Crystals of potassium chloroplatinate, studied by means of spectral and Laue photographs, are shown to have the potassium chlorostannate structure with d100 = 9.73 Å and u = 0.240 = 0.005. The reported value of u = 0.16 is shown to be incorrect, and the theoretical treatment of Jones and Dent which supported this latter value is thereby deprived of its supposed agreement with experiment. The parameters in diaspora are redetermined, and the structure is discussed from the standpoint of the coordination theory. The existence and location of hydrogen bonds in the structure are established, and representative formulas are proposed. The unit of structure, space group symmetry, and detailed atomic arrangements of lepidocrocite are determined from x-ray data, and the existence and location of hydrogen bonds in the structure are established from considerations of interatomic distances. The relationship between the diaspore and lepidocrocite structures is discussed from the standpoint of the coordination theory, and found to depend on two alternative ways of satisfying the electrostatic valence rule.