Anion-dependent structure, molecular magnetism, and oxidation catalytic ability of two iron(III) complexes with an asymmetric tetradentate N₂O₂ ligand

Mononuclear [(Hhpap)FeIII(NCS)₂] (1) and dinuclear [(Hhpap)FeIII(NO₃)]₂(NO₃)₂·2H₂O (2) (H₂hpap = 3-[(2-hydroxyethyl)(2-pyridinylmethyl)amino]-1-propanol) complexes have been prepared by treating Fe(III) salts (NCS– and NO₃–) and H₂hpap in MeOH and/or MeCN solution. Both complexes crystallized in the same space group (P1¯[jls-end-space/]) with different structures. The iron(III) ion of 1 adopts an N₄O₂ octahedral geometry, coordinated by one monodeprotonated Hhpap– and two NCS– anions. In Hhpap–, the ethanol group remains protonated, and its hydroxyl group participates in hydrogen bonds, leading to the formation of a dimeric supramolecular structure. In 2, the iron(III) ion coordinates one nitrate anion and one Hhpap⁻ ligand; each unit is dimerized by an ethoxide group. Theoretical analysis of the magnetic susceptibilities of 1 and 2 was performed to provide insight into their magnetic coupling interactions; 1 displays a very weak antiferromagnetic interaction driven by hydrogen bonds (J = –1.08 cm–1), whereas 2 exhibits a strong antiferromagnetic coupling via Fe-O-Fe bridging pathways (J = –24.2 cm–1). Complex 1 shows no observable catalytic activity, whereas complex 2 exhibits excellent catalytic efficiency for the epoxidation of diverse aliphatic, terminal, and aromatic olefins.