15 results on '"Wang, Zhenxing"'
Search Results
2. Slow magnetic relaxation in dinuclear Co(III)–Co(II) complexes containing a five-coordinated Co(II) centre with easy-axis anisotropy.
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Liu, Mengyao, Yang, Yimou, Jing, Rong, Zheng, Shaojun, Yuan, Aihua, Wang, Zhenxing, Luo, Shu-Chang, Liu, Xiangyu, Cui, Hui-Hui, Ouyang, Zhong-Wen, and Chen, Lei
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MAGNETIC relaxation , *MAGNETIC anisotropy , *SINGLE molecule magnets , *ELECTRON paramagnetic resonance , *MAGNETIC measurements , *MAGNETIC susceptibility - Abstract
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]
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- 2022
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3. Magnetic anisotropy of two tetrahedral Co(II)-halide complexes with triphenylphosphine ligands.
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Lv, Wei, Cui, Hui-Hui, Chen, Lei, Zhang, Yi-Quan, Chen, Xue-Tai, Wang, Zhenxing, Ouyang, Zhong-Wen, and Xue, Zi-Ling
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MAGNETIC anisotropy , *MAGNETIC measurements , *AB-initio calculations , *X-ray crystallography , *MAGNETIC susceptibility , *MAGNETIC properties - Abstract
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]
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- 2022
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4. Magnetic anisotropy in square pyramidal cobalt(II) complexes supported by a tetraazo macrocyclic ligand.
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Cui, Hui-Hui, Ding, Man-Man, Zhang, Xiu-Du, Lv, Wei, Zhang, Yi-Quan, Chen, Xue-Tai, Wang, Zhenxing, Ouyang, Zhong-Wen, and Xue, Zi-Ling
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MAGNETIC anisotropy , *LIGANDS (Chemistry) , *MAGNETIC measurements , *X-ray crystallography , *MAGNETIC susceptibility , *MAGNETIC relaxation - Abstract
Two five-coordinate mononuclear Co(II) complexes [Co(12-TMC)X][B(C6H5)4] (L = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (12-TMC), X = Cl− (1), Br− (2)) have been studied by X-ray single crystallography, magnetic measurements, high-frequency and -field EPR (HF-EPR) spectroscopy and theoretical calculations. Both complexes have a distorted square pyramidal geometry with the Co(II) ion lying above the basal plane constrained by the rigid tetradentate macrocyclic ligand. In contrast to the reported five-coordinate Co(II) complex [Co(12-TMC)(NCO)][B(C6H5)4] (3) exhibiting easy-axis anisotropy, an easy-plane magnetic anisotropy was found for 1 and 2via the analyses of the direct-current magnetic data and HF-EPR spectroscopy. Frequency- and temperature-dependent alternating-current magnetic susceptibility measurements demonstrated that complexes 1 and 2 show slow magnetic relaxation at an applied dc field. Ab initio calculations were performed to reveal the impact of the terminal ligands on the nature of the magnetic anisotropies of this series of five-coordinate Co(II) complexes. [ABSTRACT FROM AUTHOR]
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- 2020
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5. Structure, magnetic anisotropy and relaxation behavior of seven-coordinate Co(II) single-ion magnets perturbed by counter-anions.
