This creates an empty lobe in the vacant coordination site and is perfectly suited to form a -bonding interaction through donation of electrons from the Zn-H bond of 1. Similarly, the HOMO of [NiCp(CO)] + is constructed from an orthogonal set of orbitals (e.g. dxy) and would be expected to interact with the *-orbital of 1a through -backdonation. This molecular orbital arrangement, begins to explain the orientation of the Zn-H with respect to the Ni fragment, as maximum overlap might be expected from when the Zn-H bond is perpendicular to Ni-CO.