Mononuclear [Fe(H2LR)2]2+ and dinuclear [Fe2(H2LR)3]4+ (R = H, 2-Me, 5-Me) complexes containing the new imidazole-4-carbaldehyde azine ligand (H2LH) and its derivatives (H2L 2-Me and H2L5-Me) prepared from the condensation reaction of 4-formylimidazole or 2-methyl- or 5-methyl-4- formylimidazole with hydrazine (2:1) were prepared, and their magnetostructural relationships were studied. In the mononuclear complexes, H2L R acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom, while in the dinuclear complexes, H2LR acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate. At room temperature, [Fe2(H 2LH)3](CIO4)4 and [Fe2(H2L2-Me)3](ClO 4)4 were in the high-spin (HS) and low-spin (LS) states, respectively. The results are in accordance with the ligand field strength of H2L with electron-donating methyl groups being stronger than H 2LH, with the order of the ligand field strengths being H2L2-Me > H2LH. However, in the mononuclear [Fe(H2LH)2](ClO4) 2 and [Fe(H2L2-Me)2](ClO 4)2 complexes, a different order of ligand field strengths, H 2LH > H2L2-Me, was observed because [Fe(H2LH)2](ClO4) 2 was in the LS state while [Fe(H2L2-M) 2](ClO4)2 was in the HS state at room temperature. X-ray structural studies revealed that the interligand steric repulsion between a methyl group of an H2L2-Me ligand and the other ligand in [Fe(H2L2-Me)2](ClO 4)2 is responsible for the observed change in the spin state. Two kinds of crystals, needles and blocks, were isolated for [Fe 2(H2LH)3](BF4) 4, and both exhibited a sharp spin transition, [LS-HS] [HS-HS]. The spin transition of the block crystals is more abrupt with a hysteresis, T c↑ = 190 K and Tc↓ = 183 K withΔT= 7 K.
ASJC Scopus subject areas
- Inorganic Chemistry
- Physical and Theoretical Chemistry