Sulfate compounds arise when cations combine with the anion SO42-. Often this combination results in an ionic compound, although sulfates can engage in covalent bonding with most elements. The metal complex PtSO4P(C6H5)32 is clearly covalent Pt-O bonding. Dialkylsulfates, such as dimethylsulfate are covalent, distillable species. Many sulfate salts are highly soluble in water. Exceptions include calcium sulfate, strontium sulfate, and barium sulfate, which are poorly soluble.