Iron(III)-Pivalate-Based Complexes with Tetranuclear {Fe4(µ3-O)2}8+ Cores and N-Donor Ligands: Formation of Cluster and Polymeric Architectures

Different synthetic routes have been used for the preparation of a new tetranuclear [Fe4O2(O2CCMe3)8(bpm)] cluster (1) and a one dimensional coordination polymer [Fe4O2(O2CCMe3)8(hmta)]n (2) (bpm = 22' bipyrimidine and hmta = hexamethylenetetramine). For cluster 1 two structural isomers 1a and 1b·3MeCN have been found. X ray crystallographic analysis showed that all complexes consist of a central {Fe4(m3 O)2}8+ core. In 1a metal ions in the core are additionally linked by six bridging pivalates as two other pivalates and a bpm ligand are chelated to FeIII ions whereas in cluster 1b metal ions in the {Fe4(m3 O)2}8+ core are linked by seven bridging pivalates and only one carboxylate as well as bpm are chelated to the iron centers. In coordination polymer 2 [Fe4O2(O2CCMe3)8] clusters are bridged by hmta ligands to form zigzag chains. Magnetic measurements have been carried out to characterize these complexes and revealed antiferromagnetic interactions between FeIII ions with best fit parameters of Jwb = –72.2 (1a) and –88.7 cm–1 (1b) for wing···body interactions.