The first observation of heteronuclear two-bond J-coupling in the solid state: crystal structure and solid-state NMR spectroscopy of Rb(4)(NbO)(2)(Si(8)O(21))

High-temperature, high-pressure hydrothermal synthesis of the title compound and its (93)Nb and (29)Si MAS NMR spectra are reported. The (29)Si MAS NMR spectrum shows four signals corresponding to the four distinct Si sites in the structure. Three signals show multiplet patterns which arise from (93)Nb(spin-(9)/(2))-(29)Si J-coupling. This is the first example of two-bond J-coupling between a quadrupolar nucleus and a spin-(1)/(2) nucleus in the solid state. A combination of (93)Nb and (29)Si solid-state NMR and X-ray diffraction data has provided a correlation between NMR interaction parameters and local structure. This work opens a new opportunity to examine the relationship between (2)J-coupling and structural parameters in the solid state.     

Computational study of 19F NMR spectra of double four ring-containing Si/Ge-zeolites.

(19)F NMR chemical shifts are calculated in order to study the F(-) environment in double four ring (D4R) containing Si/Ge-zeolites. The calculations with the DFT/CSGT/B3PW91 methodology yielded an agreement within 2 ppm with respect to the experimental peaks corresponding to the D4R units containing 8Si0Ge, 7Si1Ge and 0Si8Ge of the octadecasil zeolite. The optimisation of the 7Si1Ge-, 6Si2Ge-, 5Si3Ge- and 4Si4Ge-D4R units with DFT/B3LYP methodology shows that a covalent Ge-F bond is formed and therefore a Ge atom in the D4R is pentacoordinated. The displacement of the fluoride ion towards a Ge atom in the Ge-containing D4R units locates four Si/Ge atoms in the close vicinity of the F(-) and this makes possible a rationalization of the (19)F NMR signals in groups according to the number of Si (n) and Ge (m) atoms in the nearest F(-) environment, F-Si(n)Ge(m) (where n+m=4). Thus, the calculated chemical shifts show that higher values are observed when the number of Ge atoms in the nearest F(-) environment increases.     

Reversible photoswitching of the coordination numbers of silicon in organosilicon compounds bearing a 2-(phenylazo)phenyl group

Several organosilicon compounds bearing a 2-(phenylazo)phenyl group were synthesized from the corresponding chlorosilanes and 2-lithioazobenzene prepared by halogen-lithium transmetalation of 2-iodoazobenzene. Their structures were determined by (1)H, (13)C, (19)F, and (29)Si NMR spectra, UV-vis spectra, and X-ray crystallographic analyses. In the UV-vis spectra, silyl groups caused red shifts of both the n-pi and pi-pi transitions of the azo group compared with the transitions of the unsubstituted azobenzene. The E-isomers of the fluorosilanes showed an intramolecular interaction between a nitrogen atom of the azo group and the silicon atom, leading their intermediate structures between a distorted trigonal bipyramidal structure and a tetrahedral structure around the silicon atoms, which were revealed by the X-ray crystallographic analyses and the NMR spectra. On the other hand, silanes without fluorine atoms showed tetrahedral structures in the absence of such an interaction. The photoirradiation of the E-isomers of the fluorosilanes afforded reversibly the corresponding Z-isomers in good yields. The silicon atoms of the Z-isomers were found to be tetracoordinate in the absence of Si-N interactions by the (29)Si NMR spectra. The coordination numbers of the silicon atom of the fluorosilanes were reversibly switched between four and five by photoirradiation. These properties were compared to those of a tetrafluoro[2-(phenylazo)phenyl]silicate.     

