Siloxane Framework Research Articles

Synthesis and self-assembly of monodisperse silver-nanocrystal-doped silica particles

A simple method based on the Stöber reaction was developed to prepare silver-nanocrystal-doped silica composite particles. The silane coupling agent N-[3-(trimethoxysilyl)dropyl]ethylene diamine (TSD) incorporated Ag + into a siloxane framework and a further chemical reducer reduced Ag + to silver nanoparticles. TEM images showed that, in the presence of TSD, silver nanocrystals (fcc) of 2–8 nm were homogeneously doped in the silica particles, which showed a typical surface plasmon resonance (SPR) peak. The as-prepared Ag/SiO 2 composite particles can be self-assembled into long-range ordered lattices (or photonic crystals) over large areas.

Multinuclear NMR study of phosphosilicate gels derived from POCl 3 and Si(OC 2H 5) 4

Solid state 1H, 29Si and 31P MAS NMR have been used to investigate the microstructure of phosphosilicate gels prepared by a modified sol–gel method involving hydrolysis of silicon precursors in a solely aqueous environment at 50 °C. Gels with molar compositions 5, 10, 20 and 30 mol% P 2O 5 in P 2O 5–SiO 2 were studied. After drying to 400 °C the gels have very similar structures formed by a siloxane framework containing silanol groups and trapped molecules of orthophosphoric acid together with a very small amount, of pyrophosphoric acid. Unlike the gel samples previously synthesized by the hydrolysis of the silicon precursor in alcoholic solution at room temperature, the co-polymerization of phosphorus and silicon is much reduced. Although co-polymerization increases with phosphorus content, it still represents less than 50% of the phosphorus in the 30 mol% P 2O 5 gel. Furthermore there is no evidence for six-coordinated silicon in the glassy matrix.

Polyhedral ferrous and ferric siloxanes.

The synthesis, isolation, and single-crystal X-ray structures of the first polyhedral ferrous and ferric siloxanes suggest that similar synthetic strategies will allow the preparation of other transition-metal siloxane frameworks.

Polysiloxane-Immobilized Triamine Ligand System, Synthesis and Applications

The polysiloxane-immobilized triamine ligand system of the formula P-(CH 2 ) 3 NH(CH 2 ) 2 NH(CH 2 ) 2 NH 2 (where P represents the siloxane network) has been prepared via the sol-gel process by hydrolytic polycondensation of (EtO) 4 Si and (MeO) 3 Si(CH 2 ) 3 NH(CH 2 ) 2 NH(CH 2 ) 2 NH 2 . An alternative method was used by the reaction of the iodopolysiloxane P-(CH 2 ) 3 -I and diethylenetriamine in the presence of triethylamine. The immobilized triamine ligand forms metal chelate complexes when treated with aqueous metal(II) ion solutions (Co 2+ , Ni 2+ , and Cu 2+ ). The elemental analysis and FTIR results suggest that this ligand system undergoes a substantial leaching of diethylenetriamine ligand moieties from the siloxane framework.

UPTAKE OF DIVALENT METAL IONS (CU2+, NI2+, AND CO2+) BY POLYSILOXANE IMMOBILIZED TRIAMINE-THIOL AND THIOL-ACETATE LIGAND SYSTEM

Insoluble porous solid polysiloxanes-immobilized ligand systems bearing hybrid mixture of triamine-thiol ligand and thiol-acetate ligand as chelating functional groups of the general formula P-(CH2)3-X(Y) (Where P represents a silica like siloxane framework and X represents a mixture of triamine and thiol, -NHCH2)2NH-(CH2)2-NH2 and –SH, and Y represents a thiol-acetate -SCH2COOH functional groups) has been prepared. The immobilized triamine-thiol ligand system was prepared through the sol-gel process by hydrolytic polycondensation of Si(OEt)4 and a mixture of 3-mercaptopropyltrimethoxysilane and 3-diethylenetriaminepropyltrimethoxysilane coupling agents. The immobilized thiol-acetate ligand system was prepared by the reaction of polysiloxane immobilized thiol ligand with ethylchloroacetate. These ligand systems exhibit high potential for extraction and preconcentration of divalent metal ions (Co2+, Ni2+ and Cu2+). The results indicate that the triamine-thiol ligand seems to form 1:1 metal to ligand complexes, where there is no clear stoichiometry structure in the case of the thiol-acetate ligand.

UPTAKE OF DIVALENT METAL IONS (Cu2+, Zn2+, AND Cd2+) BY POLYSILOXANE IMMOBILIZED DIAMINE LIGAND SYSTEM

Porous solid siloxane polymers carrying diamine functional group of formula P–(CH2)3NH–CH2CH2NH2 (where P–represents a silica-like siloxane framework) have been prepared by replacement of the iodine in iodopolysiloxane with ethylenediamine. The iodofunctionalized polysiloxane was prepared by polycondensation of Si(OEt)4 and (MeO)3Si(CH2)I. The polysiloxane diamine ligand system exhibits high potential for preconcentration of divalent metal ions (Cu2+, Zn2+, and Cd2+). The tendency to chemisorb these divalent metal ions by the diamine ligand system at the optimum conditions was found in the order: Cu2+ > Zn2+ > Cd2+. Diamine ligand system suffers from leaching of ligand containing groups upon treatment with acidic solutions.

