The complexes RHg(ox) (R = C6F5, p-HC6F4, or p-MeOC6F4; ox = quinolin-8-olate) have been prepared by reaction of thallous quinolin-8-olate with the appropriate organomercuric chlorides whilst PhHg(ox or meox), MeHg(ox), H2O, and MeHg(meox) (meox = 2-methylquinolin-8-olate) have been obtained from phenyl- or methyl-mercuric hydroxide and quinolin-8-ol or 2-methyl- quinolin-8-ol. Although MeHg(ox), H2O was readily dehydrated, the water could not be displaced by ligands (e.g. Ph3PO, Me2SO). Chelation of the quinolin-8-olate ligands (rather than unidentate O-bonding) was established for all complexes by ultraviolet/visible spectroscopy. Molecular weight data indicated that all complexes except MeHg(ox) and MeHg(ox), H2O are partly associated in benzene, chloroform and/or carbon tetrachloride [K(2monomer ⇌ dimer) in the range 1-40 mol-1 dm3]; this suggests an associated structure in the solid state. Some supporting evidence for associated structures was obtained by mass spectrometry. The structural conclusions are discussed in the light of crystal structures of PhHg(ox) and PhHg(meox) carried out in a concurrent investigation.