Two-dimensional iron(ii) networks - Guest-dependent structures and spin-crossover behaviors

Four compounds with general formula [Fe(4-bphz)₂(NCS) ₂]·X [4-bphz = 1,2-bis(pyridin-4-ylmethylene)hydrazine; X = 2H₂O·2CH₃CN (1·CH₃CN), 4CH ₃COCH₃ (2·CH₃COCH₃), 2.5C₁₀H₈ (3·C₁₀H₈), 2C ₆H₅NO₂ (4·C₆H ₅NO₂)] were synthesized and characterized. These compounds contain 2D gridlike networks that are diversely stacked or self-interpenetrated depending on the inclusive guest molecules. Magnetic studies showed that 1·CH₃CN undergoes a two-step and almost complete spin transition and 2·CH₃COCH₃ showed an incomplete transition, whereas 3·C₁₀H₈ and 4·C ₆H₅NO₂ are paramagnetic in the whole temperature range. Correlations between structures and magnetic properties revealed that the size and shape of the guest molecules exerted great influence on the conformation of the ligand and the 3D structures of the complexes and, hence, spin-crossover behaviors. Complexes with the general formula [Fe(4-bphz)₂(NCS)₂]·X [4-bphz = 1,2-bis(pyridin-4-ylmethylene)hydrazine, X = guest molecules] are composed of isomeric 2D gridlike networks, but show different solvation polymorphs. Whether the complex undergoes spin crossover or is just paramagnetic depends on both the inclusive guest molecules and the conformation of the ligands.