Conceptually analogous to coordination cages, so-called anioncoordination-directed assemblies (ACDAs) are composed of ligand units bridging between anionic nodes. Rather than the dative covalent, metal-ligand interactions used within coordination cages, ACDAs exploit hydrogen bonding and electrostatic interactions between anions and ligands to hold the structure together. The notion of anion coordination chemistry has been in discussion since at least the late 1970s, 59 however it is only relatively recently that the field has reached sufficient maturity to enable the design and assembly of polyhedral architectures. Detailed historical overviews of ACDAs have been covered in recent reviews. In contrast to transition metals, with their often-predictable coordination numbers and geometries, the coordination environment around anions is less well-defined and more flexible. Phosphate, PO4 3-, has become the most intensely studied anion for self-assembly, presumably due to its defined tetrahedral shape and ability to form coordinatively saturated complexes with 12 hydrogen bonds. In contrast, sulfate, SO4 2-, is known to form coordinatively unsaturated assemblies, although capsules analogous to those with phosphate have been reported; assemblies formed from tris-carboxylate anions have also been realised. In terms of "coordinating groups", urea moieties are popular choices, with ligands often consisting of bis-tris-urea units (capable of forming 4 and 6 hydrogen bonds, respectively), and the manner in which these are arranged directing the topology of assembly formed (Fig. ). In this manner, coordination of three bis-urea units around a PO4 3-anion is analogous to binding three bidentate ligands around an octahedral metal ion. For example, bis-and tris-(bis-urea) ligands (11 and 12, respectively) have been shown to assemble with PO4 3-anions to form edge-based A4L6 and face-based A4L4 tetrahedra, 65 respectively (Fig. ). Subtle structural modification of ligands, however, can result in significant changes to the resultant assembly. Whilst ligand 12 with a triphenylamine core assembled with PO4 3-to form an A4L4 tetrahedron, its phosphine oxide congener, 13, formed an A6L6 trigonal antiprism instead (Fig. ). Such structures can be inherently chiral; A4L6 tetrahedra, for example, have vertices composed of anions surrounded by three coordinating units that can adopt Δ or Λ configurations. Chiral induction of ΔΔΔΔ-and ΛΛΛΛ-A4L6 tetrahedra has been demonstrated through the incorporation of chiral auxiliary units into the ligand scaffold and through interactions with chiral cations. 68 Fig. Ligands incorporating bis-urea "coordinating" groups can be used to assemble ACDAs of different geometries with ligands occupying edge-or face-based positions using design principles analogous to those for coordination cages. R groups omitted from SCXRD structures for clarity.