Syntheses, structures, and magnetic properties of the lanthanide complexes of imidazole-substituted nitronyl nitroxide biradicals

Two new bis-bidentate imidazole-substituted nitronyl nitroxide biradicals, BNITIm-C2 (BNITIm-C2 = 1,1'-(1,2-ethanediyl)bis(1H-imidazole-2-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide)) and BNITIm-C4 (BNITIm-C4 = 1,1'-(1,4-butanediyl)bis(1H-imidazole-2-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide)), and two series of lanthanide complexes, namely [(BNITIm-C2)Ln(NO₃)₃](MeOH) (Ln = Gd (1Gd) and Tb (2Tb)), (BNITIm-C2)Dy(NO₃)₃ (3Dy) and (BNITIm-C4)[Ln(hfac)₃]₂(C₇H₈)₂ (Ln = Gd (4Gd), Tb (5Tb) and Dy (6Dy), hfac = hexafluoroacetylacetonate), have been prepared and characterized structurally and magnetically. Single crystal X-ray crystallographic analyses revealed that complexes 1Gd-3Dy exhibit 1D chain structures where the Ln(NO₃)₃ units are bridged by the BNITIm-C2 bis-bidentate biradical, while complexes 4Gd-6Dy exhibit binuclear structures with two Ln(hfac)₃ units bridged by the BNITIm-C4 biradical. The bulky hfac anions prohibit the further coordination of Ln^III to another NIT ligand and the formation of a similar 1D chain structure. Due to the very long intra- and intermolecular distances of the spin centers, complexes 1Gd-3Dy can be magnetically regarded as an isolated 2p-4f-2p tri-spin system while complex 4Gd-6Dy can be regarded as an isolated 2p-4f bi-spin system. Magnetic analyses on the two Gd^III compounds revealed the ferromagnetic Gd^III-NIT interactions and antiferromagnetic NIT-NIT interactions through the Gd^III ion in 1Gd. Alternating-current (ac) magnetic susceptibility investigations revealed that complex 5Tb exhibits the typical SMM behavior under a zero dc field while complex 6Dy was proved to be a field-induced SMM. Ab initio calculations were performed on complexes 2Tb and 5Tb to understand their magnetic anisotropy together with their different magnetic dynamics.

Crystal growth, optical, thermal and piezoelectric properties of HoCa4O(BO3)3 crystal

High-quality crystals of HoCa4O(BO3)3 were grown by the Czochralski method. The optical, thermal and piezoelectric properties were investigated.

Structures and Spectral and Magnetic Properties of a Series of Carbacylamidophosphate Pentanuclear Lanthanide(III) Hydroxo Complexes

A series of pentanuclear lanthanide complexes Ln₅L₆(μ-L)₄(μ₃-OH)₄(μ₄-OH) (Ln^III = Nd, Dy, Ho, Er, Yb; L^- = dimethyl N-benzoylamidophosphate ion, [C₆H₅C(O)-N-P(O)(OCH₃)₂]^-) was obtained by the reaction of sodium dimethyl N-benzoylamidophosphate with the corresponding lanthanide nitrates. The pentanuclear cores formed as a result of self-arrangement and their composition did not depend on the lanthanide ion. The complexes and sodium dimethyl N-benzoylamidophosphate have been characterized by single-crystal X-ray diffraction. The absorption spectra of the complexes were measured at 300 and 4 K. The dysprosium and ytterbium complexes exhibited weak emission in the visible and IR regions, respectively. Temperature dependences of magnetic susceptibility (χ_M) of the dysprosium, holmium, and erbium compounds were studied. It was found that χ_M vs T dependences were governed by the crystal field splitting effects with the Δ parameter being in the range 5-17 cm^-1. Slow magnetic relaxation was found for the dysprosium complex by ac magnetic measurements, while no significant out-of-phase signals were detected for holmium and erbium complexes.

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)₃Cu(hfac)₂(bisNITPhPyrim)] (Ln^III = Gd 1, Tb 2, and Dy 3; hfac = hexafluoroacetylacetonate) have been achieved. In these complexes, the Cu^II ions are linked by N atoms of pyrimidine rings of bisNITPhPyrim radicals to form a one-dimensional chain structure, whereas each Ln^III 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^III ion and coordinated NO groups, and between the pyrimidine-bridged copper(ii) spins, which are quantified by a magnetic model, giving J₁ = 4.20 cm^-1 and J₃ = 0.50 cm^-1 (J₁ and J₃ are magnetic exchanges for Gd^III-ON and Cu^II-Cu^II, respectively). Interestingly, ac magnetic measurements show that complex 3 exhibits slow relaxation of the magnetization.

