Metal coordination and peptide-directed self-assembly are two proven methods for creating defined supramolecular architectures. Here, we report a new class of crystalline materials based on coiled-coil peptides bearing unnatural metal-chelating terpyridine moieties. High-resolution structural characterization of lattices formed in the presence of Cu2+ reveals a general assembly mechanism. Subtle sequence variation in the modular synthetic ligand dictates assembly morphology.