Darstellung und spektroskopische Untersuchungen von hoch-verzweigten funktionellen Siloxanen

Preparation and Spectroscopic Investigations of Highly Branched Functional Siloxanes The preparation of the siloxanes [(Me₃SiO)₃SiO]_n(Me₃SiO)_3?nSiX and (Me₃SiO)₃Si[OSi(OSiMe₃)₂]₂X (n = 1?3, X = H, Cl, OC₂H₅, OH) is described. The hydride-siloxanes and the siloxanoles have been investigated by i.r. and ²⁹Si-n.m.r. spectroscopy. The frequencies of the Si? H stretching vibration, the ²⁹Si? ¹H coupling constants and the ²⁹Si-chemical shifts of the Si(H) signal for the hydride-siloxanes as well as the frequencies of the (Si)O? H stretching vibration, the relative (Si)O? H acidity, and the ²⁹Si-chemical shifts of the Si(OH) signal for the siloxanoles show a dependence on the number of the (Me₃SiO)₃SiO groups. The spectroscopic data are discussed with respect to the silicate environment of the Si(H) and Si(OH) atom, respectively. In the siloxanoles intramolecular hydrogen bondings were observed.     

Polymerization of hexamethylcyclotrisiloxane with a biscatecholsiliconate. I. Nature of polymerization

Polymerization behavior of hexamethylcyclotrisiloxane (D₃) in toluene solution with the use of benzyltrimethylammonium bis(o-p;henylenedioxy)phenylsiliconate as a catalyst, dimethyl sulfoxide as promoter, and adventitious moisture as initiator was investigated. The polymerization system gives a linear difunctional polymer, HO(Me₂SiO)_xH, with a molecular weight which is inversely proportional to the amount of water reacted rather than to the amount of catalyst employed. The polymerization in the presence of H₂O gives rise to molecular weight distributions very close to Poisson distributions. The normalized experimental GPC curve agrees very well with the theoretical GPC curve calculated from the polymerization scheme: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm H}_2 {\rm O} + ({\rm Me}_2 {\rm SiO})_3 \to {\rm HO}({\rm Me}_2 {\rm SiO})_3 {\rm H}} \\ {{\rm HO(Me}_{\rm 2} {\rm SiO)}_{\rm 3} {\rm H} + {\rm N(Me}_{\rm 2} {\rm SiO)}_{\rm 3} \to {\rm HO}({\rm Me}_2 {\rm SiO})_{3(n + 1)} {\rm H}} \\ \end{array} $$\end{document} Polymerization carried out in the combined presence of H₂O and ROH, where R is Me or Me₃Si, gives rise to bimodal molecular weight distributions. The resulting polymers consist of HO(Me₂SiO)_2xH and RO(Me₂SiO)_xH. The molecular weight of the former is twice that of the latter, and their proportion depends on the ratio of H₂O to ROH. The system is a special type of “living” polymer.     

Estimates for systematic empirical corrections of consistent 4–21G ab initio geometries and their correlations to total energy group increments

The structural parameters of the completely relaxed 4–21G ab initio geometries of more than 30 basic organic compounds are compared to experimental results. Some ranges for systematic empirical corrections, which relate 4–21G bond distances to experimental parameters, are associated with total energy increments. In general, for the currently feasible comparisons, the following corrections can be given which relate calculated distances to experimental r_g parameters and calculated angles to r_s-structures For CC single bond distances, deviations between calculated and observed parameters (r_g) are in the ranges of ?0.006(2) to ?0.010(2) Å for normal or unstrained hydrocarbons; ?0.011(3) to ?0.016(3) Å for cyclobutane type compounds; and +0.001(5) to +0.004(4) Å for CH₃ conjugated with CO. For CO single bonds the ranges are ?0.006(9) to +0.002(3) Å for CO conjugated with CO; and ?0.019(3) to ?0.027(9) Å for aliphatic and ether compounds. A very large and exceptional discrepancy exists for the highly strained ethylene oxide, r_s — r_e = ?0.049(5) Å and in CH₃OCH₃ and C₂H₅OCH₃ the r_s — r_e differences are ?0.029(5), ?0.040(10) and ?0.025(10) Å. Some of these discrepancies may also be due to deficiencies of the microwave substitution method caused by atomic coordinates close to inertial planes. For CN bonds, two types of NCH₃ corrections are from +0.005(6) to ?0.006(6) and from ?0.009(2) to ?0.014(6) Å; and the range for NCO is +0.012(3) to +0.028(4) Å. For isolated CC double bonds the range is + 0.025(2) to +0.028(2) Å. For conjugated CC double bonds the correction is less positive (+0.014(1) Å for benzene). For CO double bonds the corrections are ?0.004(3) to +0.003(3) Å. For bond angles of type HCH, CCH, CCC, CCO, CCO, OCO, NCO and CCC the corrections are of the order of magnitude about 1–2° (or better). Angles centered at heteroatoms are less accurate than that, when hydrogen atoms are involved. Differences in HOC and NHC angles were found in a range of ?2.3(5)° to ?6.2(4)°.     

