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

The use of di-2-pyridyl ketone ((py)(2)CO)/3,5-di-tert-butylcatechol (H(2)dbcat) "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).6H(2)O-(py)(2)CO-H(2)dbcat-NEt3 (1 : 1 : 1 :2) reaction system in MeOH gives [Fe-4{(py)(2)C(OMe)O}(2){(Hpy)(py)C(OMe)O}(2)(dbcat)(4)](ClO4)(2) 1, whereas reaction of Fe(ClO4)(3).6H(2)O with (py)(2)CO, H(2)dbcat and NEt3 (1 : 1 : 1 : 3) in MeCN gives (HNEt3)[Fe-3 (py)(2)C(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 eta(1):eta(2):mu(2) dbcat(2-) groups, while one eta(1):eta(2):mu(2) dbcat(2-) group and one eta(1):eta(2):eta(1):mu(2) (py)(2)C(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 Fe-2 edges are bridged by two eta(1):eta(2):mu(2) and one eta(1):eta(2) :mu(3) dbcat(2-) groups, and one eta(1):eta(2):eta(1):mu(2) (py)(2)C(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),C(OH)O- ligand. Variable-temperature magnetic susceptibility studies in the 2-300 K range reveal antiferromagnetic exchange interactions in both complexes. Variable-temperature Mossbauer 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.