Synthesis of a series of hetero-multi-spin Ln2Cu3 complexes based on a methyl-pyrazole nitronyl nitroxide radical with slow magnetic relaxation behaviors

Multinuclear hetero-tri-spin complexes based on a methyl-pyrazole nitronyl nitroxide radical, namely, [Ln2Cu3(hfac)12(4-NIT-MePyz)4] (Ln = Gd(1), Tb(2), Dy(3); hfac = hexafluoroacetylacetone; 4-NIT-MePyz = 2-{4-(1-methyl)-pyrazolyl}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) have been successfully obtained through a one-pot reaction of the radical ligand (4-NIT-MePyz) with Cu(hfac)2 and Ln(hfac)3. These 2p-3d-4f complexes exhibit five-nuclear structures with the sequence [Cu-Rad-Ln-Rad-Cu-Rad-Ln-Rad-Cu], in which each 4-NIT-MePyz radical acting as a bidentate bridging ligand is coordinated to one Ln(hfac)3 unit through one oxygen atom of the NO groups and to one Cu(hfac)2 unit with one nitrogen atom from the pyrazole ring. For complex 1, based on the spin Hamiltonian calculations and MAGPACK program, it is concluded that there exist ferromagnetic couplings between GdIII and NIT radicals, as well as between CuII and free radicals with J1 = 6.8(1) and J3 = 1.3(2) cm-1, respectively, and antiferromagnetic interactions between radical and radical with J2 = -2.8(5) cm-1. Complex 2 shows frequency-dependent out-of-phase signals under a zero or 2000 Oe dc field indicating single-molecule magnetic behavior.

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. The magnetic behavior of the two compounds results from concomitant ferro- and antiferromagnetic interactions between the spin carriers and the spin-orbit effect from Co(ii) as revealed by modeling performed for the Gd(iii) derivative.

A family of multi-spin rare-earth complexes based on a triazole nitronyl nitroxide radical: synthesis, structure and magnetic properties

The combination of Ln^III ions (Gd^III, Tb^III or Dy^III) and a triazole nitronyl nitroxide radical (4-Me-3-NITtrz) as spin carriers results in two mononuclear and one binuclear compounds, namely, [Ln(hfac)₃(4-Me-3-NITtrz)(H₂O)] (Ln = Gd(1), Tb(2); hfac = hexafluoroacetylacetone; 4-Me-3-NITtrz = 2-[3-(4-methyl-l,2,4-triazolyl)]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and [Dy(hfac)₂(4-Me-3-NITtrz)₂][Dy(hfac)₄]·CHCl₃. Compounds 1 and 2 are isostructural and crystallize in the P1̄ space group, whereas compound 3 crystallizes in the P2₁/n space group. In 1 and 2, the central Ln^III ions are nine-coordinated (LnNO₈) in a distorted spherical capped square antiprism geometry (C_4v) finished by three bischelate hfac anions and one bidentate triazole radical and one aqua molecule. While 3 is a mixed-coordinated binuclear compound with Dy1 in a triangular dodecahedron (D_2d) coordination sphere and Dy2 in a biaugmented trigonal prism (C_2v) coordination sphere. Magnetic studies show that compound 2 exhibits field-induced single-molecule magnet (SMM) behavior.

Three Ln^III–triazole–radical complexes have been synthesized, which exhibit interesting magnetic properties. The Tb^III complex shows frequency-dependent ac magnetic susceptibilities, which suggests the presence of slow magnetic relaxation.

Syntheses, structures and magnetic properties of the lanthanide complexes of the pyrimidyl-substituted nitronyl nitroxide radical

