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Iron(III)-Pivalate-Based Complexes with Tetranuclear {Fe43-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 = 2,2′-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 {Fe43-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 {Fe43-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.