Understanding d-orbital participation in alkaline earth metal complexes

[Display omitted] •In alkaline earth metal complexes a mechanism of d-orbital participation is studied.•Crystal field effects can induce the electronic ns→(n–1)d transition in complexes.•We proposed some more stable alkaline earth metal complexes in theory. Alkaline earth metal (AEM) complexes have recently been shown to possess electronic characteristics similar to those of transition metal complexes, with their d orbitals participating in bonding interactions. While this surprising discovery changes our understanding of AEM properties, the mechanism of d-orbital participation remains unclear. Moreover, AEM complexes are typically unstable. Thus, herein, we propose a mechanism for the participation of d orbitals in AEM complexes, in which crystal field effects induce an electronic transition. We explain how the crystal field and electronic back-donation influence complex stability. Finally, we provide insights on the synthesis of more stable AEM complexes using the theory proposed herein.