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[Er2(thd)4Pc]·2C6H6 (1) (Hthd = 2,2,6,6-tetramethylheptanedione), obtained as green crystals from the reaction of [Er(thd)3]·2H2O with lithium phthalocyanine, Li2Pc, is a stable dinuclear complex with two ErIII centers. Its lattice benzene solvent can be exchanged by soaking the crystals in dichloromethane to give [Er2(thd)4Pc]·2CH2Cl2 (2). The magnetic susceptibility data suggest different coupling interactions for the two complexes. While 1 exhibits fast relaxation and an estimated energy barrier of Ea = 2.6 cm-1 under 600 Oe dc field, the single-molecule magnet behavior of 2 is field-induced and the energy barrier is higher at 34.3 cm-1. Ab initio calculations were performed to understand the nature of the coupling interaction between two ErIII ions bridged by the phthalocyanine and the origin of different magnetic behavior. Importantly, the single-molecule magnetic properties can be reversibly tuned through the exchange of solvent molecules, confirmed by further measurements on the reverse solvated complexes 1-re and 2-re. This subtle control of relaxation by lattice solvents is rarely observed in single-molecule magnets, especially for ErIII-based complexes.

In search of simple approaches to rationally enhance the energy barriers in polynuclear dysprosium single-molecule magnets, a new system containing two structurally closely related dinuclear dysprosium complexes, namely [Dy2(L)2(DBM)2(DMF)2] (1) and [Dy2(L)2(DBM)2(DMA)2]·2DMA (2) (HDBM = dibenzoylmethane, H2L = 2-hydroxy-N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide), is introduced and the structure-dependent magnetic properties are investigated. The two complexes display only slight variations in the coordination geometries of the Dy(III) ion but display remarkably different magnetic behaviors. By replacing the DMF (dimethylformamide) ligand in complex 1 with DMA (dimethylacetamide) in 2 while retaining the same coordination atoms, we were able to create a 3-fold enhancement in the energy barrier, from 24 K for complex 1 to 77 K for complex 2. Complete-active-space self-consistent field (CASSCF) calculations revealed that the charge distribution surrounding the Dy(III) centers in 1 and 2 is the key factor in determining the relaxation properties of the SMMs. The introduction of an electron-donating CH3 group in DMA to replace the hydrogen in DMF resulted in a larger average charge along the magnetic axes of complex 2 compared to complex 1, which resulted in a stronger easy-axis ligand field, thus increasing the energy difference between the ground and the first excited states of complex 2. This work presents a simple method to rationally enhance the energy barrier in polynuclear lanthanide SMMs through fine-tuning of the electrostatic potential of the atoms along the magnetic axis.

Density functional theory (DFT) and ab initio methods were used to investigate the influence of both intramolecular exchange coupling and single-ion anisotropy on the relaxation barriers of a series of N2(3-) radical-bridged lanthanide complexes [{[(Me3Si)2N]2(THF)Ln}2(μ-η(2):η(2)-N2)](-) (Ln = Gd(III) (1), Tb(III) (2), Dy(III) (3), Ho(III) (4), and Er(III) (5)) reported by Long and co-workers. DFT calculations show that the exchange coupling between the lanthanide ions is very weak, but the Ln-N2(3-) coupling is strong for each complex. Moreover, the exchange couplings of Ln-N2(3-) are antiferromagnetic for Ln = Gd(III), Tb(III), Dy(III), and Ho(III) but ferromagnetic for Er(III) for the nearly orthogonal magnetic orbitals on Er(III) and N2(3-). Ab initio calculations show that both of the large magnetic anisotropy of single Tb fragment and the strong Tb-N2(3-) antiferromagnetic couplings lead to the largest energy barrier of complex 2. Although the energy barrier of a single Er fragment is the second largest, the relaxation barrier of complex 5 is only 36.0 cm(-1) due to the weak Er(III)-N2(3-) coupling. This study suggests that both intramolecular exchange coupling and single-ion anisotropy contribute greatly to the full relaxation barrier of lanthanide-based single-molecule magnets (SMMs), which expands the understanding of SMMs using only the giant-spin model.

The mononuclear complex [Ni(HOphen)(OSO3)(H2O)3]·5H2O (HOphen = 1, 10-phenanthrolin-2-ol) was prepared and its single structure was determined by X-ray crystallography. In this complex, the NiII ion has a distorted octahedral arrangement. Crystal structure analysis shows that two kinds of π–π stacking interactions and C–H···O short contact intermolecular interactions exist among the adjacent complexes. Fitting to the variable-temperature magnetic susceptibility data gave the magnetic coupling constant, 2J = –0.98 cm–1. Theoretical calculations, based on density functional theory (DFT) coupling with the broken-symmetry approach (BS), revealed that the π–π stacking magnetic coupling pathways resulted in weak ferromagnetic interactions with 2J = 4.86 cm–1 and 2J = 4.16 cm–1, respectively, for the adjacent NiII ions with separations of 8.568(19) A and 8.749(32) A, respectively; whereas the magnetic coupling pathway of the C–H···O short contact intermolecular interaction led to a weak antiferromagnetic interaction with 2J = –17.62 cm–1 for the adjacent NiII ions with a separation of 10.291(26) A. The ferromagnetic coupling sign can be explained by the McConnell I spin-polarization mechanism.

