Silsesquioxane Framework Research Articles

Tetrahedral Silsesquioxane Framework: A Feasible Candidate for Hydrogen Storage

The search for new materials that can withstand the tough demands of practical hydrogen storage for use in automotive transportation is currently receiving a great deal of attention from the scientific community because of the urgency for replacements of traditional energy resources such as fossil fuels. In this work, transition metal (TM)-decorated boron-doped tetrahedral silsesquioxane frameworks (B-TSFs) for application in hydrogen storage are investigated using first-principles density functional theory calculations. We design this plausible hydrogen storage system based on the knowledge of previous works by other groups including metal atom decoration for quasi-molecular H2 adsorption, boron substitution into benzene rings to prevent metal clustering, and assembling modified benzene rings and tetrahedral silsesquioxane cages into the framework for this study. Boron substitution substantially enhances the TM binding energy to the linker of B-TSF to suppress metal clustering as well as maintain stable ...

Preparation of imidazolium-type ionic liquids containing silsesquioxane frameworks and their thermal and ion-conductive properties

Imidazolium-type ionic liquids containing a random-structured (Im-Random-SQ-IL) and a cage-like (Im-Cage-SQ-IL) oligosilsesquioxanes were successfully prepared by hydrolytic condensation of MTICl in TFSI solutions in water and water/methanol solution, respectively.

Hollow mesoporous organosilica nanoparticles: a generic intelligent framework-hybridization approach for biomedicine.

Chemical construction of molecularly organic-inorganic hybrid hollow mesoporous organosilica nanoparticles (HMONs) with silsesquioxane framework is expected to substantially improve their therapeutic performance and enhance the biological effects beneficial for biomedicine. In this work, we report on a simple, controllable, and versatile chemical homology principle to synthesize multiple-hybridized HMONs with varied functional organic groups homogeneously incorporated into the framework (up to quintuple hybridizations). As a paradigm, the hybridization of physiologically active thioether groups with triple distinctive disulfide bonds can endow HMONs with unique intrinsic reducing/acidic- and external high intensity focused ultrasound (HIFU)-responsive drug-releasing performances, improved biological effects (e.g., lowered hemolytic effect and improved histocompatibility), and enhanced ultrasonography behavior. The doxorubicin-loaded HMONs with concurrent thioether and phenylene hybridization exhibit drastically enhanced therapeutic efficiency against cancer growth and metastasis, as demonstrated both in vitro and in vivo.

The synthesis of phosphorylated silsesquioxanes and the investigation of the ability to aggregation and interaction with aromatic dicarboxylic acids

For the first time, silsesquioxanes containing aminophosphonate fragments were synthesized by condensation of the aminophosphonate derivatives with trialkoxysilane moieties under acid catalysis conditions. According to 29Si NMR, IR-spectroscopies, the silsesquioxane obtained have ladder-like structure with T4 and T6 silicon atoms. Information obtained from the MALDI-TOF mass spectra was used to deduce the structure of both oligomeric derivatives and the silsesquioxane framework. The morphology of the polysilsesquioxanes formed was investigated by transmission electron microscopy. The T6-silsesquioxanes bearing aminophosphonate moieties contrary to T4-silsesquioxanes tend to form aggregates of prolate shape. Their aggregation behavior was analyzed by the dynamic light scattering method. T6-silsesquioxane tends to form submicron-sized aggregates in aqueous solutions. The ability of these silsesquioxanes to recognize aromatic dicarboxylic acids was studied by the UV-spectroscopy.

MALDI-TOF MS and Morphology Studies of Thiacalixarene-Silsesquioxane Products of Oligo- and Polycondensation

For the first time condensed silsesquioxane derivatives of tetratrialkoxysilyl compounds have been characterized by MALDI-TOF mass spectrometry. Tetrasubstituted p-tert-butyl thiacalix[4]arene derivatives containing organosilicon fragments with variable stereochemistry were chosen as organosilicon compounds for polycondensation. Information obtained from mass spectra was used to deduce both the structures of oligomeric derivatives, as well as the structure of silsesquioxane framework. The morphology of formed polysilsesquioxanes was investigated by scanning and transmission electron microscopy.

