Metal-organic frameworks are modular materials with a thickness of a few atomic layers. Their interest for solids and uses lies in their atomically thin-layered arrangement, surface chemical reactivity, surface/volume ratio and chemical-adsorption capacity. The study of their characteristics and features is used as a learning method. The layer-layer separation is maximal for MoS2 owing to its layered arrangement, in which a plane of Mo atoms is sandwiched by others of S2-. The periodic table of the elements shows constancy in layer-layer separations for B/C/N in row 2 of the table. Design criteria and structure-property associations follow: Linear models of atom-atom separation between layers show that this increases with atomic number. Power models, especially those with two parameters, better associations. Layer-layer separation for S deviates from the models owing to MoS2 three-strata monolayer. Miniaturization is a must for actual progress. The true control of a material or process should be done from the nanoscale. Two-dimensional nanomaterials are a way of structuring the nanoworld for this control. Monochalcogenides, dichalcogenides, etc. are easy to exfoliate. The central rule of nanoscience results: Compare cartoons with reality.

Keywords: Monolayer, Thin-layered nanostructure, Thin film, Charge transport, Host-guest chemistry.