1 and 2-Photon Fluorescence Anisotropy Decay to Probe the Kinetic and Structural Evolution of Sol-Gel Glasses: A Summary

We review recent 1- and 2-photon fluorescence studies of the formation dynamics and structure of sol-gel glasses, from nanometre-sized particles to clusters, prepared from both aqueous silicates and tetramethylorthosilicate (TMOS), over a broad pH range. Through the careful choice of a fluorescent probe, anisotropy decay has been shown to provide both silica particle size and viscosity information and offers advantages over traditional techniques for silica particle sizing based on small-angle neutron, Xray, or light scattering. Subsequently, we are now able to observe the self-assembly mechanisms (or recently termed kinetic life history) of silica, produced under both acidic and alkaline conditions from sodium silicate solution (water glass) in the case of hydrogels and from alkoxides in the case of alcogels. The controlled preparation of hydrogels, often deemed a blackart, is also discussed in some detail, as are the potential applications and benefits of fluorescence anisotropy decay to industrial sol-gel systems. The insight into the sol-gel process provided by these new interpretations of fluorescence decay data, promises to have implications for both our fundamental understanding and the production of sol-gel systems in general.     

含茂基、烷氧基及氯离子混合配镧系金属有机化合物的合成及表征

本文通过二茂基镧不金属氯化物Ｃｐ２ＬｎＣｌ（Ｃｐ＝Ｃ５Ｈ５；Ｌｎ＝Ｄｙ，Ｙｂ）与烷基醇ＲＯＨ（Ｒ＝－ＣＨ２ＣＨ２ＣＨ３，－ＣＨ２ＣＨ＝ＣＨ２）在四氢呋喃中反应，合成了四个新的含三种不同配位基的镧系金属有机化合物；元素分析，红外光谱及质谱分析表明这些化合物可能具有三聚体结构，即：［ＣｐＬｎ（ＯＲ）Ｃｌ］３。     

Synthesis, Structure and Properties of Na2Zn(OEt)4(HOEt)5

The synthesis, structure and properties of Na₂Zn(OEt)₄(HOEt)₅, having the right Na:Zn ratio for sol–gel synthesis of the highly Na-ion conducting ceramic Na_1.8Zn_0.9Si_1.1O₄, is described. It was synthesised in high yield by a metathesis reaction of ZnCl₂ and 4NaOEt in ethanol or ethanol/toluene solvent. The structure was determined by single-crystal X-ray methods and consists of two symmetry related polymeric strands with the metal sequence ...–Zn–Na–Na–Zn–.... Extensive hydrogen bonding is present within each chain. Further characterization was made with IR- and Raman-spectroscopy and thermo-calorimetry, showing that the compound is stable to 65°C.     

Isopropoxyaluminum 1,1′-biphenyl-2-oxy-2′-perfluorooctanesulfonamide as a catalyst for Tishchenko reaction

Isopropoxyaluminum 1,1′-biphenyl-2-oxy-2′-perfluorooctanesulfonamide (3) has been evaluated as an aluminum-based catalyst for the Tishchenko reaction. Compound 3 was found to exert high catalytic activity in the reaction with aliphatic aldehydes and also enabled smooth dimerization of enolizable aldehydes. This advantage was highlighted by the quantitative formation of ethyl acetate from acetaldehyde by the present system.     

Compounds of oxozirconium(IV) alkoxides with oxygen and nitrogen bases

Pyridine, quinoline, 2,2-bipyridyl, dimethylformamide, dimethylacetamide and phthalimide combine with ZrOCl(OCHMe ₂)·2Me ₂CHOH to form complexes, ZrOCl(OCHMe ₂)·Base [with the exception of dimethylsulfoxide: Zr₂O₂Cl₂(OCHMe ₂)₂·3DMSO], whereas dialkoxides, ZrO(OR)₂·ROH (R=Me, Et, Pr ⁱ ), fail to react. The complexes have been characterized through infrared, molar conductance and thermal decomposition studies.

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Komplexe von Oxozirkonium(IV)-Alkoxiden mit Sauerstoff- und Stickstoff-Basen

Zusammenfassung Pyridin, Chinolin, 2,2-Bipyridyl, Dimethylformamid, Dimethylacetamid und Phthalimid geben mit ZrOCl(OCHMe ₂)·2Me ₂CHOH Komplexe vom Typ ZrOCl(OCHMe ₂)·Base [ausgenommenDMSO: Zr₂O₂Cl₂(OCHMe ₂)₂·3DMSO], während Dialkoxide, ZrO(OR)₂·ROH (R=Me, Et, Isopr), keine Reaktion ergeben. Die Komplexe wurden durch ihre IR-Spektren, molare Leitfähigkeit und mittels Untersuchung der thermischen Zersetzung charakterisiert.

