Slow Magnetic Relaxation Behavior Research Articles

Lanthanide‐Based Molecular Magnetic Semiconductors

AbstractMagnetic semiconductors, with integrated properties of ferromagnets and semiconductors, are significant for developing next‐generation spintronic devices. Herein two atomically precise clusters of dysprosium(III) tellurides, formulated respectively as [Na2(15‐crown‐5)3(py)2][(η5‐Cp*Dy)5(Te)6](py)4 (Dy5Te6, Cp*=pentamethylcyclopentadienyl; py=pyridine) and [K(2,2,2‐cryptand)]2[(η5‐Cp*Dy)6(Te3)(Te2)2(Te)3] (Dy6Te10), are reported. Crystallographic studies revealed the presence of multifarious tellurido ligands within the polyhedral cluster cores. Spectroscopic and magnetic studies showed that both clusters are single‐molecule magnets exhibiting slow magnetic relaxation behaviors at low temperatures and semiconductors with low optical band gaps comparable to benchmark semiconductors. These clusters represent probably the first lanthanide‐based molecular magnetic semiconductors.

Chiral Homodinuclear Dysprosium Macrocyclic Complexes with Single‐Molecule Magnetic Behaviours

AbstractA pair of enantiomerically chiral dysprosium homodinuclear complexes: [(acac)4Dy2(R,R,R,R‐L)] (R‐Dy) and [(acac)4Dy2(S,S,S,S‐L)] (S‐Dy) (Hacac=acetylacetone) have been synthesized based on macrocyclic chiral ligands (R,R,R,R‐H2L or S,S,S,S‐H2L), derived from the [2+2] template condensation of 4‐tert‐butyl‐2,6‐diformylphenol, dysprosium acetylacetonate and (1R,2R)‐/(1S,2S)‐1,2‐cyclohexanediamine, respectively. Circular dichroism spectra confirms their enantiomeric chirality. Single‐crystal structures show two crystallographic independent dysprosium(III) ions have square antiprismatic coordination with different D4d local symmetry. Furthermore, the selected R‐Dy complex owns the slow magnetic relaxation behaviour with the ferromagnetic Dy3+⋅⋅⋅Dy3+ coupling.

Exploring the Magnetism of C5/C2B3 Heteroleptic Organolanthanide Sandwiches

Comprehensive SummaryTwo families of cyclopentadienyl (Cp)/carboranyl heteroleptic sandwiched organolanthanide complexes, namely [Ln{η5:σ‐Me2C(C5H4)(C2B10H10)}2][Li(DME)3] (1Ln, Ln = Tb, Dy, Ho, Er) and [2‐THF‐2'‐(μ2‐Cl)Li(THF)3‐2,2'‐Ln(nido‐1,7‐C2B9H11)Cp*] (2Dy), were synthesized. Family of 1Ln has been proposed based on the mixing‐ligands idea by linking Cp and nido‐dicarborllide. However, the carborane cage of [Me2C(C5H4)(C2B10H10)]2− deprotons and forms a mono‐C− anion rather than deboron to form dicarborllide dianion. Hence, the family of 1Ln features a dysprosocenium skeleton with extra two coordination of C− anions of carborllides. Such coordination geometry is more like a tetrahedron if abstracting the centroids of two coordinated Cp rings. In this cubic‐type geometry, no significant magnetic axiality is presented; only 1Dy and 1Tb show field‐induced slow magnetic relaxation behavior below 10 K. Inspired by 1Ln, the free pentamethylcyclopentadienyl (Cp*−) and nido‐dicarborllide ligands are used to sandwich central Dy3+ ion, achieving heteroleptic complex 2Dy. The bending angle by linking the centroid of Cp*−, Dy3+ and C2B32− in 2Dy is increased to 132.8(1)°. As such, the effective energy barrier for magnetic reversal (Ueff) and magnetic blocking temperature TB (ZFC) are both increased (Ueff = 616(10) K; TB = 6 K). The effort of further enhancing Ueff and TB in such heteroleptic organolanthanide sandwiches should rely on keeping increasing the ligand axiality.

