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

Abstract

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-N2)Lbis]− (2), where [Lbis]− 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 Fe2N2 unit with D=−5.23 cm−1 and consequent slow magnetic relaxation.