Characterisation of Siliceous Extra‐Framework Species in DAY Zeolites by 29Si MAS NMR and IR Spectroscopic Measurements

Dealuminated Y zeolites (DAY) were obtained by steaming of NH₄NaY at temperatures between 450 °C and 700 °C. They were characterised by means of ²⁷Al and ²⁹Si MAS NMR, IR spectroscopic and XRD measurements. The Si/Al framework ratios of samples were calculated using the ²⁹Si MAS NMR signal intensities, the wave numbers of the double‐ring vibration band w_DR and the asymmetrical TOT valence vibration w_TOT of IR spectra as well as the XRD lattice constant a₀. In contrast to actual Si/Al ratio obtained from w_DR and a₀, the NMR spectroscopic and w_TOT values were determined to be too high because of the superposition of the signals coming from dealuminated zeolite framework and silica gel which forms in the zeolite as a result of steaming. The differently determined Si/Al ratios characterise the siliceous extra‐framework species.     

Phase Transformations in Alkaline and Acid Leached Y Zeolites Dealuminated by Steaming

The steaming of zeolite Y (here at 873 K for 7 hours) leads to the formation of an amorphous aluminium aluminosilicate in addition to the dealuminated zeolite (DAY). An alkaline treatment of DAY causes the transformation of the non‐framework phase into an alkali aluminosilicate and the partial desilication of the DAY framework. The alkali aluminosilicate is decomposed by a moderate acid leaching under the formation of silica gel. The ²⁹Si MAS NMR and IR spectra of DAY and its chemically treated modifications are superimposed by the signals of the crystalline zeolite framework and the amorphous non‐framework materials whereas XRD measurements only characterize the current state of the framework.     

Para‐hydrogen induced polarization of Si‐29 NMR resonances as a potentially useful tool for analytical applications

Para‐hydrogen–induced polarization effects have been observed in the ²⁹Si NMR spectra of trimethylsilyl para‐hydrogenated molecules. The high signal enhancements and the long T₁ values observed for the ²⁹Si hyperpolarized resonances point toward the possibility of using ²⁹Si for hyperpolarization applications. A method for the discrimination of multiple compounds and/or complex mixtures of hydroxylic compounds (such as steroids), consisting of the silylization of alcoholic functionalities with an unsaturated silylalkyl moiety and subsequent reaction with para‐H₂, is proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

A Hybrid Assembly of MXene with NH2−Si Nanoparticles Boosting Lithium Storage Performance

A facile hybrid assembly between Ti₃C₂T_x MXene nanosheets and (3‐aminopropyl) triethoxylsilane‐modified Si nanoparticles (NH₂?Si NPs) was developed to construct multilayer stacking of Ti₃C₂T_x nanosheets with NH₂?Si NPs assembling together (NH₂?Si/Ti₃C₂T_x). NH₂?Si/Ti₃C₂T_x exhibits a significantly enhanced lithium storage performance compared to pristine Si, which is attributed to the robust crosslinking architecture and considerably improved electrical conductivity as well as shorter Li⁺ diffusion pathways. The optimized NH₂?Si/Ti₃C₂T_x anode with Ti₃C₂T_x: NH₂?Si mass ratio of 4 : 1 displays an enhanced capacity (864 mAh g^?1 at 0.1 C) with robust capacity retention, which is significantly higher than those of NH₂?Si NPs and Ti₃C₂T_x anodes. Furthermore, this work demonstrates the important effect of the MXene‐based electrode architecture on the electrochemical performance and can guide future work on designing high‐performance Si/MXene hybrids for energy storage applications.     

Synthesis and Characterization of Base‐catalyzed Phenyl Modified PDMS/PHMS Copolymers

A series of phenyl modified polydimethylsiloxane (PDMS) / polyhydrogenmethylsiloxane (PHMS) random copolymers containing both internal Si‐H and terminal SiH₂ and T (MeSiO_3/2) units was synthesized in one step through n‐BuLi‐catalyzed ring‐opening polymerization of cyclic comonomers and characterized by GPC, IR and ¹H and ²⁹Si NMR. Sequential microstructures of these copolymers were determined by ²⁹Si‐NMR spectroscopy. Epoxy‐modified polysiloxanes were prepared and used as comparable standards for the assignment of the NMR spectra. A hydride‐transfer mechanism has been proposed to account for the formation of terminal Si‐H and T group. Detailed sequential analyses and chemical shifts of ²⁹Si‐NMR for various siloxane units are reported for the first time.     

