New heterometallic pivalates with Fe III and Zn II ions: Synthesis, structures, magnetic, thermal properties

Abstract Techniques for synthesizing Zn(II)-Fe(III) heterometallic molecular complexes [Fe 2 Zn 4 O 2 (Piv) 10 ] ( 1 ), [Fe 4 Zn 3 O 3 (Piv) 12 (H 2 O)]·1.5Et 2 O ( 2 ) and [Fe 3 Zn 2 O 2 (Piv) 9 (1,10-phen)] ( 3 ) (where HPiv is pivalic acid, 1,10-phen – C 12 H 8 N 2 ) have been developed. It has been found that recrystallization of the solid product formed from reaction mixture of Fe(NO 3 ) 3 , Zn(NO 3 ) 2 , KOH and HPiv (in the 3:2:13:34 ratio) in water («Reagent A») from acetone results in hexanuclear complex 1 , whereas thermolysis of «Reagent A» at 130 °C in air followed by crystallization of the thermolysis products from ether makes it possible to isolate complex 2 . It has been found that dissolution of thermolyzed «Reagent A» in MeCN in the presence of 1,10-phenanthroline leads to formation of complex 3 . The structures of complexes 1 – 3 were determined by single crystal X-ray diffraction analysis. The doublet Mossbauer spectra of complexes 1 and 2 correspond to high-spin Fe 3+ ions in an octahedral environment of oxygen atoms, while the non-equivalence of the environment of iron ions in compound 3 (FeO 6 and FeO 4 N 2 ) is reflected by two observed doublets with different intensities. Based on the results of magnetic data simulation and quantum-chemical calculations, it has been shown that antiferromagnetic exchange coupling exists in complexes 1 and 2 ( J 12  = −3.05 cm −1 for 1 and J 12  = −0.4, J 13  = −13.5, J 23  = −3.6, J 24  = −27.2 and J 34  = −30.1 cm −1 for 2 ). The value of the exchange integral between pairs of metal ions correlates with the Fe-O distances and the Fe-O-Fe angles in the bridging oxo ligands. Processes of thermal destruction have been studied for complexes 1 and 2 in argon atmosphere in the temperature range of 25–500 °C.