A study of methanetetraol dehydration to carbonic acid

Two alternative dehydration reactions C(OH)₄ → (HO)₂CO + H₂O and C(OH)₄ + H₂O → (HO)₂CO + 2H₂O are studied by ab initio Becke3LYP/6–311 + G^** and MP2/6–31G^** methods. Calculated energy and geometry characteristics of intermediates and transition states predict a catalytic effect of one water molecule and the exothermism of the transformations. Relevant HF/6–311 + G^**, HF/6–31G^**, HF/6–31G, and HF/3–21G calculations were performed for comparison. © 1997 John Wiley & Sons, Inc.     

Acid-Base Interactions of Pyrazine,Ethyl Acetate,Di-alcohols,and Lysine with the cyclic Alumosiloxane (Ph2SiO)8[Al(O)OH]4 in View of Mimicking Al2O3(H2O) Surface Reactions

The etherate of (Ph₂SiO)₈[Al(O)OH]₄ can be transformed into the pyrazine adduct (Ph₂SiO)₈[Al(O)OH]₄ · 3N(C₂H₂)₂N ( 1 ), the ethyl acetate adduct (Ph₂SiO)₈[Al(O)OH]₄ · 3H₃C-C(O)OC₂H₅ ( 2 ), the 1,6-hexane diol adduct (Ph₂SiO)₈[Al(O)OH]₄ · 2HO–CH₂(CH₂)₄CH₂–OH ( 3 ) and the 1,4-cyclohexane diol adduct (Ph₂SiO)₈[Al(O)OH]₄ · 4HO–CH(CH₂CH₂)₂CH–OH ( 4 ). In all compounds the OH groups of the starting material bind to the bases through O–H ··· N ( 1 ) or O–H ··· O hydrogen bonds ( 2 , 3 , 4 ) as found from single-crystal X-ray diffraction analyses. Whereas in 1 only three of the central OH groups bind to the pyrazines, in 2 two of them bind to the same carbonyl oxygen atom of the ethyl acetate resulting in an unprecedented O–H ··· O ··· H–O double hydrogen bridge. The hexane diol adduct 3 in the crystal forms a one-dimensional coordination polymer with an intramolecularly to two OH groups grafted hexane diol loop, while the second hexane diol is connecting intermolecularly. In the cyclohexane diol adduct 4 all OH groups of the central Al₄(OH)₄ ring bind to different diols, leaving one alcohol group per diol uncoordinated. These “free” OH groups form an (O-H ··· )₄ assembly creating a three-dimensional overall structure. When reacting with (Ph₂SiO)₈[Al(O)OH]₄ lysine loses water, turns into the cyclic 3-amino-2-azepanone, and transforms through chelation of one of the aluminum atoms the starting material into a new polycycle. The isolated compound has the composition (Ph₂SiO)₁₂[Al(O)OH]₄[Al₂O₃]₂ · 4 C₆H₁₂N₂O · 6(CH₂)₄O ( 5 ).     

