Synthesis, Structure, and Characterization of [FeIIILCl3] (L = 1, 4, 8‐Triazacycloundecane, 1, 4, 7‐Triazacyclononane)

The structures of [FeIII(tacud)Cl3] (1) and [FeIII(tacn)Cl3] (2) (tacud = 1, 4, 8-triazacycloundecane, tacn = 1, 4, 7-triazacyclononane) are reported. Both compounds crystallize in the orthorhombic space group Pnma with a = 12.5570(9), b = 12.0028(9), c = 8.2577(6) A, V = 1244.59(16) A3, and Z = 4 for 1 and a = 12.095(4), b = 11.125(4), c = 7.963(3) A, V = 1071.5(6) A3, and Z = 4 for 2. The structures of 1 and 2 feature iron(III) in distorted octahedral arrangement with three facially coordinated nitrogen ligands and three chlorides. Bidirectional intermolecular hydrogen bonding between N–H groups and coordinated chlorides is seen for 1 and 2. Compound 1 is the first example of iron(III) bonded to tacud and compound 2 is only the second structure reported of a 1:1 complex between iron and tacn. The Fe3+/2+ redox couple for 1 is observed at E1/2 = 0.25 V (ΔEp = 99 mV), and for 2 at E1/2 = 0.09 V (ΔEp = 108 mV) versus NHE in DMF at 298 K. Comparison of structural, magnetic, and electrochemical properties for 1 and 2 reveal subtle differences consistent with the stronger coordinating properties of tacn relative to tacud.