A new 1-D MnII chain, [Mn(μ 1,3-N3)(phenCl)2]n (ClO4)n (phenCl = 2-chloro-1,10-phenanthroline), was synthesized with single μ 1,3-azido as bridge and 2-chloro-1,10-phenanthroline as coligand, and its crystal structure determined by X-ray crystallography. In the complex, MnII is located in a distorted octahedral geometry, and azide is an end-end bridge, linking two MnII ions with separation of 5.7356(10) A, forming a 1-D chain. In the crystal, there are two kinds of π-π stacking between adjacent chains. The fitting of the variable-temperature (2.00–320 K) magnetic susceptibilities gave an anti-ferromagnetic interaction of J = –5.99 cm–1 ( ), among the stronger magnetic interaction in MnII complexes with azido as single end-end bridge. Reported experimental results do not confirm clearly the magneto-structural correlations revealed by theoretical calculations.

We herein reported the synthetic, structural, computational, and magnetic studies of four air-stable heptacoordinated mononuclear cobalt(II) complexes, namely, [CoII(tdmmb)(H2O)2][BF4]2 (1), [CoII(tdmmb)(CN)2]·2H2O (2), [CoII(tdmmb)(NCS)2] (3), and [CoII(tdmmb)(SPh)2] (4) (tdmmb = 1,3,10,12-tetramethyl-1,2,11,12-tetraaza[[3](2,6)pyridino[3](2,9)-1,10-phenanthrolinophane-2,10-diene; SPh– = thiophenol anion). Constrained by the rigid pentadentate macrocyclic ligand tdmmb, the CoII centers in all of these complexes are in the heptacoordinated pentagonal-bipyramidal geometry. While the equatorial environments of these complexes remain very similar to each other, the axial ligands are systematically modified from C to N to O to S atoms. Analyses of the magnetic data and the ab initio calculations both reveal large easy-plane magnetic anisotropy (D > 0) for all four complexes. While the experimentally obtained D values do not show any clear tendency when the axial coordinated atoms change from C to N to O atoms...

Three new heterometallic single-molecule magnets (SMMs), [Dy

A distorted octahedral Co(II) complex is reported with homoscorpionate ligands. This complex comprised a field-induced single-molecule magnet, showing two slow relaxation processes under a low dc field (

A series of bis-pentamethylcyclopentadienyl-supported Dy complexes containing different ancillary ligands were synthesized and characterized. Magnetic studies showed that 1 Dy [Cp*2 DyCl(THF)], 1 Dy' [Cp*2 DyCl2 K(THF)]n , 2 Dy [Cp*2 DyBr(THF)], 3 Dy [Cp*2 DyI(THF)] and 4 Dy [Cp*2 DyTp] (Tp=hydrotris(1-pyrazolyl)borate) were single-ion magnets (SIMs). The 1D dysprosium chain 1 Dy' exhibited a hysteresis at up to 5 K. Furthermore, 3 Dy featured the highest energy barrier (419 cm(-1) ) among the complexes. The effects of ancillary ligands on single-ion magnetic properties were studied by experimental, ab initio calculations and electrostatic analysis methods in detail. These results demonstrated that the QTM rate was strongly dependent on the ancillary ligands and that a weak equatorial ligand field could be beneficial for constructing Dy-SIMs.

A series of HMq-bridged dinuclear dysprosium complexes, namely, [Dy(acac)2(CH3OH)]2(μ-HMq)2 (1), [Dy(DBM)2]2(μ-HMq)2(n-C6H14) (2), [Dy(hmac)2]2(μ-HMq)2 (3) and [Dy(hfac)3]2(μ-HMq)2 (4) (HMq = 2-methyl-8-hydroxyquinoline, acac = acetylacetone, DBM = dibenzoylmethane, hmac = hexamethylacetylacetonate and hfac = hexafluoroacetylacetonate), were structurally and magnetically characterized. X-ray crystallographic analyses of the structures reveal that HMq serves as the effective bridge to link two Dy(III) centers by means of the phenoxyl oxygen and nitrogen atoms and the periphery β-diketonate ligands complete the coordination sphere by bidentate oxygen atoms. The different substituents on the β-diketonate terminal lead to different coordination models mostly due to the steric hindrance of these substituents, and the electron-withdrawing or donating effects likely influence the strength of the ligand fields and the Dy(III) ion anisotropy. Measurements of alternating-current (ac) susceptibility on complexes 1-4 reveal that complexes 3 and 4 display significant zero-field single-molecule magnetic (SMM) behavior with barrier energy Ueff/kB = 14.8 K, τ0 = 1.8 × 10(-5) s and Ueff/kB = 9.2 K, τ0 = 1.7 × 10(-5) s, respectively, whereas 1 and 2 exhibit field-induced SMM behavior, and these differences are attributed to the alteration on the periphery β-diketonate ligands. Their distinct slow magnetic relaxation behaviors were related to their different individual Dy(III) ion magnetic anisotropy and intramolecular coupling, which were confirmed by ab initio calculations.

