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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]

Photocontrolled magnetic properties are fundamental for the applications of molecular magnets, which have the features of high time and space resolution; however, such magnetic properties are highly challenging to be achieved owing to the weak light–matter interactions. Herein, the influence of in situ light irradiation on the field-induced magnetization dynamics of two Er(III) coordination polymers 1 and 2 with the same coordination skeletons but different halogen substituents was studied. 1 and 2, and their in situ photoexcited products 1a and 2a, display field-induced magnetization dynamics based on Orbach and/or Raman processes. The magnetization dynamics are fine-modulated by the synergetic effect of light irradiation and a ligand substituent, due to the charge re-distribution of the excited states of the ligand. [ABSTRACT FROM AUTHOR]

The synthesis, single-crystal structures and magnetic properties of two new double-zigzag-chain cyano-bridged heterobimetallic {[MII(Py-NOH)2][FeIII(Tp*)(CN)3]2}·H2O ([Fe III2 MII]) (Py–NOH = 4-pyridinealdoxime, Tp* = tris(3,5-dimethylpyrazol-1-yl)borohydride, M = Ni (1), Fe (2)) compounds are reported. The crystal structures of both compounds were determined by single-crystal X-ray diffraction. Complexes 1 and 2 are isostructural, with the crystal structure comprising neutral double-zigzag (4,2-ribbon-like) bimetallic chains. The FeIII ion is coordinated by three cyanide carbon atoms and three nitrogen atoms of Tp* anions. However, the MII ion is surrounded by four cyanide nitrogen atoms and two nitrogen atoms from two Py-NOH ligands. The crystal structures and magnetic studies demonstrate that both complexes behave as single-chain magnetics (SCMs) with intrachain ferromagnetic coupling. Furthermore, [Fe III2 NiII] exhibits an excellent coercive field of 0.42 T at 1.8 K, among cyano-bridged 3d transition-metal-based SCMs reported thus far. Preliminary theoretical calculations provide a deep understanding of the magnetic properties of [Fe III2 NiII]. [ABSTRACT FROM AUTHOR]

The utilization of the di-pyrrolyl Schiff base ligand H2L (H2L = N-((1H-pyrrol-2-yl)methyl)-1-(1H-pyrrol-2-yl)methanimine) in organolanthanide chemistry is presented. The 1 : 2 reaction of [Ln(N(SiMe3)2)3] (Ln = Dy, Ho, Er, and Gd) with H2L in THF followed by recrystallization in THF/Tol or Tol generated complexes [Dy2(HL)2(L)2(THF)2]·2THF (1·2THF), [Ho2(HL)2(L)2(THF)2] (2), [Er2(HL)2(L)2(THF)2]·4Tol (3·4Tol), and [Gd2(HL)2(L)2(THF)2] (4). In the doubly deprotonated ligand [L]2−, one pyrrolyl ring adopts the η5 coordination mode, and the other pyrrolyl moiety behaves as an η1 ligand. The deprotonated pyrrolyl scaffold of the [HL]− ligand exhibits the η1 coordination mode. Thus, the two metal centers both display a half-sandwich configuration. Studies of the dc magnetic susceptibility of 1-4 at variable temperatures showed that weak antiferromagnetic interactions exist in these compounds. The ac magnetic susceptibility measurements for 1 and 2 indicated that they did not display single-molecule magnetic (SMM) properties. The magnetic properties of 1 and 2 were further explained by DFT calculations. [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]

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]

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]

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]

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]

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]

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]

Three two-dimensional CoII complexes, namely, [Co(dps)2Cl2]n (1), [Co(dps)2Br2]n (2), and [Co(dps)2(H2O)2·I2·(H2O)4]n (3) (where dps = 4,4′-dipyridyl sulfide), have been synthesized using a rationally designed synthetic approach and characterized structurally and magnetically. Although they crystallize in different space groups, these compounds all have similar two-dimensional (4,4) layer structures where the Co2+ centers are bridged by the bis(monodentate) ligand dps. In addition, the coordination geometry of the Co2+ centers is of a general CoN4X2 octahedral environment formed by four equatorial N atoms from four dps ligands and two X atoms (X = Cl, Br, and O atoms for 1–3, respectively) in the axial positions. Ab initio calculations revealed that due to the strong spin–orbit coupling, the spin Hamiltonian containing the zero-field splitting parameters D and E cannot be used to describe their magnetic anisotropy. According to the calculation, the gz values for the spin–orbit ground doublets of 1–3 are larger than the gx and gy values, which indicates the easy-axis magnetic anisotropy of these compounds. Due to the existence of the magnetic anisotropy, field-induced single-ion magnet behavior can be observed in all these complexes. This work illustrated that care should be taken to interpret the magnetic data of octahedral CoII compounds. In addition, extended frameworks with long and flexible organic spacers are good candidates for the construction of SIMs with different axial ligands and different magnetic properties. [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]

Two hydroxo-bridged complexes, {[MnIII(3-CH3O)salen]2[CrIII(salen)(OH)2]}ClO4·6H2O (1) and {[MnIII(5-CH3)salen]2(OH)}ClO4·3H2O (2) [salen = N,N′-ethylenebis(salicylideneiminato) dianion], have been synthesized by the hydrolysis of the corresponding MnIII(Schiff-Bases) derivatives and [Cr(salen)(H2O)2]Cl precursors. X-Ray structure characterization reveals the discrete linear arched trinuclear structure of 1and the 1D chain arrangement of 2. Magnetic experimental data and density functional theory (DFT) calculations both indicate the dominant antiferromagnetic interaction mediated by the hydroxo-bridges in both 1and 2. Frequency-dependent AC susceptibilities reveal slow relaxation of 1in low temperature. It is worth noting that the structure and magnetic properties of 1is comparable to a reported cyano-bridged SMM, K[(5-Brsalen)2(H2O)2Mn2Cr(CN)6]·2H2O. [ABSTRACT FROM AUTHOR]