[2] + is isostructural with 2 and is formally an 18-electron species constructed from the interaction of [NiCp(CO)] + and the molecular zinc hydride 1a. [NiCp(CO)] + was calculated to be bent with a Cpcentroid-M-CO bond angle of 134°. The frontier molecular orbitals of [NiCp(CO)] + reveal a fragment well suited to binding through -donation and -accepting bonding interactions (Figure ). The frontier molecular orbitals are delocalised across both the cyclopentadienyl and CO ligands, with only a small contribution from contracted 3d AOs of Ni. The LUMO involves constructive interference of the selected AOs of the Cp ligand and C atom of the CO group, with further contribution from the dyz orbital of Ni.