinium units to produce a binuclear {Ln O } unit.

Slow magnetic relaxation in a Dy triangle and a bistriangular Dy cluster.

Two lanthanide single-molecule magnets (SMMs) [Dy(μ-OH)(HL-1)(HO)](NO)·3HO (1, HL-1 = ()-3-(((8-hydroxyquinolin-2-yl)methylene)amino)propane-1,2-diol) and [Dy(μ-OH)(HL-2)(HL-2)(L-2)] (2, HL-2 = ()-2-hydroxy-'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide) were synthesized and characterized structurally and magnetically. Complex 1 contains a triangular Dy core in which the three Dy ions share a μ-OH anion and the deprotonated ligands of (HL-1) serve both capping and bridging functions, while 2 displays a centrosymmetric hexanuclear Dy structure with two similar Dy triangular cores ligated by two fully deprotonated (L-2) ligands, each of which shares two μ-OH anions. All the Dy ions are eight-coordinated with quasi or symmetry.

Supramolecular heptanuclear Ln-Cu complexes involving nitronyl nitroxide biradicals: structure and magnetic behavior.

Four novel heptanuclear Ln-Cu complexes with the formula [LnCu(hfac)(NITPhTzbis)][LnCu(hfac)(NITPhTzbis)] (LnCu = YCu 1, TbCu 2, DyCu 3 and HoCu 4; hfac = hexafluoroacetylacetonate) were successfully constructed by employing the triazole functionalized nitronyl nitroxide biradical ligand NITPh-Tzbis (NITPh-Tzbis = 5-(1,2,4-triazolyl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1-imidazol-2-yl)benzene). These hetero-tri-spin complexes are composed of two biradical-bridged dinuclear [(LnCu(hfac)(NITPhTzbis)] units and one trinuclear [LnCu(hfac)(NITPhTzbis)] unit which form a heptanuclear supramolecular structure through π-π interactions. Magnetic susceptibility investigations indicate that ferromagnetic exchange interactions dominate at low temperature for this supramolecular system which can be attributed to the Ln-nitroxide exchange and intramolecular NIT⋯NIT coupling mediated by the -phenylene moiety.

A metal-radical hetero-tri-spin SCM with methyl-pyrazole-nitronyl nitroxide bridges.

The preparation, crystal structures, and magnetic properties of a family of hetero-tri-spin 1-D coordination polymers with the formula [Ln(hfac)Cu(hfac)(4-NIT-MePyz)] (Ln = Gd, 1, Tb, 2, Dy, 3; hfac = hexafluoroacetylacetonate; 4-NIT-MePyz = 2-{4-(1-methyl)-pyrazolyl}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) are reported. In these complexes, the 4-NIT-MePyz radical acts as a linker to bridge the Cu and Ln ions through its pyrazole and aminoxyl groups to form a chain structure. Magnetic properties typical of spin-chains are observed for Dy and Tb derivatives but single-chain magnet (SCM) behavior was evidenced only for the Tb compound which is characterized by an energy gap for demagnetization / of 31 K.

Regulating Spin Dynamics of Nitronyl Nitroxide Biradical Lanthanide Complexes through Introducing Different Transition Metals.

Four biradical-Ln complexes with different transition metal ions, namely [LnM(hfac) (NITPh-PyPzbis)] (M =Mn and Ln =Gd 1, Dy 2; M =Ni and Ln =Tb 3, Dy 4), were prepared by the reaction of Ln(hfac)  ⋅ 2H O, Mn(hfac)  ⋅ 2H O or Ni(hfac)  ⋅ 2H O with NITPh-PyPzbis biradical (hfac=hexafluoroacetylacetonate, NITPh-PyPzbis=5-(3-(2-pyridinyl)-1H-pyrazol-1-yl)-1,3-bis(1'-oxyl-3'-oxido- 4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene). In complexes 1-4, the NITPh-PyPzbis biradical chelates one Ln ion by means of its aminoxyl moieties and the transition metal ion is introduced through the two N donors from the pyridyl pyrazolyl moiety. Magnetic investigations indicate that complex 4 displays visible maxima in frequency/temperature-dependent χ'' signals with two-step relaxation processes, but complex 2 exhibits no slow magnetization relaxation.

Modulating the magnetization dynamics in Ln-Cu-Rad hetero-tri-spin complexes through / coordination of nitronyl nitroxide radicals around the metal center.

