Crystalline MOF materials with adjustable properties are of great interest for multiple potential applications. In this study, a series of 3D isostructural mixed metal MOFs {[M₃(L)₂(4,4′-bpy)₂(H₂O)₂]·14H₂O}_n (M = Co (1), Co_0.7Ni_0.3 (2), Ni_0.5Co_0.5 (3), Co_0.3Ni_0.7 (4), Co_0.1Ni_0.9 (5), and Ni (6); H₃L = 1-aminobenzene-3,4,5-tricarboxylic acid) have been synthesized. The crystal color changed regularly with the increase in the Ni ion content from red to green, and a new ultraviolet absorption spectrophotometry method has been developed for the accurate determination of the metal content of Co in MOF materials. In the detection of magnetic behaviour, 1 shows antiferromagnetism. As the Ni ion component gradually increases in 2–6, the magnetic behaviour of the complexes appears to transition from antiferromagnetic to ferromagnetic. Moreover, complex 1 exhibits preeminent photocatalysis activity in the degradation of organic dyes under visible light irradiation. As the ratio of Ni ions increases gradually in the complexes, the photocatalytic activities of 1–6 decrease. This work offers controllable regulation of the photocatalytic properties and magnetic behaviour of MOFs by changing the metal ions.