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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. [ABSTRACT FROM AUTHOR]

A new hydrazone Schiff base ligand was condensed from 2-hydroxy-3-methoxybenzaldehyde and pyrimidine-4-carbohydrazide {H2L = (E)-N′-(2-hydroxy-3-methoxybenzylidene)pyrimidine-4-carbohydrazide}, which was used to assemble two new Dy2 complexes Dy2L2(DMF)2(NO3)2 (1) and Dy2L2(DMF)2(AcO)2 (2). Notably, the coordinated anions have a subtle effect on the coordination configurations of the Dy3+ ions and the magnetic properties of the two Dy2 complexes. The Dy3+ ions in 1 and 2 have the same N2O5 coordination environment but show the triangular dodecahedron and the biaugmented trigonal prism coordination configurations, respectively. Magnetic measurements revealed that both 1 and 2 have intramolecular ferromagnetic interactions between the Dy3+ ions and show single-molecule magnet behaviors at 0 Oe, with Ueff/k values of 58.2 K for 1 and 59.9 K for 2. These magnetic properties may be explained by theoretical calculations. [ABSTRACT FROM AUTHOR]

Synthesis of 3d–4f single molecule magnets (SMMs) with novel topologies and exploration of the magnetic relaxation mechanism of SMMs have continuously received considerable attention because high performance SMMs could be obtained. In this work, we selected N-3-methoxysalicylidene-2-amino-3-hydroxypyridine (H2L) and di-2-pyridyl ketone (dpk) for reaction with Ni(NO3)2·6H2O, Dy(NO3)3·5H2O and trimethylamine in a CH3OH solution, and a novel Ni4Dy4 complex, [Ni4Dy4(L)6(L′)2{(py)2C(OCH3)O}2(μ3-CO3)2(CH3OH)2]·10CH3OH·13H2O (1, (py)2C(OCH3)(OH) = the hemiacetal form of dpk), was obtained. The magnetic diluted complex, [Ni4Y3.91Dy0.09(L)6(L′)2{(py)2C(OCH3)O}2(μ3-CO3)2(CH3OH)2]·10CH3OH·12H2O (2), and the Y analogue of 1, [Ni4Y4(L)6(L′)2{(py)2C(OCH3)O}2(μ3-CO3)2(CH3OH)2]·10CH3OH·11H2O (3), were also obtained. The carbonate ions in 1–3 were formed by spontaneous fixation of atmospheric CO2. Structural analysis revealed that the metallic core in 1 can be viewed as a Ni2Dy2 butterfly connecting two NiDy subunits on each side. To our knowledge, the structural topologies of 1–3 were not reported previously. The magnetic susceptibilities of 3 were fitted by PHI, indicating that the magnetic coupling between Ni1 and Ni1a in the "Ni2Y2 butterfly" subunit of 3 is ferromagnetic. Alternating-current (ac) susceptibility studies revealed that 1–2 exhibit single molecule magnet behavior under a zero dc field. [ABSTRACT FROM AUTHOR]

Synthesis of air-stable and high-performance single-molecule magnets (SMMs) is challenging. Here, a heptadentate pentapyridyldiamine (BPA-TPA) ligand and fine-tuned axial phenoxy ligands are used to synthesize two triangular dodecahedral Dy(III) complexes [Dy(BPA-TPA)(4-methoxy-PhO)](BPh4)2·3CH2Cl2 (4) and [Dy(BPA-TPA)(2,4-dimethyl-PhO)](BPh4)2·0.85CH2Cl2 (5). Both complexes have high effective barriers exceeding 400 K and magnetic hysteresis up to 8 K, which is ascribed to one strong and short Dy–O bond combined with seven weak Dy–N bonds. Ab initio calculations reveal the thermally activated quantum tunneling of magnetization through the first excited Kramers doublet, due to the presence of a strong axial Dy–O crystal ligand. Substitution of the phenoxy ligand leads to more constrained vibrations, improving the magnetic hysteresis behavior for 5. [ABSTRACT FROM AUTHOR]

Three CoII complexes, [Co2(H2L1)2](ClO4)4·4CH3OH (1), [Co2(H4L2)2](ClO4)4 (2) and [Co4(H4L2)4](ClO4)8 (3), were constructed by the self-assembly of the symmetrical dihydrazone ligands H2L1 and H4L2 with CoII ions under different synthetic conditions. The fish-bone-like complex 1 was obtained using the ligand H2L1 in methanol via the solvothermal method, while the self-assembly of H4L2 with CoII ions is solvent-dependent, producing the fish-bone-like complex 2 and [2 × 2] grid-like complex 3. Magnetic susceptibility measurements and theoretical calculations reveal that the large negative D values for the three complexes stem from their easy-axis magnetic anisotropy. Ac magnetic susceptibility measurements disclosed field-induced slow magnetic relaxation behaviors and the presence of Raman and/or direct processes of the three complexes at various applied dc fields. [ABSTRACT FROM AUTHOR]

