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Two five‐coordinate mononuclear DyIII single‐molecule magnets [(TrapenTMS)Dy(L)] (Trapen=tris(2‐aminobenzyl) amine; TMS=SiMe3; L=OPMe31, OPEt32) have been synthesized by the reaction of [(TrapenTMS)Dy(THF)] and OPMe3, OPEt3, respectively. The molecular structures of 1 and 2 were fully established by single crystal X‐ray diffraction. The centre DyIII ions of both complexes exhibit distorted triangular bipyramid geometries, varying with different neutral ligands L on the apex. The TrapenTMS ligand forms the pyramid base of the trigonal bipyramid. Subtle structural modifications of the axial O‐ligand terminal substituent result in different dynamic magnetic behaviors. Magnetic data analysis reveals that 1 and 2 exhibit the characteristic behavior of SMM without a dc field, accompanying an unambiguous quantum tunneling of the magnetization. Field‐induced slow magnetic relaxation was observed for 1 and 2 under an applied bias dc field of 1000 Oe, the relaxation energy barriers are 107 K and 88 K for 1 and 2, respectively. We have investigated the differences in magnetism and magnetic anisotropy between the two complexes by ab initio calculations. [ABSTRACT FROM AUTHOR]

A new family of low-coordinate mononuclear DyIII single-molecule magnets [(TrapenTMS)Dy(LB)] (Trapen = tris(2-aminobenzyl)amine; TMS = SiMe3; LB = THF 1, pyridine 2, ONMe33) has been synthesized and structurally characterized by single crystal X-ray diffraction. The five-coordinate DyIII ions exhibit distorted triangular bipyramidal geometries, among the different neutral ligands LB on the apex and the same TrapenTMS ligand, making the pyramid base of the trigonal bipyramid. Magnetic data analysis reveals that 1–3 are characteristic of SMM behaviors without a dc field, accompanying an unambiguous quantum tunneling of magnetization. Under an extra dc field of 500 Oe, field-induced slow magnetic relaxation behaviors occur with Raman and/or QTM processes. Ab initio calculations were also performed to rationalize the observed discrepancy in the magnetic behaviors, and the result illustrates that the SMM behavior could be effectively manipulated by the axial symmetry of the triangular bipyramidal DyIII motifs. [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 air-stable Co(III)–Co(II) mixed-valence complexes of molecular formulas [CoIICoIII(L)(DMAP)3(CH3COO)]·H2O·CH3OH (1) and [CoIICoIII(L)(4-Pyrrol)3 (CH3COO)]·0.5CH2Cl2 (2) (H4L = 1,3-bis-(5-methyl pyrazole-3-carboxamide) propane; DMAP = 4-dimethylaminopyridine; and 4-Pyrrol = 4-pyrrolidinopyridine) were synthesized and characterized by single-crystal X-ray crystallography, high-field electron paramagnetic resonance (HFEPR) spectroscopy, and magnetic measurements. Both complexes possess one five-coordinated paramagnetic Co(II) ion and one six-coordinated Co(III) ion with octahedral geometry. Direct-current magnetic susceptibility and magnetization measurements show the easy-axis magnetic anisotropy that is also confirmed by low-temperature HFEPR measurements and theoretical calculations. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements reveal their field-assisted slow magnetic relaxation, which is a characteristic behavior of single-molecule magnets (SMMs), caused by the individual Co(II) ion. The effective energy barrier of complex 1 (49.2 cm−1) is significantly higher than those of the other dinuclear Co(III)–Co(II) SMMs. This work hence presents the first instance of the dinuclear Co(III)–Co(II) single-molecule magnets with a five-coordinated environment around the Co(II) ion. [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 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 β-diketonate mononuclear dysprosium compound, [Dy(DBM)2(bpy)(CH3OH)2]·Cl− (1) (DBM = dibenzoylmethane, bpy = 2,2′-bipyridine), has been prepared and structurally and magnetically characterized. The metal centers in 1 adopt an approximately square-antiprismatic (SAP) coordination environment with D4d axial symmetry. Magnetic investigations unveil that 1 displays slow magnetic relaxation of SMM behavior with an effective barrier (Ueff) of 25.13 K under a zero dc field as well as 68.30 K in the presence of a 1200 Oe dc field. The comparative studies of some known Dy(III)-based SIMs with DBM ligands show that the energy barriers can be significantly tuned by adjusting the distortion of the SAP configuration on DyIII ions. Ab initio calculations demonstrate that relaxation of the magnetization for 1 mainly takes place via the first excited-state Kramers doublet through Orbach, Raman, and thermally assisted quantum-tunnelling mechanisms. [ABSTRACT FROM AUTHOR]

