C60Pt(BINAP)金属配合物的合成表征与光电性能研究

本文利用配体取代法合成了C60Pt(BINAP)新型富勒烯膦金属配合物,采用质谱、元素分析、紫外.可见吸收光谱、红外吸收光谱、光电子能谱等对该产物进行了表征,并测定了其在光化学电池中的光伏效应.光伏效应测试结果表明:在BQ/H2Q与I2/I3-介质溶液中镀层厚度为1～2μm时,具有较好的光电转换性能,光生电压值最高达358 mV.     

C60Pt(CO)(Pph3)配合物的合成及氧化还原性能研究

采用配体取代法,即在惰性气氛下以C60取代Pt(CO)2(Pph3)2中的CO及Pph3,合成了C60Pt(CO)(Pph3)富勒烯金属配合物,利用元素分析、红外光谱、紫外可见光谱、光电子能谱等手段对产物进行鉴定和表征,结果表明,C60以σ-π配位方式与Pt形成了稳定的η2型C60配合物.由于该分子存在超共轭作用,分子内电子流动性大,因而该配合物可能具有良好的光电转化性能及催化性能.氧化还原性能研究表明,C60在与金属有机基团Pt(CO)(Pph3)形成配合物后,其还原电位向负方向发生了移动.     

2，2′—双吡啶双氯二价铂化合物Pt（bpy）Cl2（黄色）的电子结构和电子光谱性质的从头计算研究

用从头算MP2方法,采用LANL2DZ基组,对Pt(bpy)Cl2分子进行了分子轨道计算,计算得到这种分子的HOMO和LUMO都具有反键π^*轨道的性质,给出了具有较高能量的分子轨道的顺序,并分析了各分子轨道的组成,用单激发组态相互作用（CIS）方法计算了具有“单体”晶型的Pt(bpy)Cl2的电子吸收光谱的发射光谱,结果表明：最低能吸收光谱为γ＝350．99nm,具有金属到配体的电荷迁移性质;最低能发射光谱为γ＝566．39nm,具有配体内电荷迁移的性质。     

高载量PtNi金属间化合物的氧还原电催化性能

采用改进的多元醇法制备了PtNi(原子比1∶1)质量分数为60%的高金属载量碳载PtNi合金(PtNi/C), 通过在450 ℃下退火处理获得了碳载PtNi金属间化合物氧还原电催化剂. 该催化剂对氧还原的质量比活性和面积比活性分别是商业化Pt/C(JM Pt/C)催化剂的1.66和2.3倍; 并且加速耐久性测试后PtNi金属间化合物催化剂的质量比活性仍与Pt/C的初始性能相当, 耐久性得到了大幅提升. PtNi/C金属间化合物催化剂氧还原活性和稳定性的提高归因于PtNi的有序原子排布结构及催化剂表面零价金属含量的提高.     

新型富勒烯膦金属配合物的合成

用配体取代法合成了新型富勒烯膦金属配合物——C60.双(二苯基膦)戊烷合钯[C60Pd(dpppe),1],其结构经UV-Vis,IR,XPS及元素分析表征。在1的分子结构中,C60以σ-π配位方式与Pd配位,形成新型的η2-C60双齿膦金属配合物。     

C60-多吡啶Ru(II)配合物电子光谱的密度泛函理论研究

应用密度泛函理论(DFT)方法对两种C60-多吡啶Ru(II)衍生物进行理论研究. 在TZP全电子基组优化构型基础上, 通过分析前线轨道组成, 探讨金属及配体对C60母体影响; 以LB及SAOP校正局域密度近似, 用含时密度泛函(TDDFT)方法, 考虑溶剂化效应, 计算化合物1和2的电子吸收光谱. 结果表明, 化合物1和2在气相与丙酮溶液中所对应的光谱值差异较为明显, 溶剂化效应使吸收光谱蓝移. 计算得到化合物1和2在丙酮溶液中电子光谱与实验值吻合较好, 低能跃迁多为金属参与的混合跃迁, 高能跃迁主要由C60与配体部分贡献.     