Three complexes with formula {Dy(q)2(L)}2(μ3-OH)2{Dy(q)(L)}2(solvents) (where q = 8-quinolinolate; L = acetylacetone (acac) with (CH2Cl2)2 = solvent (1), 1,3-diphenyl-1,3-propanedione (DBM) and (CH2Cl2)2 = solvent (2), and hexafluoroacetylacetone (hfac) and CHCl3 = solvent (3)) were structurally and magnetically characterized. They have similar Dy4 structural cores bridged by N and O atoms from 8-quinolinolate, and only differ in the peripheral β-diketonate ligands. The variable-frequency and temperature alternating-current (ac) magnetic susceptibility measurements reveal that complexes 1 and 2 display significant zero-field single-molecule-magnet (SMM) behavior, while complex 3 exhibits the field-induced SMM behavior, albeit they possess the nearly same primary coordination sphere. The ac susceptibility measurement on the diluted samples verified that their relaxation was of purely molecular origin, and their distinct slow magnetic behaviors were related to the replacement of the peripheral β-diketonate ligand, which is responsible for their different individual Dy(III) ions’ magnetic anisotropy and intramolecular coupling, as confirmed by ab initio calculation.

In recent years, plentiful lanthanide-based (Tb(III) , Dy(III) , and Er(III) ) single-molecule magnets (SMMs) were studied, while examples of other lanthanides, for example, Tm(III) are still unknown. Herein, for the first time, we show that by rationally manipulating the coordination sphere, two thulium compounds, 1[(Tp)Tm(COT)] and 2[(Tp*)Tm(COT)] (Tp=hydrotris(1-pyrazolyl)borate; COT=cyclooctatetraenide; Tp*=hydrotris(3,5-dimethyl-1-pyrazolyl)borate), can adopt the structure of non-Kramers SMMs and exhibit their behaviors. Dynamic magnetic studies indicated that both compounds showed slow magnetic relaxation under dc field and a relatively high effective energy barrier (111 K for 1, 46 K for 2). Magnetic diluted 1 a[(Tp)Tm0.05 Y0.95 (COT)] and 2 a[(Tp*)Tm0.05 Y0.95 (COT)] even exhibited magnetic relaxation under zero dc field. Relativistic ab initio calculations combined with single-crystal angular-resolved magnetometry measurements revealed the strong easy axis anisotropy and nearly degenerated ground doublet states. The comparison of 1 and 2 highlights the importance of local symmetry for obtaining Tm SMMs.

A new dinuclear complex, [Cu2(μ1, 3-NCS)2(Ophen)2(OH2)2], (HOphen = 1, 10-phenanthrolin-2-ol) was synthesized and its crystal structure was determined by X-ray crystallography. In the complex, the CuII ion assumes a distorted square pyramidal arrangement and the thiocyanate anion functions as bridged ligand and Ophen as capped ligand. The analysis of the crystal structure shows that there exists a π–π stacking interaction between the adjacent complexes. The theoretical calculations reveal that the magnetic coupling pathways from the thiocyanate anions bridge ligand and the π–π stacking magnetic coupling pathway resulted in the weak ferromagnetic interactions with 2J = 18.46 cm–1 and 2J = 10.46 cm–1, respectively. The calculations also display that the spin delocalization and the spin polarization occur in the bridge magnetic coupling system and the π–π stacking magnetic coupling system, and the magnetic coupling mechanism of the π–π stacking can be explained with McConnell I spin-polarization mechanism. The fitting for the data of the variable-temperature magnetic susceptibility with dinuclear CuII formula gave the magnetic coupling constant 2J = 2.84 cm–1 and zJ′ = 0.03 cm–1, in which the 2J = 2.84 cm–1 is attributed to the magnetic coupling from the bridge dinuclear CuII unit and the zJ′ = 0.03 cm–1 is ascribed to the π–π stacking magnetic coupling system. The study may benefit to understand the magnetic coupling mechanism of π–π stacking system.

A new mononuclear complex, [Ni(dpphen)(NCS)2] [dpphen = 2,9-di(1H-pyrazol-1-yl)-1,10-phenanthroline], has been prepared and its crystal structure is determined by X-ray crystallography. In the NiII complex, NiII is a distorted octahedral geometry. The crystal structure analysis shows that there exist π−stacking interactions and an intermolecular interaction among adjacent complexes. The fitting to the variable-temperature magnetic susceptibility data gave the magnetic coupling constant J = −1.37 cm−1 ( ). Theoretical calculations reveal that the π-stacking magnetic coupling pathway resulted in an antiferromagnetic interaction with 2 J = −0.22 cm−1 ( ), whereas the magnetic coupling pathway of the intermolecular interaction led to a ferromagnetic interaction with 2 J = 0.10 cm−1 ( ). The calculations also display that there occur both spin delocalization and spin polarization in the π-stacking magnetic coupling system and the magnetic coupling system of the intermolecular interaction.