Vibrational Spectra of the Cluster Anions [E4]4– in the metallic Sodium and Barium Compounds Na4E4 and Ba2E4 (E = Si,Ge)

The vibrational spectra of the cluster anions [E₄]^4– (E = Si, Ge) in the metallic compounds Ba₂E₄ and Na₄E₄ have been measured and assigned based on the T_d symmetry of the discrete tetrahedranide anion. Due to the lower site‐symmetries in the respective crystals all degenerate modes are split, but to different extends. The characteristic breathing frequency ν(E–E) of the [E₄]^4– cluster appears exclusively in the Raman spectrum and is almost unaffected by the nature of counterions: ν(E–E) = 486 cm^–1 (E = Si) and 276 and 278 (Ge), respectively. The calculated valence force constants f_d (Si–Si) = 1.17 Ncm^–1 ( Na ); 1.15 Ncm^–1 ( Ba ) and f_d (Ge–Ge) = 0.98 Ncm^–1 ( Na ); 0.94 Ncm^–1 ( Ba ) are in good agreement with those previously reported.     

Solid‐state NMR study on changes of phosphate and proton species in metal pyrophosphate composite (MP2O7–MO2) ceramics

In order to investigate the effects of composite production and the role of the counter cation for metal phosphate conductors, changes in the solid‐state nuclear magnetic resonance (NMR) spectra and magnetic relaxation times caused by the removal of volatile products and water washing were examined for various metal pyrophosphate (MP₂O₇–MO₂; M = Sn, Si, Ti, and Zr). Acidic species could be detected by ¹H MAS NMR spectra for all the composites except ZrP₂O₇–ZrO₂ that had the lowest conductivity. The ³¹P DD‐MAS NMR spectra for MP₂O₇–MO₂ composites showed different signal patterns depending on the counter cations participating in the ion exchange as a result of different microstructures. Combinational analysis of ³¹P DD‐MAS and ³¹P CP‐MAS NMR spectra of the composites indicated that protonic bulk phosphates were observed at slightly lower fields than non‐protonic bulk phosphates in all of the MP₂O₇–MO₂ composites. After water washing, the acidic species and the protonic bulk phosphates of MP₂O₇–MO₂ composites disappeared or were reduced to trace amounts. The T₁H values of the water‐washed composites lengthened because of removal of orthophosphoric acid, although the T₁P values remained almost unchanged. The results of the solid‐state NMR studies suggest that the protonic bulk phosphates of MP₂O₇–MO₂ composites do not generally distribute in the bulk but exist in the interface between excess H₃PO₄ and the bulk. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and properties of two novel silicon‐containing cycloaliphatic epoxy resins for electronic packaging application

In this paper, two silicon‐containing cycloaliphatic olefins were synthesized through the nucleophilic substitution reactions of cyclohex‐3‐enyl‐1‐methanol with di‐ or tri‐chlorosilane compounds. Then, after epoxidation, two new cycloaliphatic epoxy resins with different epoxy groups were successfully prepared. Their chemical structures were confirmed by ²⁹Si NMR, ¹H NMR, and Fourier‐transform infrared spectra (FTIR). The properties of cured products, including viscoelasticity, glass transition temperature (T_g), coefficient of thermal expansion, thermal stability and water absorption, were investigated. Compared to the difunctional epoxy resin, the trifunctional one exhibited a remarkably increased cross‐linking density from 0.82 to 4.08 × 10^?3 mol/cm³ and T_g from 157 to 228°C. More importantly, prior to curing, they had viscosities of only 240–290 mPa sec at 25°C, which were much lower than that of ERL‐4221 (409 mPa sec), providing the possibility of easy processing. The high glass transition temperatures, good thermal stabilities, and mechanical properties as well as excellent flowability endow the silicon‐containing epoxy resins with promising potential in microelectronic packaging application. Copyright © 2011 John Wiley & Sons, Ltd.     