Highly stable rare earth metal-organic frameworks for proton conduction and magnetic refrigeration

Four isomorphic rare earth metal-organic frameworks designated as {[(CH3)2NH2]0.7[RE2(BTDBA)1.5(lac)0.7(H2O)2]·solvent}n (RE = Tb (JXUST-19), Eu (JXUST-29), Gd (JXUST-42), and Dy (JXUST-43), where JXUST denotes Jiangxi University of Science and Technology) have been synthesized derived from a benzothiadiazole tetracarboxylate ligand (4′,4'''-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis([1,1′-biphenyl]-3,5-dicarboxylic acid), H4BTDBA). They present chain-based three-dimensional structures with one-dimensional channels extending along the b-axis. Notably, the free [(CH3)2NH2]+ cations within the channels serve as proton carriers during proton conduction. All complexes demonstrate significant proton conductivity dependent on relative humidity and temperature. Among them, JXUST-43 displays the peak conductivity achieved 7. 38 × 10–5 S·cm-1. In terms of magnetic research, JXUST-42 exhibits potential as a magnetorefrigerant, reaching a maximum entropy change (-ΔSmmax) of 16.63 J kg-1 K-1 at 3.5 K with ΔH = 7 T. And the presence of field-induced slow magnetic relaxation behavior with antiferromagnetic coupling is observed in JXUST-43.

From Dy-chain to Dy-dimer: Significant structural variation induced only by counter cations and slow magnetic relaxation behaviors

Herein we report a family of Dy complexes with 1,1,1,5,5,5-hexafluoropentane-2,4‑dione (Hhfac), [Et2MeNH][Dy(hfac)3(OAc)] (1), [Et3NH][Dy(hfac)3(OAc)] (2) and [(n-Pr)3NH]2[Dy2(hfac)6(OAc)2] (3), among which a rare structural variation has been realized by the change of organic ammonium counter cations. These complexes are all constructed from mononuclear [Dy(hfac)3] building units and OAc− linkages, while employing different protonated tertiary amines as the counter cations. The Namine-H∙∙∙Oacetate hydrogen bonds, which are formed between counter cations and OAc− bridges in all complexes, make each counter cations just wedge into the gaps between adjacent [Dy(hfac)3] building units. The hfac‒ groups of each [Dy(hfac)3] unit thus inversed to other side along with the enlarging of the steric hindrance of counter cations, resulting in a significant structural variation from infinite chain topologies of 1 and 2 to discrete dimer structure of 3. For such significant structural variation induced only by the counter cations, to our knowledge, it is the first time in the whole lanthanide complex family. The magnetic studies revealed that 1–3 all show field-induced single-molecule magnets (SMMs) behavior, with the efficient energy barriers (Ueff) of 23.9, 8.5, and 11.2 K, respectively.

Coordination number impact on magnetic properties of Schiff base Co(II) complexes

Two mononuclear Co(II) complexes with a tetrahedral and octahedral coordination geometry with a Schiff base ligand L− (anion of 4-[(2-fluoroanilino)-phenyl-methylene]-5-methyl-2-phenyl-pyrazol-3-one) having the formulas [CoL2]·2MeCN (1) and [CoL2(H2O)2]·2MeCN (2) have been synthesized and structurally characterized. Notably, their coordination geometry and magnetic relaxation behaviors can be tuned by variation of reaction conditions. Static magnetic studies reveal that complex 1 exhibits considerable easy-axis magnetic anisotropy. Frequency-dependent susceptibility measurements revealed slow magnetic relaxation behavior with spin-reversal barriers of 79.2 K at an applied external field of 500 Oe. Clear magnetic hysteresis loops were observed for 1 at 2 K. Complex 2 show field-induced slow magnetic relaxation with Raman and direct relaxation processes. The observed magnetic behavior of 1 and 2 is confirmed by high-level ab initio calculations and simulation of χMT(T) curves.

