thionyl chloride. Reactions Molten anhydrous ZnCl2 at 500–700 °C dissolves zinc metal, and, on rapid cooling of the melt, a yellow diamagnetic glass is formed, which Raman studies indicate contains the ion. A number of salts containing the tetrachlorozincate anion, Zn, are known. "Caulton's reagent", V2Cl3(thf)6Zn2Cl6 is an example of a salt containing Zn2. The compound Cs3ZnCl5 contains tetrahedral Zn and Cl− anions. No compounds containing the Zn ion have been characterized. Zinc chloride dissolves readily in water to give ZnClxH2O(4−x) species and some free chloride. Aqueous solutions of ZnCl2 are acidic: a 6 M aqueous solution has a pH of 1. The acidity of aqueous ZnCl2 solutions relative to solutions of other Zn2+ salts (say the sulfate) is due to the formation of the tetrahedral chloro aqua complexes where the reduction in coordination number from 6 to 4 further reduces the strength of the O–H bonds in the solvated water molecules. In alkali solution, zinc chloride converts to various zinc hydroxychlorides. These include Zn(OH)3Cl2−, Zn(OH)2, ZnOH, and the insoluble Zn5(OH)8Cl2·H2O. The latter is the mineral simonkolleite. When zinc chloride hydrates are heated, HCl gas evolves and hydroxychlorides result. When solutions of zinc chloride are treated with ammonia, various complexes of "ammines" are produced. These include Zn(NH3)4Cl2·H2O and on concentration ZnCl2(NH3)2. The former contains the Zn(NH3)62+ ion, and the latter is molecular with a distorted tetrahedral geometry. The species in aqueous solution have been investigated and show that Zn(NH3)42+ is the main species present with Zn(NH3)3Cl+ also present at lower NH3:Zn ratio. Aqueous zinc chloride reacts with zinc oxide to form an amorphous cement that was first investigated in 1855 by Stanislas Sorel. Sorel later went on to investigate the related magnesium oxychloride cement, which bears his name. When hydrated zinc chloride is heated, one obtains a residue of Zn(OH)Cl e.g. ZnCl2·2H2O → ZnCl(OH) + HCl + H2O The compound ZnCl2·HCl·H2O may be prepared by careful precipitation from a solution of ZnCl2 acidified with HCl. It contains a polymeric anion (Zn2Cl5−) with balancing monohydrated hydronium ions, H5O2+ ions. Cellulose dissolves in aqueous solutions of ZnCl2, and zinc-cellulose complexes have been detected. Cellulose also dissolves in molten ZnCl2 hydrate and carboxylation and acetylation performed on the cellulose polymer. Thus, although many zinc salts have different formulas and different crystal structures, these salts behave very similarly in aqueous solution. For example, solutions prepared from any of the polymorphs of ZnCl2, as well