Two successive steps of hypercoordination at tin: The gas-phase and solid-state structures of (N,N-dimethylaminoxy)trimethylstannane Mitzel, Norbert W. Mitzel Norbert W. Losehand, U Losehand U Richardson, A Richardson A Me3SnONMe2 has been prepared from trimethyltin chloride and O-lithio-N,N-dimethyl-hydroxylamine and characterized by IR and NMR spectroscopy, mass spectrometry, and elemental analysis. Its gas-phase molecular structure has been determined by electron diffraction augmented by restraints taken from ab initio calculations at the MP2/DZ(P) level of theory. A secondary interaction (Sn ... N, 2.731(14) Angstrom) between the tin and nitrogen atoms has been detected and makes Me3SnONMe2 the first partially hypercoordinate tin compound studied in the gas phase. A solid-slate structure of Me3SnONMe2 has been determined by X-ray diffraction of an in situ grown single crystal. In the crystal lattice the coordination sphere of tin is further enlarged by a weak intermolecular Sn ... O contact (2.998(10) Angstrom) and a 4+2 coordination geometry is achieved, which can be deduced from that of a: distorted trigonal bipyramid with one of the axial substituents replaced by the two weak contacts. Important geometry parameter values are as follows (gas/solid): Sn-O 2.006(3)/2.063(6) Angstrom, O-N 1.468(6)/1.440(9) Angstrom, Sn-C(in plane) 2.148(4)/2.163(14) Angstrom, Sn-C(out of plane) 2.146(3)/2.062(9) and 2.185(10) Angstrom, Sn-O-N 102.5(8)/102.5(4)degrees, O-Sn-C(in plane) 99.6(10)/99.7(4)degrees, O-Sn-C(out of plane) 108.1(6)/119.6(4)degrees and 116.6(4)degrees. 18 14 2610-2614 2610-2614 AMER CHEMICAL SOC 1999