Trisilane-1,3-diolato complexes of Ti and Zr: syntheses and X-ray crystal structures

The syntheses and structures of zirconium and titanium complexes containing the novel chelating trisilane-1,3-diolate ligand [Me2Si(R2SiO)2]2- (R = SiMe3) (5)-H2 are reported. The chloride complexes [Me2Si(R2SiO)2]TiCl2 (7a) and [Me2Si(R2SiO)2]ZrCl2 x 2 THF (7b) were prepared by the reaction of MCl4 (M = Ti, Zr) with [Me2Si(R2SiO)2]2Ti (6a) and [Me2Si(R2SiO)2]2Zr (6b), which are derived from the reaction of 5 with M(NEt2)4, respectively. In the presence of TiCl4, complexes 6a and 7a undergo a ring-opening reaction to produce the dinuclear complex [Me2Si(R2SiO)2][TiCl3]2 (9). [Me2Si(R2SiO)2]TiMe2 (10) and [Me2Si(R2SiO)2]TiBnz2 (11) were prepared in moderate yields from reactions of 7a with 2 equiv of MeMgBr and BnzMgCl, respectively. According to NMR spectroscopic investigations, the reaction of the dimethyltitanium complex 10 with B(C6F5)3 led to full exchange of both methyl groups by C6F5 groups under quantitative formation of [Me2Si(R2SiO)2]Ti(C6F5)2 (12) and a mixture of B(C6F5)(3-n)Me(n), where n = 1-3. The structure of 12 is further evidenced by the preparation of an identical sample from the reaction of 7a with 2 equiv of C6F5MgBr. Refluxing an ether solution of 12 surprisingly gave [Me2Si(R2SiO)2]2TiC6F5]2O (13) as a result of ether cleavage. The structures of the complexes 7a, 7b, 9, 10, and 13 were determined by X-ray crystallography, and structural discussion of the bond parameters will be given.     

New homoleptic organometallic derivatives of vanadium(III) and vanadium(IV): synthesis, characterization, and study of their electrochemical behaviour

The arylation of [VCl3(thf)3] with LiR(Cl), where R(Cl) is a polychlorinated phenyl group [C6Cl5, 2,4,6-trichlorophenyl(tcp), or 2,6-dichlorophenyl (dcp)] gives four-coordinate, homoleptic organovanadium(III) derivatives with the formula [Li(thf)(4)][V(III)(R(Cl))(4)] (R(Cl) = C(6)Cl(5) (1), tcp (2), dcp (3)). The anion [V(III)(C6Cl5)4]- has an almost tetrahedral geometry, as observed in the solid-state structure of [NBu4][V(C6Cl5)4] (1') (X-ray diffraction). Compounds 1-3 are electrochemically related to the neutral organovanadium(IV) species [V(IV)(R(Cl))4] (R(Cl) = C6Cl5 (4), tcp (5), dcp (6)). The redox potentials of the V(IV)/V(III) semisystems in CH2Cl2 decrease with decreasing chlorination of the phenyl ring (E(1/2) = 0.84 (4/1), 0.42 (5/2), 0.25 V (6/3)). All the [V(IV)(R(Cl))4] derivatives involved in these redox couples could also be prepared and isolated by chemical methods. The arylation of [VCl(3)(thf)(3)] with LiC6F5 also gives a homoleptic organovanadium(III) compound, but with a different stoichiometry: [NBu4]2[V(III)(C6F5)5] (7). In this five-coordinate species, the C6F5 groups define a trigonal bipyramidal environment for the vanadium atom (X-ray diffraction). EPR spectra for the new organovanadium compounds 1-6 are also given and analysed in terms of an elongated tetrahedral structure with C(2v) local symmetry. It is suggested that the R(Cl) groups exert a protective effect towards the vanadium centre.     

