The reaction of ammonium and phosphonium iodides R3R′EI (E = N, P; R = H, Me, Bu, Ph; R′= H, Me, Bu, Am) with mercury iodide (I) (red polymorph) in acetone in 1: 1 and 1: 2 ratios (mol/mol) gave mercury complexes [H4N]n+[HgI3]n− (II), [Me3NH]n+[HgI3]n− (III), [Me3NH]2n+[Hg4I10]n2− (IV), [Me4N]n+[HgI3]n− (V), [Me3NBu]2+[Hg2I6]2− (VI), [Bu4N]2+[Hg2I6]2− (VII), [Ph3PAm]2+[Hg2I6]2− (VIII), [Me4N]2n+[Hg4I10]n2− (IX), [Me3NBu]2n+[Hg4I10]n2− (X), [Bu4N]2n+[Hg4I10]n2− (XI), and [Ph3PAm]2n+[Hg4I10]n2− (XII). According to X-ray diffraction data, crystals of I are composed of (HgI2)n polymeric layers in which each mercury atom having a tetrahedral environment (two IHgI angles equal to 103.16° and four angles of 112.72°) is bonded to four neighboring mercury atoms through iodine atoms (I-Hg, 2.818 A). In the tetrahedral cations of the complexes, the nitrogen and phosphorus atoms each have a distorted tetrahedral coordination. In the centrosymmetric binuclear [Hg2I6]2− anions, the mercury atoms having tetrahedral coordination lie in two almost perpendicular planes Hg2I6. In the polymeric anions of II and III, the HgI2 groups are linked to each other through bridging iodine atoms. The crystals of IV consist of tetrahedral trimethylammonium cations disordered over two positions and polymeric [Hg4I10]n−, anions in which the eight-membered Hg4I10 rings are connected to one another through bridging iodine atoms to form a polymeric ribbon.