有机活性中间体氮宾的研究概况

有机活性中间体氮宾的研究概况王乃兴，李纪生，吉改姣（中国科学院化学研究所北京１０００８０）氮宾是一个具有共价氮原子的不带电的活性中间体，氮原子的价电子层中含有６个电子，为一缺电子物种。氮宾可以用通式Ｒ－Ｎ：表示，式中的Ｒ代表烷基、芳基、酰基、磺酰基，...     

双卡宾、双氮宾体系基态自旋的从头算研究

采用量子化学从头算UHF方法, 对平面型双卡宾及双氮宾体系的基态自旋情况进行研究。结合前面的分析结果, 进一步探讨了多自由基体系基态自旋的耦合规律, 为有机磁性体的分子设计提供了可靠的理论依据。     

配合物[Hpip] [(salen)FeⅢ(OX)]的晶体结构和异三核配合物的合成与磁性

合成了含有草酸根(OX)桥基的铁(Ⅲ)的配合物配体[Hpip] [(salen)Fe^Ⅲ(OX)](pip=哌啶;salen=N,N'-二水杨醛缩乙二胺),并解析了其晶体结构.利用这一含有草酸根桥基的配合物配体组装了3个新的异三核配合物[(salen)Fe^Ⅲ(μ-OX)]₂[M^Ⅱ(H₂O)₂]·nH₂O[M^Ⅱ=Cu^Ⅱ(1), Ni^Ⅱ(2),Fe^Ⅱ(3)],并进行了结构表征,变温磁化率(4.2~300 K)测定结果均未表现出非正规自旋态的类铁磁行为.通过计箅和分析,讨论了满足"非正规自旋态"的充分和必要条件>     

磁性分子自旋态检测与调控的STM研究

单分子自旋态检测与可逆调控是目前物理、化学及信息技术等领域的研究热点．本文综述了扫描隧道显微镜在该领域的研究进展,着重论述了酞菁类磁性分子在金属单晶表面或绝缘层薄膜上磁性的检测;自旋交叉配合物分子自旋双稳态的检测与可逆调控;单分子磁体的表面制备及输运性质的检测．     

分子磁性材料及其研究进展(续)

4自旋交叉自旋交叉现象(spin crossover,SCO)或自旋转变(spin transition,ST)也是分子双稳态现象中引人瞩目的一个研究领域[80-82]。它是指某些具有dn(n=4～7)电子组态的第一过渡金属离子配合物,在特定外界条件下(如温度、压力、光、强磁场等)发生的低自旋态(low spin,LS)和高自旋态(high spin,HS)之间相互转变的现象。SCO在1931年由Cambi首次发现[83],1970年以后得到深入研究;但直到1980年     

二维磁性纳米材料的可控合成及磁性调控

自旋电子学的研究重点在于同时利用电子的电荷和自旋两个自由度对信息进行处理和存储,其具有运行速度快、存储密度高和能耗低等优势。毫无疑问,发展二维磁性纳米材料的可控合成方法及磁性调控策略,对于新型自旋电子学器件的构筑具有重要的科学意义和应用价值。然而,目前得到的二维磁性纳米材料的种类十分有限,而且合成方法及磁性调控手段相对单一,极大地限制了该领域的发展。本文首先根据磁性的来源,对二维磁性纳米材料进行了分类,介绍了诱导产生的磁性和具有本征磁性的二维纳米材料,然后详细地归纳了二维磁性纳米材料常见的合成方法,如机械剥离法、电化学剥离法、化学气相沉积法以及液相合成方法等。此外,着重总结了二维材料磁性的主要调控手段,最后展望了该领域遇到的瓶颈、未来的研究重点及应用前景。     

分子磁性的量子化学研究进展

本文概述了研究分子磁性的量子化学方法和研究进展。首先介绍分子磁性研究中的量子化学原理和所使用计算方法,总结了有代表性的自由基、自由基-金属配合物、桥联多核过渡金属配合物等分子磁性的研究情况,并对今后研究分子磁性的量子化学方法作了展望。     

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.     

