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)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 FeIII ions. The inner FeIII ions are bridged by two catecholate oxygen atoms from two (eta)^1: (eta)^2:(mu)2 dbcat2- groups, while one (eta)^1: (eta)^2: (mu)2 dbcat2- group and one (eta)^1: (eta)^2: (eta)^1:(mu)2(py)2C(OMe)O- ligand bridge each inner FeIII to its outer FeIII 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 (eta)^1: (eta)^2:(mu)2 and one (eta)^1: (eta)^2:(mu)3 dbcat2- groups, and one (eta)^1: (eta)^2: (eta)^1:(mu)2(py)2C(OH)O- ligand. Two FeIII ions are six-coordinate, while the third is five-coordinate. One sixcoordinate FeIII centre is chelated by a bidentate dbcat2- group and the other one by a bidentate (py)2C(OH)O- ligand. Variabletemperature 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 highspin iron(III) sites in the complex, while those of 2 analyse as one (averaged) quadrupole-split doublet.