The IR spectrum of crystalline 2 confirmed the presence of the terminal CO group exhibiting a stretching band at 1943 cm -1 . Density Functional Theory (DFT) calculations were used to probe the electronic structure and nature of the bonding within the Zn-H-Ni motif of 2. The lowest energy ground state configuration was calculated as S = ½. Natural Bond Order (NBO) calculations suggest that bonding within the 3-centre, 2-electron Zn-H-Ni motif is dominated by metal-hydride bonding rather than metal-metal bonding (Figure ). Wiberg Bond Indices (WBI) for the Ni-H bonds and the Zn-H bonds have similar values of 0.30 and 0.36 respectively, while that for the Ni---Zn interaction is only 0.14. The charges from Natural Population Analysis (NPA) are negative on the bridging H atom (-0.40) and positive on both Zn (+1.36) and Ni (+0.46) centres. Further analysis of 2 using the Quantum Theory of Atoms in Molecules (QTAIM) showed bond critical points (bcps) between the H atom and Zn atom, as well as between the H atom and Ni atom, but no bcp directly between the two metal centres consistent with the limited importance of metal-metal bonding in this system (Figure ). A simplified molecular orbital bonding description of the cationic analogue [2] + was also considered.