| Abstract
| - From EPR data as a function of deuteration, it is shown that the Jahn−Teller distortion in (NH4)2[Cu(H2O)6](SO4)2 sharply switches direction at 50% deuteration with no evidence of an intermediate phase. The temperature-dependent EPR data and a neutron diffraction study at 15 K of the compound with ∼42% deuteration indicate a structure similar to that of the fully hydrogenous compound.
- The variation of the EPR spectra with degree of deuteration of the partially deuterated Tutton salt ammoniumhexaaquacopper(II) sulfate, (NH4)2[Cu(H2O)6](SO4)2, has been measured at 293 K. The measurements indicatethat the structure changes quite abruptly from that of the pure hydrogenous salt to that of the fully deuterated saltat ∼50% deuteration. The structure of a crystal in which ∼42% of the hydrogen atoms were replaced by deuteriumwas elucidated at 15 K by single-crystal time-of-flight neutron diffraction. The hexaaquacopper(II) complex exhibitsan orthorhombically distorted, tetragonally elongated octahedral coordination geometry (Cu−O bond distancesof 2.281(1), 2.007(1), and 1.975(1) Å). The structure is very similar to that reported for the undeuterated salt at9.6 K, and markedly different from that of the fully deuterated compound at 15 K, which has similar Cu−O bondlengths but with the directions of the long and intermediate bonds interchanged. There is no evidence for disorderor partial switching of the Cu−O bond directions. This is consistent with the temperature dependence of the EPRspectrum of the ∼42% deuterated compound, which indicates a thermal equilibrium between the two structuralforms close to room temperature similar to that reported for the undeuterated compound, but complete reversionto the low-temperature phase on cooling to 5 K. The possible influence of deuteration upon the hydrogen-bondingdistances and the bearing of this upon the structural modifications of the compound are discussed.
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