Terminal fluoride ligands generate strong magnetic anisotropy in air-stable chiral dysprosium enantiomers supported by a bulky equatorial macrocycle, exhibiting a typical zero-field single-molecule magnet behaviour. [ABSTRACT FROM AUTHOR]

A dinuclear complex with the formula Dy2L2(H2L)Cl2(EtOH)2 (Dy2) has been synthesized by reacting DyCl3·H2O with a ligand H2L (H2L = N,N′-ethylenebis(salicylideneimine)) using ethanol as the solvent. Its crystal structure can be viewed as a dimer of two Dy(III) fragments, where each Dy(III) site shows a N2O6Cl coordination sphere with a pentagonal bipyramid geometry (D5h). Magnetic measurements reveal that Dy2 behaves as a single-ion magnet (SIM) under a zero field. When the field is applied, the ac magnetic susceptibilities show double and triple peaks under high (≥600 Oe) and low (<600 Oe) dc fields, respectively. In contrast to the common double relaxation pathways in SIMs, such multiple and intricate relaxation pathways have not been reported yet in the previous literature. In this work, by experimental analysis of the ac signals, we attribute the three slow relaxation pathways to quantum tunnelling of magnetization (QTM), intermolecular dipole–dipole interaction and spin reversal, respectively. In addition, ab initio calculations are used to elucidate the magnetic behaviours of Dy2. Overall, our work indicates that the interpretation of the relaxation process using double relaxation pathways is incomplete and difficult in previously reported literature. [ABSTRACT FROM AUTHOR]

Two lanthanide single-molecule magnets (SMMs) [Dy3(μ3-OH)(HL-1)3(H2O)3](NO3)2·3H3O (1, H3L-1 = (E)-3-(((8-hydroxyquinolin-2-yl)methylene)amino)propane-1,2-diol) and [Dy6(μ3-OH)4(H2L-2)4(HL-2)2(L-2)2] (2, H3L-2 = (E)-2-hydroxy-N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide) were synthesized and characterized structurally and magnetically. Complex 1 contains a triangular Dy3 core in which the three Dy3+ ions share a μ3-OH− anion and the deprotonated ligands of (HL-1)2− serve both capping and bridging functions, while 2 displays a centrosymmetric hexanuclear DyIII structure with two similar Dy3 triangular cores ligated by two fully deprotonated (L-2)3− ligands, each of which shares two μ3-OH− anions. All the DyIII ions are eight-coordinated with quasi D2d or C2v symmetry. Magnetic studies reveal that 1 exhibited two-step magnetic relaxation under an applied dc field of 800 Oe, with effective energy barriers of 40.1 and 31.0 K for the slow relaxation (SR) and fast relaxation regimes (FR), respectively. Meanwhile, 2 only showed a tail of slow magnetic relaxation at above 2 K. Ab initio calculations have been carried out to show the nature of their different magnetic properties. [ABSTRACT FROM AUTHOR]

While the interest in single-molecule magnets (SMMs) lies in their potential applications in information storage and quantum computing, the switching of their slow magnetic relaxation associated with dynamic crystal-to-crystal transformation is insufficiently exploited. Herein, three pentagonal-bipyramidal (PBP) Dy(III) complexes, [Dy(Bcpen)(Cl)3] (1), [Dy(Bcpen)(OPhCl2NO2)3] (2) and [Dy(Bcpen)(OPhCl2NO2)3]·0.5CH3CN (2·CH3CN), are successfully assembled, and structurally and magnetically studied (Bcpen = N,N-bis(4-chloro-2-methylenepyridinyl) ethylenediamine and Cl2NO2PhOH = 2,6-dichloro-4-nitrophenol). The molecular characteristics and magnetic properties of complexes 2 and 2·CH3CN, constructed with the motivation of modulating a magnetic switch by external stimuli, are systematically explored. Dramatically, 2 and 2·CH3CN can mutually transform through reversible single-crystal-to-single-crystal (SCSC) conversion associated with the capture and release of guest CH3CN molecules, resulting in an infrequent on/off switching of PBP Dy(III) molecule-based magnets. Further measurements on the desolvated and resolvated samples, complexes 2-re and 2·CH3CN-re, confirm the fascinating transformation processes. The magneto-structural relationship has been rationally investigated and discussed with ab initio calculations as well. [ABSTRACT FROM AUTHOR]

