Four-coordinate Silicon Research Articles

Reaction of LTA and FAU zeolites with NH 4H 2PO 4 melts yields crystalline NH 4AlP 2O 7

Study of the reaction of zeolites A (LTA), and X and Y (FAU) with NH 4H 2PO 4 melts at 230°C for varying time periods (30 min to 36 h) found the final product formed in each case to have a powder X-ray diffraction pattern consistent with ammonium aluminum pyrophosphate, NH 4AlP 2O 7, the single crystal structure of which has not been reported. No intermediate crystalline phases were detected. 29Si MAS NMR confirmed, however, that some Si was still present, and X-ray photoelectron spectroscopy revealed it to be located primarily at the crystallite surfaces. The crystallites were found to have an extremely low surface area (ca. 10m 2g −1), and hence not to be porous. MAS NMR studies found it to consist of six-coordinate aluminum and four-coordinate phosphorus in the aluminum pyrophosphate, and four-coordinate silicon in a highly siliceous environment. These results contradict the previous report of this reaction producing ‘phosphated aluminosilicates in which phosphorus substitutes into the zeolite framework sites thereby forming promising anion exchangers’ (A. Dyer, S.A. Malik, A. Araya, T.J. McConville, in: P.A. Williams, M.J. Hudson (Eds.), Recent Developments in Ion Exchange (Pap. Int. Conf. Ion Exch. Processes), 1987, pp. 257–263.).

ISOLATION OF THE FIRST ANIONIC FIVE-COORDINATED SILICATES WITH SIX-AND SEVEN-MEMBERED OXYGEN-CONTAINING RINGS

Abstract Reaction of PhSi(OMe)3 with KOMe and naphthalenediol led to the first five-coordinated anionic silicate with an oxygen-containing six-membered ring, [(C10H6O2)2Si(C6H5)][K, 18-c-6] (1). Reaction of the tetracoordinate spirocyclic silane (C12H8O2)2Si with either KO-t-Bu or KF in the presence of 18-crown-6 led to the isolation of the first five-coordinated anionic silicates with seven-membered oxygen-containing rings, [(C12H8O2)2SiR][K, 18-c-6], R = O-t-Bu (2), F (3). 29Si NMR spectroscopy shows that the five-coordinated silicates 2 and 3 slowly disproportionate into four-coordinate silicon compounds and organic species lacking any silicon. Syntheses similar to that for 2 and 3 conducted with other ligands containing the isopropoxy group or use of Bu4N+F− in place of potassium 18-crown-4 imparts less stability to the system and leads directly to the formation of anionic organic products consisting of two biphenolate species hydrogen bonded to each other. In the case of [(C12H8O2)2H3][(n-Bu)4N] (5) ...

Molecular dynamics of silica at high pressures: Equation of state, structure, and phase transitions

Abstract A molecular dynamics computer simulation of melting of stishovite was performed, using the potential of Tsuneyuki, Tsukuda, Aoki, and Matsui. The simulated melting is in accordance with the latest assessment of thermodynamics of stishovite and melt, and is also in good agreement with recent experimental data on coesite-stishovite-melt transformations. The pressure-volume-temperature data on stishovite and melt ( P = 1 bar-200 GPa; T = 300–5000 K) are fitted with the high-temperature form of Birch-Murnaghan equations of state. Calculations with these equations of state are generally in good agreement with the available experimental data. The molecular dynamics-simulated equations of state for silica phases provide constraints for extrapolation of the PVT properties to high temperatures and pressures. Structural analysis shows that the melting transition of stishovite coincides with a transition from six-coordinated silicon to mainly four-coordinated silicon. Coordination number of silicon increases with increasing pressure along the melting curve.

Observation of a simple lithium-associated electron trap in crystalline SiO2.

A defect consisting of an extra electron trapped at a four-coordinated silicon atom and stabilized by an adjacent interstitial lithium ion has been observed in quartz. It is formed by a double irradiation, first between 150 and 300 K to release the lithium ion from its associated ${\mathrm{Al}}^{3+}$ and then at 77 K to trap an electron at the free lithium ion. The $c$-axis ESR spectrum shows a splitting of 0.9 G from a $^{7}\mathrm{Li}$ and 404.7 G from a $^{29}\mathrm{Si}$ (thus, the defect does not resemble a lithium atom). Pairs of these defects may be responsible for the lack of electronic paramagnetism in quartz after room-temperature irradiation.

The Crystal and Molecular Structure of Bis(1,8-naphthalenedioxy) silane, a Contribution to the Controversy over Planar, Four-Coordinated Silicon in Orthosilicic Acid Esters

Angewandte Chemie International Edition in EnglishVolume 22, Issue S6 p. 668-674 Communication The Crystal and Molecular Structure of Bis(1,8-naphthalenedioxy) silane, a Contribution to the Controversy over Planar, Four-Coordinated Silicon in Orthosilicic Acid Esters† Dr. J. W. Bibber, Dr. J. W. Bibber Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Search for more papers by this authorDr. C. L. Barnes, Dr. C. L. Barnes Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Search for more papers by this authorProf. D. van der Helm, Prof. D. van der Helm Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Search for more papers by this authorProf. J. J. Zuckerman, Corresponding Author Prof. J. J. Zuckerman Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Search for more papers by this author Dr. J. W. Bibber, Dr. J. W. Bibber Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Search for more papers by this authorDr. C. L. Barnes, Dr. C. L. Barnes Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Search for more papers by this authorProf. D. van der Helm, Prof. D. van der Helm Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Search for more papers by this authorProf. J. J. Zuckerman, Corresponding Author Prof. J. J. Zuckerman Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Department of Chemistry, University of Oklahoma, Norman, OK 73019 (USA)Search for more papers by this author First published: June 1983 https://doi.org/10.1002/anie.198306680Citations: 2 † Our work is supported by the U.S. Office of Naval Research and by the U.S. National Science Foundation through Grant CHE-78-26548 (J.J.Z.) and by the U.S. National Cancer Institute through Grant CA-17562 (D.v.d.H). We thank the University of Oklahoma for providing computer time. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume22, IssueS6Supplement: Complete manuscripts of selected Communications in issue 6/1983June 1983Pages 668-674 RelatedInformation

Planar Four‐Coordinated Silicon?

Planar Four‐Coordinated Silicon?