C(sp2)–H···π(C≡N) interaction in [Ag+·Argentivorous molecule ⊃ acetonitrile] inclusion complexes

New tetra-armed cyclens (1a and 1b) with two 4-fluorobenzyl and two styrylmethyl groups have been synthesized. The structures of their silver(I) complexes have been studied using 1H 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··· π 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··· π 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(sp2)-H··· π (C≡N) interaction, with CH···N(C≡N) and CH···C(C≡N) distances of approximately 2.63–2.75 and 2.69–3.15 Å, respectively. DFT calculations suggest that the C(sp2)-H··· π interaction may be due to the electron donation from C(sp2)-H of the styrylmethyl side-arms to the π (C≡N) of acetonitrile.