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  • 1
    ISSN: 1573-4846
    Keywords: metal alkoxide complexes ; β-keto ligands ; hydrolysis ; particle size ; IR ; 13C NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The complexation degrees of Al-, Ti- and Zr-butoxide (M) with unsaturated and saturated β-diketones (3-allylpentane-2.4-dione-APD, acetylacetone-ACAC) and β-ketoesters (methacryloxyethyl-acetoacetate-MEAA, allylacetoacetate-AAA, ethylacetoacetate-EAA) as organic ligands (L) were examined by IR and 13 C NMR spectroscopy and were found to be L:M ≥ 1.5. The hydrolytic stability of the ligands of the metal alkoxide complexes (L:M = 1) during hydrolysis/condensation reactions at the molar ratio h (H2O : OR) = 0.5–2.0 decreases with increasing H〈math〉2O:complex ratio. Furthermore, the ligand stability depends on the type of metal in the complexes and decreases in the order Al- 〉 Zr- 〉 Ti-butoxide complexes at h=1. The ACAC ligand likewise shows in the Al-, Ti- and Zr-butoxide complexes a high hydrolytic stability (95–100%) at h=1 within 7 days. The Ti- and Zr-butoxide complexes with β-ketoesters as ligand show at h=1〉 a release to a different extent e.g., up to 60% in the case of the MEAA-ligand in the Ti-butoxide complex after 2 days. In general, the hydrolytic stability of the ligands in the Ti-butoxide complexes (L:M = 1, h=1) decreases in the order ACAC 〉 APD 〉 AAA 〉 EAA ≥ MEAA. The hydrolysis/condensation reaction of complexes having a weak ligand stability leads to larger particle sizes in the sols than those with stable ACAC ligands. The results contribute to a more controlled synthesis of sols and of new inorganic-organic hybrid polymers via the sol-gel process.
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  • 2
    ISSN: 1573-4846
    Keywords: epoxide ; ring-opening ; condensation ; NMR ; hardness ; nanoparticles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Glycidoxypropyltrimethoxysilane (GPTS) is frequently used as precursor for the preparation of sol-gel derived nanoscaled hybrid polymers. The influence of nanoscaled metal oxide sols of silica, boehmite, zirconia and ceria on reactions of GPTS in ethanolic hydrolysates and in corresponding gels (epoxide ring-opening, condensation degree) was examined by liquid- and solid-state 13C and 29Si NMR with regard to a better correlation between structure and material properties. Generally, a higher condensation degree of RSi(O0.5)3 units of GPTS is found after addition of metal oxide sols compared to GPTS without additives. The metal oxide sols (10 mole% series) cause an epoxide ring-opening up to 20% in GPTS hydrolysates after 24 h. A nearly complete ring opening was found in the boehmite and silica containing hybrid gels whereas gels containing ceria and other types of silica only show a low degree of ring-opening. The results show an accelerated ring-opening with increasing content of AlO/OH-species in silica sols. 13C NMR studies reveal that the epoxide ring-opening does not completely lead to polyether structures but to considerable amounts (up to 40%) of ethylether groups which can influence the material properties (hardness).
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  • 3
    ISSN: 1573-4846
    Keywords: titanosiloxanes ; siloxanes ; hydrolysis ; condensation ; structural units ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The structural units in diphenylsilanediol/titanium-isopropoxide solutions with molar ratio Si:Ti between 1:0.1 and 1:5 were examined by means of 29Si and 17O NMR. The main component in solutions with molar ratio Si/Ti=1:0.1 is the chain-like octaphenyltetrasiloxanediol. With increasing Ti-isopropoxide content (1:0.25–1:05) Si−O−Ti units of the spirocyclic titanosiloxane Ti[O5Si4(C6H5)8]2 prevail in the solutions accompanied by the chain-like tetrasiloxanediol. The 29Si NMR spectra of 1:1 solutions indicate a lot of different Si containing building units with chemical shifts mainly between-40 and-46 ppm. The signals with a chemical shift between-40 and-46 ppm are probably caused by Si atoms which are connected via oxygen bridges directly (Si−O−Ti) or indirectly (Si−O−Si−O−Ti) with titanium. Contrary to the 1:1 solutions only one or two different species with Si−O−Ti units are present in high Ti-alkoxide containing solutions (1:5). 29Si and 17O NMR results reveal a quick hydrolysis of the Ti−O−Si bonds to titanium-oxo-hydroxo-polymers and phenylsiloxanediols or their isopropyl esters after the addition of water to the solutions. This separation into species only containing either Ti−O−Ti or Si−O−Si bonds can entail a decreased homogeneity of the reaction products on a molecular level.
