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

Bis-argentivorous molecules (L and L), which have phenyl and 4,4'-biphenyl groups as linkers, have been prepared. The structures of Ag⁺ complexes with the new ligands (L and L) were investigated in solution and the solid state. The CSI-MS and ¹H NMR titration of L and L with Ag⁺ show 1:1 and 1:2 complexes depending on the [Ag⁺]:[L] ratios. In the solid-state structures, single crystals of L and L with 2 equiv of Ag⁺ were prepared. X-ray crystallography of the silver(I) complexes with L and L 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 L were all negative, indicating restricted rotation of the side arms due to their shortness, and (ii) the ΔS^⧧ values of the Ag⁺ complexes with L 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.