László Bihátsi

The molecular structure of 1-fluorosilatrane

Abstract The crystal structure of 1-fluorosilatrane has been determined by X-ray diffraction. The N → Si dative bond length is 2.042(1) A, somewhat longer than that in the 1-chloro derivative (2.023 A). The carbon atoms linked to nitrogen are disordered. The atoms in the close-packed crystal structure are well fixed and have low thermal motion. Deformation electron density calculations show considerable density in the region between the silicon and nitrogen atoms. A mass spectrometric study indicates a strong SiF bond.

The effect of the C-methyl substitution on the molecular geometry of the silatrane skeleton: The crystal structures of 1-(4′-tolyl)-silatrane and 1-(4′-tolyl)-3,7,10-trimethylsilatrane

Abstract Unsubstituted (1) and 3,7,10-trimethyl substituted (2) 1-(4′-tolyl)-silatranes were synthesized. 1H, 13C, 15N and 29Si NMR spectra were recorded and assigned. The conformation of the 2 stereoisomers in solution were characterized by the NMR spectra. 1 is monoclinic, P21/c, with a = 13.454(2), b = 13.888(2), c = 14.345(2) A, β = 99.10(2)°. The major stereoisomer fraction of 2 is orthorhombic, Pbca, with a = 12.168(2), b = 13.754(4), c = 20.260(3) A. The structures were solved by direct methods and were refined by least squares to R values of 0.039 and 0.066 for 3523 and 2158 reflexions. The N→Si distances are 1: 2.169(2) (mean) and 2: 2.236(3) A. The solid state conformation of the 2 major stereoisomer fraction is different from that in solution and this is the first example of a silatrane crystal structure where the silatrane moiety lacks C3 symmetry.

Conformational study of tetramethyl-N,N′-bis-arylcyclodisilazanes by 13C NMR and X-ray diffraction methods II. The conformation of tetramethyl-N,N′-bis(o-chlorophenyl)cyclodisilazane

Abstract The conformation of tetramethyl- N,N′ -bis( o -methoxyphenyl)cyclodisilazane was investigated by 13 C NMR in solution and by X-ray diffraction in the solid state. The conformation in solution compares to that of o -methoxyaniline. The phenyl and the cyclodisilazane ring forms a dihedral angle of 7.4° and there is a non-bonded Si ⋯ O distance of 2.73 A in the crystal. The molecular geometry suggests an analogy to S ⋯ O non-bonded interactions often observed in organosulphur chemistry.

The crystal structure of 1-m-chlorophenoxysilatrane

Summary The pentavalent silicon in the title compound is coordinated by four oxygen atoms. The N→Si dative bond is rather short (2.079(2) A). The crystal structure is partially disordered: carbon atoms attached to nitrogen appear on both sides of the Si−O(eq)−C, N plane with a population of 0.8 and 0.2, respectively. The change of the configuration around silicon and nitrogen, as a function of the N→Si dative bond length, is reviewed for several silatrane structures. Structural data suggest that different extents of the distortion of the trigonal bipyra-mid around silicon for the various compounds may represent stages along the pathway of the SN2-type reaction ≡Si−X + HN≡ → ≡Si−N≡.

Conformational study of tetramethyl-N,N′-bis-arylcyclodisilazanes by 13C NMR and X-ray diffraction methods

Abstract The conformations of tetramethyl- N , N ′-diphenylcyclodisilazane and the corresponding bis-tolylcyclodisilazanes were studied by 13 C NMR spectroscopy. The conformations of tetramethyl- N , N ′-bis- m -tolylcyclodisilazane and tetramethyl- N , N ′-bis- p -tolylcyclodisilazane were predicted by assuming additivity of substituent chemical shifts (SCS). The conformations of the m - and p -tolyl derivatives in the crystalline state were established by crystal structure analysis, and found to be identical with those determined by 13 C NMR methods in solution.

Photoelectron and Penning ionization electron spectroscopic investigation of some silazanes

Abstract Penning ionization electron spectroscopy and CNDO/S calculations have been successfully applied to the analyses of the UV photoelectron spectra of some silazanes. The relative intensities of the lone pair bands are enhanced in the Penning spectra compared with those in the UV photoelectron spectra. The intensity differences between the two spectra give useful informations for the investigation of the σ-electron systems.

UV spectroscopic investigation of N,N′-phenylcyclodisilazanes

The UV spectra of N,N′-phenylcyclodisilazanes, N-trimethylsilylaniline and N,N-bistrimethylsilylaniline have been investigated with the aid of UV and quantum mechanical calculations. The main difference between the spectra of N,N′-phenylcyclodisilazanes and that to aniline-like molecules is a strong bathochromic shift of 20–30 nm of the p-bands. This is explained in terms of significant through-space interaction between the N atoms and conjugation of in-plane phenyl groups.