Experimentally, Mg–Mg bonds have been shown to be readily elongated (e.g., when coordinated by simple Lewis bases) and their lengths can lie over a remarkably wide range (ca. The Mg–Mg σ-bonds are mainly associated with the rather diffuse highest occupied molecular orbital (MO) of the magnesium(I) compounds, whereas an empty π-type bonding orbital between the Mg centres is often associated with the lowest occupied MO or another low-lying unfilled MO.

That is, the compounds were viewed as containing a central 2+ dication, exhibiting largely ionic interactions with bulky anionic amide ligands. They possess Mg–Mg bonds, which theoretical and experimental studies initially described as being ‘normal’ covalent bonds (bond dissociation energies, BDEs, of ca. Many of these magnesium(I) compounds are remarkably thermally stable (some decompose >300 ☌) and are readily manipulated in the solid state or solution using standard Schlenk techniques. Since that time, more than 25 further examples of such compounds have come forward, in which the magnesium centres have coordination numbers of two, three or four (e.g., 2-coordinate, Fig. This impediment was finally overcome in 2007 with the synthesis of the first magnesium(I) compounds, which were kinetically stabilised towards disproportionation by the incorporation of extremely bulky, chelating, anionic N-donor guanidinate or β-diketiminate ligands (e.g., see Fig. It is not surprising that stable low oxidation-state Ae compounds were late to arrive, given many computational studies showing that their disproportionation to elemental Ae metal and Ae 2+ compounds is exothermic, and therefore thermodynamically favourable. In addition, magnesium(I) compounds, e.g., ∙ MgNC, were detected in interstellar clouds 1. Moreover, a number of solid-state materials exhibiting bonding interactions between Ae metals had been described, e.g., superconducting MgB 2. 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. This is despite related low oxidation-state chemistry of the p-block elements being well established over the preceding decades. 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.

Ca element bond