Substituent and steric effects in acyclic pentacoordinate silicon anions (siliconates)

Abstract

Substituent contributions t o t h e 19F NMR exchange barriers of a series of silicates, [RR'SiF3]-, have been measured. Both electronic a n d steric effects control t h e barriers that are measured by variabletemperature experiments and analyzed by using complete bandshape analysis. Eight new silicates, as their K+-18-crown-6 salts, were prepared a n d studied (R, R'): (1) 4-methylphenyl, 4-methylphenyl; (2) 2-methylphenyl, 2-methylphenyl; (3) p-nitrophenyl, p-nitrophenyl; (4) a-naphthyl, a-naphthyl; (5) phenyl, 2,6-dimethylphenyl; (6) phenyl, tert-butyl; (7) 2,6-dimethylphenyl, 2,6-dimethylphenyl; (8) 2-methylphenyl, 2,6-dimethylphenyl.

Exploring the Anion–Cation Interaction in m‐Terphenyltetrafluorosilicates by Using Multinuclear NMR Spectroscopy, X‐ray Diffraction, and ICR‐FT‐MS

“…Additionally, there is interaction between the cesium ion and two axial fluorine atoms of two different tetrafluorosilicate units (Cs À F1, Cs À F1': 2.918(2) ; bond length in CsF: 3.06 [28] ), which results in an increase of the corresponding SiÀF ax bond lengths (1.690(2) ) in comparison to noncoordinating SiÀF ax in Dmp-substituted fluorosilicates. As a consequence of the near linearity of the F1-Cs-F1' unit, the formation of ion channels parallel to the c axis is observed, leading to a 1D polymeric structure of fluorosilicate 2 d with a strand diameter of 5.8 and Cs···Cs' interatomic distances of (18) . Somewhat related to the first reported 1D tetrafluorosilicate polymer, in which potassium interacts with fluorine and the p system of a flanking mesityl ring of the Dmp substituent under formation of a 1D coordination polymer, [14] this is the first report of a channel-like fluorosilicate structure involving cesium.…”

“…The fluorophilicity of the metal cation can be reduced by coordination with crown ethers or cryptands, which therefore increase the stability of fluorosilicates. [17,18] In the absence of such additional ligands the nature of the countercation and its ion potential control the hydrolytic stability of the corresponding fluorosilicate. [19] Despite the importance of the hydrolysis of hypervalent flu-Abstract: The synthesis of a series of m-terphenyl-substituted tetrafluorosilicates with different cations (Na + , K + , Rb + , Cs + , Ag + , Tl + ) is described and the interactions between the anion and cation are investigated in the solid, solution, and gas states by using multinuclear NMR spectroscopy, X-ray diffraction, and ion cyclotron resonance Fourier-transform mass spectrometry (ICR-FT-MS).…”

Ligand‐site exchange in intramolecular complexes of silicon: substituent effects

“…This method does not require the knowledge of the mechanism of the ligand‐site exchange; however, it allows an understanding what substituent effects influence the free energies of activation Δ G ≠ . The Δ G ≠ values for 13 series, taken from the literature are given in Tables . In the majority of cases the free energies Δ G ≠ were calculated from the data on the coalescence of the NMR signals.…”

“…From the coalescence of these signals one can calculate the Δ G ≠ values . This approach has been developed in many publications . In specific cases (Table , Series IX, XII) the free energies Δ G ≠ are determined from results of NMR line‐shape analysis …”

Formation of Highly Ordered Nanochannel Nb Oxide by Self‐Organizing Anodization

“…The fluorophilicity of the metal cation can be reduced by coordination with crown ethers or cryptands, which therefore increase the stability of fluorosilicates 17. 18 In the absence of such additional ligands the nature of the countercation and its ion potential control the hydrolytic stability of the corresponding fluorosilicate 19. Despite the importance of the hydrolysis of hypervalent fluorosilicates in the preparation of fluoride‐enriched drinking water,20 no systematic investigation of the anion–cation interaction in such salts has been published to the best of our knowledge.…”