On the basis of the experimentally synthesized [(PY5Me2)4Mn4Re(CN)7]5+, the theoretically modeled clusters of [(PY5Me2)4V4Re(CN)7]5+ and [(PY5Me2)4Ni4Re(CN)7]5+ both have strong magnetic anisotropy energy barriers.

A novel magnetic coupling is observed in a unpublished crystal that consists of a mono-nuclear manganese(II) complex, namely, [Mn(DPP)(NCS) 2 ] (DPP = 2-(3,5-dimethyl-1H-pyrazol-1-yl)-1,10-phenanthroline), in which neutral DPP molecule functions as tridentate chelated ligand. In the complex Mn(II) ion assumes a distorted trigonal bipyramidal geometry and in the crystal there is a π–π stacking interaction between the adjacent complexes, which involves pyridyl ring and the symmetry-related pyrazolyl ring and pyridyl ring. The fitting for the data of the variable-temperature magnetic susceptibilities with infinite uniform Mn(II) chain formula gave the magnetic coupling constant J = −0.11 cm −1 , and theoretical calculations reveal that there exists a very weak anti-ferromagnetic coupling between the adjacent Mn(II) ions with J = −0.02 cm −1 . The magnetic coupling sign is explained based on McConnell I spin-polarization mechanism with the analysis of the spin density population and the factors that dominate the magnetic coupling magnitude.

A half-sandwich organolanthanide complex, [(C6Me6)Dy(AlCl4)3], in which Dy(III) is coordinated with a π-bonded arene was synthesized and magnetically characterized. This complex displays slow magnetic relaxation and a hysteresis loop associated with single-ion magnet behavior. The orientation of the magnetic anisotropy axis is analyzed using ab initio calculations.

A theoretical density functional study of the magnetostructural correlations in a series of cyano-bridged MoNi systems is presented. Our calculations by two approaches with several local density approximations (LDAs) and generalized gradient approximations (GGAs) show that: (1) the influence of the next-nearest-neighbor MoMo interactions on the MoNi interactions can be omitted; (2) the MoNi interactions strengthen with an increase in the Ni–Nbrid–Cbrid angle in the range 135° to 175° for all the functionals; (3) increasing the number of exchange coupling interactions from one to two will decrease the ferromagnetic MoNi interactions, but the influence of further increasing the number of exchange coupling interactions from two to three or four on the MoNi interactions is very small, because the peripheral units do not surround the same central metal ion in the MoNi systems that we investigated. Kahn's theory was used to interpret the above results.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A density functional study of the exchange coupling interactions between the two nearest CuII centers in [LaCu6] and [YCu6] is presented. Two approaches show that the Cu···Cu antiferromagnetic interactions increase with a decrease of the ionic radius of the diamagnetic central LaIII and YIII ions. However, the influence of the central ions on the Cu···Cu interactions is small compared to that of their structures according to our calculations. We therefore conclude that the stronger antiferromagnetic interactions between the two nearest CuII centers in [LaCu6] than in [YCu6] are not a result of the central LaIII ion but the structure. The antiferromagnetic contributions of the direct overlap between the two nearest CuII magnetic orbitals also play a major role according to the calculations of the overlap integral Sij based on Kahn's theory.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The first single-ion magnet (SIM) [Co(IMes)2][BPh4] (IMes: 1,3-dimesitylimidazol-2-ylidene) with d8 electronic configuration has been found in two-coordinate Co(i)–NHC complexes., The slow magnetic relaxation typical for single-ion magnets has been known for certain low-coordinate 3d metal complexes with d6, d7, and d9 electronic configurations, but never for d8 complexes. Herein, we report a study on two-coordinate d8 cobalt(i)–N-heterocyclic carbene complexes, for which slow magnetic relaxation behavior was observed for [Co(IMes)2][BPh4] (IMes: 1,3-dimesitylimidazol-2-ylidene) under an applied dc field. The system represents the first d8 single-ion magnet, and features a fitted energy barrier of Ueff = 21.3 cm–1 and pre-exponential factor of τ0 = 6.6 × 10–6 s. The analog two-coordinate cobalt(i) complexes with different NHC ligands, [Co(sIMes)2][BPh4] (sIMes: 1,3-dimesitylimidazolin-2-ylidene) and [Co(IAd)2][BArF4] (IAd: 1,3-dimesitylimidazol-2-ylidene; BArF4: tetra(3,5-ditrifluoromethylphenyl)borate), do not show such single-ion magnet behaviour. Ab initio calculations imply that the dihedral angle between the two NHC planes and the degree of unsaturation of the NHC ligands can dramatically alter the D value of the two-coordinate cobalt(i)–NHC ions, possibly via changing of the Co–NHC π-interactions, and hence affect the spin–orbit coupling splitting.