29Si NMR studies of zeolite precursor solutions

Solution 29Si NMR spectroscopy results of zeolite precursor solutions of composition 1 SiO2:4 C2H5OH:0.36/n R+n[OH-]n:20 H2O are reported. This work employs isotopically enriched 29Si materials to aid in spectral interpretation. Using both 1D and 2D methods, spectra of solutions containing tetrapropylammonium hydroxide are wholly consistent with the existing silicate chemistry literature and indicate that the majority of the species are high-symmetry silicate clusters previously observed in aqueous solutions. The results are inconsistent with the nanoblock or nanoslab model proposed by Kirschhock and co-workers. Mixtures containing the 4,4'-trimethylene-bis(1,1'-dimethylpiperidinium) dihydroxide cation were also studied. These mixtures have similar speciation to the TPA solutions, although the relative populations of the species are different. Preliminary variable temperature 29Si NMR of these mixtures shows that the exchange properties of the high-symmetry silicate species, most notably the tetrahedral tetramer, depend on the organocation identity.     

Accurate heteronuclear J-coupling measurements in dilute spin systems using the multiple-quantum filtered J-resolved experiment

A new solid-state MAS NMR experiment is proposed to accurately measure heteronuclear (19)F-(207)Pb J-coupling constants, even though these couplings are not visible on high speed (19)F 1D MAS spectra; in particular, we demonstrate that the J-resolved experiment combined with scalar multiple-quantum filtering considerably improves the resolution of J-multiplet patterns for dilute spin systems.     

Selective NMR measurements of homonuclear scalar couplings in isotopically enriched solids

Scalar (J) couplings in solid-state NMR spectroscopy are sensitive to covalent through-bond interactions that make them informative structural probes for a wide range of complex materials. Until now, however, they have been generally unsuitable for use in isotopically enriched solids, such as proteins or many inorganic solids, because of the complications presented by multiple coupled but nonisolated spins. Such difficulties are overcome by incorporating a z-filter that results in a robust method for measuring pure J-coupling modulations between selected pairs of nuclei in an isotopically enriched spin system. The reliability of the new experimental approach is established by using numerical simulations and tested on fully (13)C-labeled polycrystalline L-alanine. It is furthermore shown to be applicable to partially enriched systems, when used in combination with a selective double-quantum (DQ) filter, as demonstrated for the measurement of (2)J((29)Si-O-(29)Si) couplings in a 50% (29)Si-enriched surfactant-templated layered silicate lacking long-range 3D crystallinity. J-coupling constants are obtained with sufficient accuracy to distinguish between different (29)Si-O-(29)Si pairs, shedding insight on the local structure of the silicate framework. The new experiment is appropriate for fully or partially enriched liquid or solid samples.     

光固化聚氨酯丙烯酸酯杂化材料的核磁共振谱

光固化聚氨酯丙烯酸酯杂化材料的核磁共振谱;SiO2;溶胶-凝胶法     

The substitution of germanium for silicon in AST-type zeolite

The substitution of silicon by germanium in the AST zeolite framework type, [Si_nGe_40−nO₈₀]*4(SDA⁺F⁻) expressed as unit cell content in its cubic F-centered symmetry, has been studied. Three different kinds of templates, dimethyldiethylammonium, dimethyldiisopropylammonium and isopropyltrimethylammonium cations, were used in the hydrothermal synthesis process in fluoride medium. The products were identified with XRD, MAS NMR, SEM and thermal analysis. The analysis of the X-ray powder diagrams shows that AST crystallizes in different space group symmetries depending on the nature of the SDA and the degree of Ge-substitution. The resonance signals of ¹⁹F in MAS NMR experiments for the pure Si- and Ge-end members are at −38.2 and −15 ppm, respectively, indicating that the F⁻-anion is located as co-template in the double-four-ring (D4R) of the tetrahedral framework. This is confirmed by Rietveld analysis of powder diffraction data of the pure Ge-end member. The peak splitting of the ¹⁹F NMR signal in pure GeO₂AST-type material is related to the displacement of F⁻ location inside the D4R. Two more distinct signals at −8 and −19 ppm, respectively, are observed for X-ray pure AST-samples of intermediate compositions and assigned to fluoride in D4R built of 4[GeO₄]- and 4[SiO₄]-tetrahedra (4Ge, 4Si) and to (2Ge, 6Si)-D4R, respectively. An ordered distribution of Ge in the AST-framework is proposed for cubic AST with compositions around Si/Ge=1.5–1 by correlating the intensities of ¹⁹F NMR signals and the results from chemical analysis. This model is further confirmed by the quantitative analyses of the corresponding ²⁹Si MAS NMR spectra.     