A series of Zn–Ln heteronuclear SMMs constructed by using a hexadentate compartment Schiff base Zn-precursor and lanthanoid ions were structurally and magnetically characterized, in which the two [Zn–Ln] moieties are bridged by a series of hydroxamic acids, resulting in double-decker tetranuclear complexes with the molecular formulae [ZnL1Ln(C2H5O)(qua)]2(CF3SO3)2·2C2H5OH ((1) Ln = Dy; (7) Ln = Yb), [ZnL1Ln(CH3O)(bnz)]2(CF3SO3)2·2CH3OH ((2) Ln = Dy), [ZnL1Ln(CH3O)(aca)]2(CF3SO3)2·2CH3OH ((3) Ln = Dy; (8) Ln = Yb), [ZnL2Dy(CH3O)(bnz)]2(CF3SO3)2·2CH3OH (4), [ZnL2Dy(CH3O)(aca)]2(CF3SO3)2·2CH3OH (5), and [ZnL3Dy(CH3O)(bnz)]2(CF3SO3)2·2CH3OH (6) (HL1 = N,N'-bis(2-hydroxy-3-methoxybenzylidene)-1,2-phenylenediamine, HL2 = N,N'-bis(2-hydroxy-3-methoxybenzylidene)-propane-1,2-diamine, HL3 = N,N'-bis(3-methoxysalicylidene)-1,3-propanediamine, qua = 2-quinolinecarboxylic acid, bnz = benzhydroxamic acid and aca = acetohydroxamic acid). Strikingly, the slow magnetic relaxation can be tuned by modifying the steric hindrance and/or electronic effect on the backbone of the Shiff base and the terminal substituents of hydroxamic acid, as well the magneto-structural correlations are studied. Furthermore, Yb congeners 7 and 8 were synthesized to explore dual-functional materials with both magnetic and fluorescence properties, and they displayed both slow magnetic relaxation and near-infrared (NIR) properties; the low temperature NIR spectroscopic data were correlated with the corresponding slow magnetic relaxation mechanism involving thermally activated ground states to the excited state. [ABSTRACT FROM AUTHOR]

A β-diketonate mononuclear dysprosium complex, with the formula [Dy(dpq)(BTFA)3] (1), has been prepared via self-assembly between 3-benzoyl-1,1,1-trifluoroacetone (BTFA) and dipyrido [3,2-d:2′,3′-f]quinoxaline (dpq) ligands. The crystallographic data reveal that the central Dy(III) ion is eight-coordinated by six oxygen atoms from three BTFA ligands and two N atoms from auxiliary dpq ligands, forming an approximately square-antiprismatic (SAP) coordination geometry with a D4d axial symmetry. Magnetic measurements point out that complex 1 exhibits single-molecule magnet (SMM) behaviours with an anisotropy barrier of 45.65 K under a zero direct-current (dc) field. With an applied dc field of 1200 Oe, the quantum tunnelling of the magnetization (QTM) is suppressed in 1 with an enhanced effective barrier of 178.42 K. A diamagnetic Y(III) analogue [Y(dpq)(BTFA)3] (2) and diluted species [Dy0.06Y0.94(BTFA)3(dpq)] (1@Y) were constructed to further perform the dilution experiment. The results unveil that the SMM behaviour observed in 1 is of molecular origin and is related to the single-ion magnetic behaviour of Dy(III) itself, even though the elimination of the dipolar and intermolecular interactions can modestly slow down the magnetic relaxation rate. The relaxation mechanisms and magneto-structure relationship are rationally discussed by ab initio calculations as well. [ABSTRACT FROM AUTHOR]

Based on the organic ligand 2,2′-(((pyridine-2,6-diylbis(methylene))bis((pyridin-2-ylmethyl)-azanediyl))-bis(methylene))diphenol (H2L), and dysprosium salts with different anions, two mononuclear and one dinuclear complexes, namely, [Dy(L)(H2O)](ClO4)·2CH3CH2OH (1), [Dy(L)(NO3)] (2) and [Dy2(L)(dbm)4] (3, Hdbm = dibenzoylmethane), were synthesized and structurally and magnetically characterized. In complexes 1 and 3, the Dy centers are octa-coordinated with triangular dodecahedral (local D2d symmetry) environments. Complex 1 is dimeric by hydrogen bond interactions between coordinated water molecules. In complex 3, two DyIII ions are linked by two phenoxy oxygen atoms to form a dinuclear cluster. The DyIII ion in complex 2 is nine-coordinated and adopts a spherical capped square antiprism geometry with a C4v symmetry. Magnetic measurements and theoretical calculations reveal that the magnetic couplings between two phenoxyl-bridging DyIII ions in complex 3 are antiferromagnetic and mostly originate from the exchange coupling. Both complexes 1 and 2 exhibit single molecule magnet behaviors under zero direct-current field with effective energy barriers of 50.94 K and 12.26 K, respectively. Complex 3 only exhibits frequency-/temperature-dependent out-of-phase signals, and no peak is observed. [ABSTRACT FROM AUTHOR]