Three half-sandwich organometallics [(Cp(R))Dy(DBM)2(THF)]·solvent [Cp(R) = Cp* (1Dy, Cp* = C5Me5), Cp(4PrPh) (2Dy, Cp(4PrPh) = C5Pr4Ph), Cp' (3Dy, Cp' = C5Me4TMS, solvent = THF), DBM(-) = dibenzoylmethanoate anion, THF = tetrahydrofuran, TMS = trimethylsilyl] with a Janus structural motif, where the ligands of DBM(-) and [Cp(R)](-) are widely used in Dy(III)/β-diketonate and Ln(III)/cyclopentadienyl systems, were synthesized, structurally and magnetically characterized, and theoretically investigated. Single-crystal structural analysis reveals that the three complexes crystallize in the same space group P21/c. All the molecules display slow magnetic relaxation in the absence of an applied magnetic field, and the magnetic hysteresis loops of 2Dy and 3Dy can be observed under a magnetic field sweep rate of 10 Oe/s, indicating all three complexes are single-ion magnets (SIMs). The modifications of the Cp-ring lead to the distinct increment of the energy barrier from 46 K (1Dy) to 76 K (2Dy) to 320 K (3Dy). Ab initio calculations show that the ground Kramers doublet is strongly axial with gz approaching the value of 20 expected for the pure MJ = ±15/2 state, and the magnetic anisotropy axes for three complexes share a similar orientation which is perpendicular to the molecular pseudosymmetric axis. Electrostatic analyses confirm the magnetic anisotropy orientations and reveal that proper charge distribution of the coordination sphere (including the first and second) around Dy(III) ion enhances the magnetic anisotropy. Further investigation of the relaxation mechanisms suggests the energy barrier should be carefully used to evaluate single-ion magnets if Raman process is dominant in the low temperature range.

The synthesis, structures, and magnetic properties of a family of air-stable star-shaped Co(II)Co(III)3 complexes were investigated. These complexes contain only one paramagnetic Co(II) ion with the approximate D3 coordination environment in the center and three diamagnetic Co(III) ions in the peripheral. Magnetic studies show their slow magnetic relaxation in the absence of an applied dc field, which is characteristic behavior of single-molecule magnets (SMMs), caused by the individual Co(II) ion with approximate D3 symmetry in the center. Most importantly, it was demonstrated that the anisotropy energy barrier can be finely tuned by the periphery substituent of the ligand and the countercation. The anisotropy energy barrier can be increased significantly from 38 K to 147 K.

A one-dimensional cobalt(II) coordination polymer, [Co(btm)2(SCN)2·H2O]n [btm = bis(1H-1,2,4-triazol-1-yl)methane], was synthesized and magnetically characterized. The isolated slightly distorted octahedral Co(II) ion displays field-induced slow relaxation with a big positive axial and a negative rhombic magnetic anisotropy (D = 93.9 cm(-1) and E = -10.5 cm(-1)), and the anisotropy energy barrier is 45.4 K.

2D dysprosium complex exhibiting slow magnetic relaxation originating from the strong Ising anisotropy of single Dy3+ ions has been reported., A new 2D dysprosium layer compound has been successfully synthesized from reaction with 2-(3-pyridyl) pyrimidine-4-carboxylic acid (H3-py-4-pmc), in which the Dy3+ ions reside in square antiprismatic coordination environments and are connected by carboxylate/oxalate/hydroxyl bridges. Magnetic studies reveal ferromagnetic interactions between Dy3+ ions, slow magnetic relaxation with an effective energy barrier U eff of 186 K under zero dc field and pronounced hysteresis loops at low temperatures. Further dilution magnetic study suggests that the slow magnetic relaxation originates from the single-ion magnetic behavior of Dy3+ ion and that magnetic coupling suppresses the quantum tunneling of magnetization at low temperature. In addition, theoretical calculation indicates strong Ising anisotropy of the Dy3+ ion that is due to the strong interaction between Dy3+ ions and hydroxyl groups.

Ab initio methods have been used to explore the unexpectedly strong magnetic anisotropy and the magnetostructural correlations in mononuclear eight-coordinate complex [Co(II)(12-crown-4)2](2+). Our calculations showed that both decreasing α and increasing φ may enhance its magnetic anisotropy, which was rationalized by the qualitative theory proposed by Long and co-workers. Moreover, we deduced that the |D| value of [Co(II)(12-crown-4)2](2+) with α = 52° and φ = 43° is the largest one.

A dysprosium based single-ion magnet is synthesized and characterized by the angular dependence of the single-crystal magnetic susceptibility. Ab initio and effective electrostatic analyses are performed using the molecular structures determined from single crystal X-ray diffraction at 20 K, 100 K and 300 K. Contrary to the common assumption, the results reveal that the structural thermal effects that may affect the energy level scheme and magnetic anisotropy below 100 K are negligible.

