Silicon Tetrahalides Research Articles

Cyanopyridine adducts of SiF4 and SiCl4

Abstract The formation of cyanopyridine (CN-py) adducts of silicon tetrahalides was investigated for 3- and 4-cyanopyridine in combination with SiF4 and SiCl4. Whereas bubbling of SiF4 through toluene solutions of 3-CN-py and 4-CN-py afforded white precipitates, which should possess the respective composition SiF4(CN-py)2, addition of SiCl4 did not cause any precipitation. Upon storage of the toluene solution of SiCl4 and 4-CN-py at 6 °C for several weeks, some crystals of the composition SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py) ⋅ (toluene) were obtained. The use of SiCl4 as the solvent (i.e. SiCl4 in large excess) and dissolving 4-CN-py therein gave access to a crystalline adduct of the composition SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py). 3-CN-py instead recrystallized from SiCl4 without forming an adduct with the silane. Computational analyses (B2T-PLYP level) of the single-point energy differences between starting materials SiX 4 (X = F, Cl) and ‘pyridine’ (‘pyridine’ = pyridine, 3-CN-py, 4-CN-py) and their adducts SiX 4(‘pyridine’)2 revealed the tendencies toward adduct formation to decrease in the order SiF4 > SiCl4 as well as pyridine >> 4-CN-py > 3-CN-py. For SiCl4 with 4- and 3-CN-py, the energy of adduct formation (−7.0 and −5.7 kcal mol−1, respectively) is easily compensated by entropy effects at room temperature. Whereas the former explains as to why cyanopyridines and SiCl4 may co-exist without noticeable adduct formation, the crystal structures of the adducts SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py) ⋅ (toluene) and SiCl4(4-CN-py)2 ⋅ 2 (4-CN-py) reveal the additional stabilization of these solids by co-crystallization with 4-cyanopyridine, which eventually enabled the isolation of the SiCl4(4-CN-py)2 moiety in a solid. Partial decomposition (hydrolysis) during attempts of recrystallization of SiF4(4-CN-py)2 and SiF4(3-CN-py)2 afforded crystals of the ionic compounds [4-CN-PyH]+[SiF5(4-CN-py)]– and [3-CN-PyH]+ 2[SiF6]2–, respectively.

Small Neutral Geminal Silicon/Phosphorus Frustrated Lewis Pairs

Two new silicon/phosphorus‐based frustrated Lewis pairs (FLP), F3SiCH2PtBu2 (1) and Cl3SiCH2PtBu2 (2) were prepared from lithiated di‐tert‐butylmethylphosphane, LiCH2PtBu2, and the corresponding silicon tetrahalides. They were characterised by NMR spectroscopy and by single‐crystal X‐ray diffraction. A gas phase electron diffraction study of 1 identified two conformers of similar energy in the vapor. The reactivity of both, 1 and 2, towards a series of small molecules was investigated. Phenyl isocyanate was found to undergo addition reactions of its C‐N unit to afford five‐membered SiCPC(O)N‐ring structures. Cl3SiCH2PtBu2 (2) was converted with perfluorophenyllithium and 3,5‐bis(trifluoromethyl)phenyllithium. The reaction with LiC6F5 resulted in the ortho‐fluoride substitution product (C6F5)2SiCH2(C6F4)PtBu2 (5), while the aryl reagent without ortho‐fluoride groups, leads to the intramolecular Lewis pair (C8H3F6)3SiCH2PtBu2 (6). The FLP reactivity of 6 was tested.

Improving the Global Electrophilicity Index (GEI) as a Measure of Lewis Acidity.

The global electrophilicity index (GEI) has been further explored as a general and base-free metric for Lewis acidity. A number of computational methods, including post-Hartree-Fock, density functional theory, and time-dependent density functional theory, have been explored. In this fashion, we sought the method most applicable to a range of different Lewis acids with differing structural and electronic features, including boron trihalides, silicon tetrahalides, fluoroaryl boranes, and group 15 pentahalides. The most accurate and computationally efficient approach was found to use the energies of the orbitals from a geometry optimization at the B3LYP/def2-TZVP level of theory. In addition, the GEI is shown to act as an effective acidity metric that is complementary to the fluoride ion affinity. The GEI also proved to be a better gauge of Lewis acidity for softer bases, as confirmed by comparison to the iodide ion affinity of the group 15 pentahalides.