Phase Transformation of Hydrothermally Stressed Adsorbents

Inorganic materials of zeolite type, silica gel or related materials are used as adsorbents in air conditioning machines. The cooling effect is obtained by evaporation of water thereby the adsorbent acts as pump system. After itôs saturation, the storage must be regenerated by heating. The hydrothermal stress may generate decomposition of their structure accompanied by a loss of sorption capacity. This work describes the hydrothermal stability of AlPO‐5, SAPO‐34, and silica gel in comparison with a newly developed dealuminated Y zeolite DAY. DAY (Si/Al = 3.1) and AlPO‐5 zeolites are hydrothermally stable over a wide temperature range even under harsh condition of maximum water loading of their pore system. DAY exhibits a higher water sorption capacity but becomes amorphous with increasing temperature, whereas AlPO‐5 transforms into a tridymite analogous crystalline phase with an intermediate state at 140 °C. But, both phase transformation processes are not relevant for the application of the compounds in low‐temperature driven heat pumps due to less hydrothermal stressing there. SAPO‐34 decomposes already under mild hydrothermal conditions. In analogy to AlPO‐5 it forms the tridymite analogous structure at high temperature. The silica gel looses the sorption capacity systematically because of the healing of its structure by condensation of free silanol groups, whereby Q² and Q³ groups change into Q⁴ groups.     

Silicon-29 NMR studies of polymethylhydrosiloxanes: Spin-lattice relaxation time (T1) measurements

²⁹Si NMR spectra of polymethylhydrosiloxanes, Me₃SiO[MeHSiO]_nSiMe₃ from n = 3 to 8 and 35, have been determined. Both chemical shifts and spin-lattice relaxation times (T₁) have been measured. The stereochemistry at the adjacent chiral MeHSiO unit influences the nearest neighbor ²⁹Si chemical shift. The effect of chain length and position of MeHSiO units on T₁ values for Me₃SiO[MeHSiO]_nSiMe₃ systems are discussed.     

The microstructure determination of ethylene‐styrene‐propylene terpolymers at triad level by high‐temperature two‐dimensional NMR spectra

To further extend temperature range of application and low temperature performance of the ethylene‐styrene copolymers, a series of poly(ethylene‐styrene‐propylene) samples with varying monomer compositions and relatively low glass‐transition temperatures (T_g = −28 – 22 °C) were synthesized by Me₂Si(Me₄Cp)(N‐t‐Bu)TiCl2/MMAO system. Since the ¹³C NMR spectra of the terpolymers were complex and some new resonances were present, 2D‐¹H/¹³C heteronuclear single quantum coherence and heteronuclear multiple bond correlation experiments were conducted. A complete ¹³C NMR characterization of these terpolymers was performed qualitatively and quantitatively, including chemical shifts, triad sequence distributions, and monomer average sequence lengths. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 340–350     

Isolation of a Labile Homoleptic Diazenium Cation

Following our interest in nitrogen chemistry, we now describe the synthesis, structure, and bonding of labile disilylated diazene, its GaCl₃ adduct, and the intriguing trisilylated diazenium ion [(Me₃Si)₂N?N‐SiMe₃]⁺, a dark blue and highly labile (T_decomp>?30 °C) homoleptic cation of the type [R₃N₂]⁺. Although direct silylation of Me₃Si‐N?N‐SiMe₃ failed, the [(Me₃Si)₂N?N‐SiMe₃]⁺ ion was generated in a straightforward two‐electron oxidation reaction from mercury(II) dihydrazide and Ag[GaCl₄]. Moreover, previous structure data of Me₃Si‐N?N‐SiMe₃ were revised on the basis of new data.     

The Detection and Reactivity of Silanols and Silanes Using Hyperpolarized 29Si Nuclear Magnetic Resonance

Silanols and silanes are key precursors and intermediates for the synthesis of silicon‐based materials. While their characterization and quantification by ²⁹Si NMR spectroscopy has received significant attention, it is a technique that is limited by the low natural abundance of ²⁹Si and its low sensitivity. Here, we describe a method using p‐H₂ to hyperpolarize ²⁹Si. The observed signal enhancements, approaching 3000‐fold at 11.7 T, would take many days of measurement for comparable results under Boltzmann conditions. The resulting signals were exploited to monitor the rapid reaction of tris(tert‐butoxy)silanol with triflic anhydride in a T₁‐corrected process that allows for rapid quantification. These results demonstrate a novel route to quantify dynamic processes and intermediates in the synthesis of silicon materials.     

