Sn(4+) ions do not exist. In water you can have soluble tin(IV) compounds, e.g. the stannates, as mentioned above, but the free Sn(4+) ion simply is hydrolysed in water and cannot exist as such. It might be that in very strongly concentrated HCl, some SnCl4 may exist in solution, but then not as Sn(4+) and Cl(-) ions, but as covalent compound SnCl4. I, however, even doubt that this can exist in conc. HCl, even under such conditions I think it hydrolyses as metastannic acid, SnO(OH)4.
Hg(2+) ions form HgI2 with iodide ion, which is very bright orange/red. On addition of excess iodide, the colorless complex ion HgI4(2-) is formed.