C(sp(2))-H center dot center dot center dot pi(C N) interaction in [Ag+center dot Argentivorous molecule superset of acetonitrile] inclusion complexes

New tetra-armed cyclens (1a and 1b) with two 4-fluorobenzyl and two styrylmethyl groups have been synthe-sized. The structures of their silver(I) complexes have been studied using H-1 NMR titration experiments and X-ray crystallography. The results showed that these ligands are argentivorous molecules. However, the pseudo-cavities do not have sufficient space to include organic guests such as acetonitrile. The pseudo-cavities are not stable enough due to weak CH center dot center dot center dot pi interactions between the benzyl groups and the styrylmethyl groups. The binding constants for these ligands with silver(I) ions decrease with decreasing electron density of the aromatic side-arms. These findings indicate that CH center dot center dot center dot pi interactions play a crucial role in maintaining stable pseudo-cavities in the argetivorous molecules. The AgX (X = BF4, PF6, and OTf) complexes with 1a were prepared in the presence of acetonitrile. X-ray crystallography of these complexes revealed that AgX (X = PF6 and OTf) complexes with 1a form inclusion complexes with acetonitrile. The C=N moiety of acetonitrile mainly interacts with the hydrogen atoms in the styrylmethyl side-arms through C(sp(2))-H center dot center dot center dot pi (C=N) interaction, with CH center dot center dot center dot N(C N) and CH center dot center dot center dot C(C N) distances of approximately 2.63-2.75 and 2.69-3.15 angstrom, respectively. DFT calculations suggest that the C(sp(2))-H center dot center dot center dot pi interaction may be due to the electron donation from C(sp(2))-H of the styrylmethyl side-arms to the pi (C N) of acetonitrile.