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1.
Closo-B nH n−2(CO) 2 ( n = 5–12), isolobal analogues of closo-C 2B n−2H n, have been investigated at the B3LYP/6-311+G **density functional level of theory. The most stable isomers of closo-B nH n−2(CO) 2 are similar to those of closo-C 2B n−2H n in geometric patterns apart from closo-B 6H 4(CO) 2, and closo-B nH n−2(CO) 2 is much less strained than closo-C 2B n−2H n. Energetic analysis identifies closo-B 6H 4(CO) 2, closo-B 12H 10(CO) 2 and closo-B 10H 8(CO) 2 to be most stable, of which the latter two cages have been prepared experimentally. On the basis of the negative and rather large nucleus independent chemical shifts (NICS), closo-B nH n−2(CO) 2 are aromatic. To aid further experimental study, the CO stretching frequencies have been computed. 相似文献
4.
The structures of alkali halide clusters Na nF n, Li nF n and Na nCl n, and their metal-excess clusters Na nF n−1+, Li nF n−1+ and Na nCl n−1+ were investigated by the ab initio molecular orbital method for cluster sizes from 1 to 14. The magic numbers for the neutral clusters Na nF n, Li nF n and Na nCl n are 4, 6, and 8. The most stable structure for these cluster sizes is a perfect crystallite for Na nF n and Na nCl n, and a double ring for Li nF n. The magic numbers for the metal-excess clusters are 5 and 8, which are near ideal cuboids with (100) facets. 相似文献
6.
The syntheses of the 1,3,5-trimethyl- and tri- tert-butyl-1,3,5-triazacyclohexane-supported imido complexes [M(NR)(R′ 3tach)Cl 2] (M = Ti or Zr (NMR only); R = Bu t or 2,6-C 6H 3Pr i2; R′ = Me or Bu t) are reported, along with that of the thermally robust dibenzyl derivative [Ti(NBu t)(Me 3tach)(CH 2Ph) 2]. The tert-butylimido ligand in [Ti(NBu t)(Me 3tach)Cl 2] undergoes exchange with ArNH 2 (Ar = 4-C 6H 4Me or 2,6-C 6H 4Me or 2,6-C 6H 3Pr i2) to form the corresponding arylimides [Ti(NAr)(Me 3tach)Cl 2]. The Me 3tach ring in [Ti(NR)(Me 3tach)Cl 2] undergoes slow exchange with Bu t3tach or Me 3tacn (1,4,7-trimethyl-1,4,7-triazacyclononane) to give the ring-exchanged products [Ti(NR)(Bu t3tach)Cl 2] and [Ti(NR)(Me 3tacn)Cl 2], respectively. The complexes [Ti(NR)(Me 3tach)X 2] (R = Bu t or 2,6-C 6H 3Pr i2; X = Cl or CH 2Ph) exhibit room-temperature dynamic NMR behaviour via an unusual trigonal twist of the facially coordinated Me 3tach ligand, and the activation parameters for these processes have been measured and are discussed. The X-ray structures of [Ti(NR)(Bu t3tach)Cl 2] (R = Bu t or 2,6-C 6H 3Pr i2) and [Ti(NBu t)(Me 3tach)(X) 2] [X= Cl or CH 2Ph) are reported. Me 3tach and Bu t3tach = 1,3,5-trimethyl- and tri- tert-butyl-1,3,5-triazacyclohexane, respectively. 相似文献
8.
硫代嘧啶碱基是光动力疗法潜在的重要光敏剂,其最低单重激发态的光物理研究已有广泛报道。然而,其较高激发态的跃迁性质和反应动力学研究较为稀少。因此,本文采用共振拉曼光谱和密度泛函理论计算方法研究2,4-二硫代尿嘧啶的紫外光谱和几个较高单重激发态的短时结构动力学。首先,基于共振拉曼光谱强度与电子吸收带振子强度f的关系,将紫外光谱去卷积成四个吸收带,分别为358 nm(f=0.0336)中等强度吸收带(A带),338 nm(f=0.1491)、301 nm(f=0.1795)和278 nm(f=0.3532)强而宽的吸收带(B、C和D带)。这一结果既吻合密度泛函理论计算结果,又符合共振拉曼光谱强度模式对紫外光谱带的预期。据此,去卷积得到的四个吸收带被分别指认为S0→S2跃迁、S0→S6跃迁、S0→S7跃迁和S_0→S_8跃迁。同时,分别对B,C和D带共振拉曼光谱进行了详细的指认,获得了短时动力学信息。结果表明,S_8态短时动力学的显著特征是在Franck-Condon区域或附近发生了S8(ππ~*)/S(nπ~*)势能面交叉引发的、伴随超快结构扭转的非绝热过程。S7和S6态短时动力学的主要特征是反应坐标的多维性,它们分别沿C_5C_6/C_2S_8/C_4S_(10)/N_2C_3+C_4N_3H_9/N_1C_2N_3/C_2N_1C_6/C_6N_1H_7/C_5C_6H_(12)和C_5C_6/N_3C_2/C_4S_(10)/C_2S_8+C_6N_1H_7/C_5C_6H_(12)/C_5C_6N_1/C_5C_6H_(12)/C_2N_1C_6/N_1C_2N_3/C_4N_3H_9/N_1C_2N_3等内坐标演化。 相似文献
9.
