Temperature dependence of the crystal structure and g-values of trans-diaquabis(methoxyacetato)copper(II): Evidence for a thermal equilibrium between complexes with tetragonally elongated and compressed geometries
2011
The crystal structures of trans-diaquabis-
(methoxyacetato)copper(II) and the isostructural nickel(II)
complex have been determined over a wide temperature range.
In conjunction with the reported behavior of the g-values, the
structural data suggest that the copper(II) compound exhibits a
thermal equilibrium between three structural forms, two having
orthorhombically distorted, tetragonally elongated geometries
but with the long and intermediate bonds to different atoms,
and the third with a tetragonally compressed geometry. This is
apparently the first reported example of a copper(II) complex
undergoing an equilibrium between tetragonally elongated and
compressed forms. The optical spectrum of single crystals of the copper(II) compound is used to obtain metalligand bonding
parameters which yield the g-values of the compressed form of the complex and hence the proportions of the complex in each
structural form at every temperature. When combined with estimates of the JahnTeller distortions of the different forms, the latter
produce excellent agreement with the observed temperature dependence of the bond lengths. The behavior of an infrared
combination band is consistent with such a thermal equilibrium, as is the temperature dependence of the thermal ellipsoid
parameters and the XAFS. The potential surfaces of the different forms of the copper(II) complex have been calculated by a model
based upon JahnTeller coupling. It is suggested that cooperative effects may cause the development of the population of
tetragonally compressed complexes, and the crystal packing is consistent with this hypothesis, though the present model may
oversimplify the diversity of structural forms present at high temperature.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
35
References
5
Citations
NaN
KQI