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Knots may ultimately prove just as versatile and useful at the nanoscale as at the macroscale. However, the lack of synthetic routes to all but the simplest molecular knots currently prevents systematic investigation of the influence of knotting at the molecular level. We found that it is possible to assemble four building blocks into three braided ligand strands. Octahedral iron(II) ions control the relative positions of the three strands at each crossing point in a circular triple helicate, while structural constraints on the ligands determine the braiding connections. This approach enables two-step assembly of a molecular 8(19) knot featuring eight nonalternating crossings in a 192-atom closed loop similar to 20 nanometers in length. The resolved metal-free 8(19) knot enantiomers have pronounced features in their circular dichroism spectra resulting solely from topological chirality.