Slow magnetic relaxation and proton conduction in a highly hydrogen-bonded dinuclear holmium(III) complex

Multifunctional magnetic-electrical materials are highly interesting, such as proton-conductive lanthanide single-ion magnets (SIMs). Herein, we reported the synthesis, crystal structure, magnetic and electrical properties of a bifunctional binuclear holmium(III) complex, [Ho2(H2dobdc)(H2O)14]·(H2dobdc)2·8H2O (Ho2, H4dobdc = 2,5-dioxodo-1,4-benzenedicarboxylate), which was constructed by a hydroxy‑functionalizd dicarboxybenzene and holmium(III) ions. Interestingly, single-crystal X-ray diffraction analysis reveals a highly hydrogen-bonded supramolecular structure and highly oxygenated site were formed within the complex. Magnetic measurements indicate the complex exhibits filed-induced slow magnetic relaxation property. Additionally, the impedance spectroscopy measurements show the complex also exhibits humidity- and temperature-dependent proton conduction behaviour via the Grotthus mechanism. These results support a proton-conductive holmium(III) single-ion magnet of Ho2. This work not only provides the first bifunctional HoIII complexes showing slow magnetic relaxation and proton-conducting behaviour but also a supramolecular way for advanced magnetic-electrical systems linking slow magnetic relaxation with unique proton conducting behaviour exploiting a possible cooperative behaviour.

Reciprocating thermal behaviour in a series of 7-coordinate Mn(ii) and Co(ii) complexes

Four 7-coordinate Mn(ii) and Co(ii) complexes have been obtained. All the compounds exhibit not only slow magnetic relaxation behaviour under an external magnet field, but also reciprocating thermal behaviour at low temperature.

Constructing high axiality mononuclear dysprosium molecular magnets via a regulation-of-co-ligands strategy.

Two lanthanide complexes with formulae [DyIII(LN5)(pentafluoro-PhO)3] (1) and [DyIII(LN5)(2,6-difluoro-PhO)2](BPh4) (2) (LN5 = 2,14-dimethyl-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadecal (19),2,13,15,17-pentaene) were structurally and magnetically characterized. DyIII ions lie in the cavity of a five coordinate nitrogen macrocycle, and in combination with the introduction of multi-fluorinated monodentate phenoxyl coligands a high axiality coordination symmetry is built. Using the pentafluorophenol co-ligand, complex 1 with a D2d coordination environment, is obtained and displays moderate single-molecule magnets (SMMs) behavior. When difluorophenol co-ligands were used, a higher local axisymmetric pentagonal bipyramidal coordination geometry was observed in complex 2, which displays apparent slow magnetic relaxation behavior with a hysteresis temperature of up to 5 K. Further magnetic studies of diluted samples combined with ab initio calculations indicate that the high axiality plays a crucial role in suppressing quantum tunneling of magnetization (QTM) and consequently results in good slow magnetic relaxation behavior. Different fluoro-substituted phenoxyl co-ligands have phenoloxy oxygen atoms with different electrostatic potentials as well as a different number of phenoloxy coligands along the magnetic axis, resulting in different ligand field strengths and coordination symmetries.

Dinuclear lanthanide molecular magnetic materials bridged by tetrazine derivatives containing N6 and N8 atom sites display slow magnetic relaxation behavior

In this paper, the dihydro-tetrazine ligand is used for the first time to bridge with lanthanide ions to construct binuclear SMMs with TB up to 5.5 K, which is one of the highest for non-radical tetrazine-bridged lanthanide SMMs.

Reversible single-crystal-to-single-crystal transition in Gd(III) metal-organic frameworks induced by heat and solvents with a significant magnetocaloric effect.

The design and synthesis of a Gd(III) metal-organic framework with the formula [Gd4(BTDI)3(DMF)4]n (JXUST-40, H4BTDI = 5,5'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)diisophthalic acid) are reported hererin. Interestingly, a reversible single-crystal-to-single-crystal transition between JXUST-40 and {[Gd4(BTDI)3(H2O)4]·6H2O}n (JXUST-40a) was achieved under the stimulation of heat and solvents. Both JXUST-40 and JXUST-40a exhibited good stability when soaked in common solvents and aqueous solutions with pH values of 1-12. Magnetic studies showed that JXUST-40a has a larger magnetocaloric effect with -ΔSmaxm = 26.65 J kg-1 K-1 at 2 K and 7 T than JXUST-40 due to its larger magnetic density. Structural analyses indicated that the coordinated solvent molecules play a crucial role in the coordination environment around the Gd(III) ions and the change in the framework, ultimately leading to the changes in the pore size and magnetism between JXUST-40 and JXUST-40a. In addition, both isomorphic [Dy4(BTDI)3(DMF)4]n (JXUST-41) and {[Dy4(BTDI)3(H2O)4]·6H2O}n (JXUST-41a) displayed slow magnetic relaxation behaviour.

