The role of the π-bonding network for trigonal level splittings of tris-bidentate Cr(acac)3 and Cr(ox) 3 3−

The varying -bonding contributions in the title compounds caused by the different electronic and molecular structure of the chelate rings are used for explaining the large band splittings in the absorption spectra by trigonal symmetry. It is shown that usual ligand field theory and the angular overlap model are not able to account for the trigonal level splitting of Cr(acac)₃ for which the coordination sphere of oxygen atoms is nearly octahedrally arranged. The experimental finding can, however, be rationalized by an extended angular overlap model which considers the phase coupling of -orbitals in the ligands leading to non-additive contributions to the metal-ligand bond energy.On leave of absence from the Bulgarian Academy of Sciences, Sofia, Bulgaria     

Isomerization ofn-hexane overplatinum loaded zeolites

The effect of the calcination temperature of bifunctional Pt/zeolites on the isomerization ofn-hexane has been investigated. The catalyst calcined at 350°C showed the highest metal dispersity and the best activity. The higher selectivity of dimethylbutanes over Pt/H- than over Pt/H-MOR might be attributed to the combined effect of acidity, channel structure and pore size of zeolites.     

Sr3YCo4-xMgxO10.5+δ(0≤x≤0.04)多晶的制备和热电输运性质研究

采用固相反应法制备Sr3YCo4-xMgxO10.5+δ(0≤x≤0.04)系列多晶,研究了Mg掺杂对体系结构、电输运和热电性质的影响.结果表明系列多晶为四方晶系,由于掺入的Mg2+(0.066 nm)部分替代了Co3+/4+(0.053 nm/0.061 nm),使晶格膨胀;多晶热电势在340~830 K随温度升高而下降,且Mg掺杂对热电势影响不大,表明Mg掺杂对体系载流子浓度影响不大;多晶电阻率在100~300 K随温度升高而降低,且随着掺杂量增加电阻率降低,结合扫描电镜观察到多晶的气孔数目减少、晶粒连接紧密和热电势的结果认为Mg掺杂对体系电输运性质的影响机制主要是使气孔、晶界散射作用减弱、载流子迁移率变大,而Mg掺杂对载流子浓度的影响是次要的.     

室温铁磁性Sr3YCo4O10.5+δ多晶有序化的烧结工艺及电磁性能

采用固相反应法制备了不同烧结温度(950～1180℃)、烧结时间、烧结次数共7种工艺的Sr3 YCo4 O10.5+δ多晶块材,通过热分析、XRD、SEM确定了有序化相变和最佳烧结工艺(1180℃/24 h+1180℃/24 h),并研究了多晶的电磁性能.结果表明,964℃完全晶化的四方相Sr3 YCo4 O10.5在...     

Crystal and molecular structure of the inclusion compound between 1,1′-binaphthyl-2,2′-dicarboxylic acid and acetylacetone (1∶1)

The lattice type crystalline inclusion compound of 1,1-binaphthyl-2,2-dicarboxylic acid (BNDA) with acetylacetone (AcAc) 11 has been investigated by single crystal X-ray diffraction. AcAc is present as the enolic tautomer, stabilized by a notably short intramolecular hydrogen bond. This H-bond closes a six-membered ring with delocalization of the system of conjugated double bonds. In the crystal the AcAc molecules are incorporated into channels, delimited by bulky binaphyl moieties, in a hydrogen-bonded framework of BNDA, and they do not show any disorder. The strictly stoichiometric host:guest ratio seems to be enforced by packing forces only.     

Synthesis and Reactions of 1-(3-Chloropropyl)-6,7-dimethoxy-3-methylbenzo[c]pyrylium Perchlorate

Acid-catalyzed acylation of 3,4-dimethoxyphenylacetone with -chlorobutyryl chloride gave 1-(3-chloropropyl)-6,7-dimethoxy-3-methylbenzo[c]pyrylium perchlorate. Recyclization of the product with nitrogen nucleophiles (ammonia, primary amines, hydrazine derivatives, hydroxylamine) led through the corresponding isoquinolinium salts to benzo[f]indolizinium, pyridazino[2,1-b]isoquinolinium, and 1,2-oxazino[2,1-b]isoquinolinium salts.     

The management of high seas fisheries

The intergovernmental United Nations Conference on Highly Migratory and Straddling Stocks, initiated in 1993 and finished in 1995, addressed the conservation and management of fishery resources located both within the coastal state 200 mile Exclusive Economic Zone (EEZ) and the adjacent high seas. These types of marine resources continue to be a source for international conflicts and debates. The original United Nations Law of the Sea of 1982 failed to address transboundary fisheries in a proper way. In particular, the agreement did not recognize the emergence of the complicated straddling stock issue. In the new United Nations Law of the Sea agreement of 1995, a consensus was reached that the management of the straddling and highly migratory fish stocks should be carried out through regional fisheries management organizations. We present a review of the straddling stock issues in the international agreement emerging from the negotiations within the United Nations. The review is contrasted with and clarified by game theoretic analyses. We also discuss one international fishery exemplifying the case, the Norwegian springspawning herring. The main conclusion is that the local problems, faced during the stage of setting up regional fisheries organizations for the management of straddling and highly migratory fish stocks, are expected to be much more complicated and difficult to solve as compared to the cases of shared fish stocks. In the current paper, we present two reasons for this increased complexity. The first is the larger number of players as compared to the case of shared fish stocks and the second is the possibility of new members entering the regional fisheries organizations.     

室温铁磁Sr3YCo4O10.5+δ多晶的制备及其性能研究

采用传统简便的固相烧结法制备了四方相的室温铁磁Sr3YCo4O10.5+δ多晶.热分析、X射线衍射和扫描电镜结果表明Sr3 YCo4 O10.5+δ多晶最终烧结温度应在963℃以上,较佳的烧结温度为1180℃.Sr3YCo4O10.5+δ多晶在80～300K为半导体电输运行为,较佳烧结温度多晶的室温电阻率～78.8 mΩ·cm;多晶热电势在317～1018 K随温度增加而减小,317 K时为70.74 μV/K.磁化强度-温度曲线、磁滞回线结果表明,多晶在受外加磁场、温度及晶体场的影响下,内部Co3+自旋态及磁畴壁、磁矩方向发生改变,导致多晶磁化强度变化及多晶磁性的改变.外磁场(0.1 T)下的ZFC曲线在320 K出现磁化强度最大为0.46 emu/g的Hopkinson峰,居里温度(Tc) =323 K,而FC曲线在奈尔温度(TN)=264 K时磁化强度达到最大为1.1 emu/g,TC=320 K.ZFC、FC方式下多晶均表现为室温铁磁性.