The Effect of Ge Incorporation on the Brønsted Acidity of ZSM‐5

The effect of the isomorphous substitution of some of the Si atoms in ZSM‐5 by Ge atoms on the Brønsted acid strength has been investigated by i) DFT calculations on cluster models of the formula ((HO)₃SiO)₃‐Al‐O(H)‐T‐(OSi(OH)₃)₃, with T=Si or Ge, and ((HO)₃SiO)₃‐Al‐O(H)‐Si‐(OGe(OH)₃)(OSi(OH)₃)₂, ii) a ³¹P NMR study of zeolite samples contacted with trimethyl phosphine oxide probe molecules and iii) a X‐ray photoelectron spectroscopy (XPS) study of ZSM‐5 and Ge‐ZSM‐5 samples. The calculations reveal that the effect of Ge incorporation on the framework acidity strongly depends on the degree of substitution and on the exact T‐atom positions that are occupied by Ge. High Ge concentrations allow for enhanced stabilisation of the deprotonated Ge‐ZSM‐5 through structural relaxation, resulting in a slightly higher acidity as compared to ZSM‐5. This structural relaxation is not achievable in Ge‐ZSM‐5 with a low Ge content, which therefore has a slightly lower acidity than ZSM‐5. The NMR study indicates no difference between the Brønsted acidity of ZSM‐5(47) and Ge(0.09)ZSM‐5(36). Instead, evidence for the presence of a substantial amount of Ge? OH groups in the Ge‐containing samples was obtained from the NMR results, which is consistent with earlier FTIR studies. The XPS results do not point to an effect of Ge on the framework acidity of ZSM‐5(47), instead, the results can be best interpreted by assuming the presence of additional Ge? OH and Si? OH groups near the surface of the Ge(0.08)ZSM‐5(47) sample.     

Ab initio study of the topology of the charge distribution of H3SiO(H)AlH3 conformers

The topologic properties of the electronic charge distribution of conformers of H₃SiO(H)AlH₃ molecule hydroxyl groups of zeolites are reported. The studied properties—total density, Laplacian density, and bond ellipticity—were evaluated at the position of the critical points of the O Si, O Al, and O H bonds, by using Hartree–Fock and second‐order Møller–Plesset levels of theory, and the STO/6‐31+G(d,p) standard basis set. For the H₃SiO(H)AlH₃ molecule, four conformers are identified. It is demonstrated that for these conformers, the total density and Laplacian density remain almost constant by effect of the rotations of the T H bonds, T=(Si, Al), around the corresponding O T bonds, respectively. However, these rotations induce sensible variations in the ellipticity at the position of the critical point of the O Al bonds, which are reflected in the OH bond distance, OH vibrational mode, and the stabilization energy of conformers. These results lead to a linear relationship between the magnitude of the bond ellipticity at the critical point of the O Al bonds and the frequency values of the OH bonds, with a correlation coefficient of r²=0.98. In addition, a good linear relationship between the ellipticity of the O Al bond and the pattern of the stabilization energy of conformers was also found. © 1999 John Wiley & Sons, Inc. Int J Quant Chem 76: 1–9, 2000     

Hydrogen Bonding of Fluorinated Saccharides in Solution: F Acting as H‐Bond Acceptor in a Bifurcated H‐Bond of 4‐Fluorinated Levoglucosans

4‐Fluorinated levoglucosans were synthesised to test if OH???F H‐bonds are feasible even when the O???F distance is increased. The fluorinated 1,6‐anhydro‐β‐D ‐glucopyranoses were synthesised from 1,6 : 3,4‐dianhydro‐β‐D ‐galactopyranose ( 8 ). Treatment of 8 with KHF₂ and KF gave 43% of 4‐deoxy‐4‐fluorolevoglucosan ( 9 ), which was transformed into the 3‐O‐protected derivatives 13 by silylation and 15 by silylation, acetylation, and desilylation. 4‐Deoxy‐4‐methyllevoglucosan ( 19 ) and 4‐deoxylevoglucosan ( 21 ) were prepared as reference compounds that can only form a bivalent H‐bond from HO? C(2) to O? C(5). They were synthesised from the ⁱPr₃Si‐protected derivative of 8 . Intramolecular bifurcated H‐bonds from HO? C(2) to F? C(4) and O? C(5) of the 4‐fluorinated levoglucosans in CDCl₃ solution are evidenced by the ¹H‐NMR scalar couplings ^h1J(F,OH) and ³J(H,OH). The OH???F H‐bond over an O???F distance of ca. 3.0 Å is thus formed in apolar solvents, at least when favoured by the simultaneous formation of an OH???O H‐bond.     