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  • 4
    ISSN: 1573-4846
    Keywords: 29Si and 13C NMR ; hetero-condensation ; condensation degree ; titanosiloxane bonds ; epoxide ring opening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The examination of hydrolysis, homo- and hetero-condensation reactions, of the condensation degree and the extent of epoxide ring opening in the course of sol-gel process was carried out by means of liquid- and solid-state 29Si and 13C NMR in the system 3-glycidoxypropyltrimethoxysilane (GPTS)-titaniumtetraethoxide-water (molar ratio 1 : 1 : 1.5–14) which is frequently used for the synthesis of heterometal hybrid polymers. The monomeric silanol groups in the GPTS-prehydrolysate immediately co-condense with the Ti-tetraethoxide to Si–O–Ti bonds to an extent of about 50–60% which remain stable in sols and also in the corresponding gels at low amounts of free water (0.02 H2O/OR) in the sol. An increasing amount of free water in the sol (≥0.12 H2O/OR) leads to an increased hydrolytic cleavage of the heterometal bonds and to the formation of homo-condensed polysiloxanes. The condensation degree of RSiO1.5 units in the Ti-containing sols is with 30–60% relatively high in comparison to Ti-free GPTS sols (ca. 5%) whereas the condensation degree of GPTS derived gels (81%) was found to be similar to that of the Ti-containing gels (60–80%). Ti-tetraethoxide accelerates the ring opening reaction of the epoxide group in the sols in dependence on the water content. Up to 78% of the epoxide rings are opened after 24 h in the sol with the highest water content (2 H2O/OR). No epoxide rings can be detected in Ti-containing gels which derive from sols with an amount of free water of ≥0.12 H2O/OR. The results give a first insight into the different parallel reactions in this system and can contribute to more structure controlled syntheses of heterometal hybrid polymers.
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  • 5
    ISSN: 1573-4846
    Keywords: heterometal bond ; hydrolysis ; condensation ; 17O and 29Si NMR ; titanosiloxane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Heterometal materials based on glycidoxypropyltrialkoxysilane and titaniumalkoxide are used for optical applications and require a high homogeneity on the molecular level. The presence of heterometal titanosiloxanes, their distribution and hydrolytic stability should influence the homogeneity of these materials. 29Si and 17O NMR spectroscopy has been used to investigate sols with molar ratios Si : Ti = 1 and H2O : OR (H) = 0.5 − 2.0 and their gels after heat treatment at 130°C. The presence of Si—O—Ti bonds in sols with a low water content (H 〈 0.2) and in the corresponding gels was identified by the high-field shift of the 29Si NMR signals of T1 and T2 units of up to 2–3 ppm compared to corresponding signals of homo-condensed Si—O—Si bonds. The existence of Si—O—Ti bonds in the sols is supported by 17O NMR spectra which show a characteristic signal around 340 ppm. A cleavage of the Si—O—Ti bonds occurs with increasing water/OR ratio in the sols. The cleavage of the heterometal bonds and the building up of homo-condensed species leads to a separation into areas with predominantly Ti—O—Ti and Si—O—Si bonds resulting in a decreased molecular homogeneity of the materials.
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  • 6
    ISSN: 1573-4846
    Keywords: metal alkoxides ; catalysis ; phenylsiloxanes ; structural units ; 29Si NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The investigation of the effects of small amounts of Ti-, Zr-, Al-, Sn- and Si-alkoxides and those of triethylamine and hydrochloric acid on the condensation reaction of diphenylsiloxanediol (DPSD) in molar ratio Si : additive = 1:0.01 and 1:0.04 by 29Si NMR shows a decrease in their activity in the order Ti≈HCl〉Al〉Sn≈N(Et)3≈Zr〉Si after 6 h reaction time. The influence of the type of alkoxide ligands attached to the metal on the condensation rate of DPSD was found relatively low compared to the different metals. In presence of Ti-alkoxide the condensation reaction of DPSD leads to di-, tri- and tetrasiloxanediols, the latter of which dominates and crystallizes from the solution as octaphenyltetrasiloxanediol. The catalysis of DPSD solutions by Al-alkoxide and HCl results preferably in tetraphenyldisiloxanediol species even after a few days. The complexity of metal alkoxides and the hydrolytic stability of heterometallic Si−O−M bonds have been discussed as possible reasons for the differences in the catalytic activity of the metal alkoxide.
