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Three rare isostructural heterometallic complexes [Na2{Ln4(μ3‐OH)2(ppt)4(Hppt)2(OAc)2}(DMF)4] ⋅ xH2O (H2ppt=3‐(2‐hydroxyphenyl)‐5‐(pyrazin‐2‐yl)‐1,2,4‐triazole, x=2.5, Ln=Dy (1); x=2, Ln=Er (2); x=0, Ln=Yb (3)) have been obtained. The structural analysis displayed that two NaI and four LnIII ions were linked together through N−N groups and O atoms to form a metallmacrocycle with the connectivity pattern [Dy−O−Na−N−N−Dy−O]2. Such cases possess rare hexametallic ring, which further displays one tetrametallic and two trimetallic cyclic units. Magnetic measurements reveal single‐molecule magnet (SMM) behavior for 1 with the effective energy barrier of 51.6 K and pre‐exponential factor of 6.16×10−6 s deduced from frequency‐dependent magnetic susceptibilities. Ab initio calculations prove that the weak ferromagnetic coupling mainly originats from the dipolar interaction. The transversal magnetic moments in the ground Kramers could suppressed the quantum tunneling of magnetization. [ABSTRACT FROM AUTHOR]

The modular construction method provides a feasible way to construct pre-designed cyano-bridged {LnIIIMIV/V} systems with more attractive structures and adjustable interactions between 4d/5d and 4f ions. In this work, the pentadentate Schiff-base ligands H2Ln (H2L1: 2,6-diacetylpyridine bis(nicotinoylhydrazone); H2L2: 2,6-diacetylpyridine bis(isonicotinoylhydrazone)) with multiple coordination sites were designed to coordinate with DyIII ions firstly, and then combined with K4M(CN)8·2H2O (M = W, Mo) by a liquid–liquid diffusion method to successfully synthesize two trinuclear structures {Dy[MIV(CN)8]0.5(HL1)(H2O)3}2·8H2O (1: M = W; 2: M = Mo), and two dinuclear structures {[Dy[MIV(CN)8](H3L2)(H2O)3]}·sol (3: M = W, sol = 11.5H2O; 4: M = Mo, sol = 2CH3OH·9.5H2O). Interestingly, deprotonation occurs in ligand H2L1 during the formation of complexes 1 and 2, while deprotonation/protonation processes both occur in ligand H2L2 during the synthesis of complexes 3 and 4. Magnetic analyses reveal that complexes 1–4 are all field-induced single-ion magnets (SIMs). The energy barriers (Ueff/kB) of complexes 1 and 2 are 92.83 K and 101.08 K, respectively, which are nearly three-fold higher than those of complexes 3 (30.19 K) and 4 (32.77 K). Ab initio calculations were performed on these series of {LnIIIMIV} heteronuclear complexes to provide more insights into the magnetic relaxation properties. This work provides another example of improving the SMM behaviors of cyano-bridged {LnIIIMIV} systems by deprotonation/protonation at different sites in the ligands. [ABSTRACT FROM AUTHOR]

The utilization of two isomorphic ligands with different substituents leads to two centrosymmetric DyIII dimers, namely, [Dy2(bfbpen)2(H2O)2]·2I− (1) and [Dy2(bcbpen)2(H2O)2]·2I−·0.5H2O (2) (H2bfbpen = N,N′-bis-(2-hydroxy-5-fluoro-benzyl)-N,N′-bis-(pyridin-2-ylmethyl)ethylenediamine and H2bcbpen = N,N′-bis-(2-hydroxy-5-chloro-benzyl)-N,N′-bis-(pyridin-2-ylmethyl)ethylenediamine). Although Dy ions in both compounds uniformly exhibit a square-antiprism geometry, the critical difference found in the terminal substituents of the two ligands fine-tunes the local crystal field around Dy centers and the dinuclear molecular structures of 1 and 2. Magnetic investigations unveil that both 1 and 2 display dynamic magnetic relaxation of single-molecule magnet (SMM) behaviour with different energy barriers of 20.9 K for 1 and 72.7 K for 2 under a zero direct-current (dc) field, as well as 26.9 K for 1 under a 1200 Oe dc field. Compared to 1, the stronger uniaxial anisotropy and magnetic exchange in 2 render it a better SMM as evidenced by the higher energy barrier. Ab initio calculations are also performed on both Dy2 compounds to rationalize the observed discrepancy in their magnetic behaviours. The contribution illustrates that the SMM behaviour could be effectively enhanced by means of deliberate local structural manipulation. [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]