A series of five mononuclear β-diketonate-Dy(III) complexes, with formulas Dy(ntfa)3(Br-bpy) (1), Dy(ntfa)3(Br2-bpy) (2), Dy(ntfa)3(5,5-(CH3)2-bpy) (3), Dy(ntfa)3(4,4-((CH3)3)2-bpy) (4) and Dy(ntfa)3(4,4-(CH3)2-bpy) (5) (ntfa = 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione, Br-bpy = 5-bromo-2,2′-bipyridine, Br2-bpy = 4,4′-dibromo-2,2′-bipyridine, 5,5-(CH3)2-bpy = 5,5′-di-methyl-2,2′-bipyridine, 4,4-((CH3)3)2-bpy = 4,4′-di-tert-butyl-2,2′-bipyridine, and 4,4-(CH3)2-bpy = 4,4′-di-methyl-2,2′-bipyridine), have been prepared by altering the capping N-donor coligands. Dy(III) ions in all complexes possess N2O6 octa-coordinated environments, displaying a distorted square antiprismatic D4d symmetry in complexes 1–4, as well as a triangular dodecahedron D2d symmetry in 5. Magnetic investigations evidence the SIM behavior in the five complexes with the energy barriers (Ueff) of 104.19 K (1), 122.93 K (2), 84.20 K (3), 64.16 K (4) and 80.23 K (5) under zero applied dc field. The potential QTM effects in the title complexes are successfully suppressed in the presence of the extra applied fields. The crystal field parameters and orientations of the magnetic easy axes were obtained from the simulation of the magnetic data and the electrostatic model calculation. The distinct electronic effects originating from the subtle changes of the substituents on the capping N-donor coligands induce varying coordination microenvironments and geometries on the Dy(III) sites, further drastically impacting the overall magnetic properties of the title complexes. The disparities of the uniaxial anisotropy and the magnetic dynamics for 1–5 have been elucidated by ab initio calculations as well. [ABSTRACT FROM AUTHOR]

Four DyIII complexes, [Dy2(NO3)4(L)2(H2O)2]·2MeCN (1), [Dy2(NO3)4(L)2(H2O)2]·2(NO3)·DMBD·2MeOH (2), [Dy2(NO3)4(L)2(TPO)2]·2MeCN (3) and [Dy2(L′)6(H2O)2]·4MeCN (4), were elaborately synthesized, structurally characterized and magnetically investigated (HL = 2,6-dimethoxyphenol, HL′ = 4-hydroxy-3,5-dimethoxybenzaldehyde, DMBD = 1,1′-dimethyl-[4,4′-bipyridine]-1,1′-diium and TPO = phosphine triphenyl oxide). In 1–3, the nearly planar molecular structures consisting of two DyIII ions and two L ligands are almost perpendicular to four nitrate ligands, which provides an opportunity to introduce auxiliary ligands (H2O or TPO) at the terminal position along the Dy⋯Dy orientation of [Dy2]. The slightly discrepant coordination environment around the DyIII ion with different terminal ligands plays a key role in tuning the magnetic anisotropy, and further strongly affects the magnetic properties of 1–4. The magnetic studies reveal that they all behave as single-molecule magnets (SMMs) at zero dc field with ferromagnetic dipole–dipole interaction between DyIII ions. The dynamic magnetic investigations give the energy barriers of 107.5 (1), 127.1 (2), 168.7 (3) and 251.9 K (4), respectively. The magnetic axis orientation of the ground state gradually verges on the Dy–Oaux bond from 1 to 4, leading to the stronger uniaxial anisotropy of DyIII ions and better SMM properties of 3 and 4. In addition, complexes 3 and 4 possess higher energy barriers than reported dinuclear DyIII-SMMs also constructed from HL or HL' with β-diketone. It is believed that the ligands coordinating to the DyIII ion at both terminals of the Dy⋯Dy linkage improve the SMM properties of dinuclear DyIII complexes. This design may provide a new strategy for obtaining dinuclear DyIII-based SMMs. [ABSTRACT FROM AUTHOR]

To explore the influences of magnetic interactions on the relaxation dynamics of single-molecule magnets (SMMs) and to understand the relationship between single-ion relaxation and the relaxation of a molecular entity, it is very important to design dinuclear lanthanide-based SMMs with two-step relaxation processes. Here, three Dy2 complexes of compositions [Dy2(L)2(NO3)2(MeOH)2] (1), [Dy2(L)2(NO3)2(EtOH)2] (2), and [Dy2(L)2(NO3)2(DMF)2]·0.5EtOH (3) (H2L = 2-(((2-hydroxy-3-methoxybenzyl)imino)methyl)-4-methoxyphenol) were successfully synthesized via elaborately introducing different terminal solvent ligands. X-ray single-crystal diffraction analyses revealed that complexes 1–3 are isostructural. The two DyIII ions of 1 and 2 both adopt D2d symmetry, while the two DyIII centres of 3 display D2d and D4d symmetries, respectively. The magnetic property studies of 1–3 indicated that all three complexes exhibit single-molecule magnet (SMM) behaviours with energy barriers of 104 K for 1, 98.94 K for 2, and 76.28 K and 45.54 K for 3 under zero dc field. The target of assembling Dy2 SMMs with two-step relaxation processes was achieved by gradually increasing the sizes of the terminal solvent ligands. Complex 3 exhibits two-step relaxation processes. Complete active space self-consistent field (CASSCF) calculations were performed on 1–3 to rationalize the observed differences in the magnetic behaviour. It is found that both the angles between the magnetic axis and the vector connecting two DyIII ions and the symmetries of DyIII ions are vital factors that affect the energy barriers of 1–3. The high local symmetries of the central metals in 1 and 2 make the complexes act as SMMs with higher energy barriers, while the smaller angle and different symmetries of the two DyIII ions render complex 3 as a SMM with a two-step relaxation process. This work demonstrates a new methodology for preparing SMMs with two-step relaxation processes by fine-tuning the terminal solvent ligands. [ABSTRACT FROM AUTHOR]