Organocobalt cluster complexes XXIX. Novel silicon compounds containing the nonacarbonyl tricobaltcarbon substituent

The reaction of bromomethylidynetricobalt nonacarbonyl or, more effectively, of methylidynetricobalt nonacarbonyl with diverse silicon hydrides (R₃SiH, Ph₃SiH, Me₂(EtO)SiH, R_nCl_3-nSiH (n = 02), etc. results in formation of silylmethylidynetricobalt nonacarbonyl complexes. Silicon-functional interconversions such as SiCl → SiOH, SiCl → SiOMe, SiOH → SiF, and SiOH → SiOSiMe₃, have provided still other substituted silylmethylidynetricobalt nonacarbonyl complexes, generally in high yield. The compounds Me(HO)₂SiCCO₃(CO)₉ and (HO)₃SiCCo₃(CO)₉ have been incorporated into methylsilicone polymers by H₂SO₄-induced reactions with cyclo-(Me₂SiO)₃.     

tert‐Butoxysilanols as model compounds for labile key intermediates of the sol–gel process: crystal and molecular structures of (t‐BuO)3SiOH and HO[(t‐BuO)2SiO]2H

The tert‐butoxychlorosilanes (t‐BuO)₃SiCl ( 1 ), (t‐BuO)₂SiCl₂ ( 2 ), and [(t‐BuO)₂SiCl]₂O ( 3 ) were prepared by the reaction of SiCl₄ or (Cl₃Si)₂O with t‐BuOK. Subsequent hydrolysis afforded the tert‐butoxysilanols (t‐BuO)₃SiOH ( 4 ), (t‐BuO)₂Si(OH)₂ ( 5 ), HO[(t‐BuO)₂SiO]₂H ( 6 ) in high yields. The controlled condensation of 2 and 5 provided HO[(t‐BuO)₂SiO]₃H ( 7 ) in reasonable yields. The tendency of 4 – 7 to undergo self‐condensation is small, thus enabling their characterization in solution and in the solid state by ²⁹Si NMR spectroscopy, IR spectroscopy and electrospray mass spectrometry, and in the case of 4 and 6 also by X‐ray diffraction. The key feature of the crystal structures is the incorporation of tert‐butoxy groups into the hydrogen bonding. The results obtained are discussed in relation to the sol–gel process. Copyright © 2002 John Wiley & Sons, Ltd.     

Tautomerism of monochalcogenosilanoic acids CH3Si(O)XH (X = S,Se, Te) in the gas phase and in the polar and aprotic solution: An ab initio computational investigation

Computational investigations by an ab initio molecular orbital method (HF and MP2) with the 6‐311+G(d,p) and 6‐311++G(2df, 2pd) basis sets on the tautomerism of three monochalcogenosilanoic acids CH₃Si(?O)XH (X = S, Se, and Te) in the gas phase and a polar and aprotic solution tetrahydrofuran (THF) was undertaken. Calculated results show that the silanol forms CH₃Si(?X)OH are much more stable than the silanone forms CH₃Si(?O)XH in the gas‐phase, which is different from the monochalcogenocarboxylic acids, where the keto forms CH₃C(?O)XH are dominant. This situation may be attributed to the fact that the Si? O and O? H single bonds in the silanol forms are stronger than the Si? X and X? H single bonds in the silanone forms, respectively, even though the Si?X (X = S, Se, and Te) double bonds are much weaker than the Si?O double bond. These results indicate that the stability of the monochalcogenosilanoic acid tautomers is not determined by the double bond energies, contrary to the earlier explanation based on the incorrect assumption that the Si?S double bond is stronger than the S?O double bond for the tautomeric equilibrium of RSi(?O)SH (R?H, F, Cl, CH₃, OH, NH₂) to shift towards the thione forms [RSi(?S)OH]. The binding with CH₃OCH₃ enhances the preference of the silanol form in the tautomeric equilibrium, and meanwhile significantly lowers the tautomeric barriers by more than 34 kJ/mol in THF solution. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Raman and infrared spectroscopic investigation of alkyl derivatives of arsenic acid: Part VI. On the AsO-bond - calculation of force constants and vibrational energy distribution in compounds of the type RAsO3X2 And R2A

Normal coordinate analyses and force constant calculations were carried out using frequencies of infrared and Raman-spectra of the molecules and ions RAsO₃^2?, RAs(O)(OR)₂, RAs(O)(OH)₂, RAs(OH)O₂^?, RzAsO₂^?, R₂As(O)OH, and [R'₂As(OH)₂]⁺ (R = CH₃, R' = C₂H₅). Comparing bond orders of the AsO bond with those in corresponding phosphorus, selenium and sulphur compounds, we found influences of the electron deficiency effect and of bond polarity.     