Revisiting silicate substituted hydroxyapatite by solid-state NMR

Silicon-substituted hydroxyapatite (Si-HAp) has shown promising properties such as high-bone remodeling around implants. So far, the techniques used for the structural characterization of the Si-HAp have given indirect evidence of the presence of silicon inside the structure (by X-ray and neutron diffraction). In this paper, we focus on Si-HAp derivatives obtained by a precipitation method (widely described in the literature). We demonstrate here by solid-state NMR spectroscopy that only a fraction of the silicon atoms are incorporated into the HAp lattice in the form of Q(0) (SiO(4) (4-)) species, for 4.6 wt% Si-HAp. A large amount of silicate units are located outside the HAp structure and correspond to silica-gel units. All results were established through (29)Si MAS, (1)H -->(29)Si CP MAS and T(1)rho((1)H) edited (1)H -->(29)Si CP MAS experiments. This last pulse scheme acted as a powerful editing sequence, leading to unambiguous spectroscopic conclusions, concerning the location of the SiO(4) (4-) moieties.     

New sodalite frameworks; synthetic tugtupite and a beryllosilicate framework with a 3:1 Si:Be ratio

Compounds of the formula Na8[Si(6 +y)Be(y)Al(6 - 2y)O24]X2, with X = Cl and Br, and y = 1, 2 and 3 have been synthesised and structurally characterised by combined powder X-ray and neutron diffraction profile analysis. These materials adopt the sodalite framework (SOD) with the tetrahedral species, BeO4, AlO4 and SiO4, disordered across the framework positions. Na8[Si8Be2Al2O24]Cl2, (y = 2), is a synthetic analogue of the naturally occurring semi-precious gemstone tugtupite, while Na8[Si9Be3O24]X2, X = Cl and Br represents a new tetrahedral framework stoichiometry with a Si ratio Be ratio of 3 ratio 1. Additional characterisation using 29Si MASNMR, IR spectroscopy and high-temperature, neutron diffraction show that the observed structure-property trends found when modelling sodalite materials can be extended to these new framework compositions.     

Ti-ZSM-11的红外光谱研究

随着杂原子分子筛研究领域的开拓与发展，近年来，对钛硅沸石的研究逐渐增多．Ti－ZSM－11（TS－2）型分子筛是由Reddy，Ratanasarny等[1]首先合成的．钛硅沸石的表征与其它杂原子分子筛相比较为复杂，对杂原子Ti是否进入了骨架还没有一个直接的证据，且争议较多．在红外光谱的研究中，对960cm－1－980cm－1区间的特征吸收的归属也存在着很大的分歧[2－4]．钛硅沸石在H2O2对有机化合物的选择氧化领域有极其优良的催化性能[1]，因此，对它的开发有广泛的应用前景．本文以动态和静态相结合的水热晶化法合成了Ti－ZSM－11型分子筛．IR光…     

Organoaluminium complexes incorporating an amido phosphine chelate with a pendant amine arm

The palladium-catalyzed aryl amination of 1-bromo-2-fluorobenzene with N,N-dimethylethylenediamine quantitatively produces N-(dimethylaminoethyl)-2-fluoroaniline, which subsequently reacts with KPPh2 in 1,4-dioxane to afford N-(dimethylaminoethyl)-2-diphenylphosphinoaniline (H[PNN]). The reactions of trialkylaluminium with H[PNN] in toluene generate the corresponding aluminium dialkyl complexes [PNN]AlR2 (R = Me, Et, i-Bu). The solution NMR spectroscopic and X-ray crystallographic studies are indicative of a trigonal bipyramidal geometry for these aluminium complexes in which the amino nitrogen atom is trans to the phosphorus donor of the [PNN]- ligand. This study presents rare examples of structurally characterized, five-coordinate aluminium hydrocarbyl complexes supported by phosphine-derived ligands.     

