Crystal and molecular structure of W2(OBut)6 and electronic structure calculations on various conformers of W2(OMe)6

The structure of W2(OBut)6 was determined via a single crystal X-ray diffraction study. In the space group C2/c, there are 1.5 W2(OBut)6 molecules in the asymmetric unit, with one half molecule located on a crystallographic inversion center and one full molecule in a general position. The WW bond distances are 2.328(1) and 2.335(1) Å and the average W–O distances are 1.89(1) Å. The alkoxide alkyl groups are found oriented in the “one distal, two proximal” arrangement with respect to the W–W vector, giving on average, W–W–O angles of 99(1)° for the distal alkoxide and 110(1)° for the proximal. This arrangement is common to other W2(OR)6 compounds. Computational studies employing density functional theory on several conformers of the model compound W2(OMe)6 were undertaken. The results for the total bonding energies for each conformer indicate that this “one distal, two proximal” arrangement is only slightly more stable than the all-distal, D3d and the alkoxide-eclipsed D3h structures in the gas phase. This small difference in conformer energy suggests that the proximality preference is likely due to steric effects that are important in the solid state.

The X-ray crystal structure of W2(OBut)6 is reported. The structure reveals 1.5 dimers in the asymmetric unit. One of the dinuclear molecules is highly disordered with respect to the W–W vectors. The alkoxide ligands are found in the common one distal, two proximal arrangement. DFT (ADF 2003.02) computational studies on several conformers of the model compound W2(OMe)6 reveal that there is little energetic difference between conformers of different proximality in the gas phase.Figure optionsDownload as PowerPoint slide