Use of the di-2-pyridyl ketone/3,5-di-tert-butylcatechol “blend” in iron(iii) chemistry: a cationic tetranuclear cluster and an anionic trinuclear complex

Abstract

The use of di-2-pyridyl ketone ((py)₂CO)/3,5-di-tert-butylcatechol (H₂dbcat) “blend” in iron(III) chemistry has yielded a cationic tetranuclear cluster and an anionic trinuclear complex. Both complexes were prepared under anaerobic conditions. The Fe(ClO₄)₃·6H₂O–(py)₂CO–H₂dbcat–NEt₃ (1 ∶ 1 ∶ 1 ∶ 2) reaction system in MeOH gives [Fe₄{(py)₂C(OMe)O}₂{(Hpy)(py)C(OMe)O}₂(dbcat)₄](ClO₄)₂1, whereas reaction of Fe(ClO₄)₃·6H₂O with (py)₂CO, H₂dbcat and NEt₃ (1 ∶ 1 ∶ 1 ∶ 3) in MeCN gives (HNEt₃)[Fe₃{(py)₂C(OH)O}₂(dbcat)₄]·MeCN 2·MeCN. The centrosymmetric tetranuclear cation of 1 contains a zigzag array of six-coordinate Fe^III ions. The inner Fe^III ions are bridged by two catecholate oxygen atoms from two η¹:η²:μ₂ dbcat²⁻ groups, while one η¹:η²:μ₂ dbcat²⁻ group and one η¹:η²:η¹:μ₂ (py)₂C(OMe)O⁻ ligand bridge each inner Fe^III to its outer Fe^III neighbour. Each outer metal is chelated by a single bidentate (⁺Hpy)(py)C(OMe)O⁻ zwitterion. The trinuclear anion of 2·MeCN consists of a triangular unit, in which the Fe₂ edges are bridged by two η¹:η²:μ₂ and one η¹:η²:μ₃ dbcat²⁻ groups, and one η¹:η²:η¹:μ₂ (py)₂C(OH)O⁻ ligand. Two Fe^III ions are six-coordinate, while the third is five-coordinate. One six-coordinate Fe^III centre is chelated by a bidentate dbcat²⁻ group and the other one by a bidentate (py)₂C(OH)O⁻ ligand. Variable-temperature magnetic susceptibility studies in the 2–300 K range reveal antiferromagnetic exchange interactions in both complexes. Variable-temperature Mössbauer spectra of 1 analyse as two quadrupole-split doublets which were assigned to the two different high-spin iron(III) sites in the complex, while those of 2 analyse as one (averaged) quadrupole-split doublet.