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Yi, Gangji, Zhang, Chunyang, Zhao, Wen, Cui, Huihui, Chen, Lei, Wang, Zhenxing, Chen, Xue-Tai, Yuan, Aihua, Liu, Yuan-Zhong, and Ouyang, Zhong-Wen
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MAGNETIC anisotropy , *MAGNETIC relaxation , *ELECTRON paramagnetic resonance , *MAGNETS , *X-ray diffraction , *POLYHEDRA - Abstract
A series of mononuclear seven-coordinate Co(II) complexes [CoII(BPA-TPA)](ClO4)2·H2O (2-ClO4), [CoII(BPA-TPA)](PF6)2 (3-PF6) and [CoII(BPA-TPA)](BPh4)2 (4-BPh4) have been synthesized based on the ligand 2,6-bis(bis(2-pyridylmethyl)amino)methylpyridine (BPA-TPA), and their structures have been characterized by single-crystal X-ray diffraction. All these complexes feature an intermediate coordination polyhedron between a capped trigonal prism and a capped octahedron, which is perturbed by the variation of the counter anions. Easy-plane magnetic anisotropies for all complexes were revealed via the analyses of the direct-current magnetic data and high-field electron paramagnetic resonance (HFEPR) spectra. They show slow magnetic relaxation under applied direct current field, which is similar to the previously reported complex [CoII(BPA-TPA)](BF4)2 (1-BF4) with a capped trigonal prism. This work provides a new example of modulating the properties of single-ion magnets (SIMs) by changing the counter anions. [ABSTRACT FROM AUTHOR]
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- 2020
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6. 1,2-Diaza-4-phospholide complexes of chromium(II): dipotassium organochromates behaving as single-molecule magnets.
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Su, Jing, Yin, Lei, Ouyang, Zhongwen, Wang, Zhenxing, and Zheng, Wenjun
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SINGLE molecule magnets , *CHROMIUM ions , *ELECTRON paramagnetic resonance , *CHROMIUM , *MAGNETIC measurements , *COORDINATION compounds , *MAGNETIC anisotropy , *SINGLE crystals - Abstract
The 1,2-diaza-4-phospholide (dp−) dipotassium ate complexes of chromium(II) {[(η1-N-3,5-tBu2dp)4Cr][(η5-(N,N,C,C,P))2-K(η1-O-THF)2]2} (5) and {[(η1-N-3,5-Ph2dp)4Cr][(η5-(N,N,C,C,P))2-K(η1-O-THF)2]2}∞ (6) were synthesized and characterized by X-ray single crystal structure analysis. Complex 5 with a near-square planar geometry at the chromium(II) ion was unambiguously characterized by the high field electron paramagnetic resonance (HF-EPR) technique and magnetic measurements, revealing that it is a field-induced single-molecule magnet (SMM). [ABSTRACT FROM AUTHOR]
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- 2020
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7. Optimal diamagnetic dilution concentration for suppressing the dipole–dipole interaction in single-ion magnets.
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Hu, Zhao-Bo, Feng, Xin, Li, Jing, Zhang, Yi-Quan, Yin, Lei, Wang, Zhenxing, Ouyang, Zhongwen, Kurmoo, Mohamedally, and Song, You
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DIPOLE-dipole interactions , *DILUTION , *MAGNETIC relaxation , *DIPOLE interactions , *TIME reversal , *MAGNETS - Abstract
The effect of screening the CoII moment of monomeric [CoIIL2(H2O)] (L = 8-hydroxyquinaldine), having a trigonal bipyramid coordination, by diamagnetic Zn in Co x Zn 1−x solid solutions on its magnetic relaxation was explored using ac-susceptibility, high-field electron–spin-resonance measurements and CASPT2 calculations. The retention of the crystal structure for all the solid solutions was demonstrated using single crystal diffraction. The dc-magnetization and theoretical fittings of the susceptibility for Co1 and Co0.1Zn0.9 gave a large zero-field-splitting (ZFS) D of 50 ± 6 cm−1, and very weak dipole interaction between the nearest neighbors, while EPR and calculations confirmed the positive sign of the axial component (D). Consistent parameters were obtained from experiments and theory. Importantly, only field-induced relaxation was observed for the samples with less than 50% Co and a gradual change in the barrier energy to moment reversal and relaxation times was observed between 11% and 20% Co, while both were enhanced for higher dilutions. The results establish a clear barrier for extending the longevity of the magnetism for this type of single-ion species by lowering the intramolecular interactions. The results suggest that the magnetic interaction persists up to the second sphere, that is, for a dilution of 1 in 9 (11% Co). Importantly, this method is applicable to all single-ion magnet systems, that is, the optimum dilution concentration to restrain the dipole field can be given only by the single crystal structure. [ABSTRACT FROM AUTHOR]
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- 2020
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8. Magnetic anisotropy and slow magnetic relaxation processes of cobalt(ii)-pseudohalide complexes.
