Synthesis and crystal and molecular structures of six-coordinate tin dibromides and diiodides containing lactamomethyl C,O-chelating ligands

New (O-Sn)-bischelate bis(lactamomethyl)dibromo- and -diiodostannanes [L-(n )](2)SnX2 (L is the bidentate lactamomethyl C,O-chelating ligand; n is the size of the lactam ring, 5-7; X = Br or I) were prepared both by the direct method from metallic tin and the corresponding N-(halomethyl)lactams and b y the reactions of dichlorides [Li(n)](2)SnCl2 with lithium halides. Accord ing to the data of X-ray diffraction analysis, the tin atom in [L-(n)](2)Sn Br2 (n = 5-7) and [L-(n)](2)SnI2 (n = 5 or 6) adopts an octahedral configur ation with the carbon atoms in Irans positions and the coordinating oxygen and halogen atoms in cis-positions with respect to each other. A comparison with the structures of analogous lactamomethyl halide derivatives of five- and six-coordinate Si, Ge, and Sn demonstrates that the spatial structures of the hypervalent fragments containing six-coordinate atoms are less sens itive to the replacement of the halide ligands and the central atom. The co valence of the M-Hal bond increases and the covalence of the M-O bond decre ases in the series M = Si, Ge, and Sn.