Estimation of gas-phase acidities of deoxyribonucleosides: An experimental and theoretical study

We determined the gas-phase acidities (ΔH_acid) of four deoxyribonucleosides, i.e., 2′-deoxyadenosine (dA), 2′-deoxyguanosine (dG), 2′-deoxycytidine (dC), and 2′-deoxythymidine (dT) by applying the extended kinetic method. The negatively charged proton-bound hetero-dimeric anions, [A-H-B]⁻ of the deoxyribonucleosides (A) and reference compounds (B) were generated under electrospray ionization conditions. Collision-induced dissociation spectra of [A-H-B]⁻ were recorded at four different collision energies using a triple quadrupole mass spectrometer. The abundance ratios of the individual monomeric product ions were used to determine the ΔH_acid of the deoxyribonucleosides. The obtained ΔH_acid value follows the order dA7>dC7>dT7>dG. The ΔG_acid (298 K) values were determined by using ΔG_acid=ΔH_acid-TΔS_acid where the ΔH_acid and ΔS_acid values were determined directly from the kinetic method plots. The ΔH_acid values were also predicted for the deoxyribonucleosides at the B3LYP/6-311+G**//B3LYP/6-311G** level of theory. The acidity trend obtained from the computational investigation shows good agreement with that obtained experimentally by the extended kinetic method. Theoretical calculations provided the most preferred deprotonation site as C5′-OH from sugar moiety in case of dA, and as −NH₂ (dC and dG) or -NH- (dT) from nitrogenous base moiety in the case of other deoxyribonucleosides.     

Reconstructive and displacive transformations of tectosilicates

By using the thermally induced phase transformation initial zeolites were converted into pure carnegieite, stuffed derivative of cristobalite. The polymorphs obtained from Na-LTA are stoichiometric (NaAlSiO₄), since those obtained from Na-FAU zeolite are non-stoichiometric (Na_1-xAl_1-xSi_1+xO₄). Stoichiometric carnegieite have cubic structure, while non-stoichiometric carnegieite crystallized in cubic and orthorhombic forms. ²⁹Si MAS NMR spectra show a very large but expecting difference between stoichiometric and non-stoichiometric carnegieite. The spectrum of stoichiometric carnegieite has only one peak Si(4Al), while the spectrum of non-stoichiometric carnegieite consist few superimposed peaks assigned to Si(4Al), Si(3Al), Si(2Al), Si(1Al) and Si(0Al). DTA study indicates the occurrence of displacive phase transition of all synthesized carnegieite. The transition temperature is depending on silicon aluminum order: T _m=690°C for stoichiometric, T _m=565 and 660°C for non-stoichiometric, low-temperature and high-temperature carnegieite, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Charged Si9 Clusters in Neat Solids and the Detection of [H2Si9]2− in Solution: A Combined NMR,Raman, Mass Spectrometric,and Quantum Chemical Investigation

Polyanionic silicon clusters are provided by the Zintl phases K₄Si₄, comprising [Si₄]⁴⁻ units, and K₁₂Si₁₇, consisting of [Si₄]⁴⁻ and [Si₉]⁴⁻ clusters. A combination of solid‐state MAS‐NMR, solution NMR, and Raman spectroscopy, electrospray ionization mass spectrometry, and quantum‐chemical investigations was used to investigate four‐ and nine‐atomic silicon Zintl clusters in neat solids and solution. The results were compared to ²⁹Si isotope‐enriched samples. ²⁹Si‐MAS NMR and Raman shifts of the phase‐pure solids K₄Si₄ and K₁₂Si₁₇ were interpreted by quantum‐chemical calculations. Extraction of [Si₉]⁴⁻ clusters from K₁₂Si₁₇ with liquid ammonia/222crypt and their transfer to pyridine yields in a red solid containing Si₉ clusters. This compound was characterized by elemental and EDX analyses and ²⁹Si‐MAS NMR and Raman spectroscopy. Charged Si₉ clusters were detected by ²⁹Si NMR in solution. ²⁹Si and ¹H NMR spectra reveal the presence of the [H₂Si₉]²⁻ cluster anion in solution.     

Charged Si9 Clusters in Neat Solids and the Detection of [H2Si9]2− in Solution: A Combined NMR,Raman, Mass Spectrometric,and Quantum Chemical Investigation

Polyanionic silicon clusters are provided by the Zintl phases K₄Si₄, comprising [Si₄]⁴⁻ units, and K₁₂Si₁₇, consisting of [Si₄]⁴⁻ and [Si₉]⁴⁻ clusters. A combination of solid‐state MAS‐NMR, solution NMR, and Raman spectroscopy, electrospray ionization mass spectrometry, and quantum‐chemical investigations was used to investigate four‐ and nine‐atomic silicon Zintl clusters in neat solids and solution. The results were compared to ²⁹Si isotope‐enriched samples. ²⁹Si‐MAS NMR and Raman shifts of the phase‐pure solids K₄Si₄ and K₁₂Si₁₇ were interpreted by quantum‐chemical calculations. Extraction of [Si₉]⁴⁻ clusters from K₁₂Si₁₇ with liquid ammonia/222crypt and their transfer to pyridine yields in a red solid containing Si₉ clusters. This compound was characterized by elemental and EDX analyses and ²⁹Si‐MAS NMR and Raman spectroscopy. Charged Si₉ clusters were detected by ²⁹Si NMR in solution. ²⁹Si and ¹H NMR spectra reveal the presence of the [H₂Si₉]²⁻ cluster anion in solution.     

