Side-on Coordination in Fluorido Difluoroamido Complexes FMNF₂ of Heavy Alkaline Earth Metals (M = Ca, Sr, Ba)

Fluorido difluoroamido complexes F'MNF₂ of heavy alkaline earth metals (M = Ca, Sr, Ba) were prepared through the reactions of laser-ablated metal atoms with diluted NF₃ and isolated in cryogenic neon and argon matrices. They were characterized using Fourier-transform infrared (FTIR) spectroscopy, ^14/15NF₃ isotopic substitution and quantum-chemical calculations. The species feature a F'^- and a so far unknown side-on coordinated η³-NF₂ ^- ligand with the F'-M-N angle decreasing from Ca to Ba. Bonding analyses suggest that the interactions between the metal center and the ligands are mainly of electrostatic nature. Nevertheless, the orbital interaction shows that an electron donation from the ligands into the empty ns and (n - 1)d orbitals of the metal center further contributes to the electronic structure.