C60-多吡啶Ru(Ⅱ)配合物电子光谱的密度泛函理论研究

应用密度泛函理论(DFT)方法对两种C60-多吡啶Ru(Ⅱ)衍生物进行理论研究.在TZP全电子基组优化构型基础上,通过分析前线轨道组成,探讨金属及配体对C60母体影响;以LB及SAOP校正局域密度近似,用含时密度泛函(TDDFT)方法,考虑溶剂化效应,计算化合物1和2的电子吸收光谱.结果表明,化合物1和2在气相与丙酮溶液中所对应的光谱值差异较为明显,溶剂化效应使吸收光谱蓝移.计算得到化合物1和2在丙酮溶液中电子光谱与实验值吻合较好,低能跃迁多为金属参与的混合跃迁,高能跃迁主要由C60与配体部分贡献.     

氮混杂金属卟啉吸收光谱性质的理论研究

采用密度泛函理论在B3LYP/6-31+G(d)水平上研究了4种金属Mg, Ni, Cu, Zn配位的自由卟啉(FBP)及氮混杂卟啉(NECP)的几何结构及分子轨道能级. 采用含时密度泛函理论(TD-DFT)方法计算了金属与2种卟啉配位后在气体条件下的电子吸收光谱, 包括激发能、 吸收波长、 跃迁组成和振子强度.计算结果表明, 与金属配位的FBP(M-FBP)具有D_4h对称性, 分子轨道能级HOMO/HOMO-1和LUMO/LUMO+1因能级相近发生简并, HOMO-LUMO轨道能级差大约3.0 eV, 在Soret带出现较强吸收峰.由于C/N原子位置的改变, 非对称性结构的M-NECP前线轨道组成发生改变, 轨道能级差(HOMO-LUMO)减小至2.6 eV左右, 且能级发生分裂, Soret带出现多个电子吸收谱峰, Q带也出现吸收峰. 本文研究了水、 氯仿和苯3种不同极性溶剂对M-FBP和M-NECP的分子轨道及电子吸收光谱的影响, 结果表明, 随溶剂极性减弱金属配合物的电子吸收光谱发生红移, 并且吸收峰强度增强.     

含咔唑衍生物的聚硅氧烷发光材料的合成及其性能

设计并合成了含咔唑衍生物的聚硅氧烷发光材料。通过核磁共振、元素分析、紫外-可见吸收光谱、荧光光谱、热失重分析、循环伏安法对其结构和性能进行了表征。结果表明:该化合物具有良好的荧光性能和热稳定性,其发射波长为408 nm,分解温度在242℃,最高占据分子轨道能级和分子最低空轨道能级分别为4.70 eV和1.16 eV。     

直接甲醇燃料电池阴极Pt／C催化剂的制备与表征制备及处理方法的影响

 对比研究了用三种液相沉积还原法制备的20％Pt／C催化剂及在900℃下用H2还原处理的催化剂，并用XRD和TEM等技术表征了催化剂的粒子大小及粒径分布．结果表明，用乙二醇还原法制备的Pt／C催化剂的平均粒径最小（约2．4nm），且分布均匀．应用旋转圆盘电极（RDE ）法和直接甲醇燃料电池单池评价了Pt／C催化剂的氧还原反应（ORR）活性，探索了单池性能与催化剂粒径大小的关系．RDE测试结果表明，用甲醛还原法制备的Pt／C催化剂具有最高的ORR活性；而单池测试结果表明，用乙二醇还原法制备的Pt／C催化剂显示出最高的ORR活性和最优的单池性能．这可能是因为直接甲醇燃料电池中所需Pt／C催化剂最优粒径更小的缘故．另外，研究了Cl－对Pt／C催化剂ORR活性的影响．结果表明，少量Cl－即会显著降低Pt／C催化剂的ORR活性．     

Five-coordinate platinum(IV) complex as a precursor to a novel Pt(II) olefin hydride complex for alkane activation