Facile Preparation of Ionic Liquid Containing Silsesquioxane Framework

Abstract An ionic liquid containing silsesquioxane framework (SQ-IL) was successfully prepared by the hydrolytic condensation of trimethyl[3-(triethoxysilyl)propyl]ammonium chloride in aqueous solution of bis(trifluoromethanesulfonyl)imide (TFSI). The energy-dispersive X-ray analysis of SQ-IL indicated that the molar ratio of quaternary ammonium cation to TFSI anion in SQ-IL was ca. 1:1. The 29Si NMR spectrum of SQ-IL showed two broad peaks in T2 and T3 regions. The weight-average molecular weight estimated by static light-scattering measurement was ca. 1.8 × 103. In addition, the X-ray diffraction pattern of SQ-IL did not show any diffraction peaks. On the basis of these results, it was concluded that SQ-IL was an amorphous oligomeric silsesquioxane compound containing equimolar quaternary ammonium cations and TFSI anions. The differential scanning calorimetry thermogram of SQ-IL exhibited an endotherm peak due to glass transition at 15 °C, and SQ-IL showed fluidity over ca. 35 °C, indicating that SQ-IL was fluid below 100 °C (i.e., an ionic liquid). In the thermogravimetric analyses, the temperatures of thermal decomposition of SQ-IL were higher than those of N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide, which is an ionic liquid compound with the same structure as that of the side chains of SQ-IL. This result indicated that the silsesquioxane framework could suppress thermal degradation.

A glassy carbon electrode modified with bismuth nanotubes in a silsesquioxane framework for sensing of trace lead and cadmium by stripping voltammetry

Single-walled bismuth nanotubes (sw-BiNTs) were self-assembled with octa(3-aminopropyl) silsesquioxane as a framework and to govern morphology. Deposited on a glassy carbon electrode (GCE), the sw-BiNTs were used for the simultaneous analysis of Pb(II) and Cd(II) by square wave stripping voltammetry. The sw-BiNTs were prepared by (a) coordination interaction between the amino groups of the silsesquioxane and the Bi(III) ions, and by (b) reduction with sodium borohydride. Transmission electron microscopy images revealed single-walled tubular structures with diameters of ~4–6 nm, and with lengths of several hundreds nanometers. GCEs modified with such sw-BiNTs perform much better than bare GCEs in stripping analysis of Pb(II) and Cd(II). The effects of adsorption quantity of sw-BiNTs, solution pH, pulse amplitude, and pulse width were optimized. The modified electrode was then used for the analysis of Pb(II) and Cd(II) in a linear response range from 0.4 to 6 μM with a sensitivity of 4.692 μA μM−1 and 3.835 μA μM−1, and detection limits of 1 nM and 5 nM, respectively. The method was successfully applied to the analysis of Pb(II) and Cd(II) in toy leachates, and the results were in good agreement with those obtained with atomic absorption spectrometry. Sensitivity and detection limits were compared with other voltammetric methods, and the sw-BiNTs are deemed to be an attractive alternative for practical applications. Other features of the electrode include low costs, a well reproducible nanostructure, and ease of scale-up of the fabrication process.

Synthesis and characterization of tantalum silsesquioxane complexes

Tantalum polyhedral oligosilsesquioxane (POSS) complexes have been synthesised and characterized. X-ray structures of these complexes revealed that the coordination number of the tantalum center greatly affects the cube-like silsesquioxane framework.

Aqueous Colloidal Mesoporous Nanoparticles with Ethenylene-Bridged Silsesquioxane Frameworks

Aqueous colloidal mesoporous nanoparticles with ethenylene-bridged silsesquioxane frameworks with a uniform diameter of ∼20 nm were prepared from bis(triethoxysilyl)ethenylene in a basic aqueous solution containing cationic surfactants. The nanoparticles, which had higher hydrolysis resistance under aqueous conditions, showed lower hemolytic activity toward bovine red blood cells than colloidal mesoporous silica nanoparticles.

