Bis-Argentivorous Molecules Bridged by Phenyl and 4,4'-Biphenyl Groups: Structural and Dynamic Behavior of Silver Complexes.

Bis-argentivorous molecules ( and ), which have phenyl and 4,4'-biphenyl groups as linkers, have been prepared. The structures of Ag complexes with the new ligands ( and ) were investigated in solution and the solid state. The CSI-MS and H NMR titration of and with Ag show 1:1 and 1:2 complexes depending on the [Ag]:[] ratios. In the solid-state structures, single crystals of and with 2 equiv of Ag were prepared. X-ray crystallography of the silver(I) complexes with and showed that an intramolecular racemic structure (Δ()Λ() form) and a racemic mixture of Δ()Δ() and Λ()Λ() forms were formed, respectively. The dynamic H NMR studies suggest the following: (i) the activation entropies (Δ) of the side arm rotations in the Ag complex with were all negative, indicating restricted rotation of the side arms due to their shortness, and (ii) the Δ values of the Ag complexes with were negative only when the side arms of both cyclens rotated simultaneously, and the Δ values for the 1:1 and 1:2 complexes were positive when one cyclen side arm was rotated. These values of Δ indicate that the biphenyl side arms between the two cyclens are not long enough to rotate the ring freely.