Reactivity of the 1,2-Diphenytethyl Radical in a Solvent Cage

The 1,2-diphcnylethyl radical and derivatives were generated from photolysis of tran-f-stilbene and its derivatives 1–13 with secondary amines as quenchers. The 1,2-diphenylelhyl radicals that escaped from the solvent cage were trapped by 2-methyl-2-nitrosopropane (MNP) and were detected by the HPLCEPR method. The yield of the spin adduct is greater for tertiary amines. The smaller yields of the spin adduct formed from secondary amines are ascribed to greater reactivities of the 1,2-diphenylethyl and dialkylamino radicals within the solvent cage.     

Electronic structure of the enolate anion of chlorophyll b

The enolate anion of chlorophyll b (Chl b) has been synthesized under deoxygenated conditions and its electronic structure characterized for the first time by ¹H NMR and electronic absorption spectroscopy. The formation of the enolate anion caused a marked perturbation to the 18 π-electron [18]diazaannulene aromatic pathway of Chl b. This perturbation appeared as noticeable upfield shifts, exceeding 1 ppm, for the meso-CH protons of the Chl b enolate anion. Nevertheless, the enolate anion remained diatropic, maintaining aromaticity in its delocalized macrocycle.     

Multifunctionality in spin crossover materials

One of the most important trends in the spin crossover (SCO) field is focused on the synthesis of new molecule-based functional materials in which the SCO properties may be combined with other physical or chemical properties in a synergic fashion. The current stage of investigations regarding interplay and synergic effects between SCO, magnetic coupling, liquid crystalline properties, host-guest interactions, non-linear optical properties, electrical conductivity, and ligand isomerization is highlighted and discussed.     

The spherical limit forn-vector correlations

We investigate then limit of then-vector model single-spin and pairspin correlation functions. In this limit we show that the correlation functions become those of the corresponding spherical model.     

Synthesis, crystal structure and magnetic property of a new 1D molecular material [1-(4′-chlorobenzyl)-4-aminopyridinium](+) bis(maleonitriledithiolato)nickel(-)

A new ion-pair complex, [1-(4′-chlorobenzyl)-4-aminopyridinium](+)bis(maleonitrile-dithiolato)nickel(−),[ClbzPyNH₂][Ni(mnt)₂] (1), has been prepared and characterized. X-ray single crystal structure conforms that the Ni(mnt)₂⁻ anions and [ClbzPyNH₂]⁺ cations of 1 form completely segregated uniform stacking columns with the Ni?Ni distance 3.944 Å in the Ni(mnt)₂⁻ stacking column. The temperature dependence of the magnetic susceptibility reveals that 1 undergoes a magnetic transition, and exhibits ferromagnetic interaction in the high-temperature phase and spin gap system in the low-temperature phase.     

EPR spin probe and spin label studies of some low molecular and polymer micelles

The rotational mobility of spin probes of different shape and size in low molecular and polymer micelles has been studied. Several probes having nitroxide fragment localized either in the vicinity of micelle interface or in the hydrocarbon core have been used. Upon increasing the number of carbon atoms in hydrocarbon chain of detergent from 7 to 13 (sodium alkyl sulfate micelles) or from 12 to 16 (alkyltrimethylammonium bromide micelles) the rotational mobility of spin probes is decreased by the factor 1.5–2.0. The spin probe rotational mobility in polymer micelles (the complexes of alkyltrimethylammonium bromides and polymethacrylic or polyacrylic acids) is less than mobility in free micelles of the same surfactants. The study of EPR-spectra of spin labeled polymethacrylic acid (PMA) indicated that formation of water soluble complexes of polymer and alkyltrimethylammonium bromides in alkaline solutions (pH 9) does not affect the polymer segmental mobility. On the other hand, the polymer complexes formation in slightly acidic water solution (pH 6) breaks down the compact PMA conformation, thus increasing the polymer segmental mobility. Possible structures of polymer micelles are discussed.     

内含式化合物X@B12P12的结构与稳定性研究

采用B3LYP/6-31G*方法，对内含式化合物X@B₁₂P₁₂(X=Li^0/+、Na^0/+、K^0/+、Be^0/2+、Mg^0/2+、Ca^0/2+、H和He)的不同对称性构型进行了计算，讨论其最稳定构型的几何参数、布居分析、偶极矩、电离势、包含能、振动频率、能隙和自旋密度． 发现在X@B₁₂P₁₂化合物中，客体X=Li、Na^0/+、K^0/+、Mg^0/2+、Ca^0/2+和He处在偏离笼的中心0.006 nm的半径内． Be²⁺沿着C₃轴偏离中心点0.279 nm． 在Be@B₁₂P₁₂和H@B₁₂P₁₂的基态结构中，Be和H与笼上的B原子成键． 除Li@B₁₂P₁₂、 Be²⁺@B₁₂P₁₂和He@ B₁₂P₁₂外， 其余结构为C_s对称稳定构型．     

EPR studies on H-abstraction from methylbenzenes by “magic blue” reagent

After mixing a methylbenzene 4 with “magic blue” solution in F113 (CClF₂CCl₂F) containing bis{perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide 2 and perfluoro-1-nitroso-1-[1-(2-fluorosulfonyl)ethoxy]ethane 3 at room temperature, benzylic H-atom of 4 could be selectively abstracted by 2, and benzyl radical 5 thus generated was immediately trapped by 3. Based on hyper-fine splitting constants (hfsc), the structure of the spin adducts perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl benzyl nitroxides 6 derived from seven methylbenzenes have been identified. The mechanism of the H-abstraction/spin trapping process is also discussed.     

The Role of Binary and Many-centre Molecular Interactions in Spin Crossover in the Solid State. Part II. Non-ideality Parameters Defined via Binary Molecular Potentials

Summary. Parameters of the formalism [1–6] describing spin crossover in the solid state have been defined via molecular potentials in model systems of neutral and ionic complexes. In the first instance Lennard-Jones and electric dipole–dipole potentials have been used whereas in ionic systems Lennard-Jones and electric point-charge potentials have been used. Electric dipole–dipole interaction of neutral complexes brings about a positive excess energy controlled by the difference of electric dipole moments of HS and LS molecules. Differences of the order of Δμ = 1–2 D cause an abrupt spin crossover in systems with T_1/2 = 100–150 K. Magnetic coupling contributes both to the excess energy and excess entropy, however the overall effect is equivalent to a modest positive excess energy. Ionic systems in the absence of specific interactions are characterised by very small excess energies corresponding to practically linear van’t Hoff plots. Detectable positive and negative excess energies in these systems may arise from interactions of ligands belonging to neighbouring complexes. The HOMO–LUMO overlap in HS–LS pairs can bring about a nontrivial variation of the shape of transition curves. Examples of regression analysis of experimental transition curves in terms of molecular potentials are given.