Two novel Co–Dy heterometallic complexes, namely, [Co III2 Dy III2 (HL)L{(py)2CO2}{(py)2C(OCH3)O}(NO3)4CH3OH]·2CH3CN·2.5H2O (1, H3L = 2-((2-hydroxy-benzylidene)amino)propane-1,3-diol, (py)2C(OH)2 = the gem-diol form of di-2-pyridyl ketone (dpk) and (py)2C(OCH3)OH = the hemiacetal form of dpk) and [CoIII{(py)2C(OH)O}2][Co II2 Dy III4 DyIII(HL)4(L)4]·3CH3CN·15H2O (2), have been obtained by employing H3L, dpk and Dy(NO3)3·5H2O reacting with Co(NO3)2·6H2O or anhydrous Co(CH3CO2)2 in the solutions of CH3OH and CH3CN (V/V = 1/20) containing N(Me)4OH·5H2O or triethylamine. Structural analysis indicated that two DyIII and two CoIII in 1 formed a star-like topology, while the metal ions in [Co II2 Dy III4 DyIII(HL)4(L)4]− of 2 formed a cross-shaped topology, in which one DyIII and two CoII formed a linear Co II2 DyIII paramagnetic unit. Interestingly, the paramagnetic Co II2 DyIII units in 2 were isolated not only by four diamagnetic CoIII in the [Co II2 Dy III4 DyIII(HL)4(L)4]−, but also by the diamagnetic [CoIII{(py)2C(OH)O}2]+. More interestingly, the distortion of the square antiprism (SAP-8) coordination geometry of DyIII in 2 can be ascribed to the presence of four long Dy–O bonds and four short Dy–O bonds, which could result from the discrepancies of the polarization of CoII and CoIII. Magnetic studies indicated that 1 exhibit two types of magnetic relaxation behavior, in which the magnetic relaxation of the fast relaxation (FR) phase is mainly governed by QTM, while that of the slow relaxation (SR) phase is mainly governed by Orbach and Raman processes with an effective energy barrier (Ueff) value of 59.4(9) K. To our knowledge, the Ueff value is relatively high among the reported CoIII–DyIII heterometallic complexes. For 2, it only shows slow relaxation behavior with a Ueff of 6.43 K. Ab initio calculations revealed that the SR phase and FR phase are governed by the magnetic relaxation of Dy2 and Dy1, respectively, though the axial symmetry of Dy2 (muffin, Cs) is lower than that of Dy1 (triangular dodecahedron, D2d). However, for 2, the theoretical calculations indicated that the severely compressed SAP-8 geometry of DyIII leads to a relatively low Ueff value. [ABSTRACT FROM AUTHOR]

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

Based on a β-diketiminate ligand, an iron(III) tetrahedral high-spin complex, [LFeIII(Cl)2] (1), and an iron(II) high-spin triangular planar complex, [LFeIICl] (2), have been synthesized and structurally characterized. Also, complex 1 can be considered as a precursor to produce 2via a reduction process, with a concomitant change in its magnetic anisotropy. Combined experiments and ab initio calculations support the observation of field-induced single-ion magnet (SIM) behaviour for 2 with an effective spin-reversal energy barrier of Ueff = 40.02 K, as a direct consequence of the large intrinsic magnetic anisotropy (easy axis) arising from out-of-state spin-orbit coupling in the trigonal planar FeII complex. Noteworthy butterfly hysteresis loops were observed from 2 up to 8 K, which represents the first case in Fe(II) complexes. [ABSTRACT FROM AUTHOR]

Two β-Diketiminate cobalt(II) compounds of formula [LCo(μ-Cl)]2·2C6H14 (1) and [LCoClPy]·0.5C7H8·0.5C6H14 (2) (L = [PhC-(PhCN-Dip)2]−, Dip = 2,6-iPr2C6H3) have been synthesized and structurally characterized by single crystal X-ray diffraction. Compound 1 exhibits a dinuclear structure, whereas 2 is a mononuclear structure having a pyridine ligand. The tetra-coordinate CoII centers in both compounds show distorted tetrahedral geometry configuration. Magnetic measurements reveal that only 2 exhibits field-induced slow relaxation of magnetization with an effective spin-reversal energy barrier of 16.27 K, though large easy-axis magnetic anisotropies for both compounds are unveiled by the analysis of ab initio calculations. Dimeric Co–Co units in 1 indicate intramolecular antiferromagnetic interaction. Compared to individual CoII fragment of 1, the first excited quartet state of 2 is strongly destabilized, leading to a smaller unquenched orbital angular momentum and D value. The comprehensive factors above are responsible for the difference in the magnetic behavior between 1 and 2. [ABSTRACT FROM AUTHOR]

