About the calculation of exchange coupling constants in polynuclear transition metal complexes

The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H. He and CH(2). He units to compare with Hartree-Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data.     

Polyarylate–polystyrene block copolymer from macro-azoinitiator: Synthesis and its thermal properties

A macro-azoinitiator containing polyarylate segment and azo group was prepared by the solution polycondensation of azobiscyanopentanoyl chloride and hydroxy-terminated polyarylates having viscosity-average molecular weights of 6200, 8100, and 12 400. These macro-azoinitiators were used in the radical polymerization of styrene to synthesize polyarylate-polystyrene block copolymers. Thermal properties measured by the differential scanning calorimetry indicated the phase separated morphology of the block copolymers except at low molecular weight of the block constituents. © 1993 John Wiley & Sons, Inc.     

聚苯基单醚喹噁啉薄膜的性能与物理老化

研究了物理老化对聚苯基单醚喹啉薄膜的结构与力学性能的影响 .用差示扫描量热计 (DSC)及正电子湮没寿命谱 (PALS)方法表征了两种不同物理老化条件试样的凝聚结构以及自由体积的差别 .结果表明 ,物理老化使聚苯基单醚喹啉薄膜玻璃化转变温度移向高温 ,在其末端出现热焓吸收峰 ,分子链堆砌紧密使自由体积减小 ,分子可动性降低 .用动态力学分析 (DMTA)以及静态拉伸性能测试等方法研究了两类试样的力学性能 ,结果表明 ,物理老化后 ,试样的动态储能模量稍有增加 ,力学损耗降低 .而静态拉伸实验的断裂应变降低 ,屈服应力增加 ,断裂能降低 ,试样在宏观上由韧性断裂变为明显的脆性断裂 .     

(NiV13O38)7-的电子结构和催化性质的探讨

使用SCC－DV－Xα方法研究了高钒杂多化合物（NiV13O38）7-的电子结构，并探讨了它的催化性质·结果表明，（NiV13O38）7-是一种比Keggin结构更强的催化剂。分析了该阴离子中的键的强弱关系，认为配位数越少的氧与V形成的键越强．并分析了前线轨道HOMO，LUMO的组成，从而得出它的催化活性中心是Ni，V、一配位端氧，二、三配位桥氧，五配位中心氧的结论。     

新型氮杂2-β萘基苯并噁唑分子设计与光物理性质的研究

为了寻找新的有效光敏材料，设计了一系列新型氮杂2-β萘基苯并恶唑分子，用改进的PPP-SCF-CI方法，对设计分子的第一激发单线态，三线态，振子强度和跃迁矩等光物理性质进行了较为详细的研究，筛选出了一些新型的具有特殊光物理特性的分子，并预测了有可能产生新型氮杂2-β萘基苯并恶唑分子类光敏感功能材料的取代基部位。     

电视用液晶材料的研究进展

液晶电视由于其优异的显示性能将会越来越受到青睐。本文简要综述了近年来电视用液晶材料的研究进展,归纳总结了这些液晶材料的合成方法及其热性能、介电各向异性、双折射率、粘度等特性。     

Syntheses, structures and third-order non-linear optical properties of homometal clusters containing molybdenum

Both the homometal cluster [P(ph₄)]₂[Mo₂O₂(μ-S)₂(S₂)₂] (1) and [Mo₂O₂(μ-S)₂(Et₂dtc)₂] (2) (Et₂dtc=diethyl-dithiocarbamate) were successfully synthesized by low-temperature solid-state reactions. X-ray single-crystal diffraction studies suggest that compound (1) is a dinuclear anion cluster, and compound (2) is a dinuclear neutral cluster. The two compounds were characterized by elemental analyses, IR spectra and UV-Vis spectra. The third-order non-linear optical (NLO) properties of the clusters were also investigated and all exhibited nice non-linear absorption and self-defocusing performance with moduli of the hyperpolarizabilities 5.145×10⁻³⁰ esu for (1) and 5.428×10⁻³⁰ esu for (2).     

Magnetic interactions in a series of paramagnetic Ln(III) complexes with a chelated imino nitroxide radical

The magnetic interactions in a new series of isostructural imino nitroxide radical lanthanide(III) complexes, [Ln(hfac)₃(IM2py)] (Ln = Gd–Yb: IM2py = 2-(2′-pyridyl)-4,5-dihydro-4,4,5,5-tetramethyl-1H-imidazoline-1-oxy; hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione), are examined by considering the intrinsic paramagnetic contribution of the Ln(III) ion from the corresponding [Ln(hfac)₃(pybzim)] with a diamagnetic pybzim(2-(2-pyridyl)benzimidazole) ligand; the Ln(III)–IM2py interaction being antiferromagnetic for the 4f⁷ to 4f¹³ Ln(III) complexes and negligibly small for the other complexes. This series is the first example reverse to the previous cases for the series of Ln–Cu or Ln–aminoxyl(NIT) radical (4,5-dihydro-4,4,5,5-tetramethyl-1H-imidazoline-3-oxide-1-oxy) complexes, other than only a few examples of semiquinone Ln complexes. This reverse nature of the magnetic interaction, as compared with the NIT complexes, validates the empirical approach by O. Kahn et al. [Inorg. Chem. 38 (1999) 3692; J. Am. Chem. Soc. 122 (2000) 3413] in the spin-coupled systems for a series of Ln(III) complexes.     

AFM of adsorbed polyelectrolytes on cellulose I surfaces spin-coated on silicon wafers

Thin layers of cellulose I nanocrystals were spin-coated onto silicon wafers to give a flat model cellulose surface. A mild heat treatment was required to stabilize the cellulose layer. Interactions of this surface with polyelectrolyte layers and multilayers were probed by atomic force microscopy in water and dilute salt solutions. Deflection–distance curves for standard silicon nitride tips were measured for silicon, cellulose-coated silicon, and for polyelectrolytes adsorbed on the cellulose surface. Transfer of polymer to the tip was checked by running deflection–distance curves against clean silicon. Deflection–distance curves were relatively insensitive to adsorbed polyelectrolyte, but salt addition caused transfer of cationic polyelectrolyte to the tip, and swelling of the polyelectrolyte multilayers.     

Potentiometric studies on the complexation of copper(II) by phenolic acids as discrete ligand models of humic substances

Studies on the complexation of copper(II) by phenolic acids, as ligand models of humic substances were done by potentiometry. The acids under study were: 3,4-dihydroxyhydrocinnamic acid or hydrocaffeic acid (1), 3,4-dihydroxyphenylacetic acid (2) and 3,4-dihydroxybenzoic acid or protocatechuic acid (3). Acidity constants of the ligands and the formation constants of metal-ligand complexes were evaluated by computer programs. The carboxylic group of the phenolic acids has different pK_a1 values, being the dissociation constants intrinsically related with the distance between the function and the aromatic nucleus. The results obtained allow concluding that acidity constants of the catechol moiety of the compounds are similar with pK_a2 and pK_a3 values between 9.47-9.41 and 11.55-11.70. The complexation properties of the three ligands towards copper(II) ion are quite similar, being the species found not different either in nature or stability. Although the model ligands have some structural differences no significant differences were found in their complexation properties towards copper(II). So, it can be postulated that complexation process is intrinsically related with the presence of a catechol group.