Abstract: EXAF_S measurements were performed on a 12-kWrotating anode X-ray spectrometer for K₃W₂Cl₉, (NH₄)₃ W₂Cl₉ and (Bu₄N)₃W₂Cl₉. Through Fourier transformation and curve fitting processes, the bond lengths and coordination numbers were obtained. W-W 2.43(1) Å, CN 1, W-Clt 2.44(3) Å, CN 3.3; W- Cl_b2.49(3)Å, CN 3.8. In order to certify the EXAF_Sresults, the single crystal structure of (NH₄)₃W₂Cl₉ was determined on ENRAF-NONIUS CAD-4 four-circle X-ray diffractometer. (NH₄)₃W₂Cl₉ crystallizes in space group P6_θ/m and contains two formula unit in a unit cell, a = 6 = 7.216Å, c=16.518Å, dc = 3.303g/cm³. Within experimental error, the structural parameters of W,Cl₉^3- determined by EXAF_S technique are in good agreements with those by single crystal diffraction. It is infered that, combined with +1 cations, the anion W₂Cl₉^3- has the structure of two octahedra sharing a face to give D_3d symmetry, and the skeleton and bond lengths have no tremendous change due to the strong W—W multi-bond.

Key words: W₂Cl₉^3- compounds, EXAFS