Three new two-dimensional (2D) Hofmann-type coordination polymers with general formula [Fe(3-NH2PY)(2)M(CN)(4)] (3-NH(2)py = 3-aminopyridine, M = Ni (1), Pd (2), Pt (3)) have been synthesized. Magnetic susceptibility measurements show that they exhibited cooperative spin crossover (SCO) with remarkable hysteretic behaviors. Their hysteresis widths are 25, 37, and 30 K for 1-3, respectively. The single-crystal structure of 1 suggest that the pseudo-octahedral Fe sites are equatorially bridged by [M(CN)(4)](2-) to form 2D grids and axially coordinated by 3-NH(2)py ligands. The intermolecular interactions between layers (the offset face-to-face pi center dot center dot center dot pi interactions, hydrogen bonds, and weak N-amino center dot center dot center dot Ni-II contacts) together with the covalent bonds bridged by [M(CN)(4)](2-) units are responsible to the significant cooperativity.