(Re¢u le 15juin 1976(Re¢u le 15juin , aeceptd le 8juillet 1976 The crystal structure of the molecular complex HfT4-DMF (DMF is N,N-dimethylformamide, T is the bidentate CvH~O5 tropolonato ion) has been determined by single-crystal X-ray diffraction analysis. The crystal is triclinic, space group P1, with a = 12.839, b = 10.706, c = 11.708 A, a = 67-32, fl = 101.1, ), = 83.6 °, Z = 2. The structure was solved by the heavy-atom method. 5046 reflexions with F > 3o(F) were retained for the structure determination. An anisotropic least-squares refinement was carried out to an R of 6%. The Hf atom is surrounded by the eight binding O atoms of the four tropolone ligands. The coordination polyhedron is a slightly distorted dodecahedron (42m). The geometrical parameters of the dodecahedron agree with theoretical values predicted by the 'hard-sphere' and the 'most favourable polyhedra' models. The ligand rings are planar and retain the aromatic character observed in pure tropolone. The DMF molecule is found to be planar and equidistant from two tropolone rings which belong to two different HfT 4 molecules. This configuration suggests the existence of an electrostatic interaction as a result of the high dipole moments of the DMF molecule and the tropolone rings.
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