Solid-state NMR study of the post-fluorination of (C2.5F)n fluorine-GIC

The conversion of (C2.5F)n fluorine-graphite intercalation compounds (GIC) into covalent graphite fluoride during a post-treatment in pure F2 gas is studied by solid-state NMR. First, a careful characterization of the starting material is performed; in particular, for the first time for fluorinated carbons, two-dimensional 19F--> 13C cross-polarization wide-line separation (CP-WISE) experiments were carried out. This completes the classical NMR data such as 19F and 13C chemical shifts, quantitative 13C solid echo, and C-F bond length measurements, which were estimated by dipolar recoupling using inverse CP MAS. The data of the raw (C2.5F)n and of the samples post-fluorinated at 350, 450, and 550 degrees C were compared to investigate the C-F bonding as a function of the treatment temperature. The C-F bonding is discussed taking into account a hyperconjugation of the C-F bonds with neighboring unfluorinated carbon atoms.     

29Si chemical shift anisotropies in calcium silicates from high-field 29Si MAS NMR spectroscopy

29Si chemical shift anisotropy (CSA) data have been determined from (29)Si MAS NMR spectra recorded at 14.1 T for a number of synthetic calcium silicates and calcium silicate hydrates. These are beta- and gamma-Ca(2)SiO(4), Ca(3)SiO(4)Cl(2), alpha-dicalcium silicate hydrate (alpha-Ca(2)(SiO(3)OH)OH), rankinite (Ca(3)Si(2)O(7)), cuspidine (Ca(4)Si(2)O(7)F(2)), wollastonite (beta-Ca(3)Si(3)O(9)), pseudowollastonite (alpha-Ca(3)Si(3)O(9)), scawtite (Ca(7)(Si(6)O(18))CO(3).2H(2)O), hillebrandite (Ca(2)SiO(3)(OH)(2)), and xonotlite (Ca(6)Si(6)O(17)(OH)(2)). The (29)Si MAS NMR spectra of rankinite and wollastonite clearly resolve manifolds of spinning sidebands from two and three Si sites, respectively, allowing the CSA parameters to be obtained with high precision for each site. For the (29)Si Q(1) sites in rankinite and cuspidine, the CSA asymmetry parameters (eta(sigma) approximately 0.6) contrast the general expectation that sorosilicates should possess small eta(sigma) values as a result of the nearly axially symmetric environments of the SiO(4) tetrahedra. The (29)Si CSA parameters provide an improved insight into the electronic and geometric environments for the SiO(4) tetrahedra as compared to the values solely for the isotropic chemical shift. It is shown that the shift anisotropy (delta(sigma)) and the CSA asymmetry parameter (eta(sigma)) allow a clear distinction of the different types of condensation of SiO(4) tetrahedra in calcium silicates. This relationship may in general be valid for neso-, soro-, and inosilicates. The CSA data determined in this work may form a valuable basis for (29)Si MAS NMR studies of the structures for tobermorites and calcium silicate hydrate phases resulting from hydration of Portland cements.     

Investigation of the physicochemical aspects from natural kaolin to Al-MCM-41 mesoporous materials