Complexation of dysprosium(III) ions with a multidentate hydrazone ligand, N-[(E)-pyridin-2-ylmethylideneamino]pyridine-2-carboxamide (L), in the presence of different β-diketonate coligands, leads to the formation of two novel DyIII dimers, with formulas Dy2(BTFA)4(L)2 (1) and Dy2(TTA)4(L)2 (2) (BTFA = 3-benzoyl-1,1,1-trifluoroacetone and TTA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionate). They exhibit slightly different coordination geometries around DyIII centers and discrepant binuclear motifs – as a result of altering the β-diketonate coligands – which has an impact on the magnetic interactions between metal centers, the local tensor of anisotropy on each DyIII site and their relative orientations, therefore contributing to distinct magnetization dynamics. Compared to 2, complex 1 exhibits a more significant slow magnetic relaxation of SMM behavior in the absence of a dc field. The QTM effect is effectively repressed under a static field, resulting in the energy barriers of 57 K for 1 and 38 K for 2. Ab initio calculations clarify that, strong single-ion magnetic anisotropies exist in both complexes, whereas intermetallic ferromagnetic interaction and antiferromagnetic interaction are observed in 1 and 2, respectively, therefore resulting in dissimilar magnetization dynamics. [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]

By means of the solvent effect, three new azido-copper 1D coordination polymers, [Cu(4-aba)(N3)] (1), [Cu(4-aba)(N3)(CH3OH)] (2), and [Cu(4-aba)(N3)(C2H5OH)] (3) (4-aba = 4-azidobenzoic acid), were successfully prepared in the presence of Cu2+ ion, NaN3 and 4-azidobenzoic acid. Interestingly, 1 can be employed as a precursor and transformed to 2 and 3via the coordination of methanol or ethanol, respectively. Meanwhile, the identical products of 1, namely 1a and 1b, could be obtained from both 2 and 3 by a dealcoholized process. As a result, the geometric configurations of Cu(ii) ions vary from the tetracoordinated square-planar in 1 to the hexacoordinated octahedron in 2 or 3. Compound 1 displays a well-isolated 1D chain with dual-bridges of EO-azido and syn,syn-carboxylate, while isomorphic 2 and 3 are triple-bridged chain-like motifs containing EO-azido, syn,syn-carboxylate and μ2-alkanol. The structural transformations caused by the intervention of alkanol molecules modulate the intrachain Cu–Cu distances (3.570 for 1, 3.204 Å for 2 and 3.154 Å for 3) and Cu–N–Cu angles (127.3° for 1, 106.82° for 2 and 104.81° for 3). This modulation, however, further leads to different intrachain ferromagnetic interactions (J = 28.4 cm−1 for 1, 67.6 cm−1 for 2, 40.2 cm−1 for 3) that are qualitatively demonstrated by theoretical calculation. More importantly, the significant scenarios of magnetic ordering and slow magnetic relaxation, which are infrequent in most of the reported azido-copper cases, are only observed in 2 and 3, due to the distinct interchain networks among 1–3. In addition, heat-capacity measurements highlight the characteristics of long-range ferromagnetic ordering in 2 and 3. [ABSTRACT FROM AUTHOR]