The utilization of two Schiff-base ligands H2L1 and H2L2 (H2L1 = 4-chloro-2-(((3-ethoxy-2-hydroxybenzyl)imino)methyl) phenol, H2L2 = 2-(((3-ethoxy-2-hydroxybenzyl)imino)methyl)-4-methoxy-phenol) with different substituents at the backbone of phenol in the construction of dinuclear dysprosium single-molecule magnets (SMMs) is reported. Two complexes of formulae [Dy2(L1)2(NO3)2(EtOH)(DMF)]·2EtOH (1) and [Dy2(L2)2(NO3)2(MeOH)2] (2) have been prepared and structurally characterized. X-ray crystallographic analysis revealed that the four DyIII ions of 1 and 2 all adopt NO7 coordination environments. The two DyIII centers of 1 exhibit triangular dodecahedron (D2d) and square antiprism (D4d) geometries, respectively, while the two DyIII sites in 2 both show triangular dodecahedron geometry with D2d symmetry. Magnetic analyses indicated that both complexes display SMM behavior with energy barriers of 86.91 K (1) and 93.70 K (2), respectively. The slight enhancement of the energy barrier of 2 reveals that the coordination geometries of DyIII ions would affect the magnetic behaviors of 1 and 2. Complete Active Space Self-Consistent Field (CASSCF) calculations were conducted for 1 and 2 to illustrate the slight variation of the magnetic behaviors. The calculated results are well consistent with those of the experimental outcomes. [ABSTRACT FROM AUTHOR]

The photochromic and magnetic properties of two dithienylethene (DTE)-based complexes, [Dy(NO3)3(Lo)2(MeOH)] (1-o) and [Dy(NO3)3(Lo)3] (2-o) (Lo = 4,5-bis(2,5-dimethylthiophen-3-yl)-1,3-dimethyl-1,3-dihydro-2H-imidazol-2-one), were experimentally studied in detail with the help of theoretical calculations. Both complexes exhibit an instantaneous and strong reversible photochromic response to UV/Vis irradiation, as evidenced from spectroscopic tests, and complex 1-o behaves as a typical field-induced single-molecule magnet (SMM). By controlling the reaction ratio of Lo and Dy(NO)3, Lo replacing a coordinated methanol molecule in 1-o results in the production of complex 2-o, whose single-molecule behavior is off. Upon irradiation with 254 nm light, the SMM properties of 1-o deteriorate with the energy barrier decreasing from 68.1 to 44.3 K while the magnetic dynamics of complex 2-o shows no response to irradiation. Ab initio calculations reveal that the quantum tunnelling of magnetization between the ground Kramers doublets in 2-o is quite strong, leading to the disappearance of SMM behavior. For complex 1-o, the strong magnetic anisotropy and moderate quantum tunnelling of magnetization relative to 2-o give rise to an appropriate energy barrier for SMM. On the other hand, the decrease in energy barriers for 1-o after irradiation results from the weakening of magnetic anisotropy, which is caused by the stronger charge delocalization of the coordinated carbonyl oxygen atom of the ring-closed DTE ligand. By regulating the reactant ratio, two photochromic DTE-based Dy(III) complexes are obtained and the SMM properties of complex 1-o can be tuned by the light-induced isomerization of the dithienylethene ligand. [ABSTRACT FROM AUTHOR]

The novel multidentate chelating ligands N′-(2-pyridylmethylidene)-2-(2-pyridylmethylideneamino)benzohydrazide (Hpphz) and N′-(2-salicylmethylidene)-2-(2-salicylmethylideneamino)benzohydrazide (H3sshz), which incorporate both amine and acylhydrazine Schiff base groups, were synthesized and investigated in DyIII coordination chemistry. The reactions of Hpphz and Dy(OAc)3·4H2O have yielded two {Dy2} featuring double OAc− bridges: [Dy2(H2aphz)2(OAc)4(ROH)2] [R = Me (1) and Et (2)], where the Hpphz ligands were in situ hydrolyzed into 2-amino-(2-pyridylmethylideneamino)benzohydrazide ions (H2aphz−). Besides, the reaction between H3sshz and Dy(NO)3·6H2O afforded a [Dy6(sshz)4(μ3-OH)4(μ4-O)(MeOH)4]2·17.5MeOH·2H2O cluster (3). This cluster contained two discrete {Dy6} cores, each of which consisted of a pair of {Dy3} triangular units. All the complexes displayed a single relaxation process of single-molecule magnet (SMM) behaviors under a zero dc field. Both 1 and 2 showed field-induced dual magnetic-relaxation behaviors. However, their diluted samples (1@Y and 2@Y) only showed one-step relaxation behaviors whether under a zero or applied dc field, indicating that the dual magnetic-relaxation behaviors of 1 and 2 were absent after the dilution. Combined with ab initio calculations, it could be infered that the dual magnetic-relaxation behaviors of 1 and 2 might be ascribled to the joint contributions of the single ion anisotropy and magnetic interactions. Examples of this type are rather rare in previous studies. Ab initio calculations also suggested that the discrepancy between the relaxation processes of 1 and 2 may be caused by the small difference between their magnetic interactions. [ABSTRACT FROM AUTHOR]

