THE PYRAMIDAL SI2N-O SKELETON OF O-METHYL-N,N-DISILYLHYDROXYLAMINE - AN INHERENT PHENOMENON AS CONFIRMED BY STRUCTURAL STUDIES IN DIFFERENTPHASES

O-Methyl-N,N-disilylhydroxylamine, (H3Si)(2)NOCH3 (1), has been prepar ed by the reaction of bromosilane with O-methylhydroxylamine in the pr esence of 2,6-lutidine. The compound has been found to be reasonably s table at ambient temperature, but explodes if heated to 200 degrees C. 1 has been completely characterized by MS, HRMS, IR in the solid stat e and gas phase, and NMR spectra of the nuclei H-1, C-13, N-14/15, O-1 7, and Si-29. The NMR chemical shifts are compared with those of Si-me thylated derivatives and with values obtained in high-level ab initio calculations. It has been concluded that there is close similarity bet ween the structure in solution and the calculated one. A single crysta l of 1 grown in situ and studied by X-ray diffraction is orthorhombic, space group P2(1)2(1)2(1), a = 6.3664(11) Angstrom, b = 8.488(2) Angs trom, c = 11.783(4) Angstrom, rho(calc) = 1.119 g cm(-1), Z = 4. Inter molecular Si ... O interactions (2.92 Angstrom) are found in the solid state structure leading to a zigzag type aggregation of the molecules . The gas phase structure of 1 has been determined by electron diffrac tion showing the molecule to have C-S symmetry. In both phases, the cr ystalline and the gas phase, the nitrogen atom configuration of 1 is p yramidal [<Sigma < (N) GED 351.8(12)degrees XRD 352.8(3)degrees], show ing this to be an inherent feature of N-silylated hydroxylamines and n ot caused by packing farces. Most of the geometrical parameters are co nsistent for both phases showing that the intermolecular Si O interact ions cause only minor structure distortions. The structural results ar e discussed in comparison with nb initio calculated geometries, and it is concluded that the exceptional nitrogen configuration is caused by repulsion between the nitrogen and oxygen lone pairs of electrons.