Self-Assembly of Silver(I) and Gold(I) N-Heterocyclic Carbene Complexes in Solid State, Mesophase, and Solution

The assembly of silver(I) and gold(I) complexes of functionalized N-heterocyclic carbenes (NHCs) of the type [M(C-n,amide-imy)(2)][anion] were studied, in which C-n,amide-imy stands for an NHC of imidazol-2-ylidene having one N-alkyl substituent (CnH2n+1) and one N-acetamido substituent, while the anions are Br-, NO3-, BF4-, or PF6-. A single crystal X-ray diffraction study reveals that self-assembly of [Ag(C-10,amide-imy)(2)][PF6] through Coulombic, hydrogen bonding, and hydrophobic interactions gives a lamellar structure with tubular architecture around the metal ion head core. Self-assembly of these functionalized NHC complexes also leads to the formation of the first example of thermotropic liquid crystals of silver(I)-NHCs and gels of gold(I)-NHC. Results from an infrared spectroscopy study show that the degree of chain motion in the gel state is smaller than that in the mesophase, yet comparable to that in the solid state. In addition, the technique of nuclear magnetic resonance diffusion ordered spectroscopy was found for the first time to be a good tool to study the phase transition of gels. Xerogels of gold(I)-NHCs display fibers, oriental lantern-shaped bundles of belts and helical fibers when observed under scanning electron and transmission electron microscopes.