Thermal analysis, synthesis and structural studies of heterometallic {Fe₂MO} salicylate complexes

Four new trinuclear heterometallic molecular complexes with the {Fe₂^IIIM^II μ₃-O} core, where M = Mn(II), Ni(II), Cu(II) and Zn(II), have been synthesized by the reaction between iron nitrate and d-metal salts with ammonium salicylate in a mixture of solvents. The compounds were obtained as crystalline material suitable for single-crystal structure analysis with the following composition: [Fe₂MnO(SalH)₆(EtOH)(MeOH)₂]·DMAA·EtOH·2MeOH·H₂O (1); [Fe₂NiO(SalH)₆(EtOH)(MeOH)₂]⋅DMAA⋅2MeOH⋅1.5H₂O (2); [Fe₂CuO(SalH)₆(EtOH)(MeOH)₂]⋅DMAA⋅4H₂O (3); [Fe₂ZnO(SalH)₆(EtOH)(MeOH)₂]⋅DMF⋅2MeOH⋅1.5H₂O (4), where SalH = monodeprotonated salicylic ligand. The elemental analysis and IR spectra of the complexes 1–4 are in good agreement with the crystallographic data. The Mössbauer parameters are characteristic to iron(III) complexes with a spin value of S = 5/2. The thermal properties of all compounds have been studied in air and nitrogen atmosphere at the 20–1000 °C temperature range. The thermal analysis data revealed that after the elimination of external solvent molecules, the trinuclear core of the complexes is stable up to 250 °C.