Anion recognition by synthetic hosts is a rapidly emerging field.1–4 One of the challenges is the development of receptors that selectively bind polyatomic oxyanions, such as NO3 − and SO4 2−, which are important targets for environmental, industrial, and health-related applications. A successful approach for preparing molecules that coordinate with anions has been to add hydrogen-bond donors to an organic scaffold to yield charge-neutral receptors that interact with anions through hydrogen bonding.5–12 Because hydrogen bonds are directional, it should be possible to design hosts with shaped cavities that are capable of differentiating between anionic guests with different geometries. The deliberate design of host architecture requires knowledge of the structural aspects of hydrogen bonding with the guest anion. Yet, surprisingly little attention has been given to this critical facet of anion host design.