Synthesis, structure, photoluminescence and magnetism of a series of cobalt‐lanthanide heterometallic complexes originated from 2,3‐dichlorobenzoate and 1,10‐phenanthroline

AbstractA series of 3d–4f heterometallic complexes, namely [Ln2Co2(2,3‐DCB)10(phen)2] [Ln=Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), Er (7)], were obtained through the self‐assembly reactions of Ln(NO3)3 ⋅ nH2O, Co(NO3)2 ⋅ 6H2O, 2,3‐dichlorobenzoic acid (2,3‐HDCB), NaOH and 1,10‐phenanthroline (phen) under solvothermal conditions. Their crystal structures were determined by single‐crystal X‐ray diffraction. They were also characterized by elemental analysis, FT‐IR, powder X‐ray diffraction (PXRD) and thermogravimetric analysis (TGA) and differential thermoanalysis (DTA). These seven complexes have the same molecular formula but different crystal structures. Complexes 1–3, 4 and 5 as well as 6 and 7 are crystallographically isomorphous, respectively. They all exhibit zero‐dimensional (0D) linear tetranuclear cluster structures. These 0D linear tetranuclear clusters can be further connected into a two‐dimensional (2D) supramolecular network via the extensive intermolecular π–π interactions between 2,3‐DCB and phen. The photoluminescent properties of 3, 5 and 6 and the magnetic properties of 1–2 and 4–7 were investigated. Complex 6 shows a slow magnetic relaxation behavior.

Magnetic Relaxations of Chromium Nitride Porphyrinato Complexes Driven by the Anisotropic g-Factor.

Molecule-based magnetic materials are useful candidates as the spin qubit due to their long coherence time and high designability. The anisotropy of the g-values of the metal complexes can be utilized to access the individual spin of the metal complexes, making it possible to achieve the scalable molecular spin qubit. For this goal, it is important to evaluate the effect of g-value anisotropy on the magnetic relaxation behaviour. This study reports the slow magnetic relaxation behaviour of chromium nitride (CrN2+ ) porphyrinato complex (1), which is structurally and magnetically similar with the vanadyl (VO2+ ) porphyrinato complex (2) which is known as the excellent spin qubit. Detailed analyses for vibrational and dynamical magnetism of 1 and 2 revealed that g-value anisotropy accelerates magnetic relaxations greater than the internal magnetic field from nuclear spin does. These results provide a design criterion for construction of multiple spin qubit based on g-tensor engineering.

Synthesis, Structure and Magnetic Behavior of a Novel Series of Trinuclear Windwheel Complexes

Comprehensive SummaryA new family of trinuclear windwheel complexes with molecular formula [MII3(tpa)3(μ‐ttc)](ClO4)3·n(sol) (ttc = 1,3,5‐triazine‐2,4,6‐trithiol; tpa = tris(2‐pyridylmethyl)amine; M = Mn, n = 2, sol = CH3CN, 1; M = Co, n = 1, sol = CH3CN, 2; M = Ni, n = 0, 3) were synthesized and characterized. Single‐crystal X‐ray diffraction revealed that three metal centers in 1—3 are connected by ttc bridge, forming a regular triangular MII3 core. Each metal center is bonded by chelating S, N atoms from ttc and by N atoms from tpa. Magnetic studies showed that 1—3 displayed antiferromagnetic behavior and further gave the easy‐axis anisotropy (D = −0.77 cm−1 for 1 and −8.13 cm−1 for 2) and easy‐plane anisotropy (D = 5.08 cm−1 for 3). Moreover, 2 exhibited field‐induced slow magnetic relaxation behavior and their effective energy barriers were roughly evaluated Ueff = 6.9 K.

