The rational design of coordination frameworks combining more than two different metal ions using a self-assembly approach is challenging because it rarely offers sufficient control over the building blocks at the actual self-assembly stage. In this work, we present a successful two-step strategy toward heterotrimetallic coordination frameworks by employing a new bimetallic [(NC)(7)Mo-IV-CN-Pt-IV(NH3)(4)-NC-Mo-IV(CN)(7)](4-) secondary building unit (SBU). This anionic moiety has been isolated and characterized as a simple salt with an organic dppipH(2)(2+) cation (dppipH(2))(2)[(NC)(7)Mo-IV-CN-Pt-IV(NH3)(4)-NC-Mo-IV(CN)(7)]center dot 15H(2)O (1) (dppip = 1,4-di(4-pyridinyl)piperazine). The salt presents a second-order phase transition related to cation conformational change around 250 K and a photomagnetic effect after irradiation with 450 nm light at 10 K. When combined with aqueous solutions of Mn-II or Cu-II complexes, it forms either a one-dimensional chain [Mn-II(dpop)][Mn-II(dpop)(H2O)][(NC)(7)Mo-IV-CN-Pt-IV(NH3)(4)-NC-Mo-IV(CN)(7)]center dot 36H(2)O (2) (dpop = 2,13-dimethyl-3,6,9,12,18-entaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene) or a photomagnetic two-dimensional honeycomb network [Cu-II(cyclam)](2)[(NC)(7)Mo-IV-CN-Pt-IV(NH3)(4)-NC-Mo-IV(CN)(7)]center dot 40.89H(2)O (3) (cyclam = 1,4,8,11-tetraazacyclotetradecane), both characterized by very large cavities in their structure filled with solvent molecules. Both 2 and 3 incorporate three different transition-etal ions and constitute a new family of 3d-4d-5d coordination frameworks. Moreover, compound 3 inherits the photomagnetic properties of the MoPtMo SBU.