Formation of trimethylsilylated open-cage oligomeric azidophenylsilsesquioxanes

Formation of open-cage oligomeric azidophenylsilsesquioxane was surprisingly discovered in the successive reduction and azidation reactions starting from octa(nitrophenyl)octasilsesquioxane. The mixture of oligomeric products was characterized after end-capping with trimethylsilyl groups. The IR spectra confirmed the introduction of azide function to aromatic moiety, and trimethylsilyl group on silsesquioxane framework. Together with the GPC result, NMR analysis revealed the introduction of different number of trimethylsilyl groups in the structure. Some of them maintained the cage-like silsesquioxane structure characterized by XRD analysis. Their TGA profiles gave a unique pattern with clear two-step mass loss with the first mass loss of about 8–10 wt% from 180 to 225 °C corresponding to a thermal decomposition of azide groups.

Synthesis and Catalytic Activity of Titanium Silsesquioxane Frameworks as Models of Titanium Active Surface Sites of Controlled Nuclearity

The synthesis and catalytic activity of some new titanium(IV) complexes with incompletely condensed Cy6Si6O7(OH)4 and endo-Cy8Si8O11(OH)2 (Cy = c-C6H11) silsesquioxane cages have been carried out with the aim of investigating new Ti silsesquioxane frameworks as molecular models of titanium active sites of catalysts prepared by grafting Ti(IV) precursors on the surface or in a matrix of mesoporous silica. The silsesquioxane Cy6Si6O7(OH)4, which bears four potentially reactive OH groups, when reacted with TiCpCl3 (Cp = η5-C5H5) affords the new species [Cy6Si6O12Ti2(Cp)2], with two titanium atoms connected through one μ-oxygen bridge, as confirmed by a XANES and EXAFS spectroscopic investigation. By reaction of endo-Cy8Si8O11(OH)2 with [Ti(o-C6H4O2)(OCH2CH3)2] the new complex [Cy8Si8O11O2]2Ti was obtained, which exhibits a tetrapodal coordination of Ti, as shown by a X-ray diffraction investigation. The catalytic activity of these two new Ti silsesquioxane complexes was investigated for the catalytic epoxida...

Progress in the Compilation of an Oxovanada‐Silsesquioxane Portfolio and Catalytic Activity of Organometallic Representatives in Ethylene Polymerisation

AbstractEmploying various incompletely condensed silsesquioxanes as ligand precursors in reactions with simple oxovanadates a variety of oxovanadium silsequioxanes could be synthesised, that might be regarded as models for oxovanadium units on silica surfaces. These include a tetranuclear vanadium(IV) compound as well as two complexes where O2V+ units are coordinated to two siloxide functions as part of a silsesquioxane framework. Moreover, compounds containing Cp*V(O)2+ moieties were prepared, whose activities as polymerisation procatalysts were examined: They turned out to be moderately active for the polymerisation of ethylene. All compounds were fully characterised, in case of the tetranuclear vanadium(IV) complex this also includes the investigation of the magnetic behaviour. Moreover, for two complexes also the molecular structures could be determined with sufficient quality by X‐ray diffraction.

Versatile Phosphite Ligands Based on Silsesquioxane Backbones

AbstractSilsesquioxanes are employed as ligand backbones for the synthesis of novel phosphite compounds with 3,3′‐5,5′‐tetrakis(tert‐butyl)‐2,2′‐dioxa‐1,1′‐biphenyl substituents. Both mono‐ and bidentate phosphites are prepared in good yields. Two types of silsesquioxanes are employed as starting materials. The monophosphinite 1 and the monophosphite 2 are prepared from the thallium silsesquioxide derived from a completely condensed silsesquioxane framework (c‐C5H9)7Si7O12SiOTl. The diphosphite 3 is synthesized starting with the incompletely condensed monosilylated disilanol (c‐C5H9)7Si7O9(OSiMePh2)(OH)2. For monophosphite 2, the corresponding trans‐[PtCl2(2)] complex 4 is characterized by NMR spectroscopy as well as by X‐ray crystallography, as the first example of a completely condensed oxo‐functionalized silsesquioxane framework. The coordination of the bidentate ligand 3 towards Pd, Mo and Rh is studied, both by NMR spectroscopy as well as by X‐ray crystallography. Various modes of coordination are shown to be possible. The molecular structures for the complexes trans‐[PdCl2(3)] (5), cis‐[Mo(CO)4(3)] (6) and the dinuclear complex [{Rh(μ‐Cl)(CO)}2(κ2‐3)] (7) have been determined. In the rhodium‐catalyzed hydroformylation of 1‐octene high activities, with turnover frequencies of up to 6800 h−1, are obtained with these new nanosized phosphorus ligands.

