Tri- and tetranuclear heteropivalate complexes with core {Fe2NixO} (x = 1, 2): Synthesis, structure, magnetic and thermal properties.

Graphical abstract New heteronuclear Fe–Ni carboxylate complexes with 1,10-phen and 2,2-bpy with different metal core ({Fe 2 Ni} or {Fe 2 Ni 2 }) were synthesized and characterized by single crystal X-ray analysis, Mossbauer spectroscopy, magnetic measurements and thermal analysis. Exchange coupling between Fe(III) ions was described according to magnetic data simulation and quantum-chemical calculations. Abstract The reactions of complex [Fe 2 Ni(O)(Piv) 6 (Et 2 O)(H 2 O) 2 ] (1) with 1,10-phenanthroline (phen) and 2,2′-bipyridine (bpy) gave the following new coordination compounds: the trinuclear complex [Fe 2 Ni(O)(Piv) 6 (phen)H 2 O]·(C 2 H 5) 2 O (2), the tetranuclear ones [Fe 2 Ni 2 (OH) 2 (Piv) 8 (phen) 2 ] (3) and [Fe 2 Ni 2 (OH) 2 (Piv) 8 (bpy) 2 ] (4), depending on the crystallization conditions. According to single crystal X-ray diffraction data, all the compounds have molecular structures. The Mössbauer spectra of 1 – 3 correspond to high-spin Fe3+ ions in an octahedral environment consisting of oxygen atoms. The DC magnetic susceptibility studies and quantum-chemical analysis of intra- and intermolecular J pathways using broken-symmetry density functional theory (DFT) showed that all exchange interactions in tri- (1 , 2) and tetranuclear (3) complexes are antiferromagnetic. The exchange coupling is weaker in 3 due to the lower ability of the bridging OH-groups to mediate superexchange. Thermal destruction processes have been studied for 2 and 3. The final products of thermolysis are the mixed oxide NiFe 2 O 4. [ABSTRACT FROM AUTHOR]