The five-coordinate platinum(IV) complex (nacnac)PtMe3 (nacnac- = [{(o-iPr2C6H3)NC(CH3)}2CH]-) thermally eliminates ethane and methane to produce a novel olefin(hydrido)platinum(II) complex, where the olefin is part of the nacnac-type ligand. This Pt(II) product activates hydrocarbons, including alkanes under mild conditions, as indicated by scrambling of hydrogen and deuterium between the hydrocarbon solvent and selected positions on the ligand of the platinum complex. A mechanism in which olefin insertion into the metal hydride bond opens a site to allow hydrocarbon coordination and C-H bond oxidative addition is proposed.     

Composition,surface segregation,and electrochemical properties of binary PtM/C (M = Co,Ni, Cr) catalysts

The effect of the nature of transient metal and chemical treatment of binary cathodic PtM/C (M = Co, Ni, Cr) catalysts, which were prepared by high-temperature synthesis, on their structure, surface segregation, and characteristic properties (activity and stability) is studied. It is shown that, in the course of treatment in 0.5 M H₂SO₄ at the elevated temperature (60°C), the surface of nanoparticles becomes enriched in platinum with the formation of core-shell structures. The PtCo/C catalyst is the most efficient one. In this case, a compromise between the corrosion resistance and electrocatalytic activity is reached due to a higher, as compared with PtNi/C and PtCr/C, degree of alloy formation and enriching of surface in platinum in the course of corrosive attack. Thereby, the properties of platinum on the core surface change as a result of a pronounced ligand effect of the core. Thus, depending on the nature of transient metal, the binary cathodic PtM/C catalysts differ in their activity and stability, which depend on the degree of alloy formation and a possibility of formation of core-shell structure as a result of surface segregation in the course of synthesis and chemical treatment.     

New selectivity in peptide hydrolysis by metal complexes. Platinum(II) complexes promote cleavage of peptides next to the tryptophan residue

Tryptophan-containing N-acetylated peptides AcTrp-Gly, AcTrp-Ala, AcTrp-Val, and AcTrp-ValOMe bind to platinum(II) and undergo selective hydrolytic cleavage of the C-terminal amide bond; the N-terminal amide bond remains intact. In acetone solution, bidentate coordination of the tryptophanyl residue via the C(3) atom of indole and the amide oxygen atom produces complexes of spiro stereochemistry, which are characterized by (1)H, (13)C, and (195)Pt NMR spectroscopy, and also by UV-vis, IR, and mass spectroscopy. Upon addition of 1 molar equiv of water, these complexes undergo hydrolytic cleavage. This reaction is as much as 10(4)-10(5) times faster in the presence of platinum(II) complexes than in their absence. The hydrolysis is conveniently monitored by (1)H NMR spectroscopy. We report the kinetics and mechanism for this reaction between cis-[Pt(en)(sol)(2)](2+), in which the solvent ligand is water or acetone, and AcTrp-Ala. The platinum(II) ion as a Lewis acid activates the oxygen-bound amide group toward nucleophilic attack of solvent water. The reaction is unimolecular with respect to the metal-peptide complex. Because the tryptophanyl fragment AcTrp remains coordinated to platinum(II) after cleavage of the amide bond, the cleavage is not catalytic. Added ligand, such as DMSO and pyridine, displaces AcTrp from the platinum(II) complex and regenerates the promoter. This is the first report of cleavage of peptide bonds next to tryptophanyl residues by metal complexes and one of the very few reports of organometallic complexes involving metal ions and peptide ligands. Because these complexes form in nonaqueous solvents, a prospect for cleavage of membrane-bound and other hydrophobic proteins with new regioselectivity has emerged.     

