A water-tuned reversible spin transition with the largest hysteresis loop in 3D Hofmann frameworks pillared by flexible ligands

Two spin-crossover materials, [Fe(bph)M(CN) 4 ]·4.5H 2 O (M = Pt 2+ , Pd 2+ ) based on N , N ′-bis(4-picolinoyl)hydrazine (bph) have been prepared to show a hysteretic abrupt spin transition.