Octa-coordinated alkaline earth metal-dinitrogen complexes M(N) (M=Ca, Sr, Ba).

We report the isolation and spectroscopic identification of the eight-coordinated alkaline earth metal-dinitrogen complexes M(N) (M=Ca, Sr, Ba) possessing cubic (O) symmetry in a low-temperature neon matrix. The analysis of the electronic structure reveals that the metal-N bonds are mainly due to [M(d)]→(N) π backdonation, which explains the observed large red-shift in N-N stretching frequencies. The adducts M(N) have a triplet (A) electronic ground state and exhibit typical bonding features of transition metal complexes obeying the 18-electron rule. We also report the isolation and bonding analysis of the charged dinitrogen complexes [M(N)] (M=Ca, Sr).