Dinitrogen Coordination to a High-Spin Diiron(I/II) Species.

Dinitrogen coordination to iron centers underpins industrial and biological fixation in the Haber-Bosch process and by the FeM cofactors in the nitrogenase enzymes. The latter employ local high-spin metal centers; however, iron-dinitrogen coordination chemistry remains dominated by low-valent states, contrasting the enzyme systems. Here, we report a high-spin mixed-valent cis-(μ-1,2-dinitrogen)diiron(I/II) complex [(FeBr) 2 (μ-N 2 )L bis ] - (2), where [L bis ] - is a bis(β-diketiminate) cyclophane. Field-applied Mössbauer spectra, dc and ac magnetic susceptibility measurements, and computational methods support a delocalized S= 7 / 2 Fe 2 N 2 unit with D=-5.23 cm -1 and consequent slow magnetic relaxation.