Slow magnetic relaxation behaviors and diamagnetic dilution studies of a carboxyl bridged dinuclear dysprosium(III) complex

By using a rigid bulky carboxylic ligand α-cyanocinnamic acid (CCA), a dinuclear dysprosium (III) complex [Dy2(CCA)6 (MeOH)4] (1) was synthesized. Single crystal X-ray crystallography reveals that the two eight-coordinate dysprosium ions are bridged by four deprotonated carboxyl groups, forming a centrosymmetric paddle-wheel-like structure. Dynamic magnetic property measurements indicate that complex 1 displays field-induced slow magnetic relaxation. The temperature-dependent relaxation times can be fitted using Orbach and Raman processes with parameters of n = 2.8 (2), C = 27 (8) s−1/Kn, τ0 = 5 (2) × 10−10 s and Ueff = 40 (3) cm−1. Magnetic studies on the diamagnetic YIII-diluted analogue [Dy0.206Y1.794(CCA)6 (MeOH)4] (2) reveal its slow magnetic relaxation behavior without external dc field and the antiferromagnetic coupling between the DyIII ions in 1. Fits on the obtained relaxation times of 2 lead to the parameters of n = 4.5 (3), C = 0.7 (2) s−1/Kn, τ0 = 2.8 (2) × 10−9 s and Ueff = 38 (2) cm−1. The results suggest that slow magnetic relaxation originates from the single-ion relaxation of DyIII ions. Moreover, the diamagnetic dilution can suppress other fast relaxation pathways at low temperature, on account of the elimination of magnetic coupling and dipolar interaction. Ab initio calculations were then performed on the single DyIII ion species {YDy} and indicate that the first excited Kramers doublets (KDs) lie at ca. 76 cm−1, which is slightly higher than the experimental Ueff value. The intramolecular magnetic interactions were also calculated and indicate a weak ferromagnetic dipole-diploe magnetic interaction and an antiferromagnetic exchange coupling.

Structure, slow magnetic relaxation behavior and bacteriostatic activity of a novel Dy4 cluster

A novel tetranuclear Dy(III)-based cluster, namely [Dy4(CO3)L4 (acac)2(CH3OH)2(CH2OH)2]·2CH3OH (1) (where H2L is 2-(hydroxyimino)-2-[(5-bromo-2-hydroxyphenyl)methylene]hydrazide and Hacacis acetylacetonate) has been constructed by employing a newly prepared Schiff based ligand H2L. X-ray diffraction data reveal that 1 is mainly consist of a rhombic Dy4core, in which the four Dy3+ ions are bridged by six μ-O atoms from four ligands H2L and two μ2-O atoms from thein situformed CO32−via spontaneous fixation of atmospheric CO2.The crystalstructure of 1 possesses two distinct Dy3+ ions coordinationcenter, and the nine-coordinated Dy73+ionscenter presenting a distorted spherical capped square antiprism geometry and eight-coordinated Dy43+ionscenter presenting a distorted triangular dodecahedron geometry.Magnetic study indicates that 1displays slow magnetic relaxation behavior under Hdc = 0 Oe filed. Furthermore, the fluorescence property investigation reveals that 1shows DyIIIcharacteristic emission peaks. Moreover, theantibacterial activity and mechanism of 1 have been systemically studied, and cluster 1 possesses well antibacterial activity on five common bacteria (Escherichia coli, Staphylococcus aureus, Staphylococcus albus, Bacillus subtilis, and Micrococcus luteus). Inaddition,the interaction between 1 and DNA have been studied.

Slow Magnetic Relaxation in a Mononuclear 8‐Coordinate Fe(II) Compound Bearing the Phenanthroline‐Amide Ligand

AbstractA mononuclear 8‐coordinate Fe(II) compound, [FeII(L1)2](CF3SO3)2 (1), was prepared from the reaction of a neutral tetradentate ligand (L1=N2,N9‐dibutyl‐1,10‐phenanthroline‐2,9‐dicarboxamide) and hydrated Fe(CF3SO3)2 in MeOH. 1 could be considered as an ‘ideal’ 8‐coordinate Fe(II) compound as compared with the previously reported Fe(II) analogs, because all the terminal Fe−O bond lengths are in the normal range. The magnetic properties investigation shows that 1 exhibit field‐induced slow magnetic relaxation behavior.