Ab initio calculations to the reactions of HF and HCl with Si(OH)4 and (HO)3SiOSi(OH)3: Modeling of SiO2 etching reactions

The local mechanisms of dissociative chemisorption and reactive etching are investigated by molecular models modeling ?SiOH groups and ?SiOSi? bridges at SiO₂ surfaces. The elementary reaction paths for the reactions of HF and HCl with Si? O bonds of the models, Si(OH)₄ and (HO)₃SiOSi(OH)₃, are calculated by the Hartree–Fock method. The local transition-state structures are nearly plane quadrangles with neighboring pentacoordinated silicon and tricoordinated oxygen atoms. For the reaction and activation energies, the electron correlation is considered by the Møller–Plesset perturbation theory. The results agree with experimental findings. © 1994 John Wiley & Sons, Inc.     

Density functional complete study of hydrogen bonding between the water molecule and the hydroxyl radical (H2O · HO)

The hydrogen bonding complexes formed between the H₂O and OH radical have been completely investigated for the first time in this study using density functional theory (DFT). A larger basis set 6‐311++G(2d,2p) has been employed in conjunction with a hybrid density functional method, namely, UB3LYP/6‐311++G(2d,2p). The two degenerate components of the OH radical ²Π ground electronic state give rise to independent states upon interaction with the water molecule, with hydrogen bonding occurring between the oxygen atom of H₂O and the hydrogen atom of the OH radical. Another hydrogen bond occurs between one of the H atoms of H₂O and the O atom of the OH radical. The extensive calculation reveals that there is still more hydrogen bonding form found first in this investigation, in which two or three hydrogen bonds occur at the same time. The optimized geometry parameter and interaction energy for various isomers at the present level of theory was estimated. The infrared (IR) spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. The estimates of the H₂O · OH complex's vibrational modes and predicted IR spectra for these structures are also made. It should be noted that a total of 10 stationary points have been confirmed to be genuine minima and transition states on the potential energy hypersurface of the H₂O · HO system. Among them, four genuine minima were located. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

The hydrogen bond with carbonyl groups: theoretical study of the correlation between the X-H stretching frequency shift and the CO group proper

The empirical correlation between the stretching frequency of the carbonyl group and the shift of the v_XH absorption band, proposed in the literature [3], is interpreted with a simple model, where the CO group is considered as a two π-electron system in terms of the parametric Hückel approximation. The model clearly distinguishes between the associations with OH, NH and CH groups, and offers an explanation of the different behaviour based on the properties of the donor and acceptor groups.The assumptions required for the previous simple treatment have then been tested through the analysis of a CNDO/2 treatment applied to the association of methanol with formaldehyde, acetaldehyde and acetone. After optimization of the association geometry with respect to the CO, and O-H ? O bond-lengths and to the angle between the O-H and CO groups, it is found that the calculated ?v_OH correlates with the calculated association enthalpy, transferred charge, dipole moment increment, and π-bond order, and also with the observed v_CO frequency of acetaldehyde and acetone.The empirical correlation can therefore be explained in terms of both Huckel and CNDO approximations.     

Cubic Siloxanes with Both Si−H and Si−OtBu Groups for Site‐Selective Siloxane Bond Formation

Cage‐type siloxanes have attracted increasing attention as building blocks for silica‐based nanomaterials as their corners can be modified with various functional groups. Cubic octasiloxanes incorporating both Si?H and Si?OtBu groups [(tBuO)_nH_8?nSi₈O₁₂; n=1, 2 or 7] have been synthesized by the reaction of octa(hydridosilsesquioxane) (H₈Si₈O₁₂) and tert‐butyl alcohol in the presence of a Et₂NOH catalyst. The Si?H and Si?OtBu groups are useful for site‐selective formation of Si?O?Si linkages without cage structure deterioration. The Si?H group can be selectively hydrolyzed to form a Si?OH group in the presence of Et₂NOH, enabling the formation of the monosilanol compound (tBuO)₇(HO)Si₈O₁₂. The Si?OH group can be used for either intermolecular condensation to form a dimeric cage compound or silylation to introduce new reaction sites. Additionally, the alkoxy groups of (tBuO)₇HSi₈O₁₂ can be treated with organochlorosilanes in the presence of a BiCl₃ catalyst to form Si?O?Si linkages, while the Si?H group remains intact. These results indicate that such bifunctional cage siloxanes allow for stepwise Si?O?Si bond formation to design new siloxane‐based nanomaterials.     

