Si Coordination Bond Research Articles

Synthesis, experimental and computational studies of new (trifluorosilyl)propyl derivatives of cyclic imides of dicarboxylic acids

New (trifluorosilyl)propyl derivatives of cyclic dicarboxylic acid imides 1-[3-(trifluorosilyl)propyl]pyrrolidine-2,5‑dione, 1-[3-(trifluorosilyl)propyl]piperidine-2,6‑dione and 2-[3-(trifluorosilyl)propyl]-1H-isoindole-1,3(2H)‑dione were synthesized and structurally characterized by FTIR, NMR spectroscopy, mass spectrometry and elemental analysis. Intramolecular coordination interaction O→Si and the influence of the hydrocarbon chain length on the strength of the coordination interaction in Si-fluoroethyl and Si-fluoropropyl derivatives of cyclic imides of dicarboxylic acids were characterized by DFT calculations. The geometric, energetic and electronic characteristics of the investigated molecules were also determined. The intramolecular O→Si coordination bond, closing the six-membered chelate cycle SiCCN(C=O), is observed in the (trifluorosilyl)ethyl derivative phthalimide in the gas, and in the (trifluorosilyl)ethyl derivative succinimide the O→Si coordination bond is observed both in the gas phase and in DMSO solution. The coordination bond O→Si, closing the seven-membered chelate cycle SiCCCN(C=O), is found in the (trifluorosilyl)propyl derivative succinimide in the gas phase. Quantum chemical calculations were carried out at the M06/6–311G** and MP2/6–311++G**//M06/6–311G** levels with the 6–311G** basis set.

Tailoring Anti-Impact Properties of Ultra-High Performance Concrete by Incorporating Functionalized Carbon Nanotubes

Replacing micro-reinforcing fibers with carbon nanotubes (CNTs) is beneficial for improving the impact properties of ultra-high performance concrete (UHPC); however, the weak wettability and dispersibility of CNTs and the weakly bonded interface between CNTs and UHPC limit their effectiveness as composites. Therefore, this study aims to enhance the reinforcement effect of CNTs on the impact properties of UHPC via functionalization. Unlike ordinary CNTs, functionalized CNTs with carboxyl or hydroxyl groups can break the Si–O–Ca–O–Si coordination bond in the C–S–H gel and form a new network in the UHPC matrix, effectively inhibiting the dislocation slip inside UHPC matrix. Furthermore, functionalized CNTs, particularly carboxyl-functionalized CNTs, control the crystallization process and microscopic morphology of the hydration products, significantly decreasing and even eliminating the width of the aggregate–matrix interface transition zone of the UHPC. Moreover, the functionalized CNTs further decrease the attraction of the negatively charged silicate tetrahedron to Ca 2+ in the C–S–H gel, while modifying the pore structure (particularly the nanoscale pore structure) of UHPC, leading to the expansion of the intermediate C–S–H layer. The changes in the microstructures of UHPC brought about by the functionalized CNTs significantly enhance its dynamic compressive strength, peak strain, impact toughness, and impact dissipation energy at strain rates of 200–800 s −1 . Impact performance of UHPC containing a small amount of carboxyl-functionalized CNTs (especially the short ones) is generally better than that of UHPC containing hydroxyl-functionalized and ordinary CNTs; it is even superior to that of UHPC with a high steel fiber content.

Bioinspired fluorescent molecules realize super bright blue luminescence under sunlight

