The crystal structure of hydrogen chloride monohydrate

The crystal structure of HC1.H20 at about --35 °C.has been determined by X-ray diffraction.The crystal is trigonal, space group R3m.The rhombohedral cell, of dimensions a ---4.05A and a ----73 ° 30', contains one formula unit.The actual structure is disordered but is derived from an ordered structure with space group R3m.The structure is clearly H30+C1 -.The hydronium ions are flat pyramids with symmetry 3m.Each hydrogen atom forms a hydrogen bond to the nearest chlorine atom, with O • • • C1 ----2.95/~.The crystal is formed by stacking together the trigonal puckered layers composed of hydrogen-bonded hydronium and chloride ions.