Thermochromic Meltable Materials with Reverse Spin Transition Controlled by Chemical Design

We report a series of meltable Fe^II complexes, which, depending on the length of aliphatic chains, display abrupt forward low-spin to high-spin transition or unprecedented melting-triggered reverse high-spin to low-spin transition on temperature rise. The reverse spin transition is perfectly reproducible on thermal cycling and the obtained materials are easily processable in the form of thin film owing to their soft-matter nature. We found that the discovered approach represents a potentially generalizable new avenue to control both the location in temperature and the direction of the spin transition in meltable compounds.     

无自旋混杂的耦簇理论

本文用APCCSD(T)，自旋投影方法消除CCSD中的自旋混杂，自旋投影算符^P用自旋湮灭算符^As 1和^As 2的乘积近似表出，提高了计算精度。     

Spin-inversion mechanisms in O2 binding to a model heme complex revisited by density function theory calculations

Spin-inversion mechanisms in O₂ binding to a model heme complex, consisting of Fe(II)-porphyrin and imidazole, were investigated using density-functional theory calculations. First, we applied the recently proposed mixed-spin Hamiltonian method to locate spin-inversion structures between different total spin multiplicities. Nine spin-inversion structures were successfully optimized for the singlet–triplet, singlet–quintet, triplet–quintet, and quintet–septet spin-inversion processes. We found that the singlet–triplet spin-inversion points are located around the potential energy surface region at short Fe–O distances, whereas the singlet–quintet and quintet–septet spin-inversion points are located at longer Fe–O distances. This suggests that both narrow and broad crossing models play roles in O₂ binding to the Fe-porphyrin complex. To further understand spin-inversion mechanisms, we performed on-the-fly Born-Oppenheimer molecular dynamics calculations. The reaction coordinates, which are correlated to the spin-inversion dynamics between different spin multiplicities, are also discussed.     

One-bond 1J(15N─19F) spin–spin coupling constants of cationic fluorinating reagents: Insights from DFT calculations

We have investigated, by means of density functional theory protocols, the one-bond ¹J(¹⁵N─¹⁹F) spin–spin coupling constants in a series of fluorinating reagents, containing the N─F bond, recently studied experimentally. The results of the calculations show a very good linear relationship with the experimental values, even though only the M06-2X(PCM)/pcJ-2//B3LYP/6-311G(d,p) level affords a very low mean absolute error. The calculations allow to analyze the various molecular orbitals contributions to the J coupling and to rationalize the observed positive sign, corresponding to a negative sign of the reduced spin–pin coupling constant K(N─F). Moreover, of the four Ramsey contributions, only the diamagnetic spin orbit is negligible, whereas the paramagnetic spin orbit and spin dipole terms decrease the magnitude of the Fermi contact (FC) term by an amount that goes from a minimum of 35% up to more than 60% of the FC term itself. Several effects have been investigated, namely, the contribution of the long-range solvent reaction field, relativistic corrections, and conformational and vibrational effects.     

Tunneling spectroscopy of single electron spin

The possibility of detection of the electron spin of a single paramagnetic species (an atom, a radical, or an ion) on the surface was discussed. The analysis was based on spin chemistry laws taking into account the statistics of the spin states of both the tunneling electron and paramagnetic center. The equations for the tunneling current as a function of temperature and magnetic field strength were derived. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1732–1734, September, 1998.     

有机自旋阀及其磁电阻效应

随着巨磁电阻效应(GMR)的发现, 自旋电子学迅速兴起并成为一门新的学科。自旋电子学以电子的自旋属性为信息载体, 有望实现集逻辑、存储和通信于一体的多功能、低功耗器件, 为下一代电子学开辟新的路径。有机半导体具有低自旋轨道耦合、弱超精细相互作用和长自旋弛豫时间等特点, 因而受到了极大关注。有机自旋阀(OSVs)是研究有机材料中自旋注入和传输的原型器件。本文综述了有机自旋阀的发展历程, 总结了有机半导体的自旋弛豫机制, 详细分析了有机自旋阀中存在的关键科学问题, 如室温自旋传输的实现策略和磁电阻符号问题, 介绍了自旋有机发光二极管和自旋光伏器件等新型自旋器件, 最后对有机自旋电子学未来发展进行了展望。     

Determination of heisenberg exchange coupling constants in clusters with magnetic sites: A local spin approach

This work studies the ability of the two‐center local spin quantities, provided by the partitioning of the expectation value of the spin‐squared operator corresponding to N‐electron systems, for determining spin‐exchange coupling constants within the Heisenberg spin Hamiltonian model. The spin‐exchange parameters, which characterize this Hamiltonian for a determined system, have been evaluated in the HeH₂ aggregate and in several clusters (n = 2, 3, 4) with different geometrical arrangements, using internuclear distances larger than the equilibrium ones (beyond the bonding regions). The results found have been analyzed and compared with those arising from other approaches, showing the feasibility of our methodology. © 2014 Wiley Periodicals, Inc.     