Facile Syntheses of pure Uranium(III) Halides: UF3, UCl3, UBr3, and UI3

Herein we describe a convenient lab scale synthesis for pure and solvent‐free binary uranium(III) halides UCl3, UBr3, and UI3. This is achieved by the reduction of the respective uranium(IV) halides with elemental silicon in borosilicate ampoules at moderate temperature. The silicon tetrahalides SiX4 formed as a side product are utilized for the removal of excess starting material via a chemical vapor transport reaction. The syntheses introduced herein avoid the need for pure metallic uranium and are based on uranium(IV) halides synthesized from UO2 and the respective aluminum halides and purified by chemical vapor transport. These uranium(III) halides are obtained in single crystalline form. A similar reaction yields UF3 as a microcrystalline powder. However, no beneficial transport reaction occurs with this halide. Also, a higher temperature has to be applied and steel ampoules have to be used. The identities and purity of the products were checked by powder X‐ray diffraction as well as IR spectroscopy. The synthesis of UI3 enabled its crystal structure determination on single crystals for the first time. UI3 crystallizes in the PuBr3 structure type with space group type Cmcm and a = 4.3208(9), b = 13.923(3), c = 9.923(2) Å, V = 596.9(2) Å3, and Z = 4 at T = 100 K.

Crystallization by Slow Halogen Exchange in Hypercoordinate Silicon Chelates and the first X‐ray Structure of a trans‐Featured Hexacoordinate Difluorosilicon‐bis‐Chelate

AbstractStarting from silicon tetrahalides SiCl4 and SiBr4, respectively, and the bidentate 2‐iminomethylphenol‐type ligand HO‐C6H3‐2‐[C(C6H5)=N(CH2‐C6H5)]‐5‐OCH3, three novel complexes with hypercoordinate silicon atom were synthesized. Their coordination spheres consist of two halogen atoms (F, Cl, Br) and two six membered ring systems created by chelating bidentate ligands of 2‐iminomethylphenolate type. Demonstrated by crystal structure analysis, the dichloro‐ and difluorosilicon complexes {O‐C6H3‐2‐[C(C6H5)=N(CH2‐C6H5)]‐5‐OCH3}SiX2 (X = Cl, F) reveal all‐trans‐configuration in solid state. The difluorosilicon complex {O‐C6H3‐2‐[C(C6H5)=N(CH2‐C6H5)]‐5‐OCH3}SiF2 is the first X‐ray crystallographically proven example of a trans‐featured difluorosilicon‐bis‐chelate. Its all‐trans‐configuration, however, is not retained after dissolution. The formation of an octahedral complex with cis‐arranged fluorine atoms is 1H NMR spectroscopically proven by the coupling pattern of diastereotopic benzyl methylene protons of the chelating ligands.

Quantum-Chemical Study of Adducts of Silicon Halides with Nitrogen-Containing Donors: V. Adducts with 2,2'-Bipyridine and 1,10-Phenanthroline

Structural and thermodynamic characteristics of adducts of silicon tetrahalides with 2,2'-bipyridine and 1,10-phenanthroline were calculated by the DFT B3LYP method. The enthalpies of sublimation of SiCl4·2,2'-bipyridine, reconstruction energies for donor and acceptor fragments, and energies of Si-N bonds in the complexes under consideration were estimated using the data obtained. These characteristics were compared with similar data for pyridine complexes. The chelate effect on the energy of Si-N bonds upon replacement of pyridine by 2,2'-bipyridine and 1,10-phenanthroline was discussed. The significant reconstruction of the bidentate donor upon the complex formation levels off the chelate effect.

Quantum-Chemical Study of the Adducts of Silicon Halides with Nitrogen-containing Donors: II. 1 Calculation of a Donor-Acceptor Bond Energy. Complex trans -SiH 4 ·2NH 3

Structural and thermodynamic characteristics of the trans-SiH4·2NH3 adduct were obtained by ab initio and DFT (RHF and B3LYP) calculations. Scanning the potential energy surface (PES) of the com plex showed that its structure corresponds to a local minimum, whereas the global minimum corresponds to the free fragments. The energy of the silicon-nitrogen chemical bond was calculated with inclusion of fragment rearrangement energies and basis set superposition error. The procedure offered for calculating the Si-N bond energy was extended to adducts of silicon halides with ammonia. It was found that the energy of SiX4 rearrangement contributes most to the energies of donor-acceptor bonds in mono- and diammoniates of silicon tetrahalides.