The Ligand‐Based Quintuple Bond‐Shortening Concept and Some of Its Limitations

Herein, the ligand‐based concept of shortening quintuple bonds and some of its limitations are reported. In dichromium–diguanidinato complexes, the length of the quintuple bond can be influenced by the substituent at the central carbon atom of the used ligand. The guanidinato ligand with a 2,6‐dimethylpiperidine backbone was found to be the optimal ligand. The reduction of its chromium(II) chloride–ate complex gave a quintuply bonded bimetallic complex with a Cr? Cr distance of 1.7056 (12) Å. Its metal–metal distance, the shortest observed in any stable compound yet, is of essentially the same length as that of the longest alkane C? C bond (1.704 (4) Å). Both molecules, the alkane and the Cr complex, are of remarkable stability. Furthermore, an unsupported Cr^I dimer with an effective bond order (EBO) of 1.25 between the two metal atoms, indicated by CASSCF/CASPT2 calculations, was isolated as a by‐product. The formation of this by‐product indicates that with a certain bulk of the guanidinato ligand, other coordination isomers become relevant. Over‐reduction takes place, and a chromium–arene sandwich complex structurally related to the classic dibenzene chromium complex was observed, even when bulkier substituents are introduced at the central carbon atom of the used guanidinato ligand.     

Preparation and electronic spectra of some alkyl- and aryl(2,2′-bipyridine)platinum(II) complexes

A series of alkyl- and aryl-(2,2′-bipyridine)-platinum (II) complexes has been prepared by displacement of the diene ligand in the corresponding cyclooctadiene complexes with 2,2′-bipyridine. Dimethyl(1,10-phenanthroline)platinum(II) was prepared in an analogous way. The electronic spectra of the complexes contain metal to ligand charge transfer bands whose energy is dependent on the nature of the substituents on platinum and on the solvent. It is suggested that π-bonding is important in the phenyl—platinum bond.     

Spectrophotometric determination of platinum with o-phenylenediamine

Platinum(IV or II) reacts with o-phenylenediamine, at pH 6.5, to form light blue solutions having maximum absorption at 703 nm. The reaction, slow at room temperature, is complete in 3-4 min at temperatures near 100 degrees . Use of dimethylformamide in the solution prevents precipitation of the reaction product. The colour is stable for at least 24 hr. Effects of heating temperature and time, pH, reagent concentration, and other variables have been studied. The system conforms to Beer's law over the concentration range investigated. Optimum concentration range for measurement in 10-mm cells is 0.4-1.4 ppm of platinum; the molar absorptivity is 9.83 x 10(3) l. mole(-1). mm(-1). Interference from foreign ions has been evaluated, and methods for removal or masking of interferences have been tested. In the colour-forming reaction, platinum(IV) is reduced by the organic reagent to platinum(II), which is then complexed with the reagent. The metal : ligand ratio of 1 : 2 was indicated by solution spectrophotometric measurements, and was confirmed on the solid reaction product by elemental analysis and by mass spectrometric examination.     

Three Reactions,One Catalyst: A Multi-Purpose Platinum(IV) Complex and its Silica-Supported Homologue for Environmentally Friendly Processes

Although platinum nanoparticles and complexes -especially of Pt(0) and Pt(II)- are well known catalysts, siloxane-based platinum complexes are rarely reported. Herein, a Platinum(IV) complex of 4-aminopyridinium-modified disiloxane was prepared and characterized by medium and far infrared spectroscopy, NMR and EDX. The formation of the complex was monitored by UV–Vis spectroscopy, which showed the high affinity and selectivity of this ligand for Pt, with a stability constant of 7.53·10³ M⁻¹. The catalytic activity of the siloxane-based complex was tested in three types of reactions: reduction of p-nitrophenol, oxidation of glucose and starch, and hydrosilylation. The hydrophobic behavior of the permethylated disiloxane moiety ensures good hydrolytic stability, while the N-donor ligand stabilizes the in-situ formed Pt nanoparticles. The generation of Pt nanoparticles during p-nitrophenol reduction was confirmed by TEM and SEM. Contrary to most reports, the aerobic oxidation of mono- and polysaccharides occurred without oxidation agents or mediators added, in mild conditions, at room temperature and pH ~9. The same metal complex was found active in hydrosilylation of vinyl-siloxanes with temperature-modulated rate, thus being useful in silicone cross-linking systems without the need of inhibitors. The method was adapted to one-pot synthesis of silica-supported Pt(IV) complex, which acted as efficient and reusable heterogeneous hydrosilylation catalyst, limiting the contamination of the product with Pt. This approach is promising for superior valorization of scarcely available and expensive platinum metal. By the same method, multifunctional soluble complexes and mesoporous silica may be obtained, with tunable catalytic performance.     