Six dimetallic lanthanide complexes, [Ln2(L′)(acac)4] (1Dy–3Gd) (Ln = Dy (1Dy), Tb (2Tb) and Gd (3Gd)) and [Ln2(L′)(tfac)4] (4Dy–6Gd) (Ln = Dy (4Dy), Tb (5Tb) and Gd (6Gd)) (H2L′ = 1,9-dichloro-3,7,11,15-tetraaza-1,9(1,3)-dibenzenacyclohexadecaphane-2,10-diene-1,9-diol), have been synthesized by the reaction of lanthanide nitrates with the HL ligand in the presence of acetylacetonate (acac) (or trifluoroacetylacetonate (tfac) and triethylamine (HL = 4-chloro-2,6-bis(-((3-((3-(dimethylamino)propyl)amino)propyl)imino)methyl)phenol). Ln-Assisted modification of the Schiff base HL occurred and led to the formation of a new macrocyclic ligand (H2L′). X-ray crystallographic analysis revealed that the LnIII ions of complexes 1Dy–6Gd are all eight-coordinated in a square antiprismatic geometry with D4d local symmetry. Magnetic measurements of these complexes revealed that 1Dy and 4Dy show single-molecule magnet behaviour with energy barriers of 66.7 and 79.0 K, respectively, under a zero direct magnetic field. The orientations of the magnetic axes and crystal field parameters were obtained from theoretical calculations and an electrostatic model. The magneto-structural correlations of SMMs 1Dy and 4Dy are further discussed in detail. [ABSTRACT FROM AUTHOR]

The reactions of LnIII ions with a versatile pyridyl-decorated dicarboxylic acid ligand lead to the formation of a series of novel three-dimensional (3D) Ln-MOFs, [Ln3(pta)4(Hpta)(H2O)]·xH2O (Ln = Dy (1), Eu (2), Gd (3), Tb (4), H2pta = 2-(4-pyridyl)-terephthalic acid, x = 6 for 1, 2.5 for 2, 1.5 for 3 and 2 for 4). The Ln3+ ions act as nine-coordinated muffin spheres, linking to each other to generate trinuclear {Ln3(OOC)6N2} SBUs, which are further extended to be interesting 3D topological architectures. To the best of our knowledge, the Dy-MOF exhibits zero-field single-molecule magnet (SMM) behaviour with the largest effective energy barrier among the previously reported 3D MOF-based Dy-SMMs. The combined analyses of a diluted sample (1@Y) and ab initio calculations demonstrate that the thermally assisted slow relaxation is mainly attributed to the single-ion magnetism. Furthermore, fluorescence measurements reveal that H2pta can sensitize EuIII and TbIII characteristic luminescence. [ABSTRACT FROM AUTHOR]

We present the syntheses, crystal structures, magnetic properties and theoretical calculations performed on two dinuclear dysprosium complexes with formulas Dy2(L1)2(L2)2(CH3CH2OH)(CH3OH) (1) and Dy2(L1)2(L3)2(CH3OH)2·1.5CH3OH (2). Single-crystal X-ray structural data analyses showed that both complexes contain two nonequivalent dysprosium ions bridged by two phenolate oxygen atoms. In both complexes, each dysprosium site adopts a N2O6 coordination constitution and triangular dodecahedron (D2d) configuration geometry with different distortion degree. Both complexes display single-molecule magnet behavior manifested by frequency-dependent out-of-phase alternating current susceptibility signal peaks under a zero-applied dc field. The effective energy barrier of the magnetization reversal and relaxation time values are 61 K, 7.1 × 10−6 s (1) and 51 K, 1.9 × 10−6 s (2), respectively. Theoretical calculations revealed a drastic discrepancy between the orientations of the anisotropy axis of the Dy2 ion observed in these two dinuclear complexes, resulting from the different spatial arrangements of the mixed ligands in the core structure. [ABSTRACT FROM AUTHOR]