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Cui, Hui-Hui, Zhang, Yi-Quan, Chen, Xue-Tai, Wang, Zhenxing, and Xue, Zi-Ling
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MAGNETIC anisotropy , *MAGNETIC relaxation , *COBALT , *LOW temperatures , *HIGH temperatures , *ANISOTROPY - Abstract
Three mononuclear six-coordinate Co(ii)-pseudohalide complexes [Co(L)X2] with two N-donor pseudohalido coligands occupying the cis-positions (X = NCS− (1), NCSe− (2) or N(CN)2− (3)), and a five-coordinate complex [Co(L)(NCO)][B(C6H5)4] (4) [L = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane (12-TMC)] have been prepared and structurally characterized. Easy-plane magnetic anisotropy for 1–3 and easy-axis anisotropy for 4 were revealed via the analyses of the direct-current magnetic data, high-frequency and -field EPR (HFEPR) spectra and ab initio theoretical calculations. They display slow magnetic relaxations under an external applied dc field. Typically, two slow relaxation processes were found in 1 and 2 while only one relaxation process occurs in 3 and 4. The Raman-like mechanism is found to be dominant in the studied temperature range in 1. For 2–4, the Raman process is dominant in the low temperature region, while the Orbach mechanism dominates in the high temperature range. [ABSTRACT FROM AUTHOR]
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- 2019
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9. A mononuclear five-coordinate Co(ii) single molecule magnet with a spin crossover between the S = 1/2 and 3/2 states.
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Chen, Lei, Song, Jingbo, Zhao, Wen, Yi, Gangji, Zhou, Zhikuan, Yuan, Aihua, Song, You, Wang, Zhenxing, and Ouyang, Zhong-Wen
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COBALT , *MAGNETIZATION , *HYSTERESIS loop - Abstract
Although a great number of single-ion magnets (SIMs) and spin-crossover (SCO) compounds have been discovered, multifunctional materials with the combination of SCO and SIM properties are extremely scarce. Here magnetic studies have been carried out for a mononuclear, five-coordinate cobalt(ii) complex [Co(3,4-lut)4Br]Br (1) with square pyramidal geometry. Direct-current magnetic measurement confirms the spin transition between the S = 1/2 and 3/2 states in the range of 150–290 K with a small hysteresis loop. Frequency- and temperature-dependent alternating-current magnetic susceptibility reveals slow magnetization relaxation under an applied dc field of 3000 Oe. The work here presents the first instance of the five-coordinate mononuclear cobalt(ii)-based SIM exhibiting the thermally induced complete SCO. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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10. Magnetic anisotropy and relaxation behavior of six-coordinate tris(pivalato)-Co(ii) and -Ni(ii) complexes.
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Chen, Shu-Yang, Cui, Hui-Hui, Zhang, Yi-Quan, Wang, Zhenxing, Ouyang, Zhong-Wen, Chen, Lei, Chen, Xue-Tai, Yan, Hong, and Xue, Zi-Ling
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MAGNETIC anisotropy , *MAGNETIC fields , *ANGULAR momentum (Mechanics) - Abstract
Experimental and theoretical studies of magnetic anisotropy and relaxation behavior of six-coordinate tris(pivalato)-Co(ii) and -Ni(ii) complexes (NBu4)[M(piv)3] (piv = pivalate, M = Co, 1; M = Ni, 2), with a coordination configuration at the intermediate between an octahedron and a trigonal prism, are reported. Direct current magnetic data and high-frequency and -field EPR spectra (HFEPR) of 1 have been modeled by a general Hamiltonian considering the first-order orbital angular momentum, while the spin Hamiltonian was used to interpret the data of 2. Both 1 and 2 show easy-axis magnetic anisotropies, which are further supported by ab initio calculations. Alternating current (ac) magnetic susceptibilities reveal slow magnetic relaxation at an applied dc field of 0.1 T in 1, which is characteristic of a field-induced single-ion magnet (SIM), but 2 does not exhibit single-ion magnetic properties at 1.8 K. Detailed analyses of relaxation times show a dominant contribution of a Raman process for spin relaxation in 1. [ABSTRACT FROM AUTHOR]
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- 2018
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11. Slow magnetic relaxation influenced by change of symmetry from ideal Ci to D3d in cobalt(ii)-based single-ion magnets.