Desolvation-induced magnetic switching from single-ion magnetism to spin-crossover in a halogen-functionalized cobalt(II) complex

The switching between spin-crossover (SCO) and single-ion magnet (SIM) are fascinating because the process provides potential in-depth understating of different bistability. Herein, we present a rare example of the desolvation-induced magnetic switching from single-ion magnetism to SCO between a halogen-functionalized cobalt(II) complex, [Co(Brphtpy)2](PF6)2·2MeOH (Brphtpy = 4′-(4-Bromophenyl)-2,2′:6′,2′'-terpyridine, 1·2MeOH) and its desolvated material of [Co(Brphtpy)2](PF6)2 (1). The temperature-dependent magnetic susceptibility and variable-temperature single crystal X-ray diffraction results show a high spin state of the Co(II) ions in 1·2MeOH. At lower temperature, frequency- and temperature-dependent slow magnetic relaxation behaviors were evidenced under an applied dc field of 1000Oe, originating from the easy-plane magnetic anisotropy (D=43.5 cm−1) of Co(II) ions. After the release of methanol molecules, interestingly, the desovated material 1 display a complete and cooperative two-step spin transitions with transition temperatures being 350 and 125K. Differential scanning calorimetry measurements support the stepwise SCO behavior and reveal the related ΔH and ΔS.

Russian Doll-like 3d-4f Cluster Wheels with Slow Relaxation of Magnetization.

The solvothermal reactions of LnCl3·6H2O and MCl2·6H2O (M = Co, Ni) with 2,2'-diphenol (H2L1) and 5,7-dichloro-8-hydroxyquinoline (HL2) gave three 3d-4f heterometallic wheel-like nano-clusters [Ln7M6(L1)6(L2)6(µ3-OH)6(OCH3)6Cl(CH3CN)6]Cl2·xH2O (Ln = Dy, M = Co, x = 3 for 1; Ln = Dy, M = Ni, x = 0 for 2; Ln = Tb, M = Ni, x = 0 for 3) with similar cluster structure. The innermost Ln(III) ion is encapsulated in a planar Ln6 ring which is further embedded in a chair-conformation M6 ring, constructing a Russian doll-like 3d-4f cluster wheel Ln(III)⸦Ln6⸦M6. 2 and 3 show obvious slow magnetic relaxation behavior with negligible opening of the magnetic hysteresis loop. Such a Russian doll-like 3d-4f cluster wheel with the lanthanide disc isolated by transition metallo-ring is rarely reported.

Synthesis, crystal structures and magnetic properties of two Ni-Dy heterometallic complexes with the structural topologies regulated by employing different Schiff base ligands

Regulation of the structural topologies of single molecule magnets (SMMs) is one of the most important approach for enhancing their SMM performance. In this work, we first obtained a Ni2Dy trinuclear complex, [Ni2Dy(Hhmmp)2{(py)2CO2}(CH3COO)2]OH (1, H2hmmp = 2-[(2-hydroxyethylimino)methyl]-6-methoxyphenol, (py)2C(OH)2 = the gem-diol form of di-2-pyridyl ketone (dpk)) by employing H2hmmp and dpk reacting with Dy(NO3)3·5H2O and Ni(CH3COO)2·4H2O in the MeCN solution containing triethylamine. However, when H2hmmp, triethylamine and MeCN in the reaction system of 1 were replaced by 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propanediol (H4L), N(Me)4OH·5H2O and the mixture of MeCN and N,N-dimethylformamide (DMF), a Ni2Dy2 complex, [Ni2Dy2(HL)2{(py)2CO(OH)}2(CH3COO)2]·2H2O (2), was obtained. Structural analysis revealed that two NiII and one DyIII in 1 formed a “V-shaped” topology, while two NiII and two DyIII ions in 2 formed a butterfly-like topology with Ni and DyIII ions occupied on the body positions and the wing positions, respectively. Additionally, the coordination geometries of DyIII ion in 1 and 2 square antiprism geometry (D4d) and capped octahedron (C3v), respectively. Magnetic investigation indicated that 1 exhibits obviously slow magnetic relaxation behavior, with an energy barrier Ueff of ∼6 K. The orientations of the magnetic anisotropy of DyIII in 1 and 2 were estimated by Magellan software; the results indicate that few coordination atoms were located on the equatorial plane of DyIII in 1 and 2, which result in 1 and 2 exhibiting poor SMM performance.