Molecular structures of acetylene derivatives of tin: Part III. Gas phase electron diffraction study of tetrakis(trifluoropropynyl)-tin,Sn(CC-CF3)4

A gas phase electron diffraction study of tetrakis(trifluoropropynyl)tin is reported. The model, based on T_d symmetry for the carbon—tin skeleton and C_3v symmetry for the CF₃ groups, refines to the following parameters (bond lengths, r_a, in nm; valence angles in degrees): Sn—C0.2070(7), CC 0.1215(6), C—C 0.1460(7), C—F 0.1343(2), CCF 111.3(0.2). The uncertainties (given in parentheses) represent three times the standard deviation values. The results obtained point to practically free rotation of the CF₃ groups. The presence of electronegative CF₃ causes shortening of the Sn-C bonds in Sn(CC—CF₃)₄ from Me₃SnCCH and Me₃ SnCCSnMe₃. The triple CC bond length is larger than in hexafluoro-2-butyne and nearly the same as in dimethylacetylene.