Self-assembling the novel nitronyl nitroxide radical NIT-3Py-5-Ph (2-(5-phenyl-3-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) with Ln(hfac)3·2H2O and Cu(hfac)2 (hfac = hexafluoroacetylacetonate) resulted in two heterometallic complexes with formula [LnCu(hfac)5(NIT-3Py-5-Ph)2] (Ln = Gd 1, Dy 2), in which two NIT-3Py-5-Ph radicals are coordinated with the LnIII ion via their nitroxide units in the cis-arrangement manner and the CuII ion is ligated by the pyridyl N donors of the radicals. Interestingly, when the phenyl group of NIT-3Py-5-Ph was replaced with a p-pyridyl group, a new family of 2D networks, namely, {[Ln(hfac)3][Cu(hfac)2]2(NIT-3Py-5-4Py)2}n (Ln = Gd 3, Tb 4, Dy 5; NIT-3Py-5-4Py = 2-(5-(4-pyridyl)-3-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) was obtained. In the 2D sheet, each NIT-3Py-5-4Py ligand serves as a μ3-bridge to bind one LnIII center by the aminoxyl moiety and two CuII ions through two pyridine groups to form a 2D structure.

Slow relaxation of magnetization in lanthanide-biradical complexes based on a functionalized nitronyl nitroxide biradical.

Three novel lanthanide-biradical complexes {[Ln(hfac)3]2(mbisNITPyPh)(H2O)}{[Ln(hfac)3](mbisNITPyPh)}·CHCl3 (1-Gd; 2-Tb; 3-Dy) were successfully achieved by reacting the biradical mbisNITPyPh (5-(3-pyridyl)-1,3-bis(1-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene) with Ln(hfac)3·2H2O (hfac = hexafluoroacetylacetonate). These Ln-biradical complexes consist of two kinds of spin moieties, namely, dinuclear {[Ln(hfac)3]2(mbisNITPyPh)(H2O)} and mononuclear {[Ln(hfac)3](mbisNITPyPh)}, in which two adjacent dinuclear units are linked by intermolecular hydrogen bonds involving the uncoordinated nitroxide units and the coordinated water molecules of Ln ions, forming a cyclic tetranuclear structure unit. The magnetization study reveals that intramolecular Ln(iii)-coordinated NO ferromagnetic interactions are dominant in the present system.

Slow magnetic relaxation in Co-Ln heterodinuclear complexes achieved through a functionalized nitronyl nitroxide biradical.

A new nitronyl nitroxide biradical ligand NITPh-PyPzbis (5-(3-(2-pyridinyl)-1H-pyrazol-1-yl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene) has been successfully applied for constructing a 3d-4f Co-Ln system, giving rise to a family of novel hetero-tri-spin complexes, namely, [LnCo(hfac)(NITPh-PyPzbis)]·CHCl (LnCo = YCo 1, GdCo 2, TbCo 3, DyCo 4, and HoCo 5; hfac = hexafluoroacetylacetonate). In these hetero-tri-spin complexes, the NITPh-PyPzbis biradical chelates one Ln and one Co simultaneously by means of its adjacent aminoxyl moieties and two N donors from the 3-(2-pyridinyl)-1H-pyrazol-1-yl unit, respectively, realizing the unique biradical-Co-Ln heterodinuclear structure. Direct-current magnetic susceptibility investigations show that antiferromagnetic coupling is predominant in the YCo derivative, while the leading magnetic interaction in the GdCo analogue is ferromagnetic.

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 [RE(hfac)(NITPhO-3Pybis)] (RE = Gd , Tb , Dy , Ho , and Y ; NITPhO-3Pybis = 5-(3-pyridinyloxy)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1-imidazol-2-yl)benzene; hfac = hexafluoroacetylacetonate) were successfully constructed and characterized.

Heterometallic Ln-Cu complexes derived from a phenyl pyrimidyl substituted nitronyl nitroxide biradical.

Utilizing a novel nitronyl nitroxide biradical bisNITPhPyrim involving a pyrimidine group ([5-(5-pyrimidyl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)]benzene), three heterometallic Ln-Cu complexes with formulas [Ln(hfac)Cu(hfac)(bisNITPhPyrim)] (Ln = Gd 1, Tb 2, and Dy 3; hfac = hexafluoroacetylacetonate) have been achieved. In these complexes, the Cu ions are linked by N atoms of pyrimidine rings of bisNITPhPyrim radicals to form a one-dimensional chain structure, whereas each Ln ion is chelated with two neighboring NO groups of two NIT moieties of the radical. Magnetic studies reveal the presence of ferromagnetic interactions between the Gd ion and coordinated NO groups, and between the pyrimidine-bridged copper(ii) spins, which are quantified by a magnetic model, giving J = 4.

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.

Lanthanide-Nitronyl Nitroxide Chains Derived from Multidentate Nitronyl Nitroxides.

