Reaction of Ag 2 O with the N-heterocyclic carbene (NHC) precursors 3,5-bis [3-(2,4,6-trimethylphenyl)imidazolium-1-ylmethyl]-1H-pyrazole bishexafluorophosphate (1a) and 3,5-bis[3-(2,6-diisopropylphenyl)imidazolium-1-ylmethyl]-1H-pyrazole bishexafluorophosphate (1b) yielded silver(I) complexes 2 and 3, respectively. X-ray crystallography revealed a tetranuclear dimeric solid state structure in the case of 2, whereas an unprecedented octanuclear tetrameric "double-crown"-like structure was found for 3, presumably due to the slightly bulkier ligand. Unlike 2, complex 3 is not stable in solution but in equilibrium with tetranuclear and hexanuclear complexes 4 and 5, respectively. The identity of those species could be elucidated by detailed NMR spectroscopic studies ( 1 H, 13 C, 15 N, 109 Ag, and DOSY experiments), which also provide valuable benchmark data for correlating 1 J AgN couplings and 109 Ag chemical shifts with structural information.

A set of pyrazole-bridged bis(imidazolium) compounds [H 3 − or PF 6 − ) has been prepared, and three compounds have been characterized by X-ray crys-