A tetranuclear magnesium hydride complex based on the β-oxo-δ-diiminate (BODDI) ligand was isolated. In the solid state, the complex features three bridging μ2-hydrides and one unprecedented four-coordinate hydride in a nearly square-planar coordination environment. In the solid state, two different coordination polymers are observed depending on whether the axial or equatorial oxygen lone pairs of 1,4-dioxane are engaged in bonding to magnesium.