Solid state 29Si and 31P NMR study of gel derived phosphosilicate glasses

Solid state 29Si and 31P MAS NMR have been used to investigate the microstructural changes occurring in phosphosilicate gels during their conversion from a gel to the corresponding gel-derived glasses by heating. The studied gels have the molar compositions 10P2O5·90SiO2 and 30P2O5·70SiO2. It was found that the dried gels (100 °C) have very similar structures formed by a siloxane framework containing silanol groups and including trapped molecules of orthophosphoric acid along with a very small amount of pyrophosphoric acid. In spite of this initial similarity further heating causes markedly different structural rearrangements of their glassy matrices. Namely, the co-polymerisation of phosphate and silicate tetrahedra takes place at 300 °C for the gel with the higher phosphorus content whereas this occurs only after heat treatment for 30 minutes at 400 °C for the gel with the lower phosphorus content. Moreover, the presence of six-coordinated silicon in the glassy matrix of the 30P2O5·70SiO2 gel has been observed. The different evolution of the investigated gel microstructures mirrors their different crystallization behaviour: 10P2O5·90SiO2 keeps its amorphous nature up to 1000 °C while for 30P2O5·70SiO2 crystallization starts after heat treatment for 30 minutes at 400 °C.

Metal Containing New Inorganic Ring Systems Based on Siloxane and Phosphazane Frameworks

Metal Containing New Inorganic Ring Systems Based on Siloxane and Phosphazane Frameworks

Metal Containing New Inorganic Ring Systems Based on Siloxane and Phosphazane Frameworks

High-field 31P NMR spectroscopy and single crystal X-ray diffraction studies have been used to study the ring opening and nucleophilic substitution reactions of the λ3-cyclotriphosphazane [EtNPCl]3. The synthesis of the ring opened silicophosphonate [RSi(OH){OP(O)(H)(OH)}]2O (R = (2,6-iPr2C6H3)NSiMe3) (1) represents the first ever molecular silicophosphonate to be isolated bearing free reactive hydroxyl groups. The structure and conformation of the bulky aryloxide substituted λ3-cyclotriphosphazane derivative [EtNP(OAr)]3 (Ar = 2,6-iPr2C6H3) (2) has also been investigated. Interaction of 2 with transition metal precursor complexes leads to the isolation of phosphazane metal complexes with different mode of co-ordination of 2. Further, the reaction of Cp ★Ti(OAr)Cl2 (Ar = 2,6-(CH3)2C6H3OH) with O{SiPh2(OH)}2 gave the eight-membered trititanosiloxane [Cp ★Ti(Cl) (O(SiPh2O)2SiPh2O) (3). Siloxane chain expansion effects, presumed to be a consequence of ring strain, have been observed in the product. The presence of reactive Ti-Cl bond in 3 offers opportunities for its reaction chemistry to be explored.

Uptake of Divalent Metal Ions (Cu2+, Zn2+ and Cd2+) by Polysiloxane Immobilized Monoamine Ligand System

ABSTRACT Porous solid siloxane polymers carrying a monoamine functional group of formula P-(CH2)3NH2 (Where P- represents a siloxane framework silica like ) has been prepared by polycondensation of Si(OEt)4 and (MeO)3Si(CH2)3-NH2. Treatment of aqueous solutions of divalent metal ions with the polysiloxane monoamine ligand system demonstrates that this material has high potential for preconcentration of metal ions (Cu2+, Zn2+ and Cd2+). The tendency of these divalent metal ions to chemisorb by the monoamine ligand system at the optimum conditions increases in the order: Cd2+ <Zn2+ <Cu2+. The optimum pH is 5.5 for copper and 6-7 for zinc and cadmium. The ammonia/ ammonium chloride buffer solution gave maximum uptake for all metal ions. It is also found that the uptake of copper ions is concentration dependent and is independent of the presence of other competing ions. The monoamine ligand system suffers from leaching of ligand containing groups upon treatment with acidic solutions. The highest leaching occurs at low pH.

Infrared and 29Si NMR spectroscopic investigations on metallasiloxanes derived from organosilanetriols

Silanols containing one or more SiOH groups are useful synthons for the preparation of metallasiloxanes with novel SiOM frameworks. Recent reports from our laboratory in this area were centred on the synthesis of stable organosilanetriols and their use as building-blocks for the preparation of a wide range of metallasiloxanes soluble in organic solvents and incorporating various transition metals and main group elements in the siloxane framework. In addition to single crystal X-ray structural investigations, infrared and 29Si NMR spectral techniques provide useful information for elucidating the structures and type of metallasiloxanes formed in these reactions. This article summarizes the results of studies of the IR and 29Si NMR spectra of these compounds.

Peculiarities of the introduction of transition metal atoms withn-donor ligands into the siloxane framework

Peculiarities of the introduction of transition metal atoms withn-donor ligands into the siloxane framework

Molecular Siloxane Complexes of Rare Earth Metals—Model Systems for Silicate‐Supported Catalysts?

Participation of the oxygen atoms of the siloxane framework of ligand 1, and not only the terminal hydroxyl groups, may be required for the coordinative saturation of a metal center. This surprising conclusion was drawn from the X-ray structure analysis of the first rare earth metal complex with this type of ligand. Compound 1 serves as a molecular model for SiO2 supports for transition metal catalysts.

29Si-NMR-spektroskopische untersuchungen an methyl- und methyl-phenyl-siloxanen und ihre anwendung in der silikonanalytik

The 29Si NMR chemical shifts of some methyl- and methylphenyl-siloxanes were measured and are discussed with regard to their structure correlations. Depending on the number of oxygen atoms and phenyl groups connected with the silicon atom 9 different units of the siloxane framework show very characteristic and non-overlapping shift ranges. Within these ranges further systematic shift differences exist, which are caused by neighbouring group effects. The application of these results to the analytical investigations of polysiloxanes and several technical products are discussed from a general point of view.