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  • 7
    ISSN: 0044-2313
    Keywords: Silicate hydrate ; 1,1,4,4-tetramethylpiperazinium ; 1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane ; 1,1-dimethylpiperidinium ; clathrate ; crystal structure ; double four-ring silicate anion ; hydrogen bonding ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: [TMPA]4[Si8O20] · 34 H2O und [DDBO]4[Si8O20] · 32 H2O sind Heteronetzwerk-Clathrate mit 1,1,4,4-Tetramethylpiperazinium (TMPA) und 1,4-Dimethyl-1,4-Diazoniabicyclo[2.2.2]octan (DDBO) Gastkationen[TMPA]4[Si8O20] · 34 H2O (1) und [DDBO]4[Si8O20] · 32 H2O (2) wurden durch Kristallisation aus wäßrigen Lösungen der entsprechenden quartären Alkylammoniumhydroxide und SiO2 erhalten. Die Kristallstrukturen wurden mittels Einkristallröntgenbeugung bestimmt. 1: Monoklin, a = 16,056(2), b = 22,086(6), c = 22,701(2) Å, β = 90,57(1)° (T = 210 K), Raumgruppe C2/c, Z = 4. 2: Monoklin, a = 14,828(9), b = 20,201(7), c = 15,519(5) Å, β = 124,13(4)° (T = 255 K), Raumgruppe P21/c, Z = 2. Die Polyhydrate sind strukturverwandte Wirt-Gast-Verbindungen mit dreidimensionalen Wirtstrukturen aus über Wasserstoffbrücken verknüpften oligomeren Anionen [Si8O20]8- und H2O-Molekülen. Die Silicat-Anionen haben eine würfelförmige Doppelvierring-Struktur und eine lokale Umgebung, die von 24 H2O-Molekülen und sechs Kationen (TMPA, [C8H20N2]2+, oder DDBO, [C8H18N2]2+) gebildet wird. Die Kationen befinden sich als Gastspezies in großen, unregelmäßigen, käfigartigen Hohlräumen. Untersuchungen mittels der 29Si-NMR-Spektroskopie und der Trimethylsilylierungsmethode haben gezeigt, daß die gesättigten Lösungen von 1 und 2 hohe Anteile an Doppelvierring-Anionen enthalten. Derartige Anionen sind auch in der gesättigten Lösung des Heteronetzwerk-Clathrats [DMPI]6[Si8O18(OH)2] · 48,5 H2O (3) mit 1,1-Dimethylpiperidinium-Kationen (DMPI, [C7H16N]+) als Gastspezies enthalten.
    Notes: [TMPA]4[Si8O20] · 34 H2O (1) and [DDBO]4[Si8O20] · 32 H2O (2) have been prepared by crystallization from aqueous solutions of the respective quaternary alkylammonium hydroxide and SiO2. The crystal structures have been determined by single-crystal X-ray diffraction. 1: Monoclinic, a = 16.056(2), b = 22.086(6), c = 22.701(2) Å, β = 90.57(1)° (T = 210 K), space group C2/c, Z = 4. 2: Monoclinic, a = 14.828(9), b = 20.201(7), c = 15.519(5) Å, β = 124.13(4)° (T = 255 K), space group P21/c, Z = 2. The polyhydrates are structurally related host-guest compounds with three-dimensional host frameworks composed of oligomeric [Si8O20]8- anions and H2O molecules which are linked via hydrogen bonds. The silicate anions possess a cube-shaped double four-ring structure and a characteristic local environment formed by 24 H2O molecules and six cations (TMPA, [C8H20N2]2+, or DDBO, [C8H18N2]2+). The cations themselves reside as guest species in large, irregular, cage-like voids. Studies employing 29Si NMR spectroscopy and the trimethylsilylation method have revealed that the saturated aqueous solutions of 1 and 2 contain high proportions of double four-ring silicate anions. Such anions are also abundant species in the saturated solution of the heteronetwork clathrate [DMPI]6[Si8O18(OH)2] · 48.5 H2O (3) with 1,1-dimethylpiperidinium (DMPI, [C7H16N]+) guest cations.
    Additional Material: 7 Ill.
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