Aluminum-containing hexagonally ordered mesoporous silica Al-MCM-41 was synthesized by hydrothermal treatment of leached products produced by pre-grinding and subsequent acid leaching of natural kaolin, without addition of silica or aluminum regents. The resulting Al-MCM-41 had a high surface area of 1041 m(2)/g, a pore volume of 0.97 mL/g, and an average pore diameter of 3.7 nm with narrow pore size distribution centered at 2.7 nm. During the synthesis process of Al-MCM-41 from natural kaolin, the evolutions of chemical environments for Si and Al atoms should be emphasized. Wide angle X-ray diffraction (WAXRD), high-resolution transmission electron micrographs (HRTEMs), solid-state magic-angle-spinning nuclear magnetic resonance (MAS NMR), Fourier transform infrared spectroscopy (FT-IR) were used to trace the variations of chemical structures. Pretreatment of grinding and subsequent acid leaching acted as an important role in the whole synthesis process. NMR spectroscopy showed that Q(3) structure (Si(SiO)(3)(OH)), condensed Q(4) framework structure (Si(SiO)(4)), also the octahedral and tetrahedral Al existed in the leached sample and Al-MCM-41, with higher chemical contents of Q(4) structure and the octahedral Al in final product Al-MCM-41 than those in the leached sample. A possible mechanism for the formation of Al-MCM-41 from natural kaolin was suggested.     

Synthesen,Einkristall-Röntgenstrukturanalysen und 29Si-Festkörper-NMR-Untersuchungen eines zwitterionischen λ5-Spirosilicats und eines käfigartigen Octa(silasesquioxans)

Syntheses, Single-Crystal X-Ray Analyses and Solid-State ²⁹Si NMR Studies of a Zwitterionic λ⁵-Spirosilicate and a Cage-like Octa(silasesquioxane) The zwitterionic λ⁵-spirosilicate bis[2,3-naphthalenediolato(2 ?)][2-(dimethylammonio)phenyl]silicate ( 1 ; isolated as 1 · 1/2 CH₃CN) was synthesized by reaction of the [2-(dimethylamino)phenyl]dimethoxyorganosilanes 5, 6 and 7 [2-(Me₂N)C₆H₄Si(OMe)₂R: R = Ph ( 5 ), cyclo? C₆H₁₁ ( 6 ), Me ( 7 )] with 2,3-dihydroxynaphthalene in acetonitrile at room temperature. Reaction of 1 · 1/2 CH₃CN or [2-(dimethylamino)phenyl]trimethoxysilane ( 3 ) with water in acetonitrile yielded the cage-like octa{[2-(dimethylamino)phenyl]silasesquioxane} ( 2 ). The crystal structures of 1 · 1/2 CH₃CN and 2 were studied by X-ray diffraction. In addition, 1 · 1/2 CH₃CN and 2 were characterized by solid-state (²⁹Si CP/MAS) and solution NMR studies (¹H, ¹³C, ²⁹Si).     

Structure-directing roles and interactions of fluoride and organocations with siliceous zeolite frameworks

Interactions of fluoride anions and organocations with crystalline silicate frameworks are shown to depend subtly on the architectures of the organic species, which significantly influence the crystalline structures that result. One- and two-dimensional (2D) (1)H, (19)F, and (29)Si nuclear magnetic resonance (NMR) spectroscopy measurements establish distinct intermolecular interactions among F(-) anions, imidazolium structure-directing agents (SDA(+)), and crystalline silicate frameworks for as-synthesized siliceous zeolites ITW and MTT. Different types and positions of hydrophobic alkyl ligands on the imidazolium SDA(+) species under otherwise identical zeolite synthesis compositions and conditions lead to significantly different interactions between the F(-) and SDA(+) ions and the respective silicate frameworks. For as-synthesized zeolite ITW, F(-) anions are established to reside in the double-four-ring (D4R) cages and interact strongly and selectively with D4R silicate framework sites, as manifested by their strong (19)F-(29)Si dipolar couplings. By comparison, for as-synthesized zeolite MTT, F(-) anions reside within the 10-ring channels and interact relatively weakly with the silicate framework as ion pairs with the SDA(+) ions. Such differences manifest the importance of interactions between the imidazolium and F(-) ions, which account for their structure-directing influences on the topologies of the resulting silicate frameworks. Furthermore, 2D (29)Si{(29)Si} double-quantum NMR measurements establish (29)Si-O-(29)Si site connectivities within the as-synthesized zeolites ITW and MTT that, in conjunction with synchrotron X-ray diffraction analyses, establish insights on complicated order and disorder within their framework structures.