W0063
Influence of Pressure and Temperature on the Crystal
Structure Transition in
(ND4)2[Cu(D2O)6](SO4)2.
Arthur J. Schultz1, Robert W. Henning1, Michael A.
Hitchman2 and Horst Stratemeier2, 1Intense
Pulsed Neutron Source, Argonne National Laboratory, Argonne, IL 60439, and
2School of Chemistry, University of Tasmania, Box 252-75, Hobart,
Tasmania 7001, Australia.
Copper Tutton salts of the type
A2[Cu(H2O)6](SO4)2 are a
unique system in which the interplay of the Jahn-Teller expression and the
hydrogen-bonding network determines which of two dimorphs is adopted. The
direction of the Jahn-Teller distortion switches by 90º between the two
dimorphs. Adoption of one dimorph or the other can be controlled by the type of
cation (alkali metal or ammonium) or anion (sulfate or selenate), the isotopic
H/D ratio, the application of pressure, and the degree of zinc doping. The
influence of pressure on the unit cell parameters of deuterated ammonium
copper(II) sulphate hexahydrate,
(ND4)2[Cu(D2O)6](SO4)2,
at various temperatures from 50 to 325 K obtained from pulsed neutron powder
diffraction has been investigated. Application of pressure causes the structure
to switch to a packing arrangement like that observed for the corresponding
hydrogenous compound over the complete temperature range, with a higher pressure
being required at lower temperatures. A pressure hysteresis occurs upon the
release of pressure in the temperature range 303 to 275 K and below ~295 K the
compound remains in the high pressure (high density) modification at 1 bar. As
the temperature is raised from ~296 K to 298 K the structure reverts
progressively to the low pressure modification.
Work at Argonne supported by the U.S. DOE, Basic Energy
Sciences--Materials Sciences, under Contract W-31-109-ENG-38.