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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.

Germylated steroids were studied by X-ray diffraction analysis for the first time. The conformational parameters of the molecules in the crystals are discussed. The three-center hypervalent O--Ge--CI bonds are observed in two ~-isomers. The geometric parameters of the hypervalent units are compared.Key words: X-ray diffraction analysis; steroids, germanium derivatives, hypervalent bond.Steroids belong to one of the most important classes of natural biologically active compounds. Previously, we for the first time synthesized steroids modified with germanium by hydrogermylation of the double bond. t Fused steroid enones, namely, 3!3-acetoxy-5ct-pregn-16*en-20-one (1) and 3is-acetoxypregna-5,16-dien-20-one (2), were objects of studies. Addition of HGeCI 3 at the 6 t6 double bond of the above enones afforded two stereoisomers (of four theoretically possible isomers), namely, 3is-acetoxy-16ct-trichlorogermyl-5c~-pregnan-20-one (3) and 3 in the case of enone 1 and 3~-acetoxy-16c~-trichlorogermylpregn-5-en-20-one (5) and 31~-acetoxy16is-trichlorogermylpregn-5-en-20-one (6) in the case of enone 2.The crystal and molecular structures of three synthesized compounds 4--6 were established by X-ray diffraction analysis. Therefore, addition of trichlorogermane at the conjugated A 16 double bond of steroids afforded not only a-isomers, which is typical of the chemistry of steroids, but also IS-isomers. The formation of the latter is attributable to the benefit from the coordination bond between the Ge atom and the O atom of the carbonyl group.