Neutron diffraction studies of transition metal hydride complexes

Investigations of H3Ta(C5H5)2 (III), HW2(CO)9(NO) (IV), and HW2(CO)8(NO) (P(OCH3)3) (V) have been completed. Preliminary results are available for HFeCo3(CO)9[P(OCH3)3]3 (VII). This work, together with studies of HMo2(C5H5)2(CO)4(P(CH3)2) (VI) and [(C2H5)4N]+ [HCr2(CO)10]- carried out at Argonne has led to some general observations on the geometry and the nature of bonding in these compounds. For example, in the structures of IV and V, both of which have bent W--H--W linkages (less than W--H--W in the range 125-1300), there is conclusive evidence for the existence of a closed three-center W--H--W bond with significant metal-metal interaction. Such is the case, because extensions of the axial W--C and W--N bonds trans to the hydride intersect at a point near the center of the W--H--W triangle. The geometry of VI, which also contains a bent M--H--M bond, is consistent with that of IV and V. Bridging M--H bonds in these second- and third-row hydrides range in length from 1.85 to 1.89 A, compared to 1.75 A in the first-row polynuclear complex VII. For metals of corresponding rows, bridging M--H bonds are about 0.1 A longer than terminal bonds, which are classified as single covalent bonds