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 Mossbauer spectroscopies as well as density functional theory calculations suggest some (FeNO+)-N-I character and reveal that the singly occupied molecular orbital of 2, resulting from the s-antibonding interaction of Fe dz(2) 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 Mossbauer isomer shifts (similar to 0.0 mm s(-1)).