A Structurally Unique {Fe(NO)₂}¹⁰‐{Fe(NO)₂}⁹ Dinuclear Dinitrosyl Iron Complex Bridged by a μ‐ƞ²‐FBF₃⁻ Ligand and Stabilized by N‐Heterocyclic Carbenes

Reaction of a {Fe(NO) 3 } 10 trinitrosyl iron complex with a mononuclear {Fe(NO) 2 } 10 dinitrosyl iron complex furnishes a dinuclear dinitrosyl iron complex, [(NO) 2 (IMes)Fe(μ‐η 2 ‐FBF 3 )Fe(IMes)(NO) 2 ] ( 3 ) (IMes = 1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene). Single‐crystal X‐ray diffraction reveals an unprecedented μ‐η 2 ‐FBF 3 − bridge that links two [Fe(NO) 2 ] motifs, giving an Fe …. Fe separation of 3.45 Å. Nonclassical C─H … F contacts (3.21 – 3.61 Å) between the mesityl methyl groups of the IMes and the nonbridging fluorine atom cradle the anion and create a pseudo‐tridentate environment that stabilizes the mixed‐valent core. Infrared spectroscopy exhibits four ν(NO) bands at 1778, 1736, 1715, and 1682 cm −1 , inferring the presence of two electronically different {Fe(NO) 2 } units, whereas 77 K EPR spectroscopy gives a rhombic signal with g avg = 2.109, diagnostic of an s = 1/2 species in complex 3 .