Octa-coordinated alkaline earth metal-dinitrogen complexes M(N2)8 (M=Ca, Sr, Ba).

We report the isolation and spectroscopic identification of the eight-coordinated alkaline earth metal-dinitrogen complexes M(N2)8 (M=Ca, Sr, Ba) possessing cubic (Oh) symmetry in a low-temperature neon matrix. The analysis of the electronic structure reveals that the metal-N2 bonds are mainly due to [M(dπ)]→(N2)8 π backdonation, which explains the observed large red-shift in N-N stretching frequencies. The adducts M(N2)8 have a triplet (3A1g) 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(N2)8]+ (M=Ca, Sr).