Molecular recognition of upper rim functionalized cavitand and its unique dimeric capsule in the solid state.

Cavitand 1 possesses four 2,2'-bipyridyl pillars on its upper rim that encapsulates small guests, such as nitromethane, acetonitrile, methyl acetate, ethyl acetate, and N-methylacetamide, into a deep cavity to form host-guest complexes in a 1:1 ratio. Nitroethane, N,N-dimethylformamide, and N,N-dimethylacetamide were not bound in this manner. A guest-binding study and molecular mechanics calculations revealed that the four 2,2'-bipyridyl pillars of cavitand 1 created a steric boundary that is responsible for selective guest recognition. In the solid state, cavitand 2 formed a unique chiral capsule 2(2) by π-π stacking interactions between the 2,2'-bipyridyl pillars. A nitromethane molecule was unusually placed deep inside the cavity, as directed by the multiple hydrogen bonding interactions between the nitromethane oxygen atoms, the C-H bonds of the bridge methylenes and the pillar phenyl groups.