the ionic component of the bonding but also influence the relative size of the coefficients of the bonding and anti-bonding orbitals constructed from 1s and 3s/4s AOs. For the covalent component of the bonding in the corresponding σ-complexes, the interaction of the ligand SALCs with metal-based orbitals can be conceptualised in terms of the Dewar-Chatt-Duncanson model, being constructed from donation and back donation components. However, unlike the prototypical H-H coordination, the interaction is not symmetric. Based on the relative size of the coefficients on the {Zn-H} + and {Mg-H} + fragments, s-donation will occur primarily from the H atom, while back donation will occur primarily to the Zn or Mg atom.