In conclusion, we show that careful control of modulated synthetic conditions can lead to the isolation of valuable new MOF phases -in particular, MONs -in established metal-ligand systems. The use of an extended alkyne linker and formic acid as a modulator are key to the discovery of GUF-14, a two-dimensional layered MOF in which Zr6 clusters are connected by dicarboxylate linkers with hxl topology, as they allow close packing between layers in an unusual ABC stacking arrangement, in comparison to the previously reported GUF-12 which has hcp topology and Zr12 clusters. Activation at high temperatures results in the hxl topology of GUF-14 compressing along the c axis which, following ultrasound-assisted liquid phase exfoliation, undergoes a phase transition to form GUF-14 MONs, with hns topology, via delamination of the stacked layers. Acid washing to remove coordinated formate units enhances the catalytic activity of GUF-14 MONs compared to their threedimensional and 2D layered counterparts, leading to a material with excellent kinetics for hydrolysis of an organophosphate nerve agent mimic. We anticipate that these new members of the Zr MOF/MON families, capable of forming monolayer nanosheets with catalytic functionalities will prove useful in a wide range of catalysis, sensing, waterpurification, and gas-separation applications, while serving as examples of the power of modulated self-assembly in the discovery of novel, functional, network solid materials.