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Chen, Lei, Zhou, Jianjun, Cui, Hui-Hui, Yuan, Ai-Hua, Wang, Zhenxing, Zhang, Yi-Quan, Ouyang, Zhong-Wen, and Song, You
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METAL complexes , *MAGNETIC relaxation , *COBALT compounds - Abstract
The coordination geometries of the Co(ii) site in the two complexes [Co(imidazole)6][BPh4]2·0.3CH3CN (1) and [Co(imidazole)6][NO3]2 (2) were observed to display the ideal symmetries Ci and D3d, respectively. Both complexes were shown to be field-induced single-ion magnets. The effective energy barrier was found to decrease as the local symmetry changed from low-symmetry Ci to high-symmetry D3d. [ABSTRACT FROM AUTHOR]
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- 2018
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12. Ferromagnetic coupling in copper benzimidazole chloride: structural, mass spectrometry, magnetism, and DFT studies.
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Shi, Xing-Xing, Zhang, Yuexing, Chen, Qiu-Jie, Yin, Zheng, Chen, Xue-Li, Wang, Zhenxing, Ouyang, Zhong-Wen, Kurmoo, Mohamedally, and Zeng, Ming-Hua
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FERROMAGNETISM , *BENZIMIDAZOLES , *DENSITY functional theory - Abstract
Herein, quasi-square planar CuII(Hmbm)Cl2 (CBC, Hmbm = (1-methyl-1H-benzo[d]imidazol-2-yl)methanol) was arranged in a pseudo orthogonal way to form Cl-bridged chains, and further π…π interactions resulted in distorted hexagonal layers. DFT calculations reveal a bond strength order of Cu–Cl > Cu–O/N > Cu…Cl. ESI-MS data reveal several small fragments from CBC, but oligomeric [CuII2], [CuII3], and [CuII4] for non-zero in-source energies; MS data indicates the occurrence of several chemical processes, viz. splitting of the ligand, oligomerization, and redox reaction of alcohol to aldehyde and CuII to CuI. Gibbs free energies for the fragments were estimated using DFT. The magnetic susceptibility was modeled with the ferromagnetic coupling J(Cu–Cl2a…Cu) = +0.99(30) cm−1 and J′(π…π) = +0.35(16) cm−1 and g = 2.38(2). HF-EPR determined the anisotropic g-values, gx = 2.24, gy = 2.16, and gz = 2.09, and a hyperfine constant of Az = 450 G. DFT calculations from crystal structure data reveal a J(Cu–Cl2a…Cu) of +3.6 at 296 K and +4.1 cm−1 at 90 K that dominates the magnetic properties, whereas J′(π…π) = 0.04 cm−1 is negligibly small. [ABSTRACT FROM AUTHOR]
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- 2017
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13. Embedding 1D or 2D cobalt–carboxylate substrates in 3D coordination polymers exhibiting slow magnetic relaxation behaviors: crystal structures, high-field EPR, and magnetic studies.
