Search Results (45)

Given the outstanding magnetic characteristics of lanthanide ions, the development of mononuclear or multinuclear lanthanide complexes becomes imperative. Previous research showed that a series of mononuclear Dy(III) complexes of rhodamine benzoyl hydrazone Schiff base ligands exhibit remarkable single-molecule magnetic properties and fluorescence. In this study, we used analogous ligands to synthesize lanthanide complexes [Dy(HL¹-o)(NO₃)₂(CH₃OH)₂]NO₃·CH₃OH (complex 1·MeOH) and tetranuclear complexes [Ln₄(L¹-c)₂(L²)₂(μ₃-OH)₂(NO₃)₂(CH₃OH)₄](NO₃)₂·2CH₃CN·5CH₃OH·2H₂O (Ln = Dy, complex 2; Ln = Gd, complex 3). Magnetic susceptibility measurements show that 1·2H₂O is a single-molecule magnet, 2 shows slow magnetic relaxation and 3 is a magnetic cooling material with the magnetic entropy change of 9.81 J kg⁻¹ K⁻¹ at 2 K and 5 T. The theoretical calculations on 1·MeOH indicate that it shows good magnetic anisotropy with the calculated energy barrier of 194.6 cm⁻¹. Full article

Two hydrazone Schiff base-bridging ligands with different heterocycles {2-[(E)-(5-chloro-2-hydroxyphenyl)methylidene]diazanyl}(pyrazine-2-yl)methanone (H₂L_Schiff-1) and (E)-N′-(2-hydroxy-3-methoxybenzylidene)nicotinohydrazide (H₂L_Schiff-2) together with 1,3-di(2-pyridyl)-1,3-propanedione (Hdpp) were chosen to construct two new Dy₂ complexes, [Dy₂(L_Schiff-1)₂(DMF)₂(dpp)₂]·0.5DMF (1) and [Dy₂(L_Schiff-2)₂(DMF)₂(dpp)₂]·2DMF (2). Although the [N₂O₆] coordination spheres are observed for the Dy³⁺ ions in 1 and 2, their coordination configurations have some differences (both the biaugmented trigonal prism and the Snub diphenoid J84 in 1 and only the biaugmented trigonal prism in 2). Magnetic research revealed that both 1 and 2 possess ferromagnetic interactions between two Dy³⁺ ions and perform as zero-field single-molecule magnets, with U_eff/k values of 49.7 K at 0 Oe for 1 and 151.8 K at 0 Oe for 2. This work suggests that the heterocycle groups (pyrazine vs. pyridine) on the hydrazone Schiff base-bridging ligands have effects on the SMM properties of 1 and 2. Full article

Two organic–inorganic materials (TMAA)₂[CoCl₄] (1) and (TMAA)₂[MnCl₄] (2) (TMAA = N,N,N-trimethyl-1-adamantylammonium hydroxide) were synthesized and characterized. It was found that both compounds exhibit first-order structural phase transition at high-temperature regions. As the temperature approaches the phase transition point, significant abnormal changes were observed in the dielectric properties and χ_MT values of compounds 1 and 2. This phenomenon strongly highlights the dielectric bistable and spin bistable properties of compounds 1 and 2. Further research shows that the dielectric constants of the compounds undergo significant changes upon the application of an external magnetic field, providing strong evidence for the existence of magnetic–dielectric coupling effects within compounds 1 and 2. Full article

Organometallic rare-earth complexes have attracted considerable attention in recent years due to their unique structures and exceptional magnetic properties. In this study, we report the synthesis and magnetic characteristics of a family of monopentamethylcyclopentadienyl-coordinated trinuclear rare-earth hepta-chloride clusters [(Li(THF)(Et₂O))(Cp^*RE)₃(μ-Cl)₄(μ₃-Cl)₂(μ₄-Cl)] (RE₃: RE =Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Cp* = pentamethylcyclopentadienide). These clusters were synthesized by reacting LiCp* with RECl₃ in a 1:1 molar ratio within a mixed solvent system (THF: Et₂O = 1:9), resulting in high solubility in common organic solvents such as DCM, THF, and Et₂O. Magnetic studies conducted on these paramagnetic clusters reveal the coexistence of ferromagnetic and antiferromagnetic superexchange interactions in Gd₃. Additionally, Dy₃ exhibits both ferromagnetic and antiferromagnetic intramolecular dipolar interactions. Notably, slow magnetic relaxation was observed in Dy₃ below 23 K under a zero DC applied field with an energy barrier of 125(6) cm⁻¹. Full article

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 Dy(hfac)₃ and La(hfac)₃ (hfac = hexafluoroacetylacetonate) afforded a heterolanthanide complex [Dy_0.56La_1.44(hfac)₇(NITPhMeImbisH)] (1). In this complex, the biradical NITPhMeImbis ligand chelates one Ln(III) ion via its two neighboring NO units and simultaneously binds the La(III) ion through another NO group to form a dinuclear structure. Direct current (dc) magnetic measurement shows the dominant ferromagnetic couplings in Complex 1. Spin dynamics studies exhibit visible frequency-dependent peaks of χ″ signals under a dc field evidenced by field-induced magnetic relaxation behavior, which is a combination of Orbach and QTM processes, giving the U_eff, τ₀ and τ_QTM values of 15.14 K, 3.04 × 10⁻⁷ s and 3.61 × 10⁻⁴ s, respectively. Full article

The organic–inorganic hybrid (BEDT-TTF)₃[Cu₂(μ-C₂O₄)₃·CH₃CH₂OH·1.2H₂O] (I) was obtained using the electrocrystallization method. It comprises a θ²¹-phase organic donor layer and a two-dimensional inorganic antiferromagnetic honeycomb lattice. Cu(II) is octahedrally coordinated by three bisbidenetate oxalates, exhibiting Jahn–Teller distortion. CH₃CH₂OH and H₂O molecules are located within the cavities of the honeycomb lattice. The total formal charge of the three donor molecules was assigned to be +2 based on the bond lengths in the TTF core, which corresponded to the Raman spectra. It is a semiconductor with σ_rt = 0.04 S/cm and E_α = 40 meV. No long-range ordering was observed above 2 K from zero-field cooling/field cooling magnetization, as confirmed by specific heat measurements. The spin frustration with f > 10 from the antiferromagnetic copper-oxalate-framework was observed. It is a candidate quantum spin liquid. Full article

Two mononuclear octahedral Co(II) complexes, [Co(L)X₂] (L = 1-(prop-2-en-1-yl)-1H-imidazole, X = NCS⁻ (1) and NCSe⁻ (2)), have been synthesized and characterized. The central Co(II) ions in two complexes adopt an octahedral geometry, coordinated by four N atoms from the ligand and two N atoms from the anion. Direct-current magnetic data revealed large easy-plane magnetic anisotropy in both 1 and 2. Dynamic magnetic measurements demonstrated that 1 and 2 display field-induced slow magnetic relaxation. For 1 and 2, the Raman mechanism is found to the dominant process in the whole temperature range. Compared to 1, the magnetic relaxation of 2 is faster, likely due to the presence of the hydrogen bonding system in 2. Full article

Exchange bias (EB) materials, whose magnetization curve can shift along the field axis after field cooling, have attracted tremendous attention and play a crucial role in the development of fundamental physics as well as practical applications of magnetization storage. In this work, the N-, P-, and Q-type ferrimagnets of Néel’s notation were realized in mixed valence metal formates [CH₃NH₂CH₃]_n[Cr^III_1−xFe^III_xFe^II(HCO₂)₆]_n by altering x, respectively. The positive and negative EB was found in N- and P-type ferrimagnets. The exchange anisotropy originates from the antiferromagnetic exchange interaction between the uncompensated spin of the host ferrimagnetic lattice and the pinned compensated spin of the antiferromagnetic clusters as a guest, which is rooted in the valence disorder of the iron ions. Full article

In this study, we comparatively analyzed the variable-temperature crystal structures for two isomorphous salts, [1-benzyl-4-aminopyridinium][M(mnt)₂] (M = Ni or Cu; mnt²⁻ = maleonitriledithiolate; labeled as APy-Ni or APy-Cu). Both salts crystallize in the triclinic P–1 space group at 296 K, comprising linear [M(mnt)₂]⁻ (M = Ni or Cu) tetramers. A magnetostructural phase transition occurs at T_C~190 K in S = ½ APy-Ni at ambient pressure, with a conversion of paramagnetic tetramers into nonmagnetic spin-paired dimers. The discontinuous alteration of cell parameters at T_C signifies the characteristic of first-order phase transition in APy-Ni. No such transition appears in the nonmagnetic APy-Cu within the same temperature vicinity, demonstrating the magnetic interactions promoting the structural phase transition in APy-Ni, which is further reinforced through a comparison of the lattice formation energy between APy-Ni and APy-Cu. The phase transition may bear a resemblance to the mechanisms typically observed in spin-Peierls systems. We further explored the magnetic and phase transition properties of APy-Ni under varying pressures. Significantly, T_C shows a linear increase with rising pressure within the range of 0.003–0.88 GPa, with a rate of 90 K GPa⁻¹, manifesting that the applied pressure promotes the transition from tetramer to dimer. Full article

A theoretical study, based on ab initio electronic structure calculation, is performed in a group of 16 pentacoordinate Dy-SIMs. Theoretical results provide a reasonable explanation of the observed SMM performance based on a concise criterion, i.e., the co-existence of long τ_QTM and high U_eff. To have the desired electronic structure favoring good SMM performance, the contribution from the equatorial coordinating atoms might be even more important than that from the axial coordinating atoms. Widening the axial ∠O–Dy–O might be a probable way to improve the SMM performance of pentacoordinated Dy-SIMs. Starting from existing systems, a rigid-scan type exploration indicates the possibility of U_eff higher than 1600 K. Full article

Two tetranuclear Co(II) complexes, [Co₄(pmab)₄Cl₄] (1) and [Co₄(pmab)₄(OBz)₂]Cl₂ (2) [Hpmab = 2-{(p-pyridinylmethylene)amino}benzenemethanol], have been synthesized and characterized through single-crystal X-ray diffraction, IR and UV-VIS spectroscopy, and magnetic measurements. Structural analysis revealed that both complexes possess a [Co₄O₄] cubane-like metal core connected by μ₃-alkoxo bridges. Magnetic measurements of Complex 1 indicate weak ferromagnetic interactions (J ~ +0.75 cm⁻¹) within the tetranuclear core, while Complex 2 exhibits antiferromagnetic behavior due to the presence of syn-syn bridging benzoate ligands. Alternating current (AC) magnetic measurements suggest that Complex 1 exhibits slow magnetic relaxation behavior. Full article

A binuclear cobalt–radical complex formed by the reaction of Co(hfac)₂·2H₂O (hfac = hexafluoroacetylacetonate) with the 2,2-bis(1-oxyl-3-oxide-4,4,5,5-tetramethylimidazolinyl) biradical (BR) has been synthesized. The complex {(hfac)Co^II(BN)Co^II(hfac)} crystallizes in the triclinic space group P$\overline{1}$ :  C₃₄H₂₈Co₂F₂₄N₄O₁₂, a = 11.1513(5) Å, b = 12.8362(7) Å, c = 18.2903(8) Å, α = 103.061(1)°, β = 100.898(2)°, γ = 102.250(1)°, Z = 2. The compound consists of two non-equivalent pseudo-octahedral Co^II ions, each bearing two hfac ancillary ligands bridged by the tetradentate bis-nitroxide (BN). The temperature dependence of the magnetic susceptibility indicates a strong antiferromagnetic exchange between each of the Co²⁺ ions and the nitroxyl biradical, as well as between the spins within the bridging ligand, forming a spin-frustrated system. Micro-squid investigations, performed on a single crystal of {(hfac)Co^II(BN)Co^II(hfac)}, reveal a peculiarity of the M(H) graph at temperatures below 0.4 K displaying a step that is a result of ground and first excited levels mixing by the applied magnetic field due to a small energy gap between them, as inferred from ab initio calculation. The latter was also carried out for two models of mononuclear Co²⁺ complexes in order to obtain a set of initial parameters for fitting the experimental magnetic curves using the Phi program. Moreover, direct CAS(12,10)/def2-TZVP calculations of the magnetic dependences χT(T) and M(H) were performed, which satisfactorily reproduced the experimental ones. Full article