Organizing magnetically discrete 3d transition metal ions, which behave as single-ion magnet (SIM) units, in a coordination network is a promising approach to design novel single-molecule magnets (SMMs). Herein a Co(ii)-based compound of formula [Co(3-Hppt)2(adip)(H2O)2]·2H2O (1), has been prepared and structurally analyzed by single-crystal X-ray crystallography. The structure of the title compound consists of well-isolated one-dimensional chains of Co(ii) ions where the octahedral metal atoms are spatially separated from each other by adipic acid bridges (Co…Co = 11.197 Å). The resulting compound presents a negative uniaxial anisotropy parameter (D = −33.9 cm−1) by the analysis of the direct current magnetic data, which is further probed by ab initio calculations. Alternating-current magnetic susceptibility experiments on 1 exhibit field-induced double magnetic relaxation processes with an anisotropic energy barrier of 38.8 K resulting from the single-ion anisotropy of the individual Co(ii) ions. [ABSTRACT FROM AUTHOR]

Two penta-coordinate Co2+ complexes, namely [Co(PDA)(H2O)2] (1) and [Co(PDA)(1,2-BIYB)0.5(H2O)]·(H2O) (2), (H2PDA = pyridine-3,5-dicarboxylate, 1,2-BIYB = 1,2-bis(imidazol-1-ylmethyl) benzene), which have similar ligand fields except for their local symmetries due to the different coordination atoms of Co2+, were synthesized, structurally analyzed, and magnetically investigated. Complexes 1 and 2 possess 3D supramolecular structures in which the 2D structures are further cross-linked by hydrogen bonds. Complex 1 can be observed to transform into 2 in the presence of 1,2-BIYB coligand, and 1 and 2 have distortion trigonal bipyramid geometries when the space group of Co2+ ion changes from C2/c in 1 to P2(1)/c in 2. Meanwhile, the average equatorial Co–O/N bond distances of CP 1 (2.1655 Å) are clearly larger than its axial Co–O bond distances (2.0704 Å); for CP 2, the average equatorial Co–O/N bond distances (2.0814 Å) are slightly shorter than the axial Co–O/N bond distances (2.0896 Å), which leads to different axial compression and distortion of the trigonal bipyramid metal environment. Fine-tuning of the structures arising from the auxiliary ligands has a definite impact on the magnetic properties of compounds 1 and 2. Both compounds share easy-plane magnetic anisotropies of their central Co2+ ions (D = 16 cm−1 for 1 and D = 59 cm−1 for 2) and different slow magnetic relaxations of magnetization with applied magnetic fields of 1500 Oe and 3000 Oe, respectively. [ABSTRACT FROM AUTHOR]

Solvothermal reactions of copper salts with NaN3 and carboxylate led to the formation of a new magnetic compound, [Cu(3-fba)(N3)(C2H5OH)]n (3-fba = 3-fluorobenzoic acid) (1). Single crystal X-ray analysis indicates that only one crystallographically independent Cu(ii) ion in the asymmetric unit of 1 displays stretched octahedral geometry in which two azido N atoms and two carboxylic O atoms locate in the equatorial square, while two ethanol O atoms occupy the apical positions, yielding a 1D Cu(ii) chain with an alternating triple-bridge of EO-azido, syn,syn-carboxylate, and μ2-ethanol. Magnetic measurements reveal that the resulting compound is composed of well-isolated 1D Cu(ii) chains with strong intrachain ferromagnetic interactions. The dominant ferromagnetic couplings between neighbouring Cu(ii) ions occurring in the compound (J = 59.74 cm−1) are due to the counter-complementarity of the multiple superexchange pathways, contributing to inspiring plots of ferromagnetic order (Tc = 11.0 K) and slow magnetic relaxation that are rarely observed in most reported azido-Cu(ii) architectures. Heat-capacity experiments further emphasize the characteristic long-range ferromagnetic ordering in 1. Moreover, density functional theory (DFT) calculations (using different methods and basis sets) have been performed on the compound to obtain the theoretical interpretation of the magnetic behaviors. [ABSTRACT FROM AUTHOR]

A 2D oxalate-bridged dysprosium(iii) compound, formulated as [Dy(C2O4)1.5(H2O)3]n·2nH2O (1), has been hydrothermally isolated. As for compound 1, structural analysis reveals that the nine-coordinated Dy(iii) ions reside in a slightly distorted tricapped trigonal prism. Under an applied magnetic field of 700 Oe, the compound was magnetically characterized as a new example that two slow relaxations of the magnetization processes can be observed in a 2D oxalate-bridged dysprosium(iii) layer. [ABSTRACT FROM AUTHOR]