Linear Si–O–Si fragments: structure of 1,1,3,3-tetramethyl-1,3-bis[(2-oxo-1-pyrrolidinyl)methyl]disiloxane dihydrochloride and analysis of displacement parameters

Shklover, V. E.; Bürgi, Hans‐Beat; Raselli, Andrea; Armbruster, Thomas; Hummel, W.

doi:10.1107/s0108768191002707

Cited by 9 publications

(1 citation statement)

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“…The oxygen atom linking the siloxane units exhibits low Lewis basicity, which results in hydrophobic material properties, whereas the analogous oxygen atom in organic ethers (R 3 C‐O‐CR 3 ) is considerably more basic . The Si‐O‐Si angle in most siloxane compounds is between 140° and 180°, which is far higher than the tetrahedral angle of about 110° adopted by ethers . In previous studies, it has been shown that decreasing the Si‐O‐Si angle leads to a significant increase in the basicity of siloxanes .…”

Section: Introductionmentioning

confidence: 99%

Covalency and Ionicity Do Not Oppose Each Other—Relationship Between Si−O Bond Character and Basicity of Siloxanes

Fugel

Hesse

Pal

et al. 2018

Chemistry A European J

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Covalency and ionicity are orthogonal rather than antipodal concepts. We demonstrate for the case of siloxane systems [R Si-(O-SiR ) -O-SiR ] that both covalency and ionicity of the Si-O bonds impact on the basicity of the Si-O-Si linkage. The relationship between the siloxane basicity and the Si-O bond character has been under debate since previous studies have presented conflicting explanations. It has been shown with natural bond orbital methods that increased hyperconjugative interactions of LP(O)→σ*(Si-R) type, that is, increased orbital overlap and hence covalency, are responsible for the low siloxane basicity at large Si-O-Si angles. On the other hand, increased ionicity towards larger Si-O-Si angles has been revealed with real-space bonding indicators. To resolve this ostensible contradiction, we perform a complementary bonding analysis, which combines orbital-space, real-space, and bond-index considerations. We analyze the isolated disiloxane molecule H SiOSiH with varying Si-O-Si angles, and n-membered cyclic siloxane systems Si H O(CH ) . All methods from quite different realms show that both covalent and ionic interactions increase simultaneously towards larger Si-O-Si angles. In addition, we present highly accurate absolute hydrogen-bond interaction energies of the investigated siloxane molecules with water and silanol as donors. It is found that intermolecular hydrogen bonding is significant at small Si-O-Si angles and weakens as the Si-O-Si angle increases until no stable hydrogen-bond complexes are obtained beyond φ =168°, angles typically displayed by minerals or polymers. The maximum hydrogen-bond interaction energy, which is obtained at an angle of 105°, is 11.05 kJ mol for the siloxane-water complex and 18.40 kJ mol for the siloxane-silanol complex.

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Section: Introductionmentioning

confidence: 99%

Covalency and Ionicity Do Not Oppose Each Other—Relationship Between Si−O Bond Character and Basicity of Siloxanes

Fugel

Hesse

Pal

et al. 2018

Chemistry A European J

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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

Beckmann

Dakternieks

Duthie

et al. 2002

Applied Organom Chemis

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Synthesis and crystal and molecular structures of cation-anionic complexes of five-coordinate silicon-containing disiloxane dications with lactamomethyl andN-methylacetamidomethyl C,O-chelating ligands

