Characterization of the adducts WF 6·py and WF 6·2py (py = pyridine): crystal structure of WF 6·2py

Abstract

Adducts of tungsten(VI), i.e. WF 6·py and WF 6·2py (py = pyridine) have been characterized by X-ray diffraction data and vibrational spectroscopy. Solutions of these adducts in CD 2Cl 2 have also been studied by 19F, 1H and 13C NMR spectroscopy. The 19F NMR spectra, recorded at 193 K for WF 6·2py and at 140 K for WF 6·py, were both of the A 4X 2 type. The geometry of the coordination polyhedron of the W atom in WF 6·py could not be determined by X-ray diffraction methods. However, the 1:2:4 arrangement of the ligands indicated by the 19F NMR data corresponds to a monocapped trigonal prism. The approximate values of the activation energy for internal fluorine exchange calculated from the 19F NMR data are 143 and 47 kJ mol −1 for WF 6·2py and WF 6·py, respectively. The crystal structure of WF 6·2py, as determined by X-ray diffraction methods, is in agreement with the 19F NMR data. In this adduct, the tungsten atom is surrounded by an undecahedron of ligands derived from a trigonal prism by the capping of two square faces (2:2:4 ligand arrangement) with the nitrogen atoms of the organic ligand occupying the capping sites. The crystal system, space group, unit cell parameters, and R factor are as follows: orthorhombic, Pnma (No. 62), a = 14.274(2) Å, b = 13.335(2) Å, c = 6.497(2) Å, V = 1236.8(8) Å 3, Z = 4, R = 0.020.