A study of the threshold photoelectron spectra and the photoionisation yield curves of the silicon tetrahalides

The threshold photoelectron spectra and the photoionisation yield curves of SiF 4, SiCl 4 and SiBr 4 have been recorded in the photon energy range 10–240 eV using synchrotron radiation. The outer valence shell photoelectron bands exhibit effects due to spin–orbit splitting and to Jahn–Teller interactions, and vibrational progressions associated with the Jahn–Teller active modes have been observed. The continuous nature of the inner valence shell photoelectron bands and the absence of main-lines demonstrates the importance of electron correlation in redistributing the intensity amongst satellite states. New Rydberg series have been observed in the photoionisation yield curves associated with excitation from the valence shell, and the improved resolution has allowed some earlier assignment discrepancies to be clarified. The threshold photoelectron spectra and ion yield curves recorded at higher energies display features attributable to the Si 2p,2s, Cl 2p and Br 3p shells. The photoelectron spectra have enabled the following splittings to be measured: Si 2p–2s, Si 2p 1/2–2p 3/2, Cl 2p 1/2–2p 3/2 and Br 3p 1/2–3p 3/2, and the corresponding values are 51.21, 0.52, 1.62 and 4.6 eV, respectively. The interpretation of the features observed in the SiBr 4 spectra has been based upon previously reported assignments of similar structure in SiF 4.

Reaction of Silicon Monoxide with Coinage Metal Halides

Reaction of solid SiO with CuI, AgI, AgCl, or AgF results in the formation of the silicon tetrahalides SiX4 and elemental silver or copper. The crystal structure of SiI4 was re-determined (Si-I 2.427(2) and 2.416(4) A).

Complexes of mixed silicon halides with 4-picoline

The reaction products of an addition reaction of five different silicon tetrahalides with the aromatic nitro­gen base 4-methyl­pyridine are presented. The following five structures are isomorphous: (I) tetra­chloro­bis(4-methyl­pyridine)­silicon, C12H14­Cl4­N2Si, (II) bromo­tri­chloro­bis(4-methyl­pyridine)­silicon, C12H14­Br­Cl3N2Si, (III) di­bromo­di­chloro­bis(4-methyl­pyridine)­silicon, C12H14­Br2­Cl2N2Si, (IV) tri­bromo­chloro­bis(4-methyl­pyridine)­silicon, C12H14Br3­Cl­N2Si, and (V) tetra­bromo­bis(4-methyl­pyridine)­silicon, C12H14Br4N2Si. The mol­ecules of (I) and (V), with D2h symmetry, have crystallographic C2h symmetry, while the molecules of (II), (III) and (IV) have a lower molecular symmetry, but as a result of the disorder of the halogen ligands, they appear to be of the same crystallographic symmetry. The environment around the Si atom can be described as a slightly distorted octahedron with the methyl­pyridine ligands occupying axial positions and the four halogen ligands in the equatorial plane. In spite of the different substitution pattern of the silicon centre, there are only insignificant differences between these five structures.

Complexes of mixed silicon halides with 4-picoline

The reaction products of an addition reaction of five different silicon tetrahalides with the aromatic nitro­gen base 4-methyl­pyridine are presented. The following five structures are isomorphous: (I) tetra­chloro­bis(4-methyl­pyridine)­silicon, C12H14­Cl4­N2Si, (II) bromo­tri­chloro­bis(4-methyl­pyridine)­silicon, C12H14­Br­Cl3N2Si, (III) di­bromo­di­chloro­bis(4-methyl­pyridine)­silicon, C12H14­Br2­Cl2N2Si, (IV) tri­bromo­chloro­bis(4-methyl­pyridine)­silicon, C12H14Br3­Cl­N2Si, and (V) tetra­bromo­bis(4-methyl­pyridine)­silicon, C12H14Br4N2Si. The mol­ecules of (I) and (V), with D2h symmetry, have crystallographic C2h symmetry, while the molecules of (II), (III) and (IV) have a lower molecular symmetry, but as a result of the disorder of the halogen ligands, they appear to be of the same crystallographic symmetry. The environment around the Si atom can be described as a slightly distorted octahedron with the methyl­pyridine ligands occupying axial positions and the four halogen ligands in the equatorial plane. In spite of the different substitution pattern of the silicon centre, there are only insignificant differences between these five structures.

