When being straight bends rules: a rationale for the linear FeNO unit in the low-spin square-pyramidal {FeNO}7 tetracyanonitrosylferrate(2-) anion |
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Authors: | Conradie Jeanet Ghosh Abhik |
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Institution: | aDepartment of Chemistry, University of Tromsø, N-9037 Tromsø, Norway bDepartment of Chemistry, University of the Free State, 9300 Bloemfontein, South Africa |
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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. |
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Keywords: | Tetracyanonitrosylferrate NO donor Nitroprusside |
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