The structure was solved by direct methods using the SHELXS-97 program [2] , and then refined with full-matrix least-square methods based on F2 (SHELXL-97) [2] with the aid of the WINGX [3] program. All non-hydrogen atoms were refined with anisotropic atomic displacement parameters. H atoms were finally included in their calculated positions. A final refinement on F2 with 6338 unique intensities and 226 parameters converged at ωR(F2) = 0.0513 (R(F) = 0.0419) for 5373 observed reflections with I > 2σ(I).