Nanometer-sized polycarboxylate ligands are interesting building blocks for metallasupramolecular chemistry, but access to these compounds is often limited by complicated synthetic pathways. Here, we describe a simple two-step protocol, which allows preparing linear and bent dicarboxylate ligands with lengths of up to 3 nm from commercially available compounds. The ligands are prepared by iron-templated polycondensation reactions involving arylboronic acids and nioxime. The final products contain two iron clathrochelate complexes and two terminal carboxyphenylene groups. To demonstrate that the new ligands are suitable for the construction of more complex molecular nanostructures, we have prepared a Cu-based metal–organic polyhedron, which represents the largest M4L4 cage described so far.