An Fe(II) SCO complex based on an acylhydrazone ligand with an amino functional group has been prepared. The complex is able to dissociate and regather upon protonation and deprotonation, in both solid state and solution, accompanied by spin state switching, marked change of color, and distinct solubility in water. Moreover, the complex shows distinct magnetic responses toward formaldehyde and protic and nonprotic solvents, as a result of the different affinity of the amino functional site with those chemicals.