Solid‐state 1H → 19F/19F → 1H CP/MAS NMR study of poly(vinylidene fluoride)

Solid‐state ¹H → ¹⁹F and ¹⁹F → ¹H cross‐polarization magic angle spinning (CP/MAS) NMR spectra have been investigated for a semicrystalline fluoropolymer, namely poly(vinylidene fluoride) (PVDF). The ¹H → ¹⁹F CP/MAS spectra can be fitted by five Lorentzian functions, and the amorphous peaks were selectively observed by the DIVAM CP pulse sequences. Solid‐state spin‐lock experiments showed significant differences in T_1ρ^F and T_1ρ^H between the crystalline and amorphous domains, and the effective time constants, T_HF* and T_1ρ*, which were estimated from the ¹H → ¹⁹F CP curves, also clarify the difference in the strengths of dipolar interactions. Heteronuclear dipolar oscillation behaviour is observed in both standard CP and ¹H → ¹⁹F inversion recovery CP (IRCP) experiments. The inverse ¹⁹F → ¹H CP‐MAS and ¹H → ¹⁹F CP‐drain MAS experiments gave complementary information to the standard ¹H → ¹⁹F CP/MAS spectra in a manner reported in our previous papers for other fluoropolymers. The value of N_F/N_H (where N is a spin density) estimated from the CP‐drain curve is within experimental error equal to unity, which is consistent with the chemical structure. Copyright © 2001 John Wiley & Sons, Ltd.     

Synthesis of Mesoporous Silica Immobilized with 3-[(Mercapto or amino)propyl]trialkoxysilane by a Simple One-pot Reaction

Sodium silicate from rice husk ash (RHA) was transformed to functionalized silica with 3‐(mercaptopropyl)‐trimethoxysilane (MPTMS) or 3‐(aminopropyl)triethoxysilane (APTES) via a simple sol‐gel technique in a one‐pot synthesis to give RHAPrSH and RHAPrNH₂. The ²⁹Si MAS NMR of RHAPrSH and RHAPrNH₂ showed the presence of T¹, T², T³, Q², Q³ and Q⁴ silicon centers. The ¹³C MAS NMR showed that RHAPrSH had chemical shifts at δ 16.59, 32.73, consistent with two of the carbon atoms of the MPTMS moiety, while the ¹³C MAS NMR of RHAPrNH₂ had chemical shifts at δ 14.58, 26.13, 47.87, consistent with the three carbon atoms of the APTES moiety. The presence of carbon, silicon, sulfur and nitrogen in RHAPrSH and RHAPrNH₂ was determined by a combination of elemental analysis and EDX study.     

DFT assessment of the spectroscopic constants and absorption spectra of neutral and charged diatomic species of group 11 and 14 elements

The spectroscopic constants and absorption spectra of neutral and charged diatomic molecules of group 11 and 14 elements formulated as [M₂]^+/0/? (M = Cu, Ag, Au), and [E₂]^+/0/? (E = C, Si, Ge, Sn, Pb) have been calculated at the PBE0/Def2‐QZVPP level of theory. The electronic and bonding properties of the diatomics have been analyzed by natural bond orbital analysis approach and topology analysis by the atoms in molecules method. Particular emphasis was given on the absorption spectra of the diatomic species, which were simulated by time‐dependent density functional theory calculations employing the hybrid Coulomb‐attenuating CAM‐B3LYP density functional. The simulated absorption spectra of the [M₂]^+/0/? (M = Cu, Ag, Au) and [E₂]^+/0/? (E = C, Si, Ge, Sn, Pb) species are in close resemblance with the experimentally observed spectra whenever available. The neutral M₂ and E₂ diatomics strongly absorb in the ultraviolet region, given rise to UVC, UVA and in a few cases UVB absorptions. In a few cases, weak absorbion bands also occur in the visible region. The absorption bands have thoroughly been analyzed and assignments of the contributing principal electronic transitions associated to individual excitations have been made. © 2014 Wiley Periodicals, Inc.