Weiming Song

A unusual two-dimensional azido-Cu(II) network with benzoate derivative as a co-ligand exhibiting ferromagnetic order and slow magnetic relaxation

A 2D layer-like azido-copper system was constructed from linear tetranuclear metal motif with mixed-ligand bridges of carboxylate, azido and hydroxyl groups. The strong ferromagnetic coupling between Cu(II) ions was due to the counter complementarity of the multiple super-exchange pathways, leading to a dramatic magnetic order and slow relaxation.

Ferromagnetic ordering and slow magnetic relaxation observed in a triple-bridged azido-Cu(II) chain compound with mixed carboxylate/ethanol linkers

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.

One-dimensional cobalt(II) coordination polymer featuring single-ion-magnet-type field-induced slow magnetic relaxation

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 A). 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.

One-Dimensional Cu(II)Chain Compound with Simultaneous EO-Azido and Carboxylato Bridges Displaying Strong Ferromagnetic Coupling:Synthesis, Crystal Structure, Magnetic Properties with DFT Calculations

An azido-Cu(Ⅱ)compound with substituted benzoate derivative, [Cu(4-Fb)(N 3 )(H 2 O)] n ( 1 ) (4-Fb=4-form-ylbenzoate), has been successfully synthesized, and then structurally and magnetically characterized. Single crystal structure analysis demonstrates that the asymmetric unit of compound 1 possesses one crystallographically independent Cu(Ⅱ)ion that exhibits distorted tetragonal pyramid geometry. Adjacent Cu(Ⅱ)ions are linked by alternating mixed-bridges of μ -1, 1(end-on, EO) azido and syn, syn -carboxylate, forming a linear 1D Cu(Ⅱ)chain-like motif. Magnetic measurements reveal that the dominant ferromagnetic coupling between adjacent Cu(Ⅱ)ions within each chain due to the counter-complementarity of the dual superexchange pathway is observed in the resulting compounds. However, the interesting plots of magnetic ordering and slow magnetic relaxation are absent in the compound. The critical structural parameter, Cu-N-Cu angle of 113.34°, is corresponding to that of known ferromangetic copper systems containing mixed carboxylate/EO-azido connectors. Magneto-structural correlations are also investigated. Moreover, density functional theory (DFT) calculations (using different methods and basis sets) have been performed on title compound to offer qualitatively theoretical explanation for the ferromagnetic coupling between two Cu(Ⅱ)centers.CCDC:1496426.

Tuning of Exchange Coupling and Switchable Magnetization Dynamics by Displacing the Bridging Ligands Observed in Two Dimeric Manganese(III) Compounds

Two Mn(III)-based dimers, [Mn2(bpad)2(CH3O)4]n (1) and [Mn2(bpad)2(pa)2]n·2H2O (2) (Hbpad = N3-benzoylpyridine-2-carboxamidrazone, H2pa = phthalic acid), have been assembled from a tridentate Schiff-base chelator and various anionic coligands. Noteworthily, compound 1 could be identified as a reaction precursor to transform to 2 in the presence of phthalic acid, resulting in a rarely structural conversion process in which the bridges between intradimer Mn(III) ions alter from methanol oxygen atom with μ2-O mode in 1 (Mn Mn distance of 3.046 Å) to syn-anti carboxylate in 2 (Mn Mn distance of 4.043 Å), while the Mn(III) centers retain hexa-coordinated geometries with independently distorted octahedrons in two compounds. The dc magnetic determinations reveal that ferromagnetic coupling between two metal centers with J = 1.31 cm−1 exists in 1, whereas 2 displays weak antiferromagnetic interactions with the coupling constant J of −0.56 cm−1. Frequency-dependent ac susceptibilities in the absence of dc field for 1 suggest slow relaxation of the magnetization with an energy barrier of 13.9 K, signifying that 1 features single-molecule magnet (SMM) behavior. This work presents a rational strategy to fine-tune the magnetic interactions and further magnetization dynamics of the Mn(III)-containing dinuclear units through small structural variations driven by the ingenious chemistry.

Measurements of Enthalpy Change of Reaction of Formation, Molar Heat Capacity and Constant-Volume Combustion Energy of Solid Complex Yb(Et2dtc)3 (phen)

Abstract A ternary solid complex Yb(Et2dtc)3(phen) was obtained from the reaction of hydrous ytterbium chloride with sodium diethyldithiocarbamate (NaEt2dtc), and 1, 10-phenanthroline (o-phen·H2O) in absolute ethanol. The bonding characteristics of the complex were characterized by IR. The result shows Yb3+ bands with two sulfur atoms in the Na(Et2dtc)3 and two nitrogen atoms in the o-phen. The enthalpy change of liquid-phase reaction of formation of the complex ΔrHθm(1), was determined as being (-24.838±0.114) kJ·mol−1 at 298.15 K, by an RD-496 III type heat conduction microcalormeter. The enthalpy change of the solid-phase reaction of formation of the complex ΔrHθm(s), was calculated as being (108.015±0.479) kJ·mol−1 on the basis of an appropriate thermochemistry cycle. The thermodynamics of liquid-phase reaction of formation of the complex was investigated by changing the temperature during the liquid-phase reaction. Fundamental parameters, the activation enthalpy, ΔHθ≠, the activation entropy, ΔSθ≠, the activation free energy, ΔGθ≠, the apparent reaction rate constant k, the apparent activation energy E, the pre-exponential constant A, and the reaction order n, were obtained by a combination of the reaction thermodynamic and kinetic equations with the data from the thermokinetic experiments. At the same time, the molar heat capacity of the complex cm, p, was determined to be (86.34±1.74) J·mol−1·K−1 by the same microcalormeter. The constant-volume combustion energy of the complex, Δc U, was determined to be (− 17954.08±8.11) kJ·mol−1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, ΔcHθm, and standard enthalpy of formation, ΔfHθm were calculated to be (-17973.29±8.11) kJ·mol−1 and (-770.36±9.02) kJ·mol−1 respectively.