In recent years, non-aromatic fluorescent materials have attracted widespread attention, but achieving a high quantum yield (QY) in their dilute solutions still remains a challenge. In this work, inspired by the Clustering-triggered emission (CTE) phenomenon of non-aromatic amino acids and poly(amino acids), we successfully designed a bioinspired molecule with a dipeptide-like structure and active silanol groups. The as-prepared bioinspired molecule can be hydrolyzed by simple heating to obtain the hydrolysate h-PDs, which can emit strong blue fluorescence in dilute solution. And this was the first time to realize the emission behavior of non-aromatic fluorescent materials under sunlight. The QY of h-PDs in aqueous solution and solid state were as high as 98.2% and 96.3%, respectively, which were attributed to the condensation of active silanol groups at the end of the molecule, and the existence of hydrogen bonds and N → Si coordination bonds that made small molecules cross-linked and aggregated into dense clusters. Finally, the application of h-PDs in the detection of intracellular and exogenous Hg2+ and Cys and luminescent films were also explored. Significantly, this work provides a design strategy for synthesizing high-fluorescence QY non-aromatic fluorescent materials, and verifies their potential application value in the fields of environment, biology and light-emitting devices.

An unconventional chromophore in water-soluble polysiloxanes synthesized via thiol-ene reaction for metal ion detection

The unconventional chromophore S → Si coordination bonds is firstly found in water-soluble comb polysiloxanes (PETHs) with different ratios of polyether and mercaptopropyl groups as side chains. The PETHs are synthesized via efficient thiol-ene click reaction between polymercaptopropylmethylsiloxane (PMMS) and 2,5,8,11,14,17,20,23-octaoxahexacos-25-ene. The fluorescence is preliminarily assumed to be generated from through-space charge transfer because the S → Si coordination bonds make it easier to occur. The existence of S → Si coordination bonds is firstly proved by experiments, including synthesizing model compound and testing via quantum-chemical modeling (Digambara Patra, 2001), Si NMR, XPS spectra, and fluorescence spectra. Furthermore, the changing law of fluorescence intensity of those compounds with temperature, concentration and solvent are investigated. Fluorescence intensity improves with the temperature dropped down. This unconventional chromophore shows the AIEE (Valeur and Berberan-Santo, 2017) (aggregation-induced emission enhancement) phenomenon. The mercapto and thioether groups in PETHs can act on Hg2+ and Fe3+, breaking the SiS interaction and quenching the fluorescence. The quenching constant is determined by the Stern–Volmer equation. Therefore, the PETHs are used as fluorescence probes for Hg2+ and Fe3+ in water which may be applicable to metal detection.

Crystal structure of 2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undec-1-ylmethyl-2-methylacrylate

The XRD method is used to determine the molecular and crystal structure of 2,8,9-trioxa-5-aza-1-silabicyclo[3.3.3]undec-1-ylmethyl-2-methylacrylate (H2C=C(Me)C(O)OCH2Si(OCH2CH2)3N). The crystallographic data are as follows: space group Р212121, а = 9.7659(1) A, b = 10.017(1) A, с = 17.915(2) A, V = 1753.3(3) A3, Z = 4. The coordination polyhedron of the silicon atom is a distorted trigonal bipyramid. The length of the N→Si coordination bond is 2.099 A.

Unexpected Strong Blue Photoluminescence Produced from the Aggregation of Unconventional Chromophores in Novel Siloxane–Poly(amidoamine) Dendrimers

Poly(amidoamine) (PAMAM) dendrimers and hyperbranched poly(amidoamine)s are the first reported and most investigated luminescent polymers containing unconventional chromophores. The luminescence of these compounds is associated with the N-branched tertiary amine moiety, and the oxidation of the tertiary amine is assigned to the emitting source. However, in this paper, a series of novel siloxane–poly(amidoamine) (Si-PAMAM) dendrimers were synthesized by aza-Micheal reaction, and strong blue photoluminescence was observed even with the naked eye when these compounds were excited by a UV lamp. All of these compounds were not oxidated at all. Studies on the molecular structure showed that N → Si coordination bonds existed in these compounds, and those N → Si bonds caused the aggregation of carbonyl groups which show the strong luminescence.

Controllable photophysical properties and self-assembly of siloxane-poly(amidoamine) dendrimers.

