Methylmercury(II) forms complexes [MeHgL]NO3(L = 2,2′:6′,2″-terpyridyls and di-2-pyridylmethane) where the ligands L are bidentate in methanol, but tridentate and bidentate, respectively, in the solid state with co-ordination geometries for mercury based on a near linear dominant C–Hg–N unit with additional weak Hg–N bonding.