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(Cn,amide-imy)2]­[anion] were studied, in which Cn,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(C10,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.