     

PSBR季铵盐的原位反应及杂化弹性体研究

利用吡啶改性丁苯橡胶（PSBR）乳液与正溴丙烷反应后生成PSBR季铵盐,再与铝酸酯、钛酸酯以及活性硅烷醇反应,制得有机－无机杂化弹性体PSBR胶片（PSBR－MnOm)。经与天然橡胶并用,制成复合硫化胶。复合硫化胶的力学性能较好,并具有较高的滞后损耗。其压缩永久变形率与天然橡胶相似。用FTIR、高分辨NMR、DSC和TG等手段对其结果进行了分析,并认为在含有金属的复合硫化胶中可能存在“介稳巨大配合物”,对其物理性能的增强起一定作用。     

Sol–Gel Approach to Sr<Subscript>2</Subscript>CeO<Subscript>4</Subscript> Phosphor from Single Alkoxide Precursors

Syntheses and characterizations of sol–gel precursors of Sr₂CeO₄ were carried out. Each molecular precursor, [Sr₂Ce(OCH₂CH₂OCH₃)₈] (1), [Sr₂Ce(OⁱPr)₈] (2) and [Sr₂Ce₂(OⁱPr)₁₂(ⁱPrOH)₄] (3) was prepared from mixtures of Sr complexes and cerium(IV) alkoxides. The molecular structure of 3 showed that [CeO₆] octahedra are connected with distorted [SrO₆] octahedra by sharing edges with oxo bridges. X-ray powder diffraction patterns and spectrofluorometry were used to determine the evolution of structure from the precursor molecules to the luminescent oxides. The luminescent strontium cerium oxides were derived at relatively mild reaction conditions (700 °C for 1 h), and complete conversion was observed at 1000 °C for 1 h from these precursors. Comparing the spectra of the oxides derived from 2 and 3, the emission intensity of the oxide derived from 2 is much stronger.     

Reductive lithiation of alkyl phenyl sulfides in diethyl ether. A ready access to α,α-dialkylbenzyllithiums

Diethyl ether is a convenient solvent for the conversion of benzylic phenyl sulfides to the corresponding organolithiums by an uncatalyzed reductive metalation, while catalysis by naphthalene is required to achieve the same reaction for alkyl phenyl sulfides. The addition of magnesium 2-ethoxyethoxide to solutions of unstable alkyllithiums prepared in this way provides storable reagents.     

Synthesis and crystal and molecular structure of Mo4O(OCH2But)10(py): A 12-electron butterfly cluster

From the reaction between Mo₂(OCH₂Bu^t)₆ and water (1/2 equiv) in toluene solution in the presence of pyridine the oxo-alkoxide tetranuclear cluster Mo₄O(OCH₂Bu^t)₁₀(py) has been isolated as a dark crystalline compound. Crystal data at –121°C:a=24.762(12) Å,b=24.799(9) Å,c=23.021(9) Å,Z=8,d _caled=1.27 g cm^–3 in space group 14/m. The compound contains a Mo₄ butterfly with a hinge angle of 137° between the two Mo₃ triangles. The molecule has a crystallographically-imposed mirror plane of symmetry that contains the wing-tip Mo atoms. One wing-tip Mo atom is in an octahedral environment being bonded to two terminal and two-bridging OR ligands, and one pyridine ligand that is trans to a ₃-oxo bridge. The other Mo atoms are each coordinated to only four oxygen atoms. The backbone Mo atoms have one terminal and two bridging OR ligands and form one bond each to the ₃-oxo group. The other wing-tip Mo atom is coordinated to two terminal and two bridging OR groups. The five Mo-Mo distances span the range 2.43–2.59 Å. The¹H and¹³C{¹H} NMR spectra in benzene-d₆ are consistent with the presence of this structure in solution. The present results are compared to earlier findings for 12-electron alkoxide clusters of Mo and W.     

Preparation and Properties of Nb-Coated Barium Titanate Composite Particles by Surface Modification with Nb Alkoxide in Hydrophobic Solvent

Chemical processing for the preparation of Nb-coated barium titanate composite particles was investigated using surface modification technology, hydrolyzing Nb ethoxide on the surface of barium titanate particles dispersed in hydrophobic solvent.It was confirmed from the measurements of specific surface area and zeta potential as well as SEM, TEM and EDX observations of the resulting composite particles that the original barium titanate particles were coated uniformly with hydrolysis product of Nb ethoxide.Barium titanates coated with 1 wt% of Nb as oxide were well sintered at 1200–1300°C. The dielectric constants of the sintered barium titanates showed flattened temperature dependence, but it depended upon the average particle size of original barium titanate. The sintered bodies of Nb-coated barium titanate powders with average particle size of 0.2 m gave dielectric constants of 2000–3000 and those of barium titanate with average particle size of 0.5 m showed dielectric constants of 3000–4000 at room temperature.The microstructure of the sintered barium titanate coated with Nb oxide consisted of grains of about 1 m, smaller than those of sintered original barium titanate.