The reaction of Dy(NO3)3·6H2O and an asymmetric Schiff-base linker 5-chloro-2-(((2-hydroxy-3-methoxybenzyl)imino)methyl) phenol (H2L) afforded a dinuclear compound [Dy2L2(HL)(NO3)(EtOH)]·0.5C2H5OH (1). Complex 1 features two inequivalent Dy(III) sites, where three ligand sets (one HL− moiety and two L2− groups) are shared by two Dy(III) ions. The strategic introduction of CH3COOH in the reaction system used for synthesizing 1 induces the replacement of the HL− ligand by the CH3COO− ion, consequently resulting in the generation of [Et3NH][Dy2L2(NO3)(CH3COO)2] (2). In complex 2, two Dy(III) centers adopt NO7 (D2d geometry) and NO6 (C2v) coordination sphere, respectively. DC magnetic susceptibility studies for the two complexes indicate ferromagnetic interactions. Complexes 1 and 2 exhibit single-molecule magnet behavior with two-step slow relaxation processes due to the possession of inequivalent metal sites. The energy barriers of 69.19 and 45.73 K for 1, and 92.77 and 72.95 K for 2 are determined. Theoretical calculations reveal that the two-step relaxation processes in both 1 and 2 mainly originate from the single-ion magnetism of two distinct Dy(III) ions with inequivalent coordination environments. [ABSTRACT FROM AUTHOR]

Four chair-like hexanuclear Fe–Ln complexes containing mixed organic ligands, namely, [Fe4Ln2{(py)2CO2}4(pdm)2(NO3)2(H2O)2Cl4]·xCH3CN·yH2O (Ln = GdIII (1, x = 1, y = 0), DyIII (2, x = 1, y = 1), HoIII (3, x = 0, y = 2), and ErIII (4, x = 1, y = 3); (py)2CO2H2 = the gem-diol form of di-2-pyridyl ketone and pdmH2 = 2,6-pyridinedimethanol) have been obtained by employing di-2-pyridyl ketone and 2,6-pyridinedimethanol reacting with FeCl3 and Ln(NO3)3 in MeCN. The structures of 1–4 are similar to each other except for the number of lattice solvent molecules. Four FeIII and two LnIII in these complexes comprise a chair-like core with the "body" constructed by four FeIII ions and the "end" constructed by two LnIII ions. Among the four compounds, 2 shows field-induced single molecule magnet behavior as revealed by ac magnetic susceptibility studies, with the effective energy barrier and the pre-exponential factor of 22.07 K and 8.44 × 10−7 s, respectively. Ab initio calculations indicated that, among 2_Dy, 3_Ho and 4_Er fragments, the energy gap between the lowest two spin–orbit states for 2_Dy is the largest, while the tunneling gap for 2 is the smallest. These might be the reasons for complex 2 exhibiting SMM behavior. Additionally, the orientations of the magnetic anisotropy of DyIII in 2 were obtained by electrostatic calculations and ab initio calculations, both indicating that the directions of the main magnetic axis of Dy1 ions are almost aligned along Dy1–O5 (O5 from the pdm2− ligand). [ABSTRACT FROM AUTHOR]

Four tetranuclear 3d–4f complexes, namely [Fe2Ln2(L)2(teaH)2(Cl)2](NO3)2·4CH3CN (H2L = N1,N3-bis(3-methoxysalicylidene)diethylenetriamine, teaH3 = triethanolamine, Ln = Dy for 1 and Ln = Gd for 1′) and [Co2Ln2(L)2(pdm)2(CH3COO)2(CH3OH)2](NO3)2·xCH3OH·yH2O (pdmH2 = 2,6-pyridinedimethanol, Ln = Dy, x = 5 and y = 2.5 for 2 and Ln = Gd, x = 6 and y = 1.5 for 2′), have been reported. Two FeIII and two DyIII in 1 formed a zigzag Fe1–Dy1–Dy1a–Fe1a arrangement with a Fe1–Dy1–Dy1a angle of 105.328(3)°. However, in contrast to 1, two CoIII and two DyIII ions in 2 formed a more linear Co1–Dy1–Dy1a–Co1a arrangement with a Co1–Dy1–Dy1a angle of 141.86(2)°. Additionally, two DyIII ions in 1 are eight-coordinated with a triangular dodecahedron geometry, while two DyIII ions in 2 adopt nine-coordination with a muffin geometry. Magnetic studies revealed slow magnetic relaxation behavior for 1, with an energy barrier Ea of 6.9 K. For 2, single molecule magnet behavior was presented under a zero dc field with an effective energy barrier Ueff of 64.0(9) K. Ab initio calculations for 1 and 2 indicate that compared to 2, complex 1 has a larger transversal magnetic moment of its ground Kramers doublets (KD) and a larger value of the tunnelling parameter (Δt) for the exchanged coupled ground state, which may result in poor single molecule magnet behavior for 1. [ABSTRACT FROM AUTHOR]