Recently, the choice of ligand and geometric control of mononuclear complexes, which can affect the relaxation pathways and blocking temperature, have received wide attention in the field of single-ion magnets (SIMs). To find out the influence of the coordination environment on SIMs, two four-coordinate mononuclear Co(II) complexes [NEt4][Co(PPh3)X3] (X = Cl−, 1; Br−, 2) have been synthesized and studied by X-ray single crystallography, magnetic measurements, high-frequency and -field EPR (HF-EPR) spectroscopy and theoretical calculations. Both complexes are in a cubic space group Pa3¯ (No. 205), containing a slightly distorted tetrahedral moiety with crystallographically imposed C3v symmetry through the [Co(PPh3)X3]− anion. The direct-current (dc) magnetic data and HF-EPR spectroscopy indicated the anisotropic S = 3/2 spin ground states of the Co(II) ions with the easy-plane anisotropy for 1 and 2. Ab initio calculations were performed to confirm the positive magnetic anisotropies of 1 and 2. Frequency- and temperature-dependent alternating-current (ac) magnetic susceptibility measurements revealed slow magnetic relaxation for 1 and 2 at an applied dc field. Finally, the magnetic properties of 1 and 2 were compared to those of other Co(II) complexes with a [CoAB3] moiety. [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]

Four mononuclear 9-coordinate Dy-based complexes, [Dy(HL1)2(NO3)3(CH3OH)] (1Dy), [Dy(HL2)2(NO3)3(H2O)] (2Dy), [Dy(HL3)3(NO3)3]·CH3CN (3Dy), and [Dy(HL4)3(NO3)3] (4Dy), have been constructed by neutral Schiff-base ligands (1-[N-(4-R)aminomethylidene-2(1H)-naphthalenone, R = –Cl (HL1), –NO2 (HL2), –OCH3 (HL3), –I (HL4)). By tuning the terminal substituent group of HL ligands, the number of HL ligands coordinated to the central Dy3+ ion unexpectedly varies from 2 to 3, and the local symmetry around the Dy3+ ion reduces from D3h to Cs. Magnetic measurements reveal that 2Dy can display single-ion magnet (SIM) behavior in zero dc field, while 1Dy, 3Dy and 4Dy show field-induced slow magnetic relaxation. Ab initio calculations were employed to elucidate magnetic anisotropy in the complexes, including g-tensors, averaged transition magnetic moments and magnetic easy axes. The difference in magnetic behaviors of the four complexes can be ascribed to the terminal substituent effect of neutral Schiff-base ligands. [ABSTRACT FROM AUTHOR]

Three mononuclear, dinuclear and one-dimensional dysprosium(III) complexes based on 3-azotriazolyl-2,6-dihydroxybenzoic acid (H4ATB) of [Dy(H3ATB)3]·3H2O (1), [Dy2(H2ATB)2(H2DHB)2(H2O)4]·2CH3CN·5H2O (2), and [Dy2(H2ATB)2(DCB)(DMF)2(H2O)2]·4DMF (3) were synthesized and structurally characterized by X-ray single crystal diffraction (H3DHB = 2,6-dihydroxybenzoic acid, H2DCB = 1,4-dicarboxybenzene). Complex 1 was used as a precursor to synthesize complexes 2 and 3, and 2 was further used to synthesize 3. Complex 1 is a mononuclear complex, in which the Dy(III) ion is in a nine-coordinated structure surrounded by three tridentate chelate H3ATB− ligands. Complex 2 displays a dinuclear structure bridged by two μ2 carboxyl groups of two H2DHB− ligands and two μ1,1-O atoms from the phenolic hydroxyl groups of two H2ATB2− ligands. Complex 3 shows a one-dimensional structure formed by two bridging DCB2− ligands. The magnetic measurements were performed on three complexes 1–3, and they showed different magnetic behavior. Complex 1 shows a field-induced slow magnetic relaxation. Complexes 2 and 3 display distinct slow magnetic relaxation under zero dc field with energy barriers (Ueff) of 26(2) cm−1 and 11(1) cm−1, respectively. The magnetic behavior of three complexes 1–3 was investigated by ab initio calculations. [ABSTRACT FROM AUTHOR]

