Abstract
Halogenated inorganic complexes Ax[MHaly] (A = alkali metal or alkaline earth, M = transition or main group metal, x = 1-3, and y = 2-9) are an archetypal class of compounds that provide entry points to large areas of inorganic and physical chemistry. All of the hexahalo complexes adopt an octahedral, Oh, symmetry (or nearly so). Consequently, one of the bending modes is forbidden in both the infrared and Raman spectra. In the solid state, many of the complexes crystallize in the cubic space group Fm3¯ m, which preserves the octahedral symmetry. Even for those that are not cubic, the octahedral symmetry of the [MHal6]n- ion is largely retained and, to a good approximation, so are the selection rules. In the present work, we show that by using the additional information provided by neutron vibrational spectroscopy, in combination with conventional optical spectroscopies, we can generate complete and unambiguous assignments for all the modes. Comparison of the experimental and calculated transition energies for the systems where periodic-density functional theory was possible (i.e., those for which the crystal structure is known) shows that the agreement is almost quantitative. We also provide a linear relationship that enables the prediction of the forbidden mode.
| Original language | English |
|---|---|
| Pages (from-to) | 5844-5854 |
| Number of pages | 11 |
| Journal | Inorganic Chemistry |
| Volume | 61 |
| Issue number | 15 |
| DOIs | |
| State | Published - Apr 18 2022 |
Funding
The STFC Rutherford Appleton Laboratory is thanked for granting access to neutron beam facilities. We would like to thank Dr James W. Taylor for help with the Bruker Senterra instrument in the Materials Characterization Laboratory at the ISIS Neutron and Muon Source. Computing resources (time on the SCARF compute cluster for the CASTEP calculations) were provided by STFC’s e-Science facility. This research was performed with the aid of facilities at the Research Complex at Harwell, including the FT-Raman spectrometer. The authors would like to thank the Research Complex for providing access to, and support of, these facilities and equipment. The INS studies, in part, used the VISION spectrometer at the Spallation Neutron Source, Oak Ridge National Laboratory, as DOE Office of Science User Facility under contract no. DEAC0500OR22725 with UT Battelle, LLC.