In search of simple approaches to rationally enhance the energy barriers in polynuclear dysprosium single-molecule magnets, a new system containing two structurally closely related dinuclear dysprosium complexes, namely [Dy2(L)2(DBM)2(DMF)2] (1) and [Dy2(L)2(DBM)2(DMA)2]·2DMA (2) (HDBM = dibenzoylmethane, H2L = 2-hydroxy-N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide), is introduced and the structure-dependent magnetic properties are investigated. The two complexes display only slight variations in the coordination geometries of the Dy(iii) ion but display remarkably different magnetic behaviors. By replacing the DMF (dimethylformamide) ligand in complex 1 with DMA (dimethylacetamide) in 2 while retaining the same coordination atoms, we were able to create a 3-fold enhancement in the energy barrier, from 24 K for complex 1 to 77 K for complex 2. Complete-active-space self-consistent field (CASSCF) calculations revealed that the charge distribution surrounding the Dy(iii) centers in 1 and 2 is the key factor in determining the relaxation properties of the SMMs. The introduction of an electron-donating CH3 group in DMA to replace the hydrogen in DMF resulted in a larger average charge along the magnetic axes of complex 2 compared to complex 1, which resulted in a stronger easy-axis ligand field, thus increasing the energy difference between the ground and the first excited states of complex 2. This work presents a simple method to rationally enhance the energy barrier in polynuclear lanthanide SMMs through fine-tuning of the electrostatic potential of the atoms along the magnetic axis. [ABSTRACT FROM AUTHOR]

A series of HMq-bridged dinuclear dysprosium complexes, namely, [Dy(acac)2(CH3OH)]2(μ-HMq)2 (1), [Dy(DBM)2]2(μ-HMq)2(n-C6H14) (2), [Dy(hmac)2]2(μ-HMq)2 (3) and [Dy(hfac)3]2(μ-HMq)2 (4) (HMq = 2-methyl-8-hydroxyquinoline, acac = acetylacetone, DBM = dibenzoylmethane, hmac = hexamethylacetylacetonate and hfac = hexafluoroacetylacetonate), were structurally and magnetically characterized. X-ray crystallographic analyses of the structures reveal that HMq serves as the effective bridge to link two Dy(iii) centers by means of the phenoxyl oxygen and nitrogen atoms and the periphery β-diketonate ligands complete the coordination sphere by bidentate oxygen atoms. The different substituents on the β-diketonate terminal lead to different coordination models mostly due to the steric hindrance of these substituents, and the electron-withdrawing or donating effects likely influence the strength of the ligand fields and the Dy(iii) ion anisotropy. Measurements of alternating-current (ac) susceptibility on complexes 1–4 reveal that complexes 3 and 4 display significant zero-field single-molecule magnetic (SMM) behavior with barrier energy Ueff/kB = 14.8 K, τ0 = 1.8 × 10−5 s and Ueff/kB = 9.2 K, τ0 = 1.7 × 10−5 s, respectively, whereas 1 and 2 exhibit field-induced SMM behavior, and these differences are attributed to the alteration on the periphery β-diketonate ligands. Their distinct slow magnetic relaxation behaviors were related to their different individual Dy(iii) ion magnetic anisotropy and intramolecular coupling, which were confirmed by ab initio calculations. [ABSTRACT FROM AUTHOR]

Three complexes with formula {Dy(q)2(L)}2(μ3-OH)2{Dy(q)(L)}2(solvents) (where q = 8-quinolinolate; L = acetylacetone (acac) with (CH2Cl2)2 = solvent (1), 1,3-diphenyl-1,3-propanedione (DBM) and (CH2Cl2)2 = solvent (2), and hexafluoroacetylacetone (hfac) and CHCl3 = solvent (3)) were structurally and magnetically characterized. They have similar Dy4 structural cores bridged by N and O atoms from 8-quinolinolate, and only differ in the peripheral β-diketonate ligands. The variable-frequency and temperature alternating-current (ac) magnetic susceptibility measurements reveal that complexes 1 and 2 display significant zero-field single-molecule-magnet (SMM) behavior, while complex 3 exhibits the field-induced SMM behavior, albeit they possess the nearly same primary coordination sphere. The ac susceptibility measurement on the diluted samples verified that their relaxation was of purely molecular origin, and their distinct slow magnetic behaviors were related to the replacement of the peripheral β-diketonate ligand, which is responsible for their different individual Dy(iii) ions’ magnetic anisotropy and intramolecular coupling, as confirmed by ab initio calculation. [ABSTRACT FROM AUTHOR]

The π–π stacking interaction, one of the main intermolecular forces, sometimes leads to amazing magnetic properties. Although the concept has been raised that spin density is one of the main factors that contribute to the magnetic coupling strength in intermolecular magnetic coupling systems, it has not been confirmed either experimentally or theoretically to date. Herein we present a study on the magnetostructural data of seven unpublished CuII complexes and ten reported radicals. It is confirmed for the first time that the spin density on short contact atoms is a major factor that contributes to the π–π stacking magnetic coupling strength. Based on the reported data to date, when the short contact distance is larger than the default contact radius, medium or relatively strong magnetic coupling strength could be obtained only if the spin density on the short contact atoms is greater than 0.1350; when the C…C short contact is less than the default contact radius of 3.4 Å, but not less than 3.351 Å, and the spin density is less than 0.1, neither medium nor strong magnetic coupling strength could be observed. Further, when the short contact distance decreases with a temperature drop, the spin densities on the relevant short contact atoms increase. In the complexes reported the small spin densities on the relevant short contact atoms are the major factors that result in the weak π–π magnetic coupling strength. [ABSTRACT FROM AUTHOR]