Excess molar enthalpies HE and excess molar volumes VE have been measured, as a function of mole fraction x1, at 298.15 K and atmospheric pressure for the five liquid mixtures ( x11,4-C 6H 4F 2 + x2n-C lH 2l+2), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities CPE at constant pressure have been determined for the two liquid mixtures ( x1C 6F 6 + x2n-C lH 2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from HE(x1 = 0.5)/(J mol−1) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes VE are all positive and also increase with increasing l: VE(x1 = 0.5)/(cm3 mol−1) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x1C6F6 + x2n-ClH2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C6H4F2. Specifically, at 298.15 K HE(x1 = 0.5)/(J mol−1) = 1119 for (x1C6F6 + x2n-C7H16) and 1324 for (x1C6F6 + x2n-C14H30), and for the same mixtures VE(x1 = 0.5)/(cm3 mol−1) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): CPE(x1 = 0.5)/(J K−1 mol−1) = −1.18 for (x1C6F6 + x2n-C7H16), and −2.25 for (x1C6F6 + x2n-C14H30). The curve CPE vs. (x1 for x1C6F6 + x2n-C14H30) shows a sort of “hump” for x1 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures. 相似文献
13.
在流动余辉装置上, 利用N 2空心阴极放电制备活性氮, 研究了活性氮与溴代烷烃(CHBr 3、CH 2Br 2、C 2H 5Br、C 4H 9Br) 反应的化学发光.上述所有反应中, 在550~750 nm波段均观察到了较强的NBr ( b1Σ+→X3Σ-)跃迁发射谱. 同时在活性氮与CHBr3和CH2Br2的反应中, 在流动管下游还观察到了CN (A2π, B2π→X2Σ+)的发射谱. 验证性的实验表明, 激发态NBr (b1Σ+)是由二步过程形成: N(4S)与溴代烷烃反应生成NBr (X3Σ-), 再通过N2 (A 3Σu+)分子能量转移到激发态NBr (b1Σ+); 而激发态的CN是通过N(4S) + CBr→CN(A, B) + Br过程形成的. 相似文献
14.
采用浸渍提拉法制得TiO 2,ZnO,Fe 2O 3,ZnO/TiO 2,TiO 2/ZnO,Fe 2O 3/TiO 2和TiO 2/Fe 2O 3石英玻璃基底负载膜.光催化降解亚甲基蓝实验表明,TiO 2和ZnO具有良好的光催化活性,Fe 2O 3活性较差.但形成异质结后,TiO 2和Fe 2O 3的光催化降解能力发生明显的变化.用254nm紫外光光照后,TiO 2,ZnO和Fe 2O 3等3种氧化物膜与水的接触角均有不同程度的降低,TiO 2表现出超亲水性,ZnO/TiO 2和Fe 2O 3/TiO 2膜与水的接触角小于对应的单纯ZnO和Fe 2O 3膜与水的接触角,其中Fe 2O 3/TiO 2表面出现超亲水性.瞬态光电导谱的少数载流子寿命的测定表明,异质结势垒电场能有效地增强光生电子-空穴对的分离效率.根据能带理论建立的两组异质结能带模型可合理地解释实验结果. 相似文献
15.
Two types of palladiu m(Ⅱ)-based metallacalixarenes[ML] 2+and[ML 2] 2+have been synthesized through coordination-driven self-assembly from a series of flexible pyridine-bridged diimidazole ligands[2,6-bis((1 H-imidazol-1-yl)methyl)pyridine(L 1),2,6-bis((1 H-benzo[d]imidazol-1-yl)methyl)pyridine(L 2),2,6-bis((1 H-naphtho[2,3-d]imidazol-1-yl)methyl)pyridine(L 3)],with palladium(II)-based building blocks[Pd(BF 4) 2(M 1-BF_4)and(tmeda)Pd(NO 3) 2(M 2-NO 3)(tmeda=N,N,N',N'-tetramethyl-ethylenediamine)].All complexes were characterized by NMR spectroscopy( 1H NMR and 13C NMR),mass spectrometry(CSIMS,ESI-HRMS)and elemental analysis.The single crystal X-ray diffraction analysis of[M 1L 2_2](NO 3) 2,[M 1L 3_2](NO 3) 2,[M 1L 3_2](PF_6)_2 and[M~2 L 3](NO 3) 2further confirmed the uniquely single bowl-shape and double bowl-shape structures.The anion binding properties within the metallacalixarenes as receptors were also investigated by NMR titration experiments in DMSO. 相似文献
17.
复杂水盐体系存在稳态和介稳固液相平衡以及复杂的成盐规律。为了解固液平衡状态下液相的结构特征,本文采用拉曼光谱技术并结合高斯-洛伦兹去卷积分峰拟合程序对Na +, Mg 2+//SO 42-, Cl -, H 2O四元体系及其二元和三元子体系中 ν1-SO 42-的离子缔合结构特征进行了分析。研究结果表明:SO 42-在Na 2SO 4-H 2O体系存在自由态SO 42-和SO 42-离子簇两种结构,在MgSO 4-H 2O, MgSO 4-MgCl 2-H 2O及Na +, Mg 2+//SO 42-, Cl -, H 2O等含镁体系中,还有Mg 2+-H 2O-SO 42-和Mg 2+-OSO 32-两种缔合结构。在二元和三元体系中 ν1-SO 42-的离子缔合结构以自由态SO 42-为主,随着SO 42-离子总浓度的变化,上述四种结构所占比例会发生规律性变化。Na +, Mg 2+//SO 42-, Cl -, H 2O四元体系在NaCl减少及等温蒸发过程中,自由态SO 42-结构比例逐步降低, Mg 2+和SO 42-相结合形成Mg 2+-H 2O-SO 42-或Mg 2+-OSO 32-结构的机会增多,在复盐区还会形成SO 42-离子簇结构。由此判断溶液结构的适应性变化是导致介稳现象的重要原因。进一步的相关分析表明:SO 42-的浓度和耶涅克指数 J与 ν1-SO 42-峰的峰强度和峰面积存在正相关关系, Mg 2+浓度是影响 ν1-SO 42-峰中四种缔合结构的比例发生变化的主要因素。 相似文献
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