A theoretical density functional study of the relationship between the nearest-neighbor MnMo constants and the number of exchange interactions in the cyano-bridged K[(Me3tacn)6MnMo6(CN)18](ClO4)3 cluster is presented. Two approaches (the first approach consisted of evaluating the exchange coupling constant Jij between two paramagnetic metal centers i and j in the hexanuclear molecule by calculating the energy differences between the highest and broken-symmetry spin states of a model molecule in which metal atoms except for i and j are substituted by diamagnetic YIII cations, and the second is to calculate the different spin-state energies of hexanuclear complexes and use the Heisenberg Hamiltonian to obtain the exchange coupling constants between different metal centers) show that the antiferromagnetic coupling interactions between nearest neighbors weaken with the increase of the number of exchange interactions. The various θ angles have an influence on the interactions between the nearest-neighbor MoMn but do not change the trend between J12 and the number of exchange interactions. Moreover, Kahn’s qualitative theory succeeded in being applied to interpret the trend.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

A theoretical density functional study of the relationship between the nearest-neighbor constants and the number of peripheral complexes in the cyano-bridged [Cr[CNMn(salen)(H2O)]6]3+ and [(5-Brsalen)2(H2O)2Mn2Cr(CN)6] clusters is presented. Two approaches show that the antiferromagnetic coupling interactions between nearest neighbors decrease with the increase of the number of peripheral complexes, although the second approach provides better results using several exchange-correlation functionals. The first approach consisted of evaluating the exchange coupling constant J(ij) between two paramagnetic metal centers i and j in the hexanuclear molecule by calculating the energy differences between the highest and broken-symmetry spin states of a model molecule in which metal atoms except for i and j are substituted by diamagnetic Zn(II) cations, while the second consisted of calculating the different spin-state energies of hexanuclear complexes and using the Heisenberg Hamiltonian to obtain the exchange coupling constants between different metal centers. Moreover, Kahn's qualitative theory succeeded in being applied to interpret the trend.

Molecular magnetism in a series of cyano-bridged first and second transition metal complexes has been investigated using density functional theory (DFT) combined with the broken-symmetry (BS) approach. Several exchange-correlation (XC) functionals in the ADF package were used to investigate complexes I [-(Me 3 tacn) 2 (cyclam)NiMo 2 (CN) 6 ] 2+ , II [-(Me 3 tacn) 2 (cyclam)Ni-Cr 2 (CN) 6 ] 2+ , III [(Me 3 tacn) 6 MnMo 6 (CN) 18 ] 2+ , and IV [(Me 3 tacn) 6 MnCr 6 (CN) 18 ] 2+ (Me 3 tacn = N,N',N'''-trimethyl-1,4,7-triazacyclononane). For models A (the molded structure of complex I) and B (the modeled structure of complex II), all the XCs given qualitatively reasonable results and predict ferromagnetic coupling character between M (M = Mo III for A or Cr III for B) and Ni II in coincidence with the experimental results (see Tables I and II). The calculated using Operdew, OPBE, 03LYP, and B3LYP functionals and experimental J values show that substituting Cr III with Mo III will enhance the ferromagnetic exchange coupling interactions. But VWN, PW91, PBE, VSXC, and tau-HCTH functionals have no way to differentiate the relative strength of the intramolecular magnetic exchange coupling interactions of A and B correctly. For models C (the modeled structure of complex III) and D (the modeled structure of complex IV), all the XCs in ADF and B3LYP in Gaussian 03 with several basis sets show that substituting Cr III with Mo III will enhance the antiferromagnetic exchange coupling interactions. From the above calculations, the substitution of Cr III by Mo III will enhance the magnetic coupling interactions, whether the magnetic coupling interactions are ferro- or antiferromagnetic. Moreover, Kahn's model was applied to investigate the above facts.

Magnetic coupling constants J for the complete structures of [ Gd(capro) 2( H 2 O )4 Cr(CN) 6]• H 2 O (capro represents caprolactam) (a) and trans-[ Fe(CN) 4(μ- CN )2 Gd ( H 2 O )4 (bpy) ]•4 H 2 O •1.5 bpy (b) have been calculated using hybrid density functional theory (DFT) B3LYP combined with a modified broken symmetry approach (BS). The calculated J value of -0.24 cm-1 for a is very close to the experimental -0.33 cm-1. They both show the antiferromagnetic interaction between Gd(III) and Cr(III) . For b, although the sign of the calculated J value of 4.24 cm-1 is different from that of the experimental -0.38 cm-1, the two values both show the weak magnetic coupling interaction between Gd(III) and Fe(III) . The spin density distributions are discussed on the basis of Mulliken population analysis. For complexes a and b, both transition metal ( Fe(III) or Cr(III) ) and rare earth Gd(III) display a spin polarization effect on the surrounding atoms, where a counteraction of the opposite polarization effects leads to a low spin density on the bridging ligand C1N1 . For the compounds Gd(III) - Cr(III) (a) and Gd(III) - Fe(III) (b) in the HS states, Cr(III) has stronger spin polarization influence on the bridging atoms than Fe(III) even causing the positive spin population on the bridging atom N1 .