Unprecedented lanthanide (Ln)-radical loop-chain coordination polymers were achieved using multidentate pyridyl- or triazole- substituted nitronyl nitroxide ligands. Their magnetic units consist of ferromagnetic [LnRadical] moieties, leading for the dysprosium(III) derivatives to slow relaxation of magnetization, which was found to be dependent on the heterocyclic ligands.

Magnetic relaxation in [Ln(hfac)] anions with [Cu(hfac)-radical] cation chains as counterions.

Using a new nitronyl nitroxide radical Nit-Ph-PyIm, two novel 3d-4f complexes with the formula {[Ln(hfac)4]-[Cu(hfac)(Nit-Ph-PyIm)]+}n (LnIII = Gd 1, Dy 2) have been isolated (Nit-Ph-PyIm = 2-[4-[2-(2-pyridinyl)-1H-imidazol-1-yl]-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate). Interestingly, for both compounds, there are discrete [Ln(hfac)4]- anions while [Cu(hfac)-radical]nn+ chains serve as counter-ions in which the Nit-Ph-PyIm radicals link [Cu(hfac)]+ units through their NO groups and imidazolyl pyridine moieties. The [Cu(hfac)(Nit-Ph-PyIm)]+ unit is diamagnetic owing to the strong antiferromagnetic coupling between the Cu(ii) ion and the equatorially coordinated NO group.

Two-dimensional Co-Ln networks bridged by phenyl pyrimidyl substituted nitronyl nitroxides: structural and magnetic properties.

Two-dimensional hetero-tri-spin 2p-3d-4f coordination polymers involving Co(ii) and Ln(iii) ions assembled with a polydentate paramagnetic nitronyl nitroxide ligand are reported. [Ln(hfac)3{Co(hfac)2}2(NITPhPyrim)2] (LnIII = Gd 1, Tb 2; hfac = hexafluoroacetylacetonate, NITPhPyrim = 2-[4-(5-pyrimidyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) consists of a two-dimensional network in which the NITPhPyrim ligand is coordinated to the metal ions by means of its pyrimidine and aminoxyl (NO) groups. In the layer, the Tb center interacts with two NO groups from two different radical ligands, and each pyrimidine connects two Co(hfac)2 units through its two nitrogen atoms to form one-dimensional Co(ii) arrays.

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

Functionalized nitronyl nitroxide biradical ligands incorporating pyridine groups hold Co and Ln ions together, creating biradical-based 3d-4f tetranuclear complexes [LnCo(hfac)(NITPhPybis)] [Ln = 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 Co and two Ln ions, resulting in a rare octaspin system. Direct-current (dc) magnetic susceptibility studies reveal that the strong antiferromagnetic Co-NO magnetic exchange dominates the present magnetic system, while magnetic coupling of Gd-ON is ferromagnetic.

Slow Magnetic Relaxation in Ladder-Type and Single-Strand 2p-3d-4f Heterotrispin Chains.

Ladder-type and chain 2p-3d-4f complexes based on a bridging nitronyl nitroxide radical, namely, [LnCu(hfac)(NIT-Ph-p-OCHtrz)]·0.5CH [Ln = Y (1a), Dy (1b)] and [LnCu(hfac)(NIT-Ph-p-OCHtrz)] [Ln = Y (2a), Dy (2b); NIT-Ph-p-OCHtrz = 2-[4-[(1H-1,2,4-triazol-1-yl)methoxy]phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate) have been successfully achieved through a one-pot reaction of the NIT-Ph-p-OCHtrz radical with Cu(hfac) and Ln(hfac)·2HO. Complexes 1a and 1b feature a ladder-like structure, where the rails are made of Ln(III) and Cu(II) ions alternatively bridged by nitronyl nitroxide and the triazole units while the NIT-Ph-p-OCHtrz moieties act as the rungs of the ladder.

Unprecedented ferromagnetic Gdnitronyl nitroxide coupling through a hydrogen bonding bridge.

A novel lanthanide(iii)-nitronyl nitroxide chain {[Gd(hfac)(Nit-Ph-3,5-bIm)(HO)]·CHO} (1) was prepared and characterized. Strikingly, an unexpected ferromagnetic coupling between the Gd(iii) ion and the nitroxide group mediated by hydrogen bonding has been observed for the first time.

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.

Thermal Magnetic Hysteresis in a Copper-Gadolinium-Radical Chain Compound.

Magnetic bistability spanning over a temperature domain of 40 K can result from a small structural deformation of the gadolinium aminoxyl coordination. This is illustrated for a nitronyl nitroxide 3d-4f chain, [Ln(hfac)3Cu(hfac)2(NIT-Pyrim)2] (Ln(III) = Gd, Dy), which is the first example of a bistable lanthanide-based complex.