A Silsesquioxane-Based Diphosphinite Ligand: Synthesis, DFT Study, and Coordination Chemistry

The incompletely condensed silsesquioxane disilanol (c-C5H9)7Si7O9(OH)2OSiMePh2 has been used as a backbone for the synthesis of the diphosphinite ligand (c-C5H9)7Si7O9(OPPh2)2OSiMePh2 (1), based on a silsesquioxane framework. By reaction with black selenium, the corresponding selenide (2) was obtained, showing a JSe-P value of 815 Hz in the 31P NMR spectrum. DFT calculations established a good insight into the electron density of the P atoms present in the two model compounds CH3OPPh2 (3) and Ph2P(HSiOH)2OPH2 (4). The Mulliken charge distributions show a clear electron-withdrawing effect of the siloxy group, which is also present in diphosphinite ligand 1. By reaction of compound 1 with PdCl2(C6H5CN)2, the palladium complex [PdCl2R(OPPh2)2] (5) was obtained (R = (c-C5H9)7Si7O9OSiMePh2). From a similar reaction of 1 with PtCl2(cod), the platinum analogue [PtCl2R(OPPh2)2] (6) could be isolated. The equimolar reaction of Mo(CO)4(pip)2 (pip = piperidine) with 1 yielded the molybdenum complex [Mo(CO)4R(OPPh2)...

Controlled Cleavage of Fully-Condensed Silsesquioxane Frameworks: A Revolutionary New Method for Manufacturing Precursors to Hybrid Inorganic/Organic Materials

ABSTRACTThe reaction of readily available Cy8Si8O12(3) with triflic acid (TfOH) can produce two different ditriflates derived from controlled cleavage of Si-O-Si linkages. These ditriflates can be subsequently hydrolyzed to four different incompletely condensed silsesquioxanes, which are attractive precursors to hybrid inorganic/organic materials.

Amine and ester-substituted silsesquioxanes: synthesis, characterization and use as a core for starburst dendrimers

Practical procedures are reported for the syntheses of amine and ester-substituted silsesquioxane frameworks with the formula R8Si8O12 with R = CH2CH2CH2NH2 (2), [CH2CH2CH2NH3]Cl (3) and CH2CH2CMe2CH2CO2Me (4); the use of 2 as a core for starburst dendrimers with R = CH2CH2CH2N(CH2CH2CO2Me)2 (5) and CH2CH2CH2N(CH2CH2C(O)NHCH2CH2NH2)2 (6) is also described.

Practical methods for synthesizing four incompletely condensed silsesquioxanes from a single R8Si8O12 framework

The reaction of (c-C6H11)8Si8O12 1 with triflic acid (TfOH) can produce two different ditriflates with the formula (c-C6H11)8Si8O11(OTf)2, which can be hydrolyzed selectively to four different incompletely condensed silsesquioxane frameworks with the formula (c-C6H11)8Si8O11(OH)2 (2, 4, 7 and 8).

Facile Framework Cleavage Reactions of a Completely Condensed Silsesquioxane Framework

Facile Framework Cleavage Reactions of a Completely Condensed Silsesquioxane Framework

Facile and Remarkably Selective Substitution Reactions Involving Framework Silicon Atoms in Silsesquioxane Frameworks

Facile and Remarkably Selective Substitution Reactions Involving Framework Silicon Atoms in Silsesquioxane Frameworks

Synthesis and structural characterization of a remarkably stable, anionic, incompletely condensed silsesquioxane framework

The reaction of [(C 6 H 11 ) 7 Si 7 O 9 (OH) 3 ] 1 (2 equiv.) with [(C 6 H 11 ) 7 Si 7 O 9 (OTl ) 3 ] 3 affords a conproportionation product that reacts with [PPh 4 ]Cl, [PBu n 4 ]Cl and [NBu n 4 ]Br to produce the corresponding salts of [(C 6 H 11 ) 7 Si 7 O 10 (OH ) 2 ] - 5 (i.e. the monoanion derived from deprotonation of 1); a single-crystal X-ray diffraction study of the [(NBu n 4 ] + salt of 5 indicates that the molecules exist as isolated ion pairs with strong intramolecular hydrogen bonding; implications of this result for the chemistry of silica are discussed.