TRIORGANOTIN COMPOUNDS SNXME2-1,4-CYCLOHEXADIENE-COOME - INTRAMOLECULAR AND INTERMOLECULAR UNFOLDING OF AN INNER TETRAHEDRON TO DISTORTED TRIGONAL BIPYRAMIDS (X = CL, BR, I) AND A DISTORTED OCTAHEDRON (X = F)

A series of (2-carbomethoxy-1,4-cyclohexadien-1-yl)dimethyltin halides (SnXMe2-CHD-COOMe with X = F, Cl, Br, I (1b-e)) has been synthesized by halodemetalation of the related trimethyltin derivative X = Me (1a). The structure determination of compound 1b gave the monoclinic space group C2 (a = 16.255 (2), b = 7.488 (3), c = 9.946 (1) angstrom; beta = 100.53 (1)-degrees; V = 1190 (1) angstrom 3; Z = 4; R = 0.0443). The isostructural compounds 1c and 1d have the triclinic space group P1BAR (a = 7.465 (2); b = 8.896 (1); c = 9.615 (1) angstrom; alpha = 85.27 (1), beta = 88.56 (1), gamma = 77.56 (2)-degrees; V = 621 (2) angstrom 3; Z = 2; R = 0.0340 and a = 7.49 (1), b = 8.89 (1), c = 9.88 (2) angstrom; alpha = 85.4 (2), beta = 89.2 (1), gamma = 77.56 (2)-degrees; V = 621 (2) angstrom 3; Z = 2; R = 0.0825). Compound 1e crystallizes in the monoclinic space group P2(1)/c (a = 7.988 (3), b = 15.016 (2), c = 11.470 (1) angstrom; beta = 95.81 (1)-degrees; V = 1369 (1) angstrom 3; Z = 4; R = 0.0502). 1c-e exhibit five-coordination around tin, and 1b reveals six-coordinated dimers with Sn...O contacts and an additional Sn...F contact in the latter case. Hence, 1b forms the first hexacoordinated triorganotin compound with a coordinative tin-oxygen bond. The lengthening of Sn-X in relation to the single bond distances increases in the order F << Cl < Br < I. The coordinating Sn...O distances run in the order F > Cl = Br > I with the shortest Sn...O distance of 2.39 angstrom in the case of X = I (1e). This behavior is contrary to the decreasing electronegativity of the halides and is discussed in analogy to the series of the halides of boron.