Three mononuclear Co(II) complexes with the compositions of [Co(L1)2] (1), [Co(L2)2(CH3CN)] (2) and [Co(L3)2] (3) (HL1 = 2-((E)-(2-fluorobenzylimino)methyl)-4,6-dibromophenol, HL2 = 2-((E)-(3-fluorobenzylimino)methyl)-4,6-dibromophenol and HL3 = 2-((E)-(4-fluorobenzylimino)methyl)-4,6-dibromophenol) were prepared and structurally determined. The changes in the F-positions in the ligands and solvents led to the formation of these products with various coordination geometries. Both complexes 1 and 3 are four-coordinated and their coordination geometries can be described as tetrahedron and seesaw, whereas complex 2 is five coordinated with a coordination configuration in between trigonal bipyramid and square pyramid. Static magnetic studies reveal that all these complexes exhibit considerable easy-axis magnetic anisotropy. The easy-axis magnetic anisotropy of 1 and 3 mainly derives from the first quartet excited state, whereas that of 2 primarily originates from the first, third and fourth quartet excited states established by theoretical calculations. All the resulting complexes display field-induced slow magnetic relaxation. Complex 3 represents the first Co(II) single ion magnet with a seesaw coordination geometry. Ab initio calculations predict that the magnetic anisotropy will enhance when the seesaw coordination geometry varies from distortion to regulation. [ABSTRACT FROM AUTHOR]

A dinuclear dysprosium cluster [Dy2(NO3)4(H2O)2(L)2]·2CH3CN was successfully prepared by employing HL (HL = 2,6-dimethoxyphenol) and Dy(NO3)3·6H2O in a mixture of CH3OH and CH3CN. The conversion of this Dy2 compound by reaction with additional deprotonated ligand generated a Dy9 cluster [Dy9(μ4-OH)2(μ3-OH)8(μ2-OCH3)4(NO3)8(H2O)8(L)4](OH)·2H2O with the well-known "diabolo" topology. Magnetic investigation revealed that both of the clusters exhibit typical SMM characteristics, and variable magnetic relaxation with the energy barrier changing from 217.87 K to 9.24 K along with the transition from a dinuclear dysprosium cluster to a nonanuclear one. Ab initio calculations further confirm the corresponding structure–activity relationships that originate the different magnetic behaviours. This design may afford a feasible strategy for modulating the magnetic relaxation dynamics of polynuclear systems. [ABSTRACT FROM AUTHOR]

Three mononuclear tetrakis(pseudohalido)-cobalt(II) complexes (Ph4P)2[Co(E)4] (E = N3−, 1; NCO−, 2; NCS−, 3) have been synthesized and structurally characterized. Each compound contains a distorted tetrahedral Co2+ ion coordinated by four pseudohalide ligands. The magnetic properties of 1–3 have been studied using direct-current magnetic measurements and high-frequency and -field EPR spectroscopy (HFEPR), suggesting easy-axis magnetic anisotropy for 1 and 2 and easy-plane anisotropy for 3. Analysis of the HFEPR spectra yielded D values of −5.23 and +3.63 cm−1 for 2 and 3, respectively. The absence of the EPR signal in 1 is consistent with a large, negative value of the zero-field splitting (ZFS) parameter D in 1. The nature of magnetic anisotropies of 1–3 has also been confirmed by ab initio calculations. The calculated D values are consistent with those determined using magnetometry and HFEPR studies. Alternating current (AC) magnetic susceptibilities reveal slow magnetic relaxation under an applied magnetic field, thus indicating that 1–3 are field-induced single-ion magnets (SIMs). [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]

