Structure Structure D 2000 Two Mercury Chloro Thiocyanate Complexes: NH 4 [HgCl 2 (SCN)] and NH 4 [HgCl(SCN) 2 ]. -Single crystals of NH 4 [HgCl 2 (SCN)] (I) and NH 4 [HgCl(SCN) 2 ] (II) are prepared by slow evaporation of EtOH solutions of HgCl2 and NH4SCN or Hg(SCN)2 and NH4Cl. As revealed by single crystal XRD (I) crystallizes in the monoclinic space group P21 with Z = 2 and (II) in the monoclinic space group C2/c with Z = 4. The structure of (I) consists of linear HgCl 2 (SCN) chains connected by ions and (II) contains HgCl(SCN) 2 molecules. The second order nonlinear optical properties of (I) are discussed. -(GACEMI, A.; BENBERTAL, D.; BAGIEU-BEUCHER, M.; LECCHI, A.; MOSSET*, A.