Novel structures and energy spectra of hydroxylated (SiO2)8-based clusters: searching for the magic (SiO2)8O2H3- cluster

The prominent (SiO(2))(8)O(2)H(3) (-) mass peak resulting from the laser ablation of hydroxylated silica, attributed to magic cluster formation, is investigated employing global optimization with a dedicated interatomic potential and density functional calculations. The low-energy spectra of cluster isomers are calculated for the closed shell clusters: (SiO(2))(8)OH(-) and (SiO(2))(8)O(2)H(3) (-) giving the likely global minima in each case. Based upon our calculated cluster structures and energetics, and further on the known experimental details, it is proposed that the abundant formation of (SiO(2))(8)O(2)H(3) (-) clusters is largely dependent on the high stability of the (SiO(2))(8)OH(-) ground state cluster. Both the (SiO(2))(8)O(2)H(3) (-) and (SiO(2))(8)OH(-) ground state clusters are found to exhibit cagelike structures with the latter containing a particularly unusual tetrahedrally four-coordinated oxygen center not observed before in either bulk silica or silica clusters. The bare ground state (SiO(2))(8)O(2-) cluster ion core is also found to have four tetrahedrally symmetric Si==O terminations making it a possible candidate, when combined with suitable cations, for extended cluster-based structures/materials.     

A new class of silicon-phosphorus heterocycles: 4-silaphosphorinanes

Radical reactions of Me₃SiPH₂ with Me₂Si(CHCH₂)₂ or Si(CHCH₂)₄ yield the 4-silaphosphorinanes Me₂Si(CH₂CH₂)₂PSiMe₃, (CH₂CH)₂Si(CH₂CH₂)₂PSiMe₃, or [Me₃SiP(CH₂CH₂)₂]₂Si; methanolysis of these produces quantitatively the secondary phosphorinanes Me₂Si(CH₂CH₂)₂PH, (CH₂CH)₂Si(CH₂CH₂)₂PH, or [HP(CH₂CH₂)₂]₂Si. Me₂Si(CH₂CH₂)₂PSiMe₃ with O₂/H₂O yields the phosphinic acid Me₂Si(CH₂CH₂)₂P(O)OH. All compounds are characterized by spectral data; an X-ray crystal analysis confirms the structure of Me₂Si(CH₂CH₂)₂P(O)OH.     

Eine alternative Synthese des Oligoalumosiloxans [Ph2SiO]8[Al(O)OH]4 und seiner Alkohol‐Addukte

The oligoalumosiloxanes {[Ph₂SiO]₈[Al(O)OH]₄·2,5Et₂O·HOtBu} ( 6 ) and {[Ph₂SiO]₈[Al(O)OH]₄·2Et₂O·2HOiPr} ( 7 ) have been obtained from the reaction of diphenylsilanediol with aluminium‐tri‐tert‐butoxide and aluminium‐tri‐iso‐propoxide in ethyl ether with reasonable yields. In a 1:1 molar mixture of toluene and the respective alcohol (iso‐propanol or tert‐butanol), the ethyl ether molecules in {[Ph₂SiO]₈[Al(O)OH]₄·4Et₂O}, in 6 or 7 can be completely displaced forming the compounds [Ph₂SiO]₈[Al(O)OH]₄·4HOiPr ( 8 ) and [Ph₂SiO]₈[Al(O)OH]₄·nHOtBu ( 9 ). Whereas 6 , 7 and 8 are crystalline, 9 is obtained as a viscous liquid. An X‐ray structure determination on {[Ph₂SiO]₈[Al(O)OH]₄·3Et₂O·HOtBu} reveals different bonding modes of the diethyl ether molecules to the oligoalumosiloxane compared to the tert‐butanol, which forms two hydrogen bonds (one to the OH‐group of the inner Al₄(OH)₄ cycle and one through the alcohol OH‐group to a Si–O–Al moiety. The alcohol adducts have been characterized in solution through ¹H‐, ¹³C‐ and ²⁹Si‐NMR and show dynamic equilibria between the oligoalumosiloxane [Ph₂SiO]₈[Al(O)OH]₄ and the alcohol molecules.     

Geometry optimization and electronic structures of molecules H_3AXAH_3

The geometries of molecules H_3AXAH_3(X=O,S,Se and A=C,Si)have been optimizedusing STO-3G ab initio calculations and gradient method and the results are in good agreement withreported experimental values.From the STO-3G optimized geometries,we have also calculated theelectronic structures of these molecules using 4-31G and 6-31G basis sets to obtain the MO energies.atomic net charges and dipole moments.The ionization potentials calculated by 6-31G basis set are ingood agreement with experimental values.