10.1021/ic401385f.s001
Charles J. Simmons
Charles J.
Simmons
Horst Stratemeier
Horst
Stratemeier
Michael
A. Hitchman
Michael
A.
Hitchman
Mark J. Riley
Mark J.
Riley
Influence
of Lattice Interactions on the Jahn–Teller
Distortion of the [Cu(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> Ion:
Dependence of the Crystal Structure of K<sub>2<i>x</i></sub>Rb<sub>2–2<i>x</i></sub>[Cu(H<sub>2</sub>O)<sub>6</sub>](SeO<sub>4</sub>)<sub>2</sub> upon the K/Rb Ratio
American Chemical Society
2013
temperature range 90
proportion
oxygen atoms
lattice strain interactions
form B
bond lengths
Cu
potassium
formula K 2xRb
2013-09-16 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Influence_of_Lattice_Interactions_on_the_Jahn_Teller_Distortion_of_the_Cu_H_sub_2_sub_O_sub_6_sub_sup_2_sup_Ion_Dependence_of_the_Crystal_Structure_of_K_sub_2_i_x_i_sub_Rb_sub_2_2_i_x_i_sub_Cu_H_sub_2_sub_O_sub_6_sub_SeO_sub_4_sub_sub_2_sub_upon_the_K_Rb_/2558023
The temperature dependence
of the structures of a wide range of
mixed-cation Tutton’s salts of general formula K<sub>2<i>x</i></sub>Rb<sub>2–2<i>x</i></sub>[Cu(H<sub>2</sub>O)<sub>6</sub>](SeO<sub>4</sub>)<sub>2</sub> has been determined
over the temperature range 90 to 320 K. Crystals with a high proportion
of potassium adopt a different structure (form <b>B</b>) from
those with a low ratio (form <b>A</b>). In both forms, the [Cu(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> ion has an orthorhombically distorted
tetragonally elongated coordination geometry, but the long and intermediate
bonds occur with a different pair of water molecules in form <b>A</b> compared with form <b>B</b>. The alkali metal is surrounded
by seven close oxygen atoms in form <b>B</b> but eight oxygen
atoms in form <b>A</b>, and this difference in coordination
number is associated with the change in the Cu–O bond distances
via the hydrogen-bonding network. For crystals with between 32 and
∼41% potassium, a relatively sharp change from form <b>B</b> to <b>A</b> occurs on cooling, and the temperature at which
this occurs increases approximately linearly as the proportion of
potassium falls. For the whole range of mixed crystals, the bond lengths
have been determined as a function of temperature. The data have been
interpreted as a thermal equilibrium of the two structural forms of
the [Cu(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> ion that develops
gradually as the temperature increases, with this becoming more pronounced
as the proportions of the two cations become more similar. The temperature
dependence of the bond lengths in this thermal equilibrium has been
analyzed using a model in which the Jahn–Teller potential surface
of the [Cu(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> ion is perturbed
by lattice strain interactions. The magnitude and sign of the orthorhombic
component of this strain interaction depends upon the proportion of
potassium to rubidium ions in the structure.