Electrochemical processes on multi-component cathodic catalysts PtM and PtM<Subscript>1</Subscript>M<Subscript>2</Subscript> (M = Co,Ni, Cr): the effect of surface composition on the catalyst stability and its activity in O<Subscript>2</Subscript> reduction

The multi-component nanocatalysts based on platinum-transient metals alloys applied onto dispersed carbon material are considered as the most promising catalysts, which can be substituted for platinum in the fuel cell cathodes. The electrocatalytic activity of platinum in the PtM₁/C and PtM₁M₂/C alloys increases by several times with simultaneous increase in the stability. From the results obtained by structural and electrochemical methods, it is found that the synthesized binary and ternary catalysts are the metal alloys, whose surface is enriched in platinum as a result of surface segregation and subsequent chemical or electrochemical treatment. Under the corrosive attack, the less-noble metal, which has not entered into the alloy, dissolves, and the core-shell structures form. The properties of platinum in the shell differ from its properties in Pt/C due to the ligand effect of the core (metal alloy). As a result, the surface coverage with oxygen chemisorbed from water decreases in the binary and ternary systems. This causes an increase of the catalytic activity in the O₂ reduction reaction due to a decline in the effect of surface blocking against molecular oxygen adsorption and a decrease in the platinum dissolution rate, because the oxidation of platinum by water is the onset of corrosion process. For the catalytic systems studied, the mass activity decreases in the following order: 20% Pt in PtCoCr/C > 7.3% Pt in PtCo/C ≥ 7.3% Pt in PtCr/C and PtNi/C ≥ 40% Pt/C. The application of PtCoCr/C catalyst as the cathode in a low-temperature hydrogen-air fuel cell enabled one to reduce the platinum consumption by one half on retention of its performance.     

Platinum(II) Complexes of Cyclic Triphosphenium Ions: a (31)P NMR Spectroscopic and Computational Study

The first transition metal complexes of cyclic triphosphenium ions have been unequivocally identified in solution by (31)P NMR spectroscopy. The ligands coordinate to platinum(II) via the central phosphorus atom, but only when at least one of the outer phosphorus atoms has non-aromatic substituents. Depending on the system, either trans- (the kinetic reaction product) and/or cis- (the thermodynamic reaction product) complexes are formed. The (1)J coupling constants between (195)Pt and the central phosphorus atom of the CTI (P(A)) are small for both cis- and trans-isomers, between 900 and 1300 Hz, whereas other phosphanes in these complexes derived from the platinum(II) starting material show normal (1)J(PtP) values. These results suggest a possible long P-Pt bond between the overall positively charged ligand and the platinum(II) cation. Calculations including predicted (31)P NMR shifts for the CTIs and their Pt(II) complexes largely support our experimental findings.     

Zwitterionic Relatives of Cationic Platinum Group Metal Complexes: Applications in Stoichiometric and Catalytic σ‐Bond Activation

Zwitterionic platinum group metal complexes that feature formal charge separation between a cationic metal fragment and a negatively charged ancillary ligand combine the desirable reactivity profile of related cationic complexes with the broad solubility and solvent tolerance of neutral species. As such, zwitterionic complexes of this type have emerged as attractive candidates for a diversity of applications, most notably involving the breaking and/or forming of E? H and E? C σ bonds involving a main group element E. Important advances in ancillary ligand design are documented that have enabled the construction of platinum group metal zwitterions. Also summarized are the results of stoichiometric and catalytic investigations in which the reactivity of such zwitterions and their more traditionally employed cationic relatives in σ bond activation chemistry are compared and contrasted.