设计高自旋基态体系的一种新方法—具有非正规自旋态结构的三核配合物

设计具有高自旋基态分子是最终获得常温分子性铁磁体的关键一步。本文介绍一种获得高自旋基态分子的巧妙策略，即反铁磁偶合方法。     

磁性氧化铁纳米颗粒——通向肿瘤磁共振分子影像的重要基石

本文根据近年来国内外发表的相关研究成果,总结了磁性氧化铁纳米晶体制备方面的研究进展,并以磁性氧化铁纳米颗粒在肿瘤磁共振分子影像领域中的应用为背景,阐述了肿瘤分子影像领域的未来发展趋势.     

邻、间、对-二甲氧基亚甲基苯及衍生物双自由基体系的自旋耦 合规律

采用量子化学abinitio法对具有甲氧基的碳、氧双自由基邻、间、对二甲氧基亚甲基苯及衍生物体系基态自旋耦合规律进行研究,得到非平面共轭体系中自由基之间磁性耦合的拓朴规则:共轭体系中,两个自由基之间以偶数个碳原子耦合,则有效交换积分J~i~j<0,体系具有低自旋基态;两个自由基之间以奇数个碳原子耦合,则J~i~j>0,体系具有高自旋基态。自由基性质对自旋耦合的影响较大,正离子自由基间磁性耦合能力较强,这些结论为有机磁性材料的分子设计与实验合成提供了理论依据。     

The Design of Novel High Spin Molecules with Two-atoms Spin Centers

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A Rule to Design High Spin Molecules with Hetero spin Centers

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Origin of Ferromagnetism and Magnetic Anisotropy in a Family of Copper(II) Triangles

Previously reported ferromagnetic triangles (NnBu₄)₂[Cu₃(μ₃-Cl)₂(μ-4-NO₂-pz)₃Cl₃] ( 1 ), (PPN)₂[Cu₃(μ₃-Cl)₂(μ-pz)₃Cl₃] ( 2 ), (bmim)₂[Cu₃(μ₃-Cl)₂(μ-pz)₃Cl₃] ( 3 ) and newly reported (PPh₄)₂[Cu₃(μ₃-Cl)₂(μ-4-Ph-pz)₃Cl₃] ( 4 ) were studied by magnetic susceptometry, electron paramagnetic resonance (EPR) spectroscopy and ab initio calculations to assess the origins of their ferromagnetism and of the magnetic anisotropy of their ground S=3/2 state (PPN⁺=bis(triphenylphosphine)iminium, bmim⁺=1-butyl-3-methylbenzimidazolium, pz⁻=pyrazolate). Ab initio studies revealed the d character of the magnetic orbitals of the compressed trigonal bipyramidal copper(II) ions. Ferromagnetic interactions were attributed to weak orbital overlap via the pyrazolate bridges. From the wavefunctions expansions, the ratios of the magnetic couplings were determined, which were indeterminate by magnetic susceptometry. Single-crystal EPR studies of 1 were carried out to extend the spin Hamiltonian with terms which induce zero-field splitting (zfs), namely dipolar interactions, anisotropic exchange and Dzyaloshinskii–Moriya interactions (DMI). The data were treated through both a giant-spin model and through a multispin exchange-coupled model. The latter indicated that ≈62 % of the zfs is due to anisotropic and ≈38 % due to dipolar interactions. The powder EPR data of all complexes were fitted to a simplified form of the multispin model and the anisotropic and dipolar contributions to the ground state zfs were estimated.     

多核配合物高自旋基态分子的设计--一个理论和实践的总结

多核配合物高自旋基态分子的设计和合成是分子磁学的一项重要研究内容.作者结合本课题组的工作,总结了合成高自旋基态分子的几种重要模型,包括磁轨道正交、自旋极化、非正规自旋态及自旋失措模型.简要介绍了它们的基本原理和应用这些模型取得成功的一些实例,为分子磁工程的实现提供了一些可行的策略和方法.     

Magnetic Properties of Phenoxy－Bridged Binuclear Iron－Thiolato Complexes and Structure of （Et_4N）_2［Fe_2（o－OC_6H_4S）_2（o－OC_6H_4SH）_2］

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Radical-Enhanced Intersystem Crossing in Perylene-Oxoverdazyl Radical Dyads

