The synthesis and characterization of a novel dimeric N-heterocyclic carbene ligated trimercury hexachloride adduct [(IPr)Hg3Cl6]2 [IPr = (HCNDipp)2C:; Dipp = 2,6- iPr2C6H3] is reported from the disproportionation reaction of IPr with mercury(I) chloride. The molecular structure of this species in the solid state represents a new bonding motif for a mercury halide.