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

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