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)₆](SO₄)₂ 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)₆](SO₄)₂ 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.