Proton spin-lattice relaxation times and line widths have been measured in all of the alkaline earth hexaammines and in Yb(NH3)6 over the temperature range 4.2-150 K. The results are interpreted as evidence for the existence of two separate ammonia populations for portions of the range, each population undergoing hindered rotation in a different hindering potential. One of the populations is strongly involved in structural phase transitions which are inferred for Sr(NH3)6 and Ba(NH3)6, while the second is unaffected by them. The existence of the first population in Ca(NH3)6 and Yb(NH3)6 is taken as evidence that these two compounds also approach, but do not actually undergo, phase transitions of a similar kind. Details of the complex T1 data are reviewed, and relevant results of other studies of the hexaammines, principally by powder neutron diffraction and electrical resistivity measurements, are cited.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry