Pre-exponential Factor Τ0 Research Articles

Mixed‐Valence Manganese Carboxylate Clusters, {MnIII6MnII4}, {MnIII7MnII5Na}, and {MnIII7MnII5}, Derived from the Combined Use of Di‐2‐pyridyl Ketone with Selected Aliphatic Diols

AbstractThree new polynuclear clusters with the formulae [Mn10O4(OH)(OMe){(py)2C(O)2}2{(py)2C(OMe)(O)}4(MeCO2)6](ClO4)2 (1), Na[Mn12O2(OH)3(OMe){(py)2C(O)2}6{(py)2C(OH)(O)}2(MeCO2)2(H2O)10](ClO4)8 (2) and [Mn12O4(OH)2{(py)2C(O)2}6{(py)2C(OMe)(O)}(MeCO2)3(NO3)3(H2O)(DMF)2](NO3)2 (3) were prepared from the combination of di‐2‐pyridyl ketone, (py)2CO, with the aliphatic diols (1,3‐propanediol (pdH2) or 1,4‐butanediol (1,4‐bdH2)) in Mn carboxylate chemistry. The reported compounds do not include the aliphatic diols employed in this reaction scheme; however, their use is essential for the formation of 1–3. The crystal structures of 1–3 are based on multilayer cores which, to our knowledge, are reported for the first time in Mn cluster chemistry. Direct current (dc) magnetic susceptibility studies showed the presence of dominant antiferromagnetic exchange interactions within 1–3. Alternating current (ac) magnetic susceptibility studies revealed the presence of out‐of‐phase signals below 3.0 K for 2 and 3 indicating the slow relaxation of the magnetization vector, characteristic of single‐molecule magnets; the Ueff value of 2 was found to be 23 K and the preexponential factor τ0 ~7.6×10−9 s.

Magnetic refrigeration property and single-molecule magnetic behavior of three asymmetric Ln2 (LnIII = Gd, TB and Dy) compounds

Three new dinuclear Ln(III)-based compounds formulated as {Ln2(dbm)5L}·nMeOH (Ln = Gd (1), Tb (2), and Dy (3), Hdbm = dibenzoylmethane, HL = 2-hydroxyimino-propionic acid (6-methoxy-pyridin-2-ylmethylene)-hydrazide, MeOH = methanol) have been successfully synthesized under solvothermal conditions. The structures and magnetic properties of 1–3 have been systematically studied. The single-crystal X-ray diffraction analysis shows that compounds 1–3 are dinuclear structures with two asymmetric LnIII ion centres. The magnetic properties study suggests that compound 1 displays cryogenic magnetic refrigeration property, while compound 3 exhibits single-molecule magnetic behavior with an energy barrier (ΔE/kB) of 62.3 K and pre-exponential factor τ0 = 2.93 × 10-8 s under a zero direct-current field.

Lanthanide Single-molecule Magnets: Synthetic Strategy, Structures, Properties and Recent Advances.

Single-molecule magnets (SMMs) show wide potential applications in the field of ultrahigh-density storage materials, quantum computing, spintronics, and so on. Lanthanide (Ln) SMMs, as an important category of SMMs, open up a promising prospect due to their large magnetic moments and huge magnetic anisotropy. However, the construction of high performance for Ln SMMs remains an enormous challenge. Although remarkable advances are focused on the topic of Ln SMMs, the research on Ln SMMs with different nuclear numbers is still deficient. Therefore, this review summarizes the design strategies for the construction of Ln SMMs, as well as the metal skeleton types. Furthermore, we collect reported Ln SMMs with mononuclearity, dinuclearity, and multinuclearity (three or more Ln spin centers) and the SMM properties including energy barrier (Ueff ) and pre-exponential factor (τ0 ) are described. Finally, Ln SMMs with low-nuclearity SMMs, especially for single-ion magnets (SIMs), are highlighted to understand the correlations between structures and magnetic behavior of the detail SMM properties are described. We expect the review can shed light on the future developments of high-performance Ln SMMs.

Synthesis, luminescence and magnetic properties of dinuclear complexes based on a “pincer” Schiff base and different β-diketonate ligands

Twelve new dinuclear rare earth complexes in three series were successfully synthesized with a “pincer” Schiff base H2L and different β-diketonate ligands: Ln2(acac)2(L)2·2C2H5OH (Ln = Eu (1), Tb (2), Dy (3), Er (4)), Ln2(dbm)2(L)2·2C3H7NO (Ln = Eu (5), Tb (6), Dy (7), Er (8), Yb (9)), Ln2(TTA)2(L)2·2H2O (Ln = Eu (10), Tb (11), Dy(12)). (H2L = 3-aminopyrazine-2-carboxylic acid [(2-hydroxybenzylidene)] hydrazide; Hacac = acetylacetone; Hdbm = dibenzoylmethane; HTTA = 2-thiophene trifluoroacetone). These complexes are centrosymmetric dinuclear structures and RE3+ ions are bridged by oxygen atoms in carbonyl of Schiff base to form the core unit of Ln2O2. The characteristic emission peaks of Er3+ and Yb3+ in 4, 8 and 9 can be observed in Near-infrared luminescence spectra, that is confirmed the central ions were sensitized effectively via ligands. Moreover, 1, 5, 6 and 10 were sensitized in various degrees. The dynamic magnetization curves indicate that 3, 7 and 12 are typical SMMs with slow magnetic relaxation behaviors. Their effective energy barriers are 48.20 K (3) and 42.30 K (12) under 3000 Oe dc field and 81.89 K (7) under zero dc field. The pre-exponential factors (τ0) are 1.35 × 10−6 s (3), 1.38 × 10−10 s (7) and 4.93 × 10−6 s (12), respectively. It is confirmed that the magnetic properties of SMMs can be regulated by different β-diketonate ligands.

Homochiral SCM Built of Tetrahedral and Pentagonal Bipyramidal Fe(II) Units Bridged by Chlorine

Each enantiomer of a chiral pentagonal bipyramidal (PBP) FeII complex ([FeLN5R,RCl(MeOH)]Cl·H2O, 1R, or [FeLN5S,SCl(MeOH)]Cl·H2O, 1S) has been obtained using either the R or the S stereoisomer of the macrocyclic pentadentate ligand formed in a template-condensation reaction of the tetraamine N,N′-Bis-{(1R,2R)-[2-(amino)]cyclohexyl}-1,2-diaminoethane, or its (1S,2S) enantiomer, and 2,5-diacetylpyridine, respectively LN5R,R and LN5S,S. Subsequently, the 1-D coordination polymers [FeLN5R,R{FeCl4}], 2R, and [FeLN5S,S{FeCl4}], 2S, were formed by reacting respectively 1R or 1S with 1 equiv of FeCl2(H2O)4. These chain compounds consist of an alternation of PBP and tetrahedral FeII units sharing a Cl atom. Theoretical calculations reveal large magnetic anisotropy for each Fe center but of different type with axial zero-field splitting parameter D of respectively −30 cm–1 and 15 cm–1. The magnetic behavior for the 1-D compound revealed canted antiferromagnetic Fe–Fe interactions (J = −6 cm–1) and SCM behavior characterized by Δ/kB = 42 K with pre-exponential factor τ0 = 2.17 × 10–10 s. It was noted that this SCM behavior was accompanied by a magnetic order leading to a weak ferromagnet (i.e., canted antiferromagnet). The preparations, crystal structures (CCDC references 2214580–2214583), spectroscopic data, magnetic behaviors, and theoretical investigations are reported.

Nondestructive analysis of solute carbon in the ferrite phase in dual-phase steels containing Mn or Si by mechanical loss measurements

As a development of an earlier attempt to determine the concentration of mobile carbon atoms in the ferrite phase in dual-phase (DP, ferrite + martensite) steels by means of mechanical loss measurements, which was made on binary Fe-C alloys [Honda et al., Solid State Phenom. 184 (2012) 87–91], we have investigated effects of Mn and Si on the mechanical loss profiles, aiming at establishing a method for quantitatively evaluating the distribution of carbon in practical DP steels. First we re-examined the effects of Mn and Si on the relation between the strength of the Snoek relaxation and the concentration of carbon in iron by measuring the mechanical loss of solution-treated, single-phase ferrite samples of dilute Fe-Mn-C and Fe-Si-C alloys. We then measured mechanical loss of ferrite + martensite two-phase alloys of various carbon contents, after equilibrating at a temperature where the material consists of ferrite and austenite, and then quenching. The concentrations of carbon in solution in the ferrite phase can be estimated from the observed magnitude of the Snoek relaxation peak, using the linear relation obtained in the first set of experiments, and correcting for the volume fraction of the ferrite phase. These estimates agree reasonably well with those expected from the compositions expected from the ternary phase diagrams, as in the previous case of simple Fe-C alloys. This renders the basis for determining the carbon concentration in the ferrite phase by measuring mechanical loss of DP steels with alloying elements. As another development, the properties of the characteristic mechanical loss due to the martensite phase have been studied. The mechanical loss, which steadily increase above room temperature, turned out to exhibit a maximum at 480–500 K. It is found to be a thermally activated relaxation, with the following parameters of the relaxation time: pre-exponential factor τ0 ≃ 10−14 s and activation energy E ≃ 1.2 eV. However, its magnitude does not show a simple linear relation with the carbon content, unlike the case of the Snoek relaxation in ferrite.

A series of tetranuclear rare-earth complexes and two-step slow magnetic relaxation in Dy4 complex

A series of new tetranuclear lanthanide metal complexes of [Ln4(μ4-O2−)(HL)2(L)2]·0.5(H2NCH2CHOHCH2NH2)·(CH3CN)·1.25(H2O) (Ln = Tb(1)), [Ln4(μ4-O2−)(HL)2(L)2]·0.5(H2NCH2CHOHCH2NH2)·0.5(CH3CN)·0.25(H2O) (Ln = Dy(2) or Ho(3)), were elaborately synthesized using a Schiff base ligand, 1,3-bis(5-bromosalicylideneamino)-2-propanol) (H3L). They were structurally and magnetically characterized. The crystallographic data reveal the tetranuclear lanthanide core of complexes 1–3 bridged by one μ4-O2− ion. Complexes 1–3 contained one unusual Ln4 boat-shaped unit, forming a novel Ln4 cluster. Detailed static and dynamic magnetic analysis of complexes 1–3 revealed single-molecule magnet (SMM) behavior with anisotropy barrier of Ueff = 20.98 K and Ueff = 43.47 K and two pre-exponential factors τ0 = 7.66 × 10−7 s and τ0 = 9.75 × 10−7 s for complex 2.

Slow relaxation of the magnetization in a {CoIIIMnIII} heterometallic brick-wall network

The use of the cyanide-bearing dicobalt(III) complex (PPh4)2[Co2III(μ−2,5-dpp)(CN)8] as a metalloligand towards [Mn(salen)(H2O)]ClO4 afforded the heterobimetallic two-dimensional compound of formula [{MnIII(salen)}2{(μ-NC)4Co2III(μ−2,5-dpp)(CN)4}]n (1) [PPh4+ = teraphenylphosphonium cation, 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine and H2salen = N,N’-ethylenebis(salicylideneimine)] whose structure has been determined by single crystal X-ray diffraction. Compound 1 exhibits a neutral brick-wall structure, where each [Co2III(μ−2,5-dpp)(CN)8]2− unit adopts a tetrakis-monodentate bridging mode towards four {MnIII(salen)}+ fragments through four of its eight cyanide ligands. Each cobalt(III) ion is six-coordinate with one pyrazine- and one pyridine-nitrogen atoms of the 2,5-dpp molecule and four cyanide-carbon atoms describing a somewhat distorted octahedral surrounding. The two crystallographically independent manganese(III) ions are also six-coordinate in an elongated octahedral environment with two imino-nitrogen and two phenoxo-oxygen atoms occupying the equatorial positions and two cyanide-nitrogen atoms filling the axial sites. Variable-temperature direct- (1.9–300 K) and alternating-current (2.0–5.0 K) magnetic measurements of 1 show the occurrence of magnetically isolated manganese(III) ions with a local negative zero-field splitting (D = −5.87 cm−1) and slow magnetic relaxation, this compound being a new example of field-induced Single-Ion Magnet (SIM). The analysis of the ac magnetic data of 1 under an applied dc field of 5000 G reveals that the value of the energy barrier (Ea) to reverse the magnetization direction and that of the pre-exponential factor (τ0) are 10.8 cm−1 and 2.7 × 10−8 s, respectively. These values compare well with those reported for the few examples of manganese(III)-based SIMs nowadays.

Syntheses, characterization, and slow magnetic relaxation or luminescence properties of three new 2D coordination polymers

Three new 2D coordination polymers (CPs), namely, {[CoL0.5(4,4′-bbib)]}n(1), {[ZnL0.5(4,4′-bbib)]·3DMF·3H2O}n(2) and {[CdL0.5(4,4′-bbib)]·4H2O}n(3), have successfully been constructed by solvothermal method based on H4L, 4,4′-bbib and M(NO3)2 {M = Co (1), Zn (2), Cd (3); H4L = 5,5’-(1,3,6,8-tetraoxobenzo[lmn] [3,8]phenanthrolin-2,7-diyl)bis-1,3-benzenedicarboxylic acid; 4,4′-bbib = 4,4′-bis(benzoimidazo-1-yl)biphenyl}, and studied by structural analysis, magnetic properties and luminescence properties. The structural analysis shows that CPs 1-3 are 4-c 2D network structures with the point symbol of {32.62.72}, which are further expanded into 3D supramolecular architectures by the π … π and hydrogen bonding (O–H⋯O) interactions between the adjacent 2D layers. Magnetic properties show 1 presents a single-molecule magnet (SMM) and slow magnetic relaxation behavior with the energy barrier (Ueff) of 49.73 K and a pre-exponential factor (τ0) of 1.84 × 10−10 s. Luminescent experiments revealed that 2 and 3 can serve as sensors towards Fe3+ and nitroaromatic compounds (NACs) in aqueous medium with high sensitivity and selectivity.

Dielectric properties of amorphous BiFeO3

An amorphous material based on multiferroic BiFeO3 was obtained, using melt quenching method. Its dielectric properties were studied within the temperature range −200 to 600°С. The material is characterized by a high dielectric permittivity ε ≈104 (at 200°С and a frequency of 100 Hz), due to the contribution of migration polarization. Using the DTA method, the glass transition temperature Tg ≈ 400°С and crystallization temperature Tcr ≈ 490°С were determined. It was found that the temperatures Tg and Tcr correspond to anomalies of ε, the superposition of which forms a diffuse maximum of the dielectric permittivity. Staged annealing leads to decrease of these anomalies and their shift along the temperature axis in opposite directions. Substantially below of Tg two thermally activated dielectric relaxation processes were revealed. The relaxation time of one of them is obeyed to the Arrhenius law with an activation energy U ≈ 0.53 eV and preexponential factor τ0 ≈ 4.38 10−12 s.

Two Ln(III)2 (Ln = Gd and Dy) compounds showing magnetic refrigeration and slow magnetic relaxation

Two new Ln2 compounds, namely [Ln2(L)2(CH3OH)2] (Ln = Gd (1) and Dy (2)), have been successfully synthesized and further characterized by crystallography. Structural analysis shows that both 1 and 2 are binuclear compounds, and each LnIII ion is eight-coordinated model and the coordination polyhedron of centre LnIII ion can be represented as a distorted dodecahedron with triangular faces. The magnetic studies reveal that weak antiferromagnetic exchange is existed between the two neighbouring Gd(III) ions in 1. Furthermore, for 1, it exhibits magnetic refrigeration property (magnetic entropy changes −ΔSm = 24.75 J kg−1 K−1 for magnetic field intensity ΔH = 7.0 T at 3.0 K); while for 2, it displays slow magnetic relaxation behavior under zero dc field. When under an external dc field (dc = 3000 Oe), remarkable single-molecule-magnet (SMM) behavior was observed in 2 with the anisotropic barrier (ΔE/kB) of 16.65 K and pre-exponential factor (τ0) of 3.12 × 10−6 s.

Modulating single-molecule magnet behaviors of Dy4III clusters through utilizing two different β-diketonate coligands

In search of simple approaches to rationally modulate the single-molecule magnet behaviors in polynuclear lanthanide clusters, a new system containing two structurally closely related rhombus-shaped Dy4 clusters, Dy4(tmhd)4L6(μ3-OH)2·5CH3CN (1) and Dy4(acac)4L6(μ3-OH)2 (2) (HL = 5-(4-ethyoxylbenzylidene)-8-hydroxylquinoline, Htmhd = 2,2,6,6-tetramethyl-3,5-heptanedione and Hacac = acetylacetonate), have been obtained by employing two dysprosium β-diketonate salts to react with a bidentate Schiff base ligand (HL). The two Dy4 clusters have similar structures and possess a structure in which four Dy3+ ions remain in a perfect plane with a rhombus-shaped geometric construction. Dynamic magnetic analysis revealed different single-molecule magnet (SMM) behaviors occurs in 1 and 2. Under zero direct-current (dc) field, 1 displays typical SMMs behavior with ΔE/kB = 39.6 K and τ0 = 2.1 × 10−6 s. However, for 2, a peculiar feature of the χ″ versus temperature curves is that more than two peaks that are frequency-dependent are revealed, indicating the occurrence of multifold relaxation processes that lead to two ΔE/kB (31.3 K and 81.6 K) and pre-exponential factors (τ0 = 3.1 × 10−6 s, τ0 = 2.2 × 10−7 s).

Syntheses, structure and single-molecule magnet behavior of a rhombus shaped Dy4 cluster

A new Dy4 cluster, namely, Dy4(acac)4L6(μ3-OH)2·4CH3CN (1) (HL = 5-(2-hydroxy-5-methylbenzylidene)-8-hydroxylquinoline, acac = acetylacetonate), has been synthesized based on a bidentate Schiff base ligand. Furthermore, elemental analysis (EA), powder X-ray diffraction (PXRD), single-crystal X-ray diffraction and magnetic properties of cluster 1 have been characterized. The X-ray structural analysis exhibits that cluster 1 is a tetranuclear dysprosium cluster with rhombus-shaped arrangement, and each Dy(III) ion of 1 is eight coordinated, and their coordination polyhedrons can be described as a distorted square-antiprismatic geometry. Magnetic properties measurement indicate that two magnetic relaxation processes phenomenon occurs for cluster 1 under 0 dc filed, with pre-exponential factor τ0 = 8.19 × 10−7 s and ΔE/kB = 37.73 K for the LT relaxation and τ0 = 4.36 × 10−8 s and ΔE/kB = 105.97 K for the HT relaxation.

Synthesis, structure and slow magnetic relaxation of a linear Ho4 cluster

A new Ho4 cluster, namely, [Ho4(tmhd)8(L)2(CH3OH)2]·CH3OH (1) (tmhd = 2,2,6,6‑tetramethyl‑3,5‑heptanedione, H3L = 2‑[(2‑(hydroxyimino)propanehydrazide)methyl]), has been successfully synthesized via using a multidentate Schiff base ligand, and further characterized by crystallography. Structural analysis shows that four HoIII ions in cluster 1 are linearly arranged. The magnetic study reveals that 1 exhibits slow magnetic relaxation under zero dc field. When under an external 3000 Oe dc field, we obtained the effective energy barrier ΔE/kB = 13.8 K and the pre-exponential factor τ0 = 2.8 × 10−6 s.

Synthesis, crystal structure, and magnetic properties of a series of binuclear lanthanide compounds derived from the 4-Bromo-2-((quinolin-8-ylimino)methyl)phenol ligand

A series of binuclear lanthanide compounds, derived from the Schiff-base ligand 4-bromo-2-((quinolin-8-ylimino)methyl)phenol (HL), namely [Ln2(L)2(CH3CH2CH2 COO)2(NO3)2(MeOH)2] (Ln = Gd (1), Tb (2), Dy (3), Ho (4)), has been synthesized. Compounds 1–4 have a similar dinuclear lanthanide core bridged by a butyrate ion. Magnetic studies reveal that compound 1 has a weak ferromagnetic interaction. On the other hand, compound 3 displays slow magnetic relaxation under an external dc field with the anisotropic barrier of 27.08 K and pre-exponential factor τ0 = 4.12 × 10−6 s. Therefore the Dy(III) compound is a field-induced SMM.

Near-infrared luminescence and solvent modulation of the magnetic relaxation behavior of dinuclear lanthanide complexess

Seven new dinuclear centrosymmetric complexes, [Ln2(dbm)2L2(DMF)2]·2DMF (Ln = Nd (1), Eu (2), Tb (3), Dy (4), Er (5), Yb (6)) and [Dy2(dbm)2L2(CH3OH)2]·2CH3OH (7) (Hdbm = 1,3-diphenyl-1,3-propanedione, H2L = 2-[(2-(amino)benzhydrazide)-methyl]-8-hydroxylquinoline, DMF = dimethyl-formamide) have been synthesized and structurally characterized. Dynamic magnetic studies reveal the slow magnetic relaxation of complexes 4 and 7 are influenced by a fast quantum tunneling relaxation of the magnetization (QTM). However, the different magnetic relaxation behaviors were observed apparently in the two Dy2 complexes under a 3000 Oe dc field and modulated by the subtle change of solvents from DMF to CH3OH. For complex 7, the temperature dependence curves of in-phase (χ′) and out-of-phase (χ″) show better frequency-dependent signals, suggesting a slow relaxation of magnetization, typical of SMM behavior. Fitting the dynamic magnetic data of complex 7 to the Arrhenius law gives the energy barrier Ueff/kB = 44.06 K with the pre-exponential factor τ0 = 2.17 × 10−7 s under a 3000 Oe dc field.

Lanthanide-directed fabrication of three phenoxo-O bridged dinuclear compounds showing magnetic refrigeration and single-molecule magnet behavior

A series of lanthanide based dinuclear compounds, namely, [Ln(bfa)2L]2 (Ln = Gd (1), Tb (2), and Dy (3), bfa = benzoyltrifluoroacetone and HL = 2-[5-methyl-1,2-oxazol-imino]methyl]-8-hydroxyquinoline), were synthesized by employing a multidentate 8-hydroxyquinoline Schiff base derivative ligands (HL) and a bidentate β-diketonate coligand (bfa). The elemental analysis (EA), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), single-crystal X-ray diffraction and magnetic properties of the three Ln2 compounds were completely characterized. Structures of 1–3 are similar to each other with a parallelogram Ln2O2 core. Magnetic properties study indicates that 1 exhibits antiferromagnetic exchange interaction between two nearby GdIII centers and shows magnetic refrigeration (−ΔSm = 17.78 J kg−1 K−1 for ΔH = 7 T at 2.0 K). Ac magnetic susceptibility measurements of 3 demonstrate that slow relaxation behavior is observed in 3, with effective energy barrier Ueff = 24.3 K and pre-exponential factor τ0 = 1.71 × 10−6 s.

Impedance and dielectric relaxation spectroscopy studies on the calcium modified Na0.5Bi0.44Ca0.06TiO2.97 ceramics

Na0.5Bi0.44Ca0.06TiO2.97 ceramics were synthetized by conventional solid-state reaction. XRD measurement analysis shows that the Na0.5Bi0.44Ca0.06TiO2.97 sample is the single perovskite structures. The oxide ion conductivity of the Na0.5Bi0.44Ca0.06TiO2.97 sample was investigated by AC impedance spectroscopy measurement. The bulk conductivity of Na0.5Bi0.44Ca0.06TiO2.97 sample can arrive at 2.22×10-4 S/cm at 573 K in air atmosphere. By changing measuring temperature of dielectric frequency spectroscopy measurement, the activation energy E and pre-exponential factor τ0 are E= 0.81 eV, τ0=1.5×10-13 s for Na0.5Bi0.44Ca0.06TiO2.97 sample, respectively. Judging from the relaxation parameters, the dielectric loss peaks correspond to oxide ion via vacancies diffusion in Na0.5Bi0.44Ca0.06TiO2.97 sample. Compared with the same dopant amount Na0.5Bi0.5Ti0.94Mg0.06O2.94 compound, the better oxygen vacancy mobility and larger specific free volume Vsf might be responsible for the favourable oxide ion conductivity in the Na0.5Bi0.44Ca0.06TiO2.97 sample, indicating that calcium modified Na0.5Bi0.5TiO3 materials are promising for intermediate-temperature solid electrochemical devices.

2D carboxylate-bridged LnIII coordination polymers: displaying slow magnetic relaxation and luminescence properties in the detection of Fe3+, Cr2O72- and nitrobenzene.

Eight new 2D isostructural lanthanide coordination polymers (Ln-CPs), [Ln(HL)(H2O)2(NO3)]·NO3 (1-Ln), Ln = NdIII, SmIII, EuIII, GdIII, TbIII, DyIII, HoIII, and YbIII ions, H2L = 4-(3,5-dicarboxylphenyl)-2-methylpyridine, were synthesized by using solvothermal methods and studied by structural analyses, magnetic analyses and luminescent probes. Crystallographic studies revealed that these compounds are 2D frameworks in which dinuclear units with double μ-syn,syn-carboxylate bridges are interlinked by single μ-trans,trans-carboxylate bridges from organic spacers. The layers are further stabilized and combined into 3D architectures through intra- and interlayer ππ stacking interactions and hydrogen bonding, respectively. Magnetic investigations indicated that the carboxylate bridges transmit intralayer antiferromagnetic coupling in 1-Nd, 1-Gd and 1-Ho but transmit intralayer ferromagnetic coupling in 1-Dy. Furthermore, 1-Dy also displays slow magnetic relaxation behavior with a high relaxation energy barrier (ΔUeff) of 100.7 K and a pre-exponential factor (τ0) of 1.4 × 10-8 s under zero dc field. The luminescence investigations showed that CPs 1-Eu and 1-Tb can serve as highly selective and recyclable sensing materials for Fe3+, Cr2O72- and nitrobenzene. Thus, both 1-Eu and 1-Tb should be excellent candidates for multifunctional sensors.

Two 3D Isostructural Ln(III)-MOFs: Displaying the Slow Magnetic Relaxation and Luminescence Properties in Detection of Nitrobenzene and Cr2O72.

Two new three-dimensional isostructural lanthanide metal-organic frameworks (Ln(III)-MOFs), [LnL(H2O)3]·3H2O·0.75DMF (1-Ln; Ln = Dy(III) and Eu(III) ions, H3L = biphenyl-3'-nitro-3,4',5-tricarboxylic acid, DMF = N,N'-dimethylformamide), were synthesized and characterized. The appearance of temperature-dependent out-of-phase (χ″M) signal reveals that complex 1-Dy displays slow magnetic relaxation behavior with the energy barrier (ΔUeff) of 57 K and a pre-exponential factor (τ0) of 3.89 × 10-8 s at 1200 Oe direct current field. The luminescence explorations demonstrated that 1-Eu exhibits high quenching efficiency and low detection limit for sensing nitrobenzene and Cr2O72-. Meanwhile, the fluorescence intensity of the quenched 1-Eu samples will be resumed after washing with DMF or water, indicating that 1-Eu may be used as a highly selective and recyclable luminescence sensing material for sensing nitrobenzene and Cr2O72- anion.