The synthesis of 3D covalent organic frameworks (COFs) adopting novel topologies is challenging, and so far 3D COFs have only been reported for nets based on building blocks with tetrahedral geometry. We demonstrate the targeted synthesis of an anionic 3D COF crystallizing in a three-coordinated srs net by exploiting a recently developed linkage for the formation of anionic silicate COFs based on hypercoordinate silicon nodes. The framework, named SiCOF-5, was synthesized by reticulating dianionic hexacoordinate [SiO6]2- nodes with triangular triphenylene building blocks and adopts a two-fold interpenetrated srs-c net with an overall composition of Na2[Si(C18H6O6)] (where C18H6O6 is triphenylene-2,3,6,7,10,11-hexakis(olate)). A key requirement for the crystallization of SiCOF-5 was the careful control over the nucleation and growth rate by gradual generation of the silicon source during the course of the reaction.