Building block is a term in chemistry which is used to describe a virtual molecular fragment or a real chemical compound the molecules of which possess reactive functional groups.[1] Building blocks are used for bottom-up modular assembly of molecular architectures: nano-particles,[2][3] metal-organic frameworks,[4] organic molecular constructs, supra-molecular complexes.[5] Using building blocks ensures strict control of what a final compound or a (supra)molecular construct will be.[6]