Octahedral nickel(II) complexes are among the simplest systems that exhibit zero-field splitting by having two unpaired electrons. For the purpose of clarifying the relationship between structure and zero-field splitting in a low-symmetric system, distorted octahedral nickel(II) complexes were prepared with a tetradentate ligand, 2-[bis(2-methoxyethyl)aminomethyl]-4-nitrophenolate(1−) [(onp)⁻]. The complex [Ni(onp)(dmso)(H₂O)][BPh₄]·2dmso (1) (dmso = dimethyl sulfoxide) was characterized as a bulk sample by IR, elemental analysis, mass spectrometry, electronic spectra, and magnetic properties. The powder electronic spectral data were analyzed based on the angular overlap model to conclude that the spectra were typical of D₄-symmetric octahedral coordination geometry with a weak axial ligand field. Simultaneous analysis of the temperature-dependent susceptibility and field-dependent magnetization data yielded the positive axial zero-field splitting parameter D (H = g_uβS_uH_u + D[S_z² − S(S + 1)/3]), which was consistent with the weak axial ligand field. Single-crystal X-ray analysis revealed the crystal structures of [Ni(onp)(dmso)(H₂O)][BPh₄]·dmso (2) and [Ni(onp)(dmf)₂][BPh₄] (3) (dmf = N,N-dimethylformamide). The density functional theory (DFT) computations based on the crystal structures indicated the D₄-symmetric octahedral coordination geometries with weak axial ligand fields. This study also showed the importance of considering g-anisotropy in magnetic analysis, even if g-anisotropy is small. Full article

The mononuclear and dinuclear ruthenium(III) complexes trans-Ph₄P[Ru^III(acac)₂Cl₂] (1), Ph₄P[{Ru^III(acac)Cl}₂(μ-Cl)₃] (2) and trans-Ph₄P[Ru^III(acac)₂(NCS)₂]·0.5C₆H₁₄ (3·0.5C₆H₁₄) were synthesized. Single crystals of 1, 2·H₂O and 3·CH₃CN suitable for X-ray crystal structure analyses were obtained through recrystallization from DMF for 1 and 2·H₂O and from acetonitrile for 3·CH₃CN. An octahedral Ru with bis-chelate-acac ligands and axial chlorido or κ-N-thiocyanido ligands (for 1 and 3·CH₃CN) and triply µ-chlorido-bridged dinuclear Ru₂ for 2·H₂O were confirmed through the structure analyses. The Ru–Ru distance of 2.6661(2) of 2·H₂O is indicative of the existence of the direct metal–metal interaction. The room temperature magnetic moments (μ_eff) are 2.00 and 1.93 μ_B for 1 and 3·0.5C₆H₁₄, respectively, and 0.66 μ_B for 2. The temperature-dependent (2–300 K) magnetic susceptibility showed that the strong antiferromagnetic interaction (J ≤ −800 cm⁻¹) is operative between the ruthenium(III) ions within the dinuclear core. In the ¹H NMR spectra measured in CDCl₃ at 298 K, the dinuclear complex 2 showed signals for the acac ligand protons at 2.50 and 2.39 ppm (for CH₃) and 5.93 ppm (for CH), respectively, while 1 and 3·0.5C₆H₁₄ showed signals with large paramagnetic shifts; −17.59 ppm (for CH₃) and −57.01 ppm (for CH) for 1 and −16.89 and −17.36 ppm (for CH₃) and −53.67 and −55.53 ppm (for CH) for 3·0.5C₆H₁₄. Cyclic voltammograms in CH₂Cl₂ with an electrolyte of ⁿBu₄N(ClO₄) showed the Ru^III → Ru^IV redox wave at 0.23 V (vs. Fc/Fc⁺) for 1 and the Ru^III → Ru^II waves at −1.39 V for 1 and −1.25 V for 3·0.5C₆H₁₄ and the Ru^III–Ru^III → Ru^III–Ru^IV and Ru^III–Ru^III → Ru^III–Ru^IV waves at 0.91 V and −0.79 V for 2. Full article

The hexacoordinate Co(II) complex [Co(neo)₂(cin)][BPh₄]·½Me₂CO (1·½Me₂CO) containing trans-cinnamic acid (Hcin) and neocuproine (neo) was prepared. The compound 1·½Me₂CO was characterized via single-crystal X-ray analysis, FT-IR spectroscopy, and magnetic measurements. The coordination polyhedron of the complex cation adopts a deformed octahedron shape, and cinnamate exhibits a bidentate mode of coordination, which is unusual for mononuclear Co(II) cinnamate complexes. The analysis of DC magnetic measurements with zero-field splitting (ZFS) spin Hamiltonian revealed large magnetic anisotropy defined by the axial ZFS parameter D = +53.2 cm⁻¹. AC susceptibility measurements revealed the slow relaxation of magnetization under the applied field; thus, 1·½Me₂CO behaves as a field-induced single-molecule magnet. The analysis of magnetic properties was also supported by CASSCF/NEVPT2 calculations. Full article