A family of cyano-bridged 3d–4f 1D chain compounds, {RE[TM(CN)6(2-PNO)5]}·(H2O)4 {RE = YIII, TM = [FeIII]LS (1); RE = DyIII, TM = CoIII (3); RE = ErIII, TM = [FeIII]LS (4), CoIII (5); 2-PNO = 2-picoline-N-oxide} and {RE[TM(CN)6(2-PNO)5]} {RE = DyIII, TM = [FeIII]LS (2)}, were synthesized and characterized. Single-crystal X-ray diffraction studies reveal that compounds 1 and 3–5 are isostructural, while compound 2 has a similar 1D chain structure with a different chain to chain arrangement. An axially-elongated pentagonal bipyramidal (D5h) coordination geometry is formed with five 2-PNO ligands in the equatorial plane and two [TM(CN)6]3− on the apical sites around the rare earth ions in these compounds. A comparison of the magnetic relaxation behaviour in detail reveals that it is more favorable for the Er (4 and 5) than the Dy analogues (2 and 3) to exhibit SIM properties in this axially-elongated D5h coordination environment. Under zero dc field, ac susceptibility measurements show that the Dy analogues have no magnetic relaxation behaviour, while the Er analogues exhibit frequency dependence despite the strong QTM effect. Under a 1 kOe dc field, the Er analogues generally show 1–2 orders of magnitude longer relaxation time at each selected temperature and a higher relaxation energy barrier than the Dy analogues. And the RECo compounds (3 and 5) show a more suppressed QTM effect than the corresponding REFe (2 and 4) compounds, which may be ascribed to the elimination of the fluctuation field from the neighbouring [FeIII]LS ions. The ab initio calculations indicate the misplacement between the orientation of the main magnetic axis and the structural axis in the Dy analogues, and the relative consistency in the Er analogues, which should be the source of the Er analogues showing better SIM properties than the Dy analogues. [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]

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]

A class of cyano-bridged 3d–4f zig-zag chain compounds, {RE[TM(CN)6] (PNO)2(H2O)4}·(H2O) {RE = YIII, TM = [FeIII]LS (1); RE = DyIII, TM = [FeIII]LS (2), CoIII (3)}, have been synthesized and characterized by single-crystal X-ray diffraction. The rare earth ions in these compounds are situated in a slightly distorted triangular dodecahedral (D2d) coordination environment. The magnetic properties of compounds 1–3 have been comparatively studied in detail. Under a zero dc field, the temperature dependence of ac susceptibility measurements for YFe (1) indicates the absence of magnetic relaxation stemming from the single anisotropic [FeIII]LS ion. The dysprosium analogue DyFe (2) shows only magnetic relaxation behavior with a prominent QTM effect, while DyCo (3) exhibits SIM properties not completely covered by QTM, with an extracted energy barrier of 73 K under a zero dc field. The ab initio calculations indicate that both compounds 2 and 3 are SMMs with well-behaved magnetic relaxation properties primarily from the individual DyIII ion. Therefore, the different magnetic behaviors exhibited by compound 2 compared to 3 may be ascribed to the stronger QTM effect caused by the extra weak interaction of [FeIII]LS ions in 2 as a fluctuating transverse field around the DyIII ion. The QTM effect for both 2 and 3 is suppressed under an applied dc field with an effective energy barrier of 134 and 150 K, respectively. Compared with compound 2, the higher extracted Ueff/kB and χ′′(T) peak temperature for 3 should be further attributed to its slightly higher single-ion axiality as calculated and the elimination of the transverse field from the [FeIII]LS ion. [ABSTRACT FROM AUTHOR]

The complexes of lanthanide metals, especially dysprosium, can generally exhibit excellent magnetic properties. By means of modifying ligands, dual functions or even multi-functions can be achieved. Here, we synthesized an eight-coordinate Dy(III) complex 1, [Dy(HL-o)2(MeOH)2](ClO4)3·4.5MeOH, which is single-molecule magnet (SMM), and the introduction of the rhodamine 6G chromophore in the ring-opened ligand HL-o realizes ligand-centered fluorescence in addition to SMM. Magnetic measurements and ab initio calculations indicate that the magnetic relaxation for complex 1 should be due to the Raman relaxation process. Studies on magneto-structural correlationship of the rhodamine salicylaldehyde hydrazone Dy(III) complexes show that the calculated energy of the first Kramers Doublet (EKD1) is basically related to the Ophenoxy-Dy-Ophenoxy bond angle, i.e., the larger Ophenoxy-Dy-Ophenoxy bond angle corresponds to a larger EKD1. [ABSTRACT FROM AUTHOR]