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The hydration structure of Cu2+: More tetrahedral than octahedral?

DOI: 10.1039/c3ra42400f DOI Help

Authors: Daniel Bowron (ISIS Facility, Rutherford Appleton Laboratory) , Monica Amboage (Diamond Light Source) , Roberto Boada Romero (Diamond Light Source) , Adam Freeman (Diamond Light Source) , Shusaku Hayama (Diamond Light Source) , Sofia Diaz-moreno (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Rsc Advances

State: Published (Approved)
Published: July 2013

Abstract: A comprehensive multi-technique approach has been used to address the controversial question of the preferred geometric form of the Cu2+ aqua-ion hydration shell. A combination of H/D isotopic substitution neutron scattering and X-ray scattering has been used to refine atomistic models of 0.5 m and 2.0 m solutions of Cu(ClO4)2, that have also been constrained to simultaneously reproduce detailed local structure information about the cation environment obtained by X-ray Absorption spectroscopy. The adoption of the Empirical Potential Structure Refinement (EPSR) technique as a single unified analytical framework minimises the chances for biasing the result in favour of a specific pre-conceived outcome. The results are consistent with an average coordination for each Cu2+ ion of 4.5 ± 0.6 water molecules that matches the more recent picture of five-fold coordination in a 2.0 m solution, but interestingly this combined study highlights that the preferred local geometry of the ion sites is found to have a mixed character of tetrahedral, trigonal bipyramidal and octahedral components. A further point to note is that this new model adds support to a largely ignored result in the literature relating to the linear electric field effect induced g-shifts observed in the electron paramagnetic resonance spectra of glassy Cu2+ complexes (Peisach and Mims, Chem. Phys. Lett., 1976, 37, 307–310) that first highlighted the importance of tetrahedral distortions in the cation's hydration shell structure.

Journal Keywords: Preferred Geometric Form

Subject Areas: Chemistry, Materials

Instruments: I20-Scanning-X-ray spectroscopy (XAS/XES)

Other Facilities: ISIS Neutron Source