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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]

Using a novel tricompartmental hydrazone ligand, a set of trinuclear Dy3 complexes has been isolated and structurally characterized. Complexes Dy3 ⋅ Cl, Dy3 ⋅ Br, and Dy3 ⋅ ClO4 feature a similar overall topology but different anions (Cl−, Br−, or ClO4−) in combination with exogenous OH− and solvent co‐ligands, which is found to translate into very different magnetic properties. Complex Dy3 ⋅ Cl shows a double relaxation process with fast quantum tunneling of the magnetization, probably related to the structural disorder of μ2‐OH− and μ2‐Cl− co‐ligands. Relaxation of the magnetization is slowed down for Dy3 ⋅ Br and Dy3 ⋅ ClO4, which do not show any structural disorder. In particular, fast quantum tunneling is suppressed in case of Dy3 ⋅ ClO4, resulting in an energy barrier of 341 K and magnetic hysteresis up to 3.5 K; this makes Dy3 ⋅ ClO4 one of the most robust air‐stable trinuclear SMMs. Magneto‐structural relationships of the three complexes are analyzed and rationalized with the help of CASSCF/RASSI‐SO calculations. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Precise modulation of the magnetic anisotropy of metal ions remains highly important for the development of high–performance single‐molecule magnets (SMMs). We herein reported the synthetic, structural, spectral, magnetic, and computational studies on four mononuclear CoII complexes in a distorted octahedral environment. The change of the organosulfonate anions triggers significant modification of the distorted octahedral CoN6 coordination sphere, which enables us to tackle the influence of the structural distortion on the magnetic anisotropy in these complexes. Magnetic measurements revealed that the four complexes possess easy–plane magnetic anisotropy with large and positive zero‐field splitting parameters, which decrease with the increasing distortion of the pseudo–octahedral CoII coordination geometry. This correlation was further confirmed by high–frequency/–field EPR (HF–EPR) spectra and theoretical calculations. Dynamic magnetic susceptibility measurements indicate that these complexes both exhibit slow magnetic relaxation under an external dc field, indicating the field‐induced single‐ion magnets (SIMs) of the four complexes. These results indicate that structural distortion plays an important role in the magnetic anisotropy of CoII complexes and should be carefully considered in the design of molecular complexes with high magnetic anisotropy. [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]

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]

While assembling superparamagnetic units in a controlled manner is crucial for future applications of molecular nanomagnets, optimizing their magnetic properties while achieving directional assembly of these units still remains a formidable challenge. Herein, we demonstrate how the assembly of two dysprosium chain complexes, namely, [Dy2(L)2Cl2(CH3OH)3]n·nCH3OH (1) and [Dy(L)Cl(DMF)]n (2) (H2L = N'-(5-bromo-2-hydroxybenzylidene)pyrazine-N-oxide-carbohydrazide), can be successfully manipulated using an appropriate bridging ligand design. Both complexes contain similar dimeric units bridged by two alkoxido oxygens from an L2− ligand, but extended by its pyrazine-N-oxide group exhibiting two distinct coordination modes, namely, single and double pyrazine-N-oxide bridges, respectively. Magnetic studies reveal that both complexes display typical slow magnetic relaxation under zero direct-current field; however, the anisotropy barrier and the coercive field at 2 K for complex 2 are twice as much as that of 1. A further theoretical study indicates that switching the coordination mode from a single pyrazine-N-oxide bridge to double bridges can enhance both the magnetic anisotropy of dysprosium ions and magnetic coupling within the dimeric cores. The synergistic effect between the magnetic anisotropy of dysprosium ions and magnetic interactions among them directly contributes to the overall better performance of complex 2. [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 first bis-tridentate nitronyl nitroxide mono-radical was synthesized. From this ligand and a bis-bidentate nitronyl nitroxide ligand, metal complexes of MnII and CoII ions were also synthesized and characterized. Field-induced slow magnetic relaxation was observed in the radical-bridged CoII complex. [ABSTRACT FROM AUTHOR]

