CHARACTERIZATION OF THE ADDUCTS WF6.PY AND WF6.2PY (PY=PYRIDINE) - CRYSTAL-STRUCTURE OF WF6.2PY

Adducts of tungsten(VI), i.e. WF6 . py and WF6 . 2py (py=pyridine) hav e been characterized by X-ray diffraction data and vibrational spectro scopy. Solutions of these adducts in CD2Cl2 have also been studied by F-39, H-1 and C-13 NMR spectroscopy. The F-19 NMR spectra, recorded at 193 K for WF6 . 2py and at 140 K for WF6 . py, were both of the A(4)X (2) type. The geometry of the coordination polyhedron of the W atom in WF6 . py could not be determined by X-ray diffraction methods. Howeve r, the 1:2:4 arrangement of the ligands indicated by the F-19 NMR data corresponds to a monocapped trigonal prism. The approximate values of the activation energy for internal fluorine exchange calculated from the F-19 NMR data are 143 and 47 kJ mol(-1) for WF6 . 2py and WF6 . py , respectively. The crystal structure of WF6 . 2py, as determined by X -ray diffraction methods, is in agreement with the F-19 NMR data. In t his adduct, the tungsten atom is surrounded by an undecahedron of liga nds derived from a trigonal prism by the capping of two square faces ( 2:2:4 ligand arrangement) with the nitrogen atoms of the organic ligan d occupying the capping sites. The crystal system, space group, unit c ell parameters, and R factor are as follows: orthorhombic, Pnma (No. 6 2), a=14.274(2) Angstrom, b=13.335(2) Angstrom, c=6.497(2) Angstrom, V =1236.8(8) Angstrom(3), Z=4, R=0.020.