An Exclusively Organometallic {FeNO}7 Complex with Tetracarbene Ligation and a Linear FeNO Unit

The iron­(II) complex 1 of a macrocyclic tetracarbene binds NO to form a low-spin (S = 1/2) {FeNO}7 complex (2) with a linear FeNO unit and a short Fe–NO bond. IR, electron paramagnetic resonance, and Mössbauer spectroscopies as well as density functional theory calculations suggest some FeINO+ character and reveal that the singly occupied molecular orbital of 2, resulting from the σ-antibonding interaction of Fe dz2 and the NO lone pair, is largely iron-based. Reduction yields a quite stable {FeNO}8 species (3); both 2 and 3 feature very low Mössbauer isomer shifts (∼0.0 mm·s–1).