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Mao, Nannan, Zhang, Biquan, Yu, Fan, Chen, Xi, Zhuang, Gui-lin, Wang, Zhenxing, Ouyang, Zhongwen, Zhang, Tianle, and Li, Bao
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COORDINATION polymers , *MAGNETIC relaxation , *CRYSTAL structure - Abstract
By utilizing well-designed bifunctional ligands derived from 1H-imidazole-4,5-dicarboxylic acid, magnetic coordination polymers (CPs) that exhibit slow magnetic relaxation at the low temperature regions were constructed and further structurally characterized. In 1, 1D cobalt–carboxyl chains were stabilized in the final structure. In contrast, by adjusting the length of the substituted arms on imidazole-4,5-dicarboxylic acid, a novel 3D CP, 2 containing 2D 63 cobalt–carboxyl layer was obtained. A combination of Quantum Monte Carlo (QMC) simulations and the first-principles Density functional theory (DFT) calculations showed that compound 2 features weak ferro- and antiferro-magnetic coupling mechanisms with two different super-exchange paths of −/+/− for syn–anti carboxylate bridges and −/−/− for syn–syn carboxylate bridges. Through HF-EPR measurements performed on polycrystalline samples over the frequency range of 60–260 GHz and field range of 0–12 T, the effective g-values of 1 and 2 were all larger than 2.00, and the signs of their D values were probably positive. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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14. Magnetostructural relationship for μ2-phenoxido bridged ferric dimers.
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Yu, Fei, Cao, Zi-Heng, Ge, Jing-Yuan, Sun, Yi-Chen, Ouyang, Zhong-Wen, Zuo, Jing-Lin, Wang, Zhenxing, and Kurmoo, Mohamedally
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PHENOXIDES , *DIMERS - Abstract
Three Fe(iii) dimers, [Fe2(L-H)2]·2CH3CN (1), [Fe2(L-OCH3)2] (2) and [Fe2(L-OC2H5)2]·2CH3CN (3), containing the pentadentate O,N,N,O,O-donor Schiff-base ligands with variable size pendants, were synthesized and structurally characterized. The three ligands were generated in situ from 2-(iminomethyl)phenol, 2-methoxy-6-(iminomethyl)phenol and 2-ethoxy-6-(iminomethyl)phenol, respectively. All three crystal structures contain centrosymmetric dimers of edge-sharing octahedra of Fe(iii) ions through a pair of μ2-phenoxido bridges. The exchange coupling is ferromagnetic for 1 (J = +0.47(1) cm−1, 〈Fe–O–Fe = 98.02°) and 2 (J = +0.86(1) cm−1, 〈Fe–O–Fe = 97.17°), but antiferromagnetic for 3 (J = −0.72(1) cm−1, 〈Fe–O–Fe = 98.53°), which are correlated by high-field electron paramagnetic resonance revealing moderate magneto-anisotropy of D = −0.24(3) cm−1, E = 0.08(1) cm−1 for 1, D = −0.38(1) cm−1, E = 0.11(1) cm−1 for 2, and D = 0.30(3) cm−1, E = 0.02(1) cm−1 for 3. The exchange couplings were further estimated by DFT calculations, which gave the finest Fe–O–Fe angle of 97.83° for the ferromagnetic–antiferromagnetic crossover. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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15. Slow magnetic relaxation in mononuclear seven-coordinate cobalt(ii) complexes with easy plane anisotropy.
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Chen, Lei, Chen, Shu-Yang, Sun, Yi-Chen, Guo, Yu-Mei, Yu, Lu, Chen, Xue-Tai, Wang, Zhenxing, Ouyang, Z. W., Song, You, and Xue, Zi-Ling
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MAGNETIC relaxation , *COBALT , *ANISOTROPY , *PARAMAGNETIC resonance , *X-ray crystallography - Abstract
Two mononuclear seven-coordinate cobalt(ii) complexes [Co(L)3(NO3)2] (L = 4-tert-butylpyridine, 1; L = isoquinoline, 2) were prepared and structurally analyzed by single-crystal X-ray crystallography. The coordination spheres of 1 and 2 exhibit distorted pentagonal bipyramid geometry. Analysis of their direct-current magnetic data reveals the existence of easy plane anisotropy (D > 0) with a small transverse anisotropy (E), which was further confirmed by high-field electron paramagnetic resonance (HFEPR) spectroscopy. Field-induced slow magnetic relaxations were observed under the applied dc field in complexes 1 and 2 by alternating-current magnetic susceptibility measurements. Importantly, these complexes are new instances of mononuclear high-coordinate cobalt(ii)-based single-molecule magnets. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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