在两个稳定基之间对全有机二元合金进行磁调
Gonca Seber1, Rafael S Freitas, Joel T Mague
1Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, USA.
Journal of the American Chemical Society
|February 11, 2012
概括
化和非化二氧化的固体溶液形成具有可调节磁性特性的合金. 这些材料表现出由联链驱动的准一维铁磁行为.
科学领域:
- 材料科学 材料科学 材料科学
- 固态化学 固态化学
- 磁力学 磁力学 是一种
背景情况:
- 2-(4,5,6,7-tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (F4BImNN) 和2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (BImNN) 的混合物是固体形式的溶液.
- 这些固体溶液表现出不同的结晶相 (正方形和单形),取决于组成 (x).
研究的目的:
- 研究F4BImNN和BImNN的二元固体溶液的结构和磁性特性.
- 了解组成,晶体结构和磁性行为之间的关系.
主要方法:
- 二元固体溶液 (F4BImNN) 的合成和结晶 (F4BImNN) 的合成和结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4BImNN) 的结晶 (F4-X)).
- 用X射线结晶学来确定单元细胞结构.
- 从0.4K到300K的磁性敏感度测量.
主要成果:
- 固体溶液在广泛的组成范围内形成,表现为正方形 (x < 0.8) 和单晶 (x ≥ 0.9) 晶体结构.
- 一维 (1D) 的结链主导着分子间的包装,导致准-1D铁磁交换 (J/k = 12-22 K).
- 抗铁磁排序发生在低温 (0.4-1.2 K) 时,因为链间交换较弱,比链内交换弱33-150倍.
结论:
- 在正弦波样本中的磁性排序温度随着BImNN含量增加而线性增加,与链间距离和交换相互作用的减少相关.
- 单临床阶段表现出不同的链间排列,偏离了在形阶段观察到的趋势.
- 组合控制允许调整这些准1D磁性材料中的磁性特性.
相关概念视频
Radical Reactivity: Overview
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three...
Radical Formation: Addition
Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...
Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals
Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
Radical Reactivity: Nucleophilic Radicals
Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For instance, consider...
π Molecular Orbitals of the Allyl Radical
Allyl radicals are three-carbon conjugated systems. They are readily formed as intermediates in halogenation reactions of alkenes involving the addition of halogen to the allylic carbon instead of the double bond. As seen in allyl cations and anions, each of the three sp2-hybridized carbon atoms in allyl radicals has an unhybridized p orbital. These orbitals combine to give three π molecular orbitals.
The allyl systems have identical molecular orbitals but differ in the number of π electrons.
The allyl systems have identical molecular orbitals but differ in the number of π electrons.
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...