Four 2p-4f Ln^III-radical complexes, [(NIT-2-Pm)Ln(hfac)₃]·0.5C₇H₁₆ (NIT-2-Pm = 2-pyrimidyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide, hfac = hexafluoroacetylacetonato, Ln = Tb (1), Dy (2), Ho (3) and Er (4)), and four 4f-2p-4f Ln^III-radical-Ln^III complexes, [(μ-NIT-2-Pm)Ln₂(hfac)₆(H₂O)₂]·0.5C₇H₁₆ (Ln = Tb (5), Dy (6), Ho (7) and Er (8)) have been synthesized and characterized structurally and magnetically. These compounds can be selectively obtained by controlling the reaction ratio of Ln(hfac)₃·2H₂O to the radical ligand NIT-2-Pm. The crystal structures show that in the former four complexes 1-4, the NIT-2-Pm radical acts as a terminal bidentate ligand chelating to one Ln^III ion, while in 5-8, the NIT-2-Pm acts as a bridging ligand linking two Ln^III ions to form a binuclear three-spin system. Magnetic studies revealed that complexes 1-4 and 6 show frequency-dependent ac magnetic susceptibilities, suggesting a possible single-molecule magnet behavior. To the best of our knowledge, complexes 3 and 4 are the first Ho-NIT and Er-NIT compounds showing slow magnetic relaxation. Compounds 5-8 represent a rare family of compounds showing the NIT bridged 4f-2p-4f three-spin motif, while complex 6 is a rare NIT bridged multinuclear lanthanide compound possessing SMM-like behaviour. Ab initio calculations were performed on all these complexes. The fitting of the magnetic susceptibilities of these compounds suggests weak antiferromagnetic coupling between the Ln^III and NIT radical in 1-8 and weak ferromagnetic Ln^III-Ln^III interactions in 5-8.

Single-molecule magnet behavior in a mononuclear dysprosium(iii) complex with 1-methylimidazole

Using 1-methylimidazole ligand and Dy(hfac)₃·2H₂O salt achieved a new single-molecule magnet of [Dy(hfac)₃·(1-MeIm)₂] with an energy barrier of 42.54 K.

Functionalized nitronyl nitroxide biradical bridged one-dimensional lanthanide chains: slow magnetic relaxation in the Tb and Dy analogues

The first examples of Ln-nitronyl nitroxide 1D chains based on the functionalized nitronyl nitroxide biradical have been obtained, and complexes Dy and Tb exhibit slow magnetic relaxation behavior.

Modulating spin dynamics of binuclear LnIII–radical complexes by using different indazole radicals

Four Ln^III–indazole–radical complexes have been synthesized. By changing the location of the radical in the indazole ring, they exhibit interesting magnetic properties.

Modulating spin dynamics of LnIII-radical complexes by using different coligands

Six Ln^III-triazole-radical complexes have been synthesized by using different β-diketonate coligand. They exhibit interesting magnetic properties. 3 and 5 show magnetic slow relaxation resembling SMM behavior.

Three new mononuclear tri-spin lanthanide-nitronyl nitroxide radical compounds: syntheses, structures and magnetic properties

Based on the nitronyl nitroxide radical, 2-(4-(methoxycarbonyl)phenyl)-4,4,5,5-tetramethylimidazolin-1-oxyl-3-oxide (1, NITPhCOOMe), and three mononuclear tri-spin compounds [Ln(hfac)3(NITPhCOOMe)2] (Ln = Gd (2), Tb (3), Dy (4); hfac = hexafluoroacetylacetonate) are successfully synthesized and fully characterized. Compounds 2 and 4 are isostructural and crystallize in the C2/c space group, while compound 3 crystallizes in the P2₁/c space group. For compounds 2-4, the central metal ions are all eight-coordinate in distorted triangular dodecahedral LnO8 coordination geometry (D(2d) symmetry) completed by three bischelate hfac(-) ligands and two monodentate radicals. Magnetic studies show that radical 1 undertakes the transition from the paramagnetic state to 3D antiferromagnetic ordering at 4.2 K. In addition, compound 3 exhibits field-induced single-molecule magnet (SMM) behavior.

A series of heterospin complexes based on lanthanides and pyridine biradicals: synthesis, structure and magnetic properties

Six Ln^III-biradical tri-spin complexes have been synthesized, and they exhibit interesting magnetic properties.

A family of rare earth complexes with chelating furan biradicals: syntheses, structures and magnetic properties

Six Ln^III–furan-biradical tri-spin complexes have been synthesized, they exhibit interesting magnetic properties. Dy^IIIcomplex shows frequency-dependent ac magnetic susceptibilities, which suggests the presence of slow magnetic relaxation.

A new D2d-symmetry DyIII mononuclear single-molecule magnet containing a monodentate N-heterocyclic donor ligand

By adopting pyrazole to the system of Ln(hfac)₃·2H₂O with the strong electron-withdrawing effect, a D_2d-symmetry Dy^III mononuclear single-molecule magnet containing a monodentate N-heterocyclic ligand was designed and synthesized.