Studies of a Large Odd‐Numbered Odd‐Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8Mn

The spin dynamics of Cr₈Mn, a nine‐membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr₈Mn is a rare example of a large odd‐membered AF ring, and has an odd‐number of 3d‐electrons present. Odd‐membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated‐spin ground states. The chemical synthesis and structures of two Cr₈Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground‐spin‐state crossing from S=1/2 to S=3/2 in Cr₈Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin‐pair correlations and scalar‐spin chirality, shows a non‐collinear spin structure that fluctuates between non‐planar states of opposite chiralities.     

密度泛函理论方法研究双核铜化合物的磁性和自旋密度分布

Magnetic coupling constants J between Cu ions and spin density map for a binuclear complex Cu₂(2,2′-bpy)₂(4,4′-bpy)₂L₂ have been calculated by the combination of the broken symmetry approach with the spin project method under the DFT framework and the effect of nonorthogonality between magnetic α and β orbitals in the broken symmetry solution. The result indicates that using SV/SVP basis sets in the calculation of Gaussian 98 is much better than using LanL2DZ pseudo-potential function in above system. It is interesting that calculated J value is quite near to the experimental value in the studies of magnetic susceptibility.     

SPINS: A collection of algorithms for symbolic generation and transformation of many-electron spin eigenfunctions

Summary SPINS represents a collection of algorithms intended to provide an efficient, robust and easy-to-use quantum-chemical toolbox capable of performing a wide range of operations on spin eigenfunctions in the Rumer, Kotani and Serber spin bases. It includes routines for symbolic generation of the Rumer spin eigenfunctions as linear combinations of elementary spin products, for computing all transformation matrices relating the Rumer, Kotani and Serber spin bases and for calculation of the matrices of the irreducible representations of the symmetric group carried by the Rumer, Kotani and Serber spin eigenfunctions, as well as facilities for interpreting general spin-coupling patterns such as those used in spin-coupled theory. The resulting codes, written in Fortran-77 and available on the Internet (from P.B.Karadakov@Bristol.AC.UK or DLC@Liverpool.AC.UK) are so compact and efficient that they even run on IBM PC-compatible personal computers.     

DFT calculations of 31P spin-spin coupling constants and chemical shift in dioxaphosphorinanes

One-bond heteronuclear spin-spin coupling constants (1)J(PX) (X=H, O, S, Se, C and N) between the phosphorus atom and axial and equatorial substituents in dioxaphosphorinanes are computed using density functional theory (DFT). The experimental values of these coupling constants for a variety of substituents can be applied to identify different diastereoisomers. The DFT calculations confirm the systematic trend observed in experiment, and indicate that the computed (1)J(PX) coupling constants are related to the length of the axial and equatorial bonds. A similar relation between the phosphorus chemical shift and the R(PX) bond length appears to be valid, with the exception of selenium substituents.     

Recent progress in EPR study of spin labeled polymers and spin probed polymer systems

The EPR technique is commonly used for the detection and characterization of paramagnetic centers in chemical science. This method can provides a lot of information, such as identity, structure, dynamics, interaction, orientation, glass transition temperature, adsorption behavior, functionality, phase behavior, nano-inhomogeneities, and conformation of the free-radical portion of the polymer chain. Most polymers intrinsically possess diamagnetic properties, so in order to study polymers with EPR, paramagnetic centers need to be incorporated into the polymer systems. Spin labeling and spin probing are main methods of covalently attaching paramagnetic centers to polymer chains or embedding them in polymer matrices through non-covalent interactions, respectively. Spin labeling and spin probing techniques for polymers and polymer systems (especially with nitroxide radicals) have also been studied, which have a profound impact on polymer science. This review focuses on the continuous wave EPR technique and introduces the recent advances in spin labeled polymers and spin probed polymer systems in EPR research.     

两个Fe(II)配合物的合成、结构、磁性和穆斯堡尔谱 —— 配合物[Fe(dpq)(Mepy)2(NCS)2]的室温自旋交叉行为

设计制备了两个新的配合物[Fe(dpq)(Mepy)2(NCS)2](1)和[Fe(Medpq)(Mepy)2 (NCS)2](2)。室温下X衍射结果表明配合物（2）为正交晶系,晶胞参数为a = 15.057(3) Å, b = 14.569(3) Å, c = 13.180(3) Å, a = 90.00°, b=90.00°, g = 90.00°。[FeN6] 变型八面体构型中,两个NCS-与其顺式配位,其余四个氮分别来自Medpq和两个Mepy。变温磁化率和穆斯堡尔谱学的研究表明配合物（1）（2）存在自旋交叉,配合物（1）的自旋转换温度为 T1/2 =340K,而配合物（2）在低温条件下的转换是不完全的。     

The Electron Spin as a Chiral Reagent

We show that enantioselective reactions can be induced by the electron spin itself and that it is possible to replace a conventional enantiopure chemical reagent by spin‐polarized electrons that provide the chiral bias for enantioselective reactions. Three examples of enantioselective chemistry resulting from electron‐spin polarization are presented. One demonstrates the enantioselective association of a chiral molecule with an achiral self‐assembled monolayer film that is spin‐polarized, while the other two show that the chiral bias provided by the electron helicity can drive both reduction and oxidation in enantiospecific electrochemical reactions. In each case, the enantioselectivity does not result from enantiospecific interactions of the molecule with the ferromagnetic electrode but from the polarized spin that crosses the interface between the substrate and the molecule. Furthermore, the direction of the electron‐spin polarization defines the handedness of the enantioselectivity. This work demonstrates a new mechanism for realizing enantioselective chemistry.     

常温自旋交叉配合物[Fe(dpp)(Mepy)2(NCS)2]的合成与磁性研究

设计制备了一个新的常温自旋交叉配合物[Fe(dpp)(Mepy)2(NCS)2]。通过元素分析、红外光谱、电喷雾质谱和紫外光谱等方法对该配合物进行结构表征。变温磁化率研究发现该配合物的自旋转换温度Tc为330K。通过与同体系其他配合物的比较发现,配体的修饰对自旋交叉临界温度以及回滞宽度都有显著影响。     

Solvent effects on optically detected magnetic resonance in triplet spin labels

We have calculated solvent effects on the zero-field splitting (ZFS) constants induced by electron spin–spin coupling (SSC) in the low-lying triplet states of azaaromatic molecules in solutions using multiconfiguration self-consistent-field wave functions and the polarizable continuum model. The second-order spin–orbit coupling (SOC) contribution to the splitting of the ^3* states is found to be almost negligible, and the calculations therefore provide a good estimate of the ZFS parameters and their solvent dependence based only on the electron spin–spin coupling expectation values. The correlation between the shift in the ZFS and the phosphorescence frequency that has been observed in optically detected magnetic resonance experiments in low-temperature glasses is supported by our direct SSC calculations without taking SOC into account. This makes it possible to distinguish between the two theories that earlier were proposed to explain the inhomogeneous broadening of triplet state spectra, and discard the one that is exclusively based on the SOC-induced mixing of the singlet and triplet states.Contribution to the Jacopo Tomasi Honorary IssueAcknowledgments. This work was supported (B. M.) by the Swedish Royal Academy of Science (KVA). This work was also supported by the Norwegian Research Council through a grant of computer time from the Program for Supercomputing. We are grateful to B. Schimmelpfenning for his valuable assistance in the computations.     

Dynamic Nuclear Polarization in Suspensions Consisting of Xylene Isomers and Asphaltene Extracted from MC‐800 Liquid Asphalt

Overhauser effect type dynamic nuclear polarization experiments were performed to study suspensions of asphaltene in the xylene isomers (o‐, m‐, p‐) at a low magnetic field of 1.44 mT and three different temperatures (15, 25, and 35°C). The asphaltene was extracted from MC‐800 liquid asphalt. Intermolecular spin‐spin interactions occur between nuclear spins of hydrogen in the solvent medium and the free electron spins in the asphaltene micelles. The electron paramagnetic resonance spectrum of the asphaltene was obtained and the saturation experiments were applied to the samples prepared in vacuum. For all media, the dipole‐dipole interaction is predominant due to the negative signal enhancements. In all temperatures, the ultimate enhancement is the smallest for the p‐xylene solvent medium which has the lowest electrical dipole moment. The normalized low frequency relaxation components were calculated for 25°C, and the behavior of the nuclear‐electron coupling parameter according to this component is in agreement with the other works in the literature.     

稳定氮氧自由基TMPO和TMPRO的合成与应用

本文评述了近年来4-氧-2,2,6,6-四甲基哌啶-1-氧自由基(TMPO)和2,2,5,5-四甲基吡咯啉-1-氧自由基(TMPRO)及其衍生物在合成和应用方面的进展,着重讨论了这些氮氧自由基的合成方法和作为自旋标记试剂的应用。     

Spin coating process of sol-gel silicate films deposition: Effect of spin speed and processing temperature

The effect of two factors having the most important influence on spin coating process of sol-gel films: the spin speed and the temperature (of the substrate and the applied solution) during film deposition is discussed. It is shown, that film thickness and thickness uniformity are determined by centrifugal driving force dynamics, viscous polymer rheology, solvent evaporation dynamics, and film porous microstructure.