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Pressure Dependence of the Crystal Structures and EPR Spectra of Potassium Hexaaquacopper(II) Sulfate and Deuterated Ammonium Hexaaquacopper(II) Sulfate

journal contribution
posted on 2023-05-16, 10:18 authored by Rauw, R, Ahsbahs, H, Hitchman, MA, Lukin, S, Reinen, D, Schultz, AJ, Simmons, CJ, Stratemeier, H
The crystal structures of (ND4)2[Cu(D2O)6](SO 4)2 at 295 K, determined by X-ray diffraction at pressures of 1 bar, ∼1.5 kbar and ∼3.0 kbar, are reported. Between 1 bar and 1.5 kbar, the crystal structure changes to one almost identical to that of the corresponding hydrogenous compound at 1 bar. The structural change involves a 90° switch in the direction of the long bonds of the Cu(D2O)6 2+ ion, accompanied by a change in the hydrogen-bonding interactions of the ammonium cations. Comparison of these two structures with those at ∼15 K shows that at room temperature, for both the high (H) and low (L) pressure phases, the Cu complexes are in thermal equilibrium with the other structural isomer. Though one of these is energetically preferred in the H and the other in the L phase, the variation of the powder EPR spectrum with pressure indicates a continuous transition between both within ∼1 kbar and suggests that at ∼0.5 kbar the two orientations of the copper complex are similar in energy. However, the underlying thermally induced equilibrium is little affected by pressure, and this is also the case for the Cu(H2O)6 2+ ion in Cu2+-doped K2[Zn(H2O)6](SO4)2. The crystal structure of K2[Cu-(H2O)6](SO4)2 at 15 K and 1.4 kbar, determined by time-of-flight neutron diffraction, is similar to that at 295 K and 1 bar, except for indications that here also a thermal population of the higher energy form in which the directions of the long and intermediate Cu-O bonds interchange occurs at 295 K. The powder EPR spectrum of the potassium salt at 295 K shows little change between 1 bar and 11 kbar.

History

Publication title

Inorganic Chemistry

Volume

35

Issue

7

Pagination

1902-1911

ISSN

0020-1669

Department/School

School of Natural Sciences

Publisher

Amer Chemical Soc

Place of publication

United States of America

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the chemical sciences

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