Prior to 2007, the extensively developed chemistry of the group 2 (alkaline earth, Ae) metals had not been extended to the isolation of any stable molecular compound containing those metals in anything but the +2 oxidation state. This is despite related low oxidation-state chemistry of the p-block elements being well established over the preceding decades. With that said, a number of transient low oxidation-state Ae compounds, e.g., XMgMgX and ∙MgX (X = H or halide), had been studied in solid matrices at very low temperature (typically <10 K), or in the gas phase at low pressure. Moreover, a number of solid-state materials exhibiting bonding interactions between Ae metals had been described, e.g., superconducting MgB2. In addition, magnesium(I) compounds, e.g., ∙ MgNC, were detected in interstellar clouds1.