Water molecules insert into N-H...Cl-M hydrogen bonds while M-Cl...X-C halogen bonds remain intact in dihydrates of halopyridinium hexachloroplatinates.

The crystal structures of the 3-halopyridinium hexachloroplatinate(IV) dihydrates (HPyX-3)(2)[PtCl(6)]x2H(2)O [(1), X = Br; (2a), (2b), X = I] comprise networks in which the molecular components are linked via N-H...O and O-H...Cl-Pt hydrogen bonds and Pt-Cl...X-C halogen bonds (X = Br, I). The iodo derivative has been isolated in two polymorphic forms. Of particular interest to the understanding of the utility of the hydrogen bonds and M-X...X'-C halogen bonds that propagate the networks in anhydrous salts of this type is that the water molecules insert exclusively into the putative N-H...Cl-Pt hydrogen bonds, while the Pt-Cl...X'-C halogen bonds remain undisrupted by the presence of water molecules.