Poly(amidoamine) dendrimers are typical luminescent polymers containing unconventional chromophores. A series of novel siloxane-poly(amidoamine) (Si-PAMAM) dendrimers were synthesized and investigated in this study. Their structures and properties were determined by NMR, XPS, LC/MS, and fluorescence spectroscopy. The introduction of Si-O-Si units in Si-PAMAM changed the photophysical properties of the dendrimers. The luminescence of Si-PAMAM was associated with the aggregation of its carbonyl groups, which was caused by N → Si coordination bonds. The strong blue luminescence of Si-PAMAM was also studied in detail, and it was found to be quite different from the ethanediamine-based poly(amidoamine). Results indicated that the luminescence of Si-PAMAM could be controlled by solvents, acids, metal ions, temperature, or degree of aggregation of the carbonyl groups. Moreover, micron-sized tubes composed of Si-PAMAM molecules were generated and found in water/methanol solution.

Crystal and molecular structure of 4-chloro×(benzoyloxymethyl)trifluorosilane at 120 K

The crystal and molecular structure of 4-chloro(benzoyloxymethyl)trifluorosilane 4-ClC6H4COOCH2SiF3 was redetermined using X-ray diffraction. The coordination polyhedron of the silicon atom in this structure is a trigonal bipyramid. The length of the axial O → Si coordination bond is 2.074(1) A.

Synthesis and structure of (C=O→Si←O′=C′)bis(2-methyl-4-oxopyran-3-yloxy)difluoro-(λ6)siliconium

A new six-coordinate silicon compound, (C=O→Si←O′=C′)bis(2-methyl-4-oxopyran-3-yloxy)-difluoro(λ6)siliconium, containing two five-membered rings closed by C=O→Si coordination bonds, forms o protodesilylation trifluoro(phenyl)silane with 3-hydroxy-2-methylpyran-4-one (maltol). According to multinuclear NMR and IR spectral data and quantum-chemical calculations, the silicon atom in this compound has an octahedral environment with two cis-arranged C=O→Si bonds

Si-Fluoro substituted quasisilatranes (N→Si) FYSi(OCH2CH2)2NR

The reaction of fluorosilanes XYSiF2 (X = Y = F; X = F, Y = Ph; X = Ph, Y = Me) with diethanolamines and their O-trimethylsilyl derivatives affords novel Si-fluoro substituted quasisilatranes 3, 5 and 9. These compounds were characterized by the multinuclear NMR spectroscopy and X-ray diffraction analysis. Experimental and theoretically calculated electron density distribution functions in crystal structure of 9 have shown that the N ? Si coordination bond corresponds to polar bond with pronounced ionic contribution. Calculated N ? Si bond order in the compound 9 does not exceed 1/3 of the normal Si–N bond. A strong N ? Si coordination bond exists in compounds 3, 5 and 9 the length of which varies in the range 1.98–2.175 A. 2008 Published by Elsevier B.V.

N,N,N′,N′,N″‐Pentamethyl‐N″‐[(trifluorosilyl)methyl] phosphoric triamide. First example of the existence of intramolecular PO→Si coordination bond in the Si‐containing phosphoric triamides

AbstractThe N,N,N′,N′,N″‐pentamethyl‐N″‐(trifluorosilylmethyl)phosphoric triamide OP(NMe2)2N(Me) CH2SiF3 with intramolecular PO→Si coordination was formed by the reaction of N,N,N′,N′,N″‐pentamethyl‐N″[(triethoxysilyl)methyl]phosphoric triamide with BF3·Et2O. Copyright © 2007 John Wiley & Sons, Ltd.