Komplexe gemischter Siliciumhalogenide mit 3,4-Lutidin / Complexes of Mixed Silicon Halides with 3,4-Lutidine

Abstract The first single crystal X-ray investigations of 3,4-lutidine complexes with mixed silicon tetrahalides were carried out

Halogen exchange and expulsion: ligand stabilized dihalogen silicon dications

The first ligand stabilized SiCl22+ dications were synthesized using N-methylimidazole as co-ordinating ligand. The compounds SiCl4, SiBr2Cl2, and SiH2Cl2 form six-co-ordinated dicationic compounds of almost octahedral symmetry with similar structures which were investigated by single crystal X-ray analysis and density functional calculations. The structures exhibit particularly short dative Si–N bonds of about 1.90 Å. Complexes crystallized from the same solvent are isostructural. A different solvent, though, leads to geometrical variations. It was also discovered that the halogen exchange process among mixed silicon tetrahalides occurs under much milder conditions than previously thought and proceeds with considerable speed even without a catalyst.

Spin—orbit effect on the magnetic shielding constant using the ab initio UHF method: silicon tetrahalides

The 29Si NMR chemical shifts of silane, SiH 4, and silicon tetrahalides, SiX 4 (X = F, Cl, Br and I) and SiXI 3 (X = Cl and Br), are calculated by the ab initio unrestricted Hartree-Fock/finite perturbation method including the spin-orbit (SO) interaction proposed previously. The SO effect is included through the effective core potentials for the halogens. The chemical shifts calculated with the SO effects show good agreement with experiment for all the compounds studied. The SO effects of the halogen ligands, especially of bromine and iodine, are large and move the chemical shift to higher magnetic field. The inverse halogen dependence on the substitution of F by Cl is derived from the paramagnetic term, but the normal halogen dependence on the substitution from Cl to I is caused mainly by the SO effect.

A study on the reaction of silicon tetrahalides with phosphorus pentoxide and of alkali metal fluorosilicates with phosphorus pentoxide and sulphur trioxide

Silicon tetrahalides, SiX 4 (X=F, Cl, Br) and the fluorosilicates of sodium and potassium react with phosphorus pentoxide above 300°C. The tetrahalides give rise to the corresponding phosphoryl halides and silica, while the fluorosilicates form the corresponding metal fluorophosphates and silicon tetrafluoride. The reaction of the fluorosilicates of sodium and potassium with sulphur trioxide occurs at room temperature to give rise to the corresponding metal fluorosulphates and silicon tetrafluoride.

The I.R. Spectra of Matrix‐isolated SiBr2 and SiCl2

AbstractThe divalent silicon species SiBr2 and SiCl2 were produced by the reaction of the corresponding silicon tetrahalides with elemental silicon at temperatures between 900 and 1150°. The I.R. spectra of these molecules trapped in different matrices (Ne, Ar, N2) were observed, and the fundamentals assigned. A set of valence force constants and the bond angles were obtained from accurate measurements of chlorine and silicon isotopic splittings.

Reaction of silicon tetrahalides with methyl amines

The interaction of silicon tetrahalides (Cl, Br, I) with methyl amines leads to the formation of substances having the stoichiometry SiX 4·6 amine. These substances are not adducts, but are a mixture of amine hydrogen halide and an appropriate silicon-nitrogen condensed species. With SiF 4 only adducts are formed at room temperature.

A reinvestigation of the enthalpies of reaction of silicon, germanium, and tin tetrahalides with pyridine and isoquinoline

Enthalpies of formation of crystalline MX4,2L complexes (where M = Si, Ge, or Sn; L = pyridine or isoquinoline; X = F, Cl, or Br, except X = Cl only when M = Sn) have been redetermined with a more sensitive calorimeter and improved techniques to exclude water impurity. Contrary to previous results, values do not vary greatly in each series of related adducts, except for the order GeF4,2L > SiF4,2L.

Heats of reaction of silicon, germanium, and tin tetrahalides with pyridine and isoquinoline

Heats of formation of crystalline MX4,2L complexes (where M = Si, Ge, or Sn; L = pyridine or isoquinoline; X = F, Cl, or Br, except X = Cl only when M = Sn) have been measured calorimetrically. Values decrease in the order MF4 > MCl4 > MBr4, GeX4 > SiX4, and SnCl4 > GeCl4 > SiCl4, except that those for SiCl4,2py and SiBr4,2py are abnormally high. Comparisons are drawn with results from other sources and attempts are made to explain the observed orders.

672. The stereochemistry of some addition compounds of silicon tetrahalides

Download options Please wait... Article information DOI https://doi.org/10.1039/JR9650003672 Article type Paper Download Citation J. Chem. Soc., 1965, 3672-3678 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions 672. The stereochemistry of some addition compounds of silicon tetrahalides I. R. Breattie and M. Webster, J. Chem. Soc., 1965, 3672 DOI: 10.1039/JR9650003672 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author I. R. Breattie M. Webster