Molecular magnetism in cyano-bridged Mo I I I binuclear complexes [Mo 2 (CN) 1 1 ] 5 - and [(Me 3 tacn) 2 Mo 2 (CN) 5 ] + (Me 3 tacn=N, N', N"-trimethyl-1,4,7-triazacyclononane) has been calculated using Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Parr (B3LYP), a hybrid density functional theory (DFT), combined with a modified broken symmetry (BS) approach and the post-Hartree-Fock (post-HF) method difference-dedicated configuration interaction (DDCI). We find B3LYP combined with broken-symmetry approach (DFT-BS) give the similar J values to those calculated by DDCI. So we use B3LYP combined with BS approach to investigate the magnetism above two molecules. Through calculations, we find that the absolute J values decrease with the increase of r (the Mo(2)-C b r i d and Mo(1)-N b r i d distances) and are linearly related to the differences of the squared spin populations [(ρ2 H S - ρ 2 B S )] on Mo I I I atoms between the highest-spin (HS) state and the broken symmetry (BS) state. Moreover, the absolute J values are linearly related to the sum of the square of the difference in energy of the unpaired electrons (ξ) with a limited variation of the r distance. We conclude that ξ can be used to scale the degree of the antiferromagnetic coupling interactions. At the end of the paper, the spin density distributions and the mechanisms of magnetic coupling interactions are analyzed by us.

The quest for the single-molecular magnets (SMMs) based on mononuclear transition-metal complexes is focused on the low-coordinate species. No transition-metal complex with a coordination number of eight has been shown to exhibit SMM properties. Here the magnetic studies have been carried out for a mononuclear, eight-coordinate cobalt(II)-12-crown-4 (12C4) complex [Co(II)(12C4)2](I3)2(12C4) (1) with a large axial zero-field splitting. Magnetic measurements show field-induced, slow magnetic relaxation under an applied field of 500 Oe at low temperature. The magnetic relaxation time τ was fitted by the Arrhenius model to afford an energy barrier of Ueff = 17.0 cm(-1) and a preexponential factor of τ0 = 1.5 × 10(-6) s. The work here presents the first example of the eight-coordinate, mononuclear, 3d metal complex exhibiting the slow magnetic relaxation.

A series of six-coordinate lanthanide complexes {(H3O)(Ln(NA)2)·H2O}n (H2NA = 5-hydroxynicotinic acid; Ln = Gd III (1·Gd); Tb III (2·Tb); Dy III (3·Dy); Ho III (4·Ho)) have been synthesized from aqueous solution and fully characterized. Slow relaxation of the magnetization was observed in 3·Dy. To suppress the quantum tunneling of the magnetization, 3·Dy diluted by diamagnetic Y III ions was also synthesized and magnetically studied. Interesting butterfly-like hysteresis loops and an enhanced energy barrier for the slow relaxa- tion of magnetization were observed in diluted 3·Dy. The energy barrier (Dt) and pre-exponential factor (t0) of the di- luted 3·Dy are 75 K and 4.21 � 10 � 5 s, respectively. This work illustrates a successful way to obtain low-coordination- number lanthanide complexes by a framework approach to show single-ion-magnet-like behavior.

Our calculations show that the substitution of metal ions using Co(II) is not the main reason that Co(II)(9)M(6) (M = Mo(V) or W(V)) exhibits single-molecule-magnet behavior, whereas the unsymmetrical distribution of three CH(3)OH ligands surrounding each Co(II) is the main one.

The origin of the magnetic anisotropy energy barriers in a series of bpym− (bpym = 2,2′-bipyrimidine) radical-bridged dilanthanide complexes [(Cp*2Ln)2(μ-bpym)]+ [Cp* = pentamethylcyclopentadienyl; Ln = GdIII (1), TbIII (2), DyIII (3), HoIII (4), ErIII (5)] has been explored using density functional theory (DFT) and ab initio methods. DFT calculations show that the exchange coupling between the two lanthanide ions for each complex is very weak, but the antiferromagnetic Ln-bpym− couplings are strong. Ab initio calculations show that the effective energy barrier of 2 or 3 mainly comes from the contribution of a single TbIII or DyIII fragment, which is only about one third of a single Ln energy barrier. For 4 or 5, however, both of the two HoIII or ErIII fragments contribute to the total energy barrier. Thus, it is insufficient to only increase the magnetic anisotropy energy barrier of a single Ln ion, while enhancing the Ln-bpym− couplings is also very important. © 2014 Wiley Periodicals, Inc.

The π-π stacking interaction, one of the main intermolecular forces, sometimes leads to amazing magnetic properties. Although the concept has been raised that spin density is one of the main factors that contribute to the magnetic coupling strength in intermolecular magnetic coupling systems, it has not been confirmed either experimentally or theoretically to date. Herein we present a study on the magnetostructural data of seven unpublished Cu(II) complexes and ten reported radicals. It is confirmed for the first time that the spin density on short contact atoms is a major factor that contributes to the π-π stacking magnetic coupling strength. Based on the reported data to date, when the short contact distance is larger than the default contact radius, medium or relatively strong magnetic coupling strength could be obtained only if the spin density on the short contact atoms is greater than 0.1350; when the C···C short contact is less than the default contact radius of 3.4 A, but not less than 3.351 A, and the spin density is less than 0.1, neither medium nor strong magnetic coupling strength could be observed. Further, when the short contact distance decreases with a temperature drop, the spin densities on the relevant short contact atoms increase. In the complexes reported the small spin densities on the relevant short contact atoms are the major factors that result in the weak π-π magnetic coupling strength.

