New Nitrosyl Bis‐ o ‐iminobenzosemiquinonato Complexes of M(ISQ) 2 (NO) Type

The tetracoordinate bis ‐o ‐iminobenzosemiquinonato cobalt and iron complexes, Co(ISQ‐Pr i ) 2 ( 1 ), Co(ISQ‐Me) 2 ( 2 ), Fe(ISQ‐Pr i ) 2 ( 3 ), Fe(ISQ‐Me) 2 ( 4 ), (ISQ‐Pr i is 4,6‐di‐ tert ‐butyl‐ N ‐(2,6‐di‐ iso ‐propylphenyl)‐ o ‐iminobenzosemiquinone and ISQ‐Me is 4,6‐di‐ tert ‐butyl‐ N ‐(2,6‐dimethylphenyl)‐ o ‐iminobenzosemiquinone, respectively) react with nitrogen(II) oxide to form the pentacoordinate nitrosyl derivatives M(ISQ‐R) 2 (NO) 5 – 8 (M = Co, R = Pr i ( 5 ), R = Me ( 6 ); M = Fe, R = Pr i ( 7 ), R = Me ( 8 )). NO binding is reversible. Complexes have been characterized by IR, UV‐vis spectroscopy, EPR and Mössbauer (for 7 ) spectroscopy. The molecular structure of cobalt nitrosyl complex 6 was determined by X‐ray diffraction analysis. The spectroscopic and X‐ray structural features of the complexes are consistent with the {Co‐NO} 8 and {Fe‐NO} 7 formulations. The nitrosyl ligand in cobalt complexes 5 and 6 is coordinated in a bent fashion. In the case of iron complexes 7 and 8 , neutral NO· ligand is coordinated to low‐spin iron(II).