The structural characterization and magnetic studies of three mononuclear MnIII complexes based on the dibenzoylmethanido (dbm-) ligand, Mn(dbm)3 ( 1) and [Mn(dbm)2(L)2](ClO4) (L = dimethyl sulfoxide, 2; L = pyridine, 3), are reported. The MnIII ions are in an axially elongated octahedral coordination geometry. The axial zero-field-splitting parameters D, ranging from -3.42 to -4.52 cm-1 for the three complexes, were obtained by fitting magnetic-susceptibility and magnetization data. Ab initio calculations also show the axial magnetic anisotropy in the molecules of 1- 3. With an applied dc field, the ac susceptibility measurements reveal slow magnetic relaxation in 1- 3. The possible relationship between the structures and the magnetic properties in these complexes are discussed. [ABSTRACT FROM AUTHOR]

The magnetic properties of five DyIII-MII 3d-4f complexes (M = Mn, Fe, Co, Ni and Zn) were studied in detail by comparison due to the same molecule construction. The DyIII-MII assemble (M = Mn, Fe and Ni) behave as field-induced SMMs resulting from the ferromagnetic coupling between DyIII and MII ions, while DyIII-ZnII is SIM and DyIII-CoII does not show the magnetic relaxation. [Display omitted] • In this paper, A series of DyIII-MII 3d-4f complexes (M = Mn, Fe, Co, Ni and Zn) were synthesized. • Their magnetic properties were compared by the magnetostructural correlation. • The coupling between DyIII and MII ions (M = Mn, Fe and Ni) is ferromagnetic. Four Dy-based 3d-4f complexes [MIIDyIII(H 2 L)(NO 3) 3 ](CH 3 OH) 2 (H 4 L = N , N' , N'' , N''' -tetra(2-hydroxy-3-methoxy-5-methylbenzyl)-1,4,7,10-tetraazacyclododecane, M = Mn (2), Fe (3), Co (4) and Ni (5), the solvent of compound 5 is uncertain) were synthesized through the reference method of complex [ZnIILnIII(H 2 L)(NO 3) 3 ](CH 3 OH) 2 (1). The magnetic properties of all the five complexes were measured for comparison. The magnetic results show that all the complexes except 4 behave as single-molecule magnets (SMMs). The magnetostructural analysis and theoretical calculation indicate the ferromagnetic coupling in 2 , 3 and 5 as well as the antiferromagnetic coupling in 4 between DyIII and transition metal ions, while the SMM properties of 1 are caused by the anisotropy of single DyIII ions only. Unexpectedly, neither of the magnetic anisotropic ions in one molecule, namely DyIII and CoII, provides greater advantages for SMM performance. This investigation experimentally proves that the coexistence of magnetic anisotropy of lanthanide ions and ferromagnetic coupling between lanthanide and transition metal ions is important for the design of 3d-4f SMMs. [ABSTRACT FROM AUTHOR]

Inserting 3d metal-cmplex Cu(acac) 2 into the crystal lattice of paramagnetic Dy(hfac) 3 (H 2 O) 2 leads to the formation of the first true 3d-4f cocrystal made up of only reactants, which exhibits improved magnetic performance with evident SIM behavior. • A genuine 3d-4f complex cocrystal only composed of reactants. • The cocrystal displays evident SIM behavior. • Co-crystallization is a useful tool for improving the magnetic property of LnIII complex. Employing Cu(acac) 2 to react with Dy(hfac) 3 (H 2 O) 2 (where acac− = acetylacetonate and hfac− = 1,1,1,5,5,5-hexafluoroacetylacetonate), the first true 3d-4f metal-complex cocrystal with the composition of [Cu(acac) 2 ·Dy(hfac) 3 (H 2 O) 2 that only consists of reactants, was acquired and structurally characterized. Magnetic investigations revealed that the 4f coformer Dy(hfac) 3 (H 2 O) 2 does not show slow magnetic relaxation behavior even under an applied dc field of 2000 Oe down to 1.9 K, while the obtained 3d-4f cocrystal displays evident slow magnetic relaxation behavior associated with single-ion magnet (SIM) characteristic under the same dc field. This phenomenon is further supported and elucidated by the results of theoretical calculations together with the analyses of their crystal structures. Thus our results first indicate that 3d-4f co-crystallization technique is a useful tool for improving the magnetic performance of lanthanide complexes. [ABSTRACT FROM AUTHOR]