Side-On Coordination in Molecular Alkaline Earth Metal Hypofluorites FM(η-OF) (M = Mg, Ca, Sr, and Ba).

Side-on coordinated molecular hypofluorites FM(η-OF) (M = Mg, Ca, Sr, and Ba) were prepared by co-deposition of laser-ablated alkaline earth metal atoms with diluted OF in cryogenic matrices. The structures parallel the non-VESPR structures of alkaline earth metal difluorides and dihydrides, such that FMg(η-OF) is planar, FCa(η-OF) is planar but with a shallow bending-potential curve, while FSr(η-OF) and FBa(η-OF) are non-planar. Bonding analyses show that the interactions between the metal center M and the negatively charged ligands F and OF are mainly electrostatic. Moreover, for FMg(η-OF), donation of electron density from OF to empty s and p orbitals of magnesium is involved. However, for the heavier alkaline earth metal compounds, the donation to empty d orbitals of the metal center becomes dominant in orbital interactions, which contributes to their non-planar structures.