The rational design and construction of Metal-Organic Frameworks (MOFs) with intricate structural complexity are of prime importance in reticular chemistry. However, the design of intricate structures that can practically be synthesized is very difficult, and the suitable targeted intricate nets are still unexplored. Evidently, it is of great value to build the fundamental theory for the design of intricate structures. This dissertation is focused on the exploration of cutting-edge design methodologies in reticular chemistry. This research shows the design and synthesis of several MOF platforms (hex, fcu, gea and the) based on rare earth polynuclear clusters. Furthermore, this research unveils the latest addition, named merged nets approach, to the design toolbox in reticular chemistry for the rational design and construction of intricate mixed-linker MOFs. In essence, a valuable net for design enclosing two edges is rationally generated by merging two edge-transitive nets, spn and hxg. The resultant merged net, named sph net, offers potential for the deliberate design and construction of highly symmetric isoreticular intricate mixed-linker MOFs, sph-MOF-1 to 4, which represent the first examples of MOFs where the underlying net is merged from two 3-periodic edge-transitive nets. Furthermore, the underlying principle of the merged net approach, the fundamental merged net equation, and two key parameters are disclosed. Also, we discovered three analysis methods to check and validate corresponding signature nets in an edge-transitive net. Based on these analysis methods, a signature map of all edge-transitive nets was established. This map showing the systematic relationship among edge-transitive nets will help the material chemist to comprehend more about the underlying nets in reticular chemistry. Based on the revealed map, we systematically described the nine types of merging combination and 140 merged nets based on two edge-transitive nets. Among these enumerated nets, only 18 of them was shown on the RCSR database before. These enumerated merged nets significantly increased the designable targets in reticular chemistry. Using an example of enumerated sub net, we show how this approach can be utilized to design and synthesis mixed-linker porous materials based on the intricate sub-MOF platform, which presents one of the most intricate MOF structures synthesized by design.