The synthesis of new Schiff base-like ligands with extended π-system and their iron complexes is described. Some of the iron(II) complexes with N-heterocycles as axial ligands show spin crossover behaviour. The influence of the extended aromatic system on cooperative interactions is investigated by single crystal X-ray structure analysis, X-ray powder diffraction, and magnetic measurements. A combination of C–H⋯π and C–H⋯O interactions is made responsible for up to 10 K wide thermal hysteresis loops.