Spin crossover cations have been successfully synthesized in the pores of a mesoporous robust Metal–Organic Framework (MOF) MIL-100(Al) through sequential introduction of Fe(III) cations and a sal₂trien ligand. The MIL-100(Al)@Fe(sal₂trien) hybrid material retains its crystallinity and partial porosity compared to the parent MOF. The spin state of the Fe(sal₂trien)⁺ cations can be modulated at room temperature through sorption of guest molecules, paving the way to the design of a new generation of sensors based on MOF@spin crossover complex solids.