Single-crystal neutron-diffraction study of 3.4% Zn-doped (ND4)2[Cu(D2O)6](SO4)2 at 20 K.

Doping the perdeuterated ammonium copper Tutton salt (ND4)2Cu(D2O)62 [perdeuterated diammonium hexaaquacopper(II) bis(sulfate)] with Zn leads to a change in the structure from dimorph A (low density) to dimorph B (high density). This change, which accompanies a switch in the direction of the Jahn-Teller distortion, had previously been observed to occur with substitution of Zn2+ at the Cu2+ site of between 1.3 (A) and 3.4% (B). In this study, the single-crystal neutron-diffraction analysis of (ND4)2(Cu/Zn)(D2O)62 at 20 K, with 3.4% Zn doping and a deuterium substitution of 85% on the H-atom sites, reveals that the structure is entirely of type B, with the Cu/Zn site at an inversion centre and with no evidence of disorder or unusual atomic displacement parameters that might occur near a phase transition boundary.