New three-dimensional spin crossover (SCO) coordination polymers systematically constructed by the novel building unit [Ag I 2 (CN) 3 ], Fe II (3-Br-5-CH 3 pyridine) 2 [Ag I 2 (CN) 3 ][Ag I (CN) 2 ] ( 1 ), Fe II (3-Br-5-Clpyridine) 2 [Ag I 2 (CN) 3 ][Ag I (CN) 2 ] ( 2 ), and Fe II (3,5-Brpyridine) 2 [Ag I 2 (CN) 3 ][Ag I (CN) 2 ] ( 3 ), have been synthesized and characterized. The bismonodentate binuclear [Ag 2 (CN) 3 ] − and mononuclear [Ag I (CN) 2 ] − units and Fe II atoms assemble to form a 3D network structure. The structures of 1 – 3 are crystallographically identical, which made up the triply interpenetration combined with complicated intermolecular interactions including Ag···Ag, Ag···X (pyridine substituents) and π-stacking interactions. Magnetic and differential scanning calorimetry studies were performed for 1 – 3 . These compounds display a similar SCO behavior, while the critical temperatures ( T c ) are shifted by the substituent effect. Due to the identical structures of 1 – 3 , the order of T c clearly corresponds with the Hammett constant.