Intramolecular O → Si donor-acceptor interaction in R2P(=O)CH2CH2SiF3 molecules: Synthesis of dialkyl [2-(trifluorosilyl)ethyl]phosphonate and bis[(chloromethyl)dimethylsilyl] styrylphosphonate

The reaction of diethyl [2-(triethoxysilyl)ethyl]phosphonate with boron trifluoride etherate was used to synthesize diethyl [2-(trifluorosilyl)ethyl]phosphonate. The reaction of bis(trimethylsilyl) styrylphosphonate with chloro(chloromethyl)dimethylsilane gave bis[(chloromethyl)dimethylsilyl] styrylphosphonate. Multinuclear 1H, 13C, 19F, 29Si, and 31P NMR spectroscopy established the absence of a P=O → Si coordination bond in these compounds and the four-coordinate state of the silicon atom. Evidence for this finding was obtained by B3LYP/6-31G(d) quantum-chemical calculations. However, the same calculations for R2P(=O)· CH2CH2SiF3 (R = Me, Me2N) showed the presence in such molecules of an O → Si coordination bond both in the gas phase and in CHCl3 solution. The distance between the O and Si atoms in this series molecules decreases with R in the order: MeO > Me > Me2N. The axial Si-F bond length increases in the same order and parallels the order of the Hammet σ 0 m constants of these substituents, relating to their interaction with π-electron systems.

Donor-stabilized silyl cations: Part 7: Neutral hexacoordinate and ionic pentacoordinate silicon chelates with N-isopropylideneimino-acylimidato ligands

Silicon complexes with a new chelating donor group, the isopropylideneimino-acylimidato( N, O) moiety [OC(R)NNCMe 2], have been prepared ( 9– 12, 15), and their properties are compared with previously described silicon chelates ( 1, 2, and 16, respectively). The new ligand acts as a more powerful donor than the NNMe 2 ligand, based on three criteria: (a) the new complexes form directly as pentacoordinate siliconium salts 9– 12, i.e., the expected neutral hexacoordinate precursors ionize spontaneously; (b) comparison of crystallographic bond lengths with those of the NNMe 2 complexes shows consistently shorter NSi coordination bonds and longer Sihalogen bonds in equally substituted new relative to the previously studied complexes; (c) while in the previous series 1, the dihalo complexes 20– 22, 25, resisted ionization at any temperature or solvent, the dibromo-isopropylideneimino complexes 19a and 19b ionize reversibly upon decrease of temperature in chloroform solution. Steric congestion forces the trans-dihalo configuration on the dichloro and bibromo complexes 18, 19. The ionization-resistant complexes 17, 18 and the partly ionized 19 form stable ionic siliconium salts when their counterions are replaced by I −, BPh 4 −, or by reaction with strong Lewis acids, AlCl 3 and AlBr 3.

N-substituted (3-aminopropyl)trifluorosilanes and [3-(trifluorosilyl)propyl]diorganylamine-trifluoroboranes

The possibility of the formation of an intramolecular N ,Si coordination bond in (3-aminopropyl)triethoxysilane and its N-substituted derivatives has been discussed previously [1-4]. The likelihood of the existence of an N ,. Si bond in (3-aminopropyl)trifluorosilane and its N-substituted derivatives is beyond doubt because of the high electrophilicity of the silicon atom linked to the three fluorine atoms. However, such compounds have not yet successfully prepared.

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

The reactions of bis(chloromethyl)dichlorosilane withN-trimethylsilyl lactams andN-trimethylsilyl-N-methylacetamide taken in a ratio of 1∶2 followed either by treatment with HgCl2 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 orN-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 whenN-methylacetamidomethyl ligands are present, the bischelate ligands adopt identical configurations. The first example of the presence of a hydroxonium trichloride ion as a counter-ion in the crystal has been found. It consists of the hydroxonium cation, which holds three Cl− anions through strong hydrogen bonds.

Unusual Spin−Spin Interactions across the Coordination Bond in Hexacoordinate Silicon Complexes: Crystal-Structure Coupling Relationship

Two-, three-, and even four-bond coupling constants are reported for the first time across the N→Si coordination bond in neutral, hexacoordinate silicon chelates. Two-bond coupling constants depend critically on bond angles, and three-bond couplings follow a Karplus-type correlation with dihedral angles obtained from X-ray crystallographic analyses.