et al. 1998

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The reactions of bis(chloromethyl)dichlorosilane with N-trimethylsilyl lactams and N-trimethylsilyl-N-methylacetamide taken in a ratio of 1 : 2 followed either by treatment with HgCI 2 in the presence of atmospheric moisture or by hydrolysis under a wet atmosphere afforded cation-anionic complexes, which contain disiloxane dications of the general formula [L2SiOSiL2]2+ (L is the lactamomethyl or N-methylacetamidomethyl bidentate ligand) and hexachlorodimercurate, tetrachloromercurate, and hydroxonium trichloride counter-ions, respectively. X-ray diffraction analysis demonstrated that the disiloxane dications in these complexes contain two five-coordinate Si atoms and occur as silicenium ions stabilized through two O~Si coordination bonds. In the case of lactamomethyl ligands, the disiloxane dications exist as diastereomers whose bischelate ligands adopt opposite configurations, whereas when N-methylacetamidomethyl ligands are present, the bischelate ligands adopt identical configurations. The first example of the presence of a hydroxonium tnchloride ion as a counter-ion in the crystal has been found. It consists of the hydroxonium cation, which holds three CI-anions through strong hydrogen bonds.Key words: silicenium ions, five-coordinate silicon; cation-anionic complexes, X-ray diffraction analysis; quantum-chemical calculations, MNDO/PM3 method The possibility of stabilization of silicenium cations through intramolecular coordination bonding represents a new line of investigations of hypervalent compounds of silicon (see, for example, the review 1, Ref. 2, and references cited therein). However, the available data concern mainly compounds with C,N-chelating ligands, t,z In particular, the structures of five-coordinate silyl cations 1 3 and 2 4 of the general formula [R:SiH} +, which are stabilized through two intraionic N~Si coordination bonds, were established by X-ray diffraction analysis.Most known compounds in which the five-coordinate Si atom bears two O,O-or two C,O-chelating ligands exist as anions 5-[~ containing O4SiX or O2C2SiX coordination units (X = C or Hal). Some their germanium analogs occur also as anions. !1,12 Recently, we have studied for the first time t3 the disilicenium dication {R2SiOSiR2] 2+, which contains O3SiC 2 fragments as central coordination units, using l,t,3,3-tetrakis[(2-oxopyrrolidino)methyl]disiloxane ditrifiate (3) asan example. Its structure in the solid state was established by X-ray diffraction analysis. Conductometrie study in solution confirmed the structure of the cation.In this work, we report the results of synthesis of new cation-anionic complexes that contain disitoxane dications of the general tbrmuta {L2SiOSiL2] 2+ (k is the

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Linear Si–O–Si fragments: structure of 1,1,3,3-tetramethyl-1,3-bis[(2-oxo-1-pyrrolidinyl)methyl]disiloxane dihydrochloride and analysis of displacement parameters

Abstract: An X-ray diffraction study of 1,1,3,3-tetramethyl-1,3-bis[(2-oxo-l-pyrrolidinyl)methyl]disiloxane di-* To whom correspondence should be addressed.0108-7681/91/040544-05503.00hydrochloride, C14H30N203SizZ+.2C1 -, Mr=357

Cited by 9 publications

References 2 publications

Covalency and Ionicity Do Not Oppose Each Other—Relationship Between Si−O Bond Character and Basicity of Siloxanes

Covalency and Ionicity Do Not Oppose Each Other—Relationship Between Si−O Bond Character and Basicity of Siloxanes

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

Synthesis and crystal and molecular structures of cation-anionic complexes of five-coordinate silicon-containing disiloxane dications with lactamomethyl andN-methylacetamidomethyl C,O-chelating ligands

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Linear Si–O–Si fragments: structure of 1,1,3,3-tetramethyl-1,3-bis[(2-oxo-1-pyrrolidinyl)methyl]disiloxane dihydrochloride and analysis of displacement parameters

Abstract: An X-ray diffraction study of 1,1,3,3-tetramethyl-1,3-bis[(2-oxo-l-pyrrolidinyl)methyl]disiloxane di-* To whom correspondence should be addressed.0108-7681/91/040544-05503.00hydrochloride, C14H30N203SizZ+.2C1 -, Mr=357

Cited by 9 publications

References 2 publications

Covalency and Ionicity Do Not Oppose Each Other—Relationship Between Si−O Bond Character and Basicity of Siloxanes

Covalency and Ionicity Do Not Oppose Each Other—Relationship Between Si−O Bond Character and Basicity of Siloxanes

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

Synthesis and crystal and molecular structures of cation-anionic complexes of five-coordinate silicon-containing disiloxane dications with lactamomethyl andN-methylacetamidomethyl C,O-chelating ligands

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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