title: When being straight bends rules: a rationale for the linear FeNO unit in the low-spin square-pyramidal {FeNO}7 tetracyanonitrosylferrate(2-) anion.
abstract: All low-spin S=1/2 heme-NO complexes feature FeNO angles of about 140 degrees . In contrast, the square-pyramidal [Fe(CN)(4)(NO)](2-) complex features an exactly linear {FeNO}(7) unit. We have sought here to determine a possible, simple molecular orbital (MO) rationale for these structural variations. A DFT-based (DFT=density functional theory) MO analysis shows that the linearity of the latter stems from the greater pyramidalization of the Fe center, relative to nitrosylheme, which results in significant differences in d orbital hybridization. Thus, the singly occupied molecular orbital (SOMO) of [Fe(CN)(4)(NO)](2-) , while primarily Fe dz2-based, also has a significant amount of 4p(z) character, which makes it less stereochemically active, accounting for the linearity of the FeNO unit.
authors.affiliation: Department of Chemistry, University of Tromsø, N-9037 Tromsø, Norway.
authors.forename: Jeanet
authors.initials: J
authors.lastname: Conradie
authors.forename: Abhik
authors.initials: A
authors.lastname: Ghosh
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D008958:Models, Molecular; D009566:Nitrates / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D009566:Nitrates; C517182:tetracyanonitrosylferrate; C025302:ferric nitrate