To construct the mutants of biofilm related genes in Vibrio parahaemolyticus and confirm the mutants.The homologous upstream and downstream flanking fragments of target gene were amplified by using PCR, and the fusion homologous fragment was amplified by using the two flanking fragments as template. Then the fusion homologous fragment was digested by restriction enzyme and cloned into suicide plasmid pDS132. The recombinant plasmid was transferred into Vibrio parahaemolyticus RIMD 2210633 through conjugation. The mutants were screened and identified by PCR and the phenotype of one mutant was analyzed in order to verify that the mutants were constructed successfully.Six recombinant plasmids carrying the fusion homologous fragments of genes vbfR, crp, hns, swrZ, swrT and cpsR respectively were constructed and identified by PCR. The amplification products of 1190, 1128, 1136, 953, 1242 and 1112 bp were obtained respectively. The six mutants (ΔvbfR, Δcrp, Δhns, ΔswrZ, ΔswrT and ΔcpsR) were constructed using recombinant plasmids. Verified by PCR, the size of amplification products of mutants (1190, 1128, 1136, 953, 1242 and 1112 bp respectively) was less (610, 739, 421, 542, 427 and 1367 bp respectively) than the corresponding positive control. Meanwhile, none of the products was amplified using the primers locating on the target gene. One mutant Δhns was selected to test the ability of biofilm formation. The result showed that the ability of biofilm formation of mutant Δhns was increased compared with the wild type.Six mutants of biofilm related genes in Vibrio parahaemolyticus were constructed and tested by molecular and phenotype experiment to confirm that the mutants were constructed successfully.

This study is to verify the use of rich BHI medium to substitute synthetic media for gene regulation studies in Yersinia pestis.The transcriptional regulation of rovA by PhoP or via temperature upshift, and that of pla by CRP were investigated when Y. pestis was cultured in BHI. After cultivation under 26 °C, and with temperature shifting from 26 to 37 °C, the wild-type (WT) strain or its phoP or crp null mutant (ΔphoP or Δcrp, respectively) was subject to RNA isolation, and then the promoter activity of rovA or pla in the above strains was detected by the primer extension assay. The rovA promoter-proximal region was cloned into the pRW50 containing a promoterless lacZ gene. The recombinant LacZ reporter plasmid was transformed into WT and ΔphoP to measure the promoter activity of rovA in these two strains with the β-Galactosidase enzyme assay system.When Y. pestis was cultured in BHI, the transcription of rovA was inhibited by PhoP and upon temperature upshift while that of pla was stimulated by CRP.The rich BHI medium without the need for modification to be introduced into the relevant stimulating conditions (which are essential to triggering relevant gene regulatory cascades), can be used in lieu of synthetic TMH media to cultivate Y. pestis for gene regulation studies.

A theoretical density functional study of the magnetic coupling interactions and magnetic anisotropy in a family of experimentally synthesized and theoretically modeled M' 6 M 8 (CN 24 ) (M'= Cu II , Ni II or Co II ; M=Fe III or Cr III ) systems is presented. The calculations show that the interactions in the selected M' 6 M 8 (CN 24 ) are all ferromagnetic and the near cubic symmetry of Cu 6 Fe 8 is the origin of its negative magnetic anisotropy parameter D.

Magnetic properties of four high-spin molecules [M'{M'(MeOH)3}8(mu-CN)30{M(CN)3}6] (M' = Mn(II) and M = Mo(V) for A; M' = Mn(II) and M = W(V) for B; M' = Ni(II) and M = Mov for C; M' = Ni" and M = W(V) for D) have been investigated using hybrid density functional theory (DFT) B3LYP with LANL2DZ basis set. Our calculations suggest that models [M'(mu-CN)6{M(CN)7}6](16-) (M' = Mn(II) and M = Mo(V) for A6; M' = Mn" and M = W(V) for B6; M' = Ni(II) and M = Mo(V) for C6; M' = Ni(II) and M = W(V) for D6) and [M'(MeOH)3(mu-CN)3{M(CN)7}3](7-) (M' = Mn(II) and M = Mo(V) for A3; M' = Mn(II) and M = W(V) for B3; M' = Ni(II) and M = Mo(V) for C3; M' = Ni(II) and M = W(V) for D3) are good candidates to model the complete molecular structures of A, B, C and D. For all complexes and models, the antiferromagnetic or ferromagnetic exchange interactions through equatorial cyanides are all stronger than those through apical cyanides. In Mn9M6 (A and B) systems, substituting Mo with W always enhances the antiferromagnetic interactions for the apical and equatorial cyanides and the different Cbrid-Nbrid-Mn angles, but the behavior is more complicated for Ni9M6 (C and D). Moreover, the calculated delta(xy) values of a series of binuclear models according to Kahn-Briat model were used to confirm our conclusions.