The compounds Me3SiONMe2 and Me3GeONMe2 have been prepared by reacting Me3SiCl and Me3GeBr with LiONMe2. Their identity was proven by gas-phase IR and solution NMR spectroscopy of the nuclei H-1, C-13, N-15, O-17, Si-29, and Ge-73 and by mass spectrometry and elemental analyses. Their molecular structures in the gas phase have been determined by analysis of electron diffraction data augmented by restraints derived from ab initio calculations. The molecules adopt C-s symmetry. Important geometry parameter values for Me3SiONMe2 are: Si-O 1.688(2), Si-Cin-plane 1.870(4), Si-Cout-of-plane 1.872(2), O-N 1.481(6) Angstrom, Si-O-N 107.9(6), O-Si-Cin-plane 102.1(6), O-Si-Cout-of-plane 110.9(7)degrees, for Me3GeONMe2: Ge-O 1.812(2), Ge-Cin-plane 1.949(3), Ge-Cout-of-plane 1.950(2), O-N 1.475(6) Angstrom, Ge-O-N 108.9(7), O-Ge-Cin-plane 101.7(6), O-Ge-Cout-of-plane 110.3(14)degrees. The structure data are interpreted in terms of weak attractive interactions between the nitrogen donor and the silicon/germanium acceptor atoms. The results are discussed in comparison with other structure data from the literature: the strength of a donor-acceptor interaction in Me3SiONMe2 is weaker than in H3SiONMe2 or ClH2SiONMe2, but stronger than in Me3SiON(CF3)(2).