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New (O--Sn)-bischelate bis(lactamomethyl)dibromo-and -diiodostannanes [L(n)I2SnX 2 (L is the bidentate lactamomethyt C,O-chelating ligand: n is the size of the lactam ring, 5--7; X = Br or 1) were prepared both by the direct method from metallic tin and the corresponding N-(halomethyl)lactams and by the reactions of dichlorides [k(n)]2SnCI 2 with lithium halides. According to the data of X-ray diffraction analysis, the tin atom in {L(n)I2SnBr2 (n = 5--7) and [L(nqzSnl2 (n = 5 or 6) adopts an octahedral configuration with the carbon atoms in trans positions and the coordinating oxygen and halogen atoms in cispositions with respect to each other. A comparison with the structures of analogous lactamomethyl halide derivatives of Give-and six-coordinate Si, Ge. and Sn demonstrates that the spatial structures of the hypetwalent fragments containing six-coordinate atoms are less sensitive to the replacement of the halide ligands and the central atom. The covalence of the M--Hal bond increases and the covalence of the M--O bond decreases in the series M = Si, Ge, and Sn.Key words: six-coordinate tin compounds, synthesis, multinuclear N MR spectroscopy. X-ray diffraction study.Recentl3/~ we l~ave perforrfled sy~femati~ StudiesO1 s-ix= coordinate silicon, germanium, and tin compounds containing the amidomethyl and related C,O-chelating ligands. !-4 These studies were an extension of investigations of analogous five-coordinate silicon 5,6 and germanium 7,8 derivatives. One of the major lines of investigation of the characteristic features of these compounds involves the elucidation of the properties of three-center hypervalent X--:M::Y-bonds, where-Mis an atom with-an increased coordination number (Si, Ge, or Sn) and X and Y are electronegative atoms or groups (N--C=O, Hal, OTf, etc.).Investigations of tin derivatives as compounds containing six-coordinate atoms allow one to reveal the effects of the involvement of the M atom simultaneously in two hypervalent bonds and to follow the dependence of the properties of these bonds in the series M = Si, Ge, and Sn.

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