Attaching stable radicals to organic chromophores is an effective method to enhance the intersystem crossing (ISC) of the chromophores. Herein we prepared perylene-oxoverdazyl dyads either by directly connecting the two units or using an intervening phenyl spacer. We investigated the effect of the radical on the photophysical properties of perylene and observed strong fluorescence quenching due to radical enhanced ISC (REISC). Compared with a previously reported perylene-fused nitroxide radical compound (triplet lifetime, τ_T=0.1 μs), these new adducts show a longer-lived triplet excited state (τ_T=9.5 μs). Based on the singlet oxygen quantum yield (Φ_Δ=7 %) and study of the triplet state, we propose that the radical enhanced internal conversion also plays a role in the relaxation of the excited state. Femtosecond fluorescence up-conversion indicates a fast decay of the excited state (<1.0 ps), suggesting a strong spin-spin exchange interaction between the two units. Femtosecond transient absorption (fs-TA) spectra confirmed direct triplet state population (within 0.5 ps). Interestingly, by fs-TA spectra, we observed the interconversion of the two states (D₁↔Q₁) at ∼80 ps time scale. Time-resolved electron paramagnetic resonance (TREPR) spectral study confirmed the formation of the quartet sate. We observed triplet and quartet states simultaneously with weights of 0.7 and 0.3, respectively. This is attributed to two different conformations of the molecule at excited state. DFT computations showed that the interaction between the radical and the chromophore is ferromagnetic (J>0, 0.05∼0.10 eV).     

The heisenberg exchange integral in a non-orthogonal basis for antiferromagnetic and ferromagnetic systems

The Dirac-Van Vleck-Serber permutation degeneracy method is used to demonstrate that the Heisenberg spin exchange Hamiltonian, –2J ₁₂s₁·s₂, is a good approximate Hamiltonian for the theoretical interpretation of antiferromagnetic and ferromagnetic systems. The approach does not neglect double or higher-order permutations and covers the general case of a singleN-electron configuration as well as that of configuration interaction. An analogy between antiferromagnetic and hydrogen-molecule-like systems is established, and a formula for the estimation of the Heisenberg exchange integral is derived.     

Seeking Hidden Magnetic Phenomena by Theoretical Means in a Thiooxoverdazyl Adduct

The oxidation of 1,5‐dimethyl‐3‐(2′‐pyridyl)‐6‐thiooxotetrazane (SvdH₃py) by benzoquinone leads to a 1:1 adduct of 1,5‐dimethyl‐3‐(2′‐pyridyl)‐6‐thiooxoverdazyl radical (Svdpy) with hydroquinone (hq). The single‐crystal X‐ray diffraction of this adduct at room temperature (RT) shows that the radicals exhibit a slight curvature that leads to the formation of alternating head‐to‐tail (antiparallel) stacked 1D chains. Moreover, temperature‐dependent X‐ray measurements at 100, 200, and 303 K reveal that the lateral slippages between the radicals of the stacks |δ₁| and |δ₂| vary from 0.64 to 0.78 Å and 0.54 to 0.40 Å between 100 and 303 K. Despite the alternation of the inter‐radical distances and lateral slippages, the magnetic susceptibility data can be fitted with excellent agreement using a regular one‐dimensional antiferromagnetic chain model with J=?5.9 cm^?1. Wavefunction‐based calculations indicate an alternation of the magnetic interaction parameters correlated with the structural analysis at RT. Moreover, they demonstrate that the thermal slippage of the radicals induces a switching of the physical behavior, since the exchange interaction changes from antiferromagnetic (?0.9 cm^?1) at 100 K to ferromagnetic (1.4 cm^?1) at 303 K. The theoretical approach thus reveals a much richer magnetic behavior than the analysis of the magnetic susceptibility data and ultimately questions the relevance of a spin‐coupled picture based on temperature‐independent parameters.     

低压离子色谱法测定土壤中速效钾

通常对土壤中速效钾的测定方法所用仪器昂贵。而低压离子色谱分析仪结构简单,操作简便,速度快,灵敏度高,价格低[1]。本文通过试验,确立了低压离子色谱法测定土壤速效钾的最佳条件,对实际样品的测定结果与推荐值呈显著相关性。1　实验部分土壤经风干、研磨,过100目土壤筛,测定其水份系数[2],贮存于密闭玻璃瓶内备用。准确称取2 0000g土样于50ml烧杯内,加20ml提取剂(0 05mol/LHCl+0 0125mol/LH2SO4),摇匀,25℃提取25分钟,离心分离。连接色谱仪、记录仪、蠕动泵(图1)。自制2J 3低压离子色谱仪,量程10×10μs,蠕动泵流速10刻度,记录仪量…