Syntheses, structures and magnetic properties of a series of iron(II)-triazole crystalline coordination compounds: Solvent effect, different substituted groups and incomplete spin transition

Based on 4-substituted mono- and bis-triazole ligands 4-2-pyridyl-1,2,4-triazole (L1) and 2,6-(1,2,4-triazole-4-yl)-pyridine (L2), a series of iron(II)-triazole complexes, namely [Fe2(μ2-L1)3(L1)2(NCS)4] 2H2O (1), [Fe2(μ2-L1)3(L1)2(NCS)4] CH3OH CH3CH2OH (2) and [Fe(μ2-L2)2(NCS)2]n (3) have been isolated. For the Fe(II)-L1 system, though dinuclear complexes were obtained in both aqueous solution and methanol/ethanol solution for 1 and 2, respectively, anti-ferromagnetic interactions were found in 1 while incomplete spin transition phenomenon was found in 2. Low temperature structural analysis (100 K) of 2 is consistent with one of the Fe(II) centers within the dinuclear complex at low spin (LS) state and the other at high-spin (HS) state resulting in a [LS:HS] species. When L2 is used under the similar preparation method for 1–2, one-dimensional neutral iron (II) chain complex 3 is isolated. The different substituted groups